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Sökning: WFRF:(Herrmann Martin J)

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1.
  • Niemi, MEK, et al. (författare)
  • 2021
  • swepub:Mat__t
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2.
  • Abelev, B., et al. (författare)
  • Multiplicity dependence of two-particle azimuthal correlations in pp collisions at the LHC
  • 2013
  • Ingår i: Journal of High Energy Physics. - 1029-8479. ; :9
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the measurements of particle pair yields per trigger particle obtained from di-hadron azimuthal correlations in pp collisions at root s = 0.9, 2.76, and 7TeV recorded with the ALICE detector. The yields are studied as a function of the charged particle multiplicity. Taken together with the single particle yields the pair yields provide information about parton fragmentation at low transverse momenta, as well as on the contribution of multiple parton interactions to particle production. Data are compared to calculations using the PYTHIA6, PYTHIA8, and PHOJET event generators.
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3.
  • Abelev, B., et al. (författare)
  • Upgrade of the ALICE Experiment Letter Of Intent
  • 2014
  • Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 41:8
  • Tidskriftsartikel (refereegranskat)abstract
    • ALICE (A Large Ion Collider Experiment) is studying the physics of strongly interacting matter, and in particular the properties of the Quark–Gluon Plasma (QGP), using proton–proton, proton–nucleus and nucleus–nucleus collisions at the CERN LHC (Large Hadron Collider). The ALICE Collaboration is preparing a major upgrade of the experimental apparatus, planned for installation in the second long LHC shutdown in the years 2018–2019. These plans are presented in the ALICE Upgrade Letter of Intent, submitted to the LHCC (LHC experiments Committee) in September 2012. In order to fully exploit the physics reach of the LHC in this field, high-precision measurements of the heavy-flavour production, quarkonia, direct real and virtual photons, and jets are necessary. This will be achieved by an increase of the LHC Pb–Pb instant luminosity up to 6×1027 cm−2s−1 and running the ALICE detector with the continuous readout at the 50 kHz event rate. The physics performance accessible with the upgraded detector, together with the main detector modifications, are presented.
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4.
  • Abelev, B, et al. (författare)
  • Directed Flow of Charged Particles at Midrapidity Relative to the Spectator Plane in Pb-Pb Collisions at sqrt[s_{NN}]=2.76 TeV.
  • 2013
  • Ingår i: Physical Review Letters. - 1079-7114. ; 111:23
  • Tidskriftsartikel (refereegranskat)abstract
    • The directed flow of charged particles at midrapidity is measured in Pb-Pb collisions at sqrt[s_{NN}]=2.76 TeV relative to the collision symmetry plane defined by the spectator nucleons. A negative slope of the rapidity-odd directed flow component with approximately 3 times smaller magnitude than found at the highest RHIC energy is observed. This suggests a smaller longitudinal tilt of the initial system and disfavors the strong fireball rotation predicted for the LHC energies. The rapidity-even directed flow component is measured for the first time with spectators and found to be independent of pseudorapidity with a sign change at transverse momenta p_{T} between 1.2 and 1.7 GeV/c. Combined with the observation of a vanishing rapidity-even p_{T} shift along the spectator deflection this is strong evidence for dipolelike initial density fluctuations in the overlap zone of the nuclei. Similar trends in the rapidity-even directed flow and the estimate from two-particle correlations at midrapidity, which is larger by about a factor of 40, indicate a weak correlation between fluctuating participant and spectator symmetry planes. These observations open new possibilities for investigation of the initial conditions in heavy-ion collisions with spectator nucleons.
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5.
  • Abelev, B., et al. (författare)
  • Multiplicity dependence of the average transverse momentum in pp, p-Pb, and Pb-Pb collisions at the LHC
  • 2013
  • Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 727:4-5, s. 371-380
  • Tidskriftsartikel (refereegranskat)abstract
    • The average transverse momentum (p(T)) versus the charged-particle multiplicity N-ch was measured in p-Pb collisions at a collision energy per nucleon-nucleon root S-NN = 5.02 TeV and in pp collisions at collision energies of root s = 0.9, 2.76, and 7 TeV in the kinematic range 0.15 < p(T) < 10.0 GeV/c and vertical bar eta vertical bar < 0.3 with the ALICE apparatus at the LHC. These data are compared to results in Pb-Pb collisions at root S-NN = 2.76 TeV at similar charged-particle multiplicities. In pp and p-Pb collisions, a strong increase of (p(T)) with N-ch is observed, which is much stronger than that measured in Pb-Pb collisions. For pp collisions, this could be attributed, within a model of hadronizing strings, to multiple-parton interactions and to a final-state color reconnection mechanism. The data in p-Pb and Pb-Pb collisions cannot be described by an incoherent superposition of nucleon-nucleon collisions and pose a challenge to most of the event generators. (C) 2013 CERN. Published by Elsevier B.V. All rights reserved.
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6.
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7.
  • Abelev, B., et al. (författare)
  • D Meson Elliptic Flow in Noncentral Pb-Pb Collisions at root(S)(NN)=2.76 TeV
  • 2013
  • Ingår i: Physical Review Letters. - 1079-7114. ; 111:10
  • Tidskriftsartikel (refereegranskat)abstract
    • Azimuthally anisotropic distributions of D-0, D+, and D*+ mesons were studied in the central rapidity region (vertical bar y vertical bar < 0.8) in Pb-Pb collisions at a center-of-mass energy root(S)(NN) = 2.76 TeV per nucleon-nucleon collision, with the ALICE detector at the LHC. The second Fourier coefficient upsilon(2) (commonly denoted elliptic flow) was measured in the centrality class 30%-50% as a function of the D meson transverse momentum p(T), in the range 2-16 GeV/c. The measured upsilon(2) of D mesons is comparable in magnitude to that of light-flavor hadrons. It is positive in the range 2 < p(T) < 6 GeV/c with 5.7 sigma significance, based on the combination of statistical and systematic uncertainties.
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8.
  • Abelev, B., et al. (författare)
  • Multiplicity dependence of pion, kaon, proton and lambda production in p-Pb collisions at root s(NN)=5.02 TeV
  • 2014
  • Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 728, s. 25-38
  • Tidskriftsartikel (refereegranskat)abstract
    • In this Letter, comprehensive results on pi(+/-), K-+/-, K-S(0), p((p) over bar) and A((A) over bar) production at mid-rapidity (0 < y(CMS) < 0.5) in p-Pb collisions at root s(NN) = 5.02 TeV, measured by the ALICE detector at the LHC, are reported. The transverse momentum distributions exhibit a hardening as a function of event multiplicity, which is stronger for heavier particles. This behavior is similar to what has been observed in pp and Pb-Pb collisions at the LHC. The measured pr distributions are compared to d-Au, Au-Au and Pb-Pb results at lower energy and with predictions based on QCD-inspired and hydrodynamic models. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.
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9.
  • Abbas, E., et al. (författare)
  • Charmonium and e(+)e(-) pair photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at root s(NN)=2.76 TeV
  • 2013
  • Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 73:11
  • Tidskriftsartikel (refereegranskat)abstract
    • The ALICE Collaboration at the LHC has measured the J/psi and psi' photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at root s(NN) = 2.76 TeV. The charmonium is identified via its leptonic decay for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 23 mu b(-1). The cross section for coherent and incoherent J/psi production in the rapidity interval -0.9 < y < 0.9, are d sigma(coh)(J/psi)/dy = 2.38(-0.24)(+0.34)(sta + sys) mb and d sigma(inc)(J/psi)/dy = 0.98(-0.17)(+0.19)(sta + sys) mb and , respectively. The results are compared to theoretical models for J/psi production and the coherent cross section is found to be in good agreement with those models incorporating moderate nuclear gluon shadowing at Bjorken-x around 10(-3), such as EPS09 parametrization. In addition the cross section for the process gamma gamma -> e(+)e(-) has been measured and found to be in agreement with models implementing QED at leading order.
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10.
  • Abbas, E., et al. (författare)
  • Mid-rapidity anti-baryon to baryon ratios in pp collisions at root s=0.9, 2.76 and 7 TeV measured by ALICE
  • 2013
  • Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 73:7
  • Tidskriftsartikel (refereegranskat)abstract
    • The ratios of yields of anti-baryons to baryons probes the mechanisms of baryon-number transport. Results for (p) over bar /p, (Lambda) over bar/Lambda, (Xi) over bar (+)/(Xi) over bar (-) and (Omega) over bar (+)/(Omega) over bar (-) in pp collisions at root s = 0.9, 2.76 and 7 TeV, measured with the ALICE detector at the LHC, are reported. Within the experimental uncertainties and ranges covered by our measurement, these ratios are independent of rapidity, transverse momentum and multiplicity for all measured energies. The results are compared to expectations from event generators, such as PYTHIA and HIJING/B, that are used to model the particle production in pp collisions. The energy dependence of (p) over bar /p, (Lambda) over bar/(Lambda) over bar, (Xi) over bar (+)/(Xi) over bar (-) and (Omega) over bar (+)/(Omega) over bar (-), reaching values compatible with unity for root s = 7 TeV, complement the earlier (p) over bar /p measurement of ALICE. These dependencies can be described by exchanges with the Regge-trajectory intercept of alpha(J) approximate to 0.5, which are suppressed with increasing rapidity interval Delta y. Any significant contribution of an exchange not suppressed at large Delta y (reached at LHC energies) is disfavoured.
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11.
  • Abbas, E., et al. (författare)
  • Performance of the ALICE VZERO system
  • 2013
  • Ingår i: Journal of Instrumentation. - 1748-0221. ; 8
  • Tidskriftsartikel (refereegranskat)abstract
    • ALICE is an LHC experiment devoted to the study of strongly interacting matter in proton-proton, proton-nucleus and nucleus-nucleus collisions at ultra-relativistic energies. The ALICE VZERO system, made of two scintillator arrays at asymmetric positions, one on each side of the interaction point, plays a central role in ALICE. In addition to its core function as a trigger source, the VZERO system is used to monitor LHC beam conditions, to reject beam-induced backgrounds and to measure basic physics quantities such as luminosity, particle multiplicity, centrality and event plane direction in nucleus-nucleus collisions. After describing the VZERO system, this publication presents its performance over more than four years of operation at the LHC.
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12.
  • Abelev, B., et al. (författare)
  • J/psi production and nuclear effects in p-Pb collisions at=5.02 TeV
  • 2014
  • Ingår i: Journal of High Energy Physics. - 1029-8479. ; :2
  • Tidskriftsartikel (refereegranskat)abstract
    • Inclusive J/psi production has been studied with the ALICE detector in p-Pb collisions at the nucleon-nucleon center of mass energy = 5.02 TeV at the CERN LHC. The measurement is performed in the center of mass rapidity domains 2.03 < y (cms) < 3.53 and -4.46 < y (cms) < -2.96, down to zero transverse momentum, studying the mu (+) mu (-) decay mode. In this paper, the J/psi production cross section and the nuclear modification factor R (pPb) for the rapidities under study are presented. While at forward rapidity, corresponding to the proton direction, a suppression of the J/psi yield with respect to binary-scaled pp collisions is observed, in the backward region no suppression is present. The ratio of the forward and backward yields is also measured differentially in rapidity and transverse momentum. Theoretical predictions based on nuclear shadowing, as well as on models including, in addition, a contribution from partonic energy loss, are in fair agreement with the experimental results.
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13.
  • Abelev, B, et al. (författare)
  • K_{S}^{0} and Λ Production in Pb-Pb Collisions at sqrt[s_{NN}]=2.76 TeV.
  • 2013
  • Ingår i: Physical Review Letters. - 1079-7114. ; 111:22
  • Tidskriftsartikel (refereegranskat)abstract
    • The ALICE measurement of K_{S}^{0} and Λ production at midrapidity in Pb-Pb collisions at sqrt[s_{NN}]=2.76 TeV is presented. The transverse momentum (p_{T}) spectra are shown for several collision centrality intervals and in the p_{T} range from 0.4 GeV/c (0.6 GeV/c for Λ) to 12 GeV/c. The p_{T} dependence of the Λ/K_{S}^{0} ratios exhibits maxima in the vicinity of 3 GeV/c, and the positions of the maxima shift towards higher p_{T} with increasing collision centrality. The magnitude of these maxima increases by almost a factor of three between most peripheral and most central Pb-Pb collisions. This baryon excess at intermediate p_{T} is not observed in pp interactions at sqrt[s]=0.9 TeV and at sqrt[s]=7 TeV. Qualitatively, the baryon enhancement in heavy-ion collisions is expected from radial flow. However, the measured p_{T} spectra above 2 GeV/c progressively decouple from hydrodynamical-model calculations. For higher values of p_{T}, models that incorporate the influence of the medium on the fragmentation and hadronization processes describe qualitatively the p_{T} dependence of the Λ/K_{S}^{0} ratio.
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14.
  • Abelev, B., et al. (författare)
  • Long-range angular correlations of pi, K and p in p-Pb collisions at root s(NN)=5.02 TeV
  • 2013
  • Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 726:1-3, s. 164-177
  • Tidskriftsartikel (refereegranskat)abstract
    • Angular correlations between unidentified charged trigger particles and various species of charged associated particles (unidentified particles, pions, kaons, protons and antiprotons) are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV in the transverse-momentum range 0.3 < p(T) < 4 GeV/c. The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range vertical bar n(lab)vertical bar < 0.8. Fourier coefficients are extracted from the long-range correlations projected onto the azimuthal angle difference and studied as a function of p(T) and in intervals of event multiplicity. In high-multiplicity events, the second-order coefficient for protons, 4, is observed to be smaller than that for pions, v(2)(pi), up to about p(T) = 2 GeV/c. To reduce correlations due to jets, the per-trigger yield measured in low-multiplicity events is subtracted from that in high-multiplicity events. A two-ridge structure is obtained for all particle species. The Fourier decomposition of this structure shows that the second-order coefficients for pions and kaons are similar. The v(2)(p) is found to be smaller at low P-T and larger at higher p(T) than v(2)(pi), with a crossing occurring at about 2 GeV/c. This is qualitatively similar to the elliptic-flow pattern observed in heavy-ion collisions. A mass ordering effect at low transverse momenta is consistent with expectations from hydrodynamic model calculations assuming a collectively expanding system. (C) 2013 CERN. Published by Elsevier B.V. All rights reserved.
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15.
  • Abbas, E., et al. (författare)
  • J/psi Elliptic Flow in Pb-Pb Collisions at root s(NN)=2.76 TeV
  • 2013
  • Ingår i: Physical Review Letters. - 1079-7114. ; 111:16
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on the first measurement of inclusive J/psi elliptic flow v(2) in heavy-ion collisions at the LHC. The measurement is performed with the ALICE detector in Pb-Pb collisions at root s(NN) = 2.76 TeV in the rapidity range 2.5 < y < 4.0. The dependence of the J/psi v(2) on the collision centrality and on the J/psi transverse momentum is studied in the range 0 <= p(T) < 10 GeV/c. For semicentral Pb-Pb collisions at root s(NN) = 2.76 TeV, an indication of nonzero v(2) is observed with a largest measured value of v(2) = 0.116 +/-0.046(stat) +/- 0.029(syst) for J/psi in the transverse momentum range 2 <= p(T) < 4 GeV/c. The elliptic flow measurement complements the previously reported ALICE results on the inclusive J/psi nuclear modification factor and favors the scenario of a significant fraction of J/psi production from charm quarks in a deconfined partonic phase.
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16.
  • Abelev, B., et al. (författare)
  • Charge correlations using the balance function in Pb-Pb collisions at root s(NN)=2.76 TeV
  • 2013
  • Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 723:4-5, s. 267-279
  • Tidskriftsartikel (refereegranskat)abstract
    • In high-energy heavy-ion collisions, the correlations between the emitted particles can be used as a probe to gain insight into the charge creation mechanisms. In this Letter, we report the first results of such studies using the electric charge balance function in the relative pseudorapidity (Delta eta) and azimuthal angle (Delta phi) in Pb-Pb collisions at root s(NN) = 2.76 TeV with the ALICE detector at the Large Hadron Collider. The width of the balance function decreases with growing centrality (i.e. for more central collisions) in both projections. This centrality dependence is not reproduced by HIJING, while AMPT, a model which incorporates strings and parton rescattering, exhibits qualitative agreement with the measured correlations in Delta phi but fails to describe the correlations in Delta eta. A thermal blast-wave model incorporating local charge conservation and tuned to describe the p(T) spectra and v(2) measurements reported by ALICE, is used to fit the centrality dependence of the width of the balance function and to extract the average separation of balancing charges at freeze-out. The comparison of our results with measurements at lower energies reveals an ordering with root s(NN): the balance functions become narrower with increasing energy for all centralities. This is consistent with the effect of larger radial flow at the LHC energies but also with the late stage creation scenario of balancing charges. However, the relative decrease of the balance function widths in Delta eta and Delta phi, with centrality from the highest SPS to the LHC energy exhibits only small differences. This observation cannot be interpreted solely within the framework where the majority of the charge is produced at a later stage in the evolution of the heavy-ion collision. (C) 2013 CERN. Published by Elsevier B.V. All rights reserved.
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17.
  • Abelev, B., et al. (författare)
  • Energy dependence of the transverse momentum distributions of charged particles in pp collisions measured by ALICE
  • 2013
  • Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 73:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Differential cross sections of charged particles in inelastic pp collisions as a function of pT have been measured at root s = 0.9, 2.76 and 7 TeV at the LHC. The pT spectra are compared to NLO-pQCD calculations. Though the differential cross section for an individual root s cannot be described by NLO-pQCD, the relative increase of cross section with root s is in agreement with NLO-pQCD. Based on these measurements and observations, procedures are discussed to construct pp reference spectra at root s = 2.76 and 5.02 TeV up to pT = 50 GeV/c as required for the calculation of the nuclear modification factor in nucleus-nucleus and proton-nucleus collisions.
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18.
  • Abelev, B., et al. (författare)
  • Multi-strange baryon production at mid-rapidity in Pb-Pb collisions at root s(NN)=2.76 TeV
  • 2014
  • Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 728, s. 216-227
  • Tidskriftsartikel (refereegranskat)abstract
    • The production of Xi(-) and Omega(-) baryons and their anti-particles in Pb-Pb collisions root s(NN) = 2.76 TeV has been measured using the ALICE detector. The transverse momentum spectra at mid-rapidity (vertical bar y vertical bar < 0.5) for charged Xi and Omega hyperons have been studied in the range 0.6 < P-T < 8.0 GeV/c and 1.2 < p(T) < 7.0 GeV/c, respectively, and in several centrality intervals (from the most central 0-.10% to the most peripheral 60-80% collisions). These spectra have been compared with the predictions of recent hydrodynamic models. In particular, the Krakow and EPOS models give a satisfactory description of the data, with the latter covering a wider P-T range. Mid-rapidity yields, integrated over p(T), have been determined. The hyperon-to-pion ratios are similar to those at RHIC: they rise smoothly with centrality up to < N-part > similar to 150 and saturate thereafter. The enhancements (yields per participant nucleon relative to those in pp collisions) increase both with the strangeness content of the baryon and with centrality, but are less pronounced than at lower energies. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.
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19.
  • Abbas, E., et al. (författare)
  • Centrality dependence of the pseudorapidity density distribution for charged particles in Pb-Pb collisions at root s(NN)=2.76 TeV
  • 2013
  • Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 726:4-5, s. 610-622
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the first wide-range measurement of the charged-particle pseudorapidity density distribution, for different centralities (the 0-5%, 5-10%, 10-20%, and 20-30% most central events) in Pb-Pb collisions at root s(NN) = 2.76 TeV at the LHC. The measurement is performed using the full coverage of the ALICE detectors, -5.0 < eta < 5.5, and employing a special analysis technique based on collisions arising from LHC 'satellite' bunches. We present the pseudorapidity density as a function of the number of participating nucleons as well as an extrapolation to the total number of produced charged particles (N-ch = 17165 +/- 772 for the 0-5% most central collisions). From the measured dN(ch)/d eta distribution we derive the rapidity density distribution, dN(ch)/dy, under simple assumptions. The rapidity density distribution is found to be significantly wider than the predictions of the Landau model. We assess the validity of longitudinal scaling by comparing to lower energy results from RHIC. Finally the mechanisms of the underlying particle production are discussed based on a comparison with various theoretical models. (C) 2013 CERN. Published by Elsevier B.V. All rights reserved.
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20.
  • Abelev, B., et al. (författare)
  • Centrality dependence of pi, K, and p production in Pb-Pb collisions at root s(NN)=2.76 TeV
  • 2013
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 88:4
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper measurements are presented of pi(+/-), K-+/-, p, and (p) over bar production at midrapidity (vertical bar y vertical bar < 0.5), in Pb-Pb collisions at root s(NN) = 2.76 TeV as a function of centrality. The measurement covers the transverse-momentum (p(T)) range from 100, 200, and 300 MeV/c up to 3, 3, and 4.6 GeV/c for pi, K, and p, respectively. The measured p(T) distributions and yields are compared to expectations based on hydrodynamic, thermal and recombination models. The spectral shapes of central collisions show a stronger radial flow than measured at lower energies, which can be described in hydrodynamic models. In peripheral collisions, the p(T) distributions are not well reproduced by hydrodynamic models. Ratios of integrated particle yields are found to be nearly independent of centrality. The yield of protons normalized to pions is a factor similar to 1.5 lower than the expectation from thermal models.
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21.
  • Abelev, B., et al. (författare)
  • Centrality determination of Pb-Pb collisions at root s(NN)=2.76 TeV with ALICE
  • 2013
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 88:4
  • Tidskriftsartikel (refereegranskat)abstract
    • This publication describes the methods used to measure the centrality of inelastic Pb-Pb collisions at a center-of-mass energy of 2.76 TeV per colliding nucleon pair with ALICE. The centrality is a key parameter in the study of the properties of QCD matter at extreme temperature and energy density, because it is directly related to the initial overlap region of the colliding nuclei. Geometrical properties of the collision, such as the number of participating nucleons and the number of binary nucleon-nucleon collisions, are deduced from a Glauber model with a sharp impact parameter selection and shown to be consistent with those extracted from the data. The centrality determination provides a tool to compare ALICE measurements with those of other experiments and with theoretical calculations.
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22.
  • Abelev, B., et al. (författare)
  • Charged kaon femtoscopic correlations in pp collisions at root s=7 TeV
  • 2013
  • Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 87:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Correlations of two charged identical kaons (KchKch) are measured in pp collisions at root s = 7 TeV by the ALICE experiment at the Large Hadron Collider (LHC). One-dimensional (KKch)-K-ch correlation functions are constructed in three multiplicity and four transverse momentum ranges. The (KKch)-K-ch femtoscopic source parameters R and lambda are extracted. The (KKch)-K-ch correlations show a slight increase of femtoscopic radii with increasing multiplicity and a slight decrease of radii with increasing transverse momentum. These trends are similar to the ones observed for pi pi and K-s(0) K-s(0) correlations in pp and heavy-ion collisions. However at high multiplicities, there is an indication that the one-dimensional correlation radii for charged kaons are larger than those for pions in contrast to what was observed in heavy-ion collisions at the Relativistic Heavy-Ion Collider. DOI:10.1103/PhysRevD.87.052016
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23.
  • Abelev, B., et al. (författare)
  • Coherent J/psi photoproduction in ultra-peripheral Pb-Pb collisions at root s(NN)=2.76 TeV
  • 2013
  • Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 718:4-5, s. 1273-1283
  • Tidskriftsartikel (refereegranskat)abstract
    • The ALICE Collaboration has made the first measurement at the LHC of J/psi photoproduction in ultra-peripheral Pb-Pb collisions at root s(NN) = 2.76 TeV. The J/psi is identified via its dimuon decay in the forward rapidity region with the muon spectrometer for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 55 mu b(-1). The cross section for coherent J/psi production in the rapidity interval -3.6 < y < -2.6 is measured to be d sigma(coh)(J/psi)/dy = 1.00 +/- 0.18(stat)(-0.26)(+0.24)(syst) mb. The result is compared to theoretical models for coherent J/psi production and found to be in good agreement with those models which include nuclear gluon shadowing. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.
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24.
  • Abelev, B., et al. (författare)
  • Pseudorapidity Density of Charged Particles in p plus Pb Collisions at root s(NN)=5.02 TeV
  • 2013
  • Ingår i: Physical Review Letters. - 1079-7114. ; 110:3
  • Tidskriftsartikel (refereegranskat)abstract
    • The charged-particle pseudorapidity density measured over four units of pseudorapidity in nonsingle-diffractive p + Pb collisions at a center-of-mass energy per nucleon pair root s(NN) = 5.02 TeV is presented. The average value at midrapidity is measured to be 16.81 +/- 0.71 (syst), which corresponds to 2.14 +/- 0.17 (syst) per participating nucleon, calculated with the Glauber model. This is 16% lower than in nonsingle-diffractive pp collisions interpolated to the same collision energy and 84% higher than in d + Au collisions at root s(NN) = 0.2 TeV. The measured pseudorapidity density in p + Pb collisions is compared to model predictions and provides new constraints on the description of particle production in high-energy nuclear collisions. DOI: 10.1103/PhysRevLett.110.032301
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25.
  • Abelev, B., et al. (författare)
  • Transverse Momentum Distribution and Nuclear Modification Factor of Charged Particles in p plus Pb Collisions at root(NN)-N-s=5.02 TeV
  • 2013
  • Ingår i: Physical Review Letters. - 1079-7114. ; 110:8
  • Tidskriftsartikel (refereegranskat)abstract
    • The transverse momentum (pT) distribution of primary charged particles is measured in minimum bias (non-single-diffractive) p + Pb collisions at root(NN)-N-s = 5.02 TeV with the ALICE detector at the LHC. The pT spectra measured near central rapidity in the range 0.5< p(T) < 20 GeV/c exhibit a weak pseudorapidity dependence. The nuclear modification factor R-pPb is consistent with unity for p(T) above 2 GeV/c. This measurement indicates that the strong suppression of hadron production at high p(T) observed in Pb + Pb collisions at the LHC is not due to an initial-state effect. The measurement is compared to theoretical calculations. DOI: 10.1103/PhysRevLett.110.082302
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26.
  • Abelev, B., et al. (författare)
  • Measurement of the inclusive differential jet cross section in pp collisions at root s=2.76 TeV
  • 2013
  • Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 722:4-5, s. 262-272
  • Tidskriftsartikel (refereegranskat)abstract
    • The ALICE Collaboration at the CERN Large Hadron Collider reports the first measurement of the inclusive differential jet cross section at mid-rapidity in pp collisions at root s = 2.76 TeV, with integrated luminosity of 13.6 nb(-1). Jets are measured over the transverse momentum range 20 to 125 GeV/c and are corrected to the particle level. Calculations based on Next-to-Leading Order perturbative QCD are in good agreement with the measurements. The ratio of inclusive jet cross sections for jet radii R = 0.2 and R = 0.4 is reported, and is also well reproduced by a Next-to-Leading Order perturbative QCD calculation when hadronization effects are included. (c) 2013 CERN. Published by Elsevier B.V. All rights reserved.
  •  
27.
  • Campbell, PJ, et al. (författare)
  • Pan-cancer analysis of whole genomes
  • 2020
  • Ingår i: Nature. - : Springer Science and Business Media LLC. - 1476-4687 .- 0028-0836. ; 578:7793, s. 82-
  • Tidskriftsartikel (refereegranskat)abstract
    • Cancer is driven by genetic change, and the advent of massively parallel sequencing has enabled systematic documentation of this variation at the whole-genome scale1–3. Here we report the integrative analysis of 2,658 whole-cancer genomes and their matching normal tissues across 38 tumour types from the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium of the International Cancer Genome Consortium (ICGC) and The Cancer Genome Atlas (TCGA). We describe the generation of the PCAWG resource, facilitated by international data sharing using compute clouds. On average, cancer genomes contained 4–5 driver mutations when combining coding and non-coding genomic elements; however, in around 5% of cases no drivers were identified, suggesting that cancer driver discovery is not yet complete. Chromothripsis, in which many clustered structural variants arise in a single catastrophic event, is frequently an early event in tumour evolution; in acral melanoma, for example, these events precede most somatic point mutations and affect several cancer-associated genes simultaneously. Cancers with abnormal telomere maintenance often originate from tissues with low replicative activity and show several mechanisms of preventing telomere attrition to critical levels. Common and rare germline variants affect patterns of somatic mutation, including point mutations, structural variants and somatic retrotransposition. A collection of papers from the PCAWG Consortium describes non-coding mutations that drive cancer beyond those in the TERT promoter4; identifies new signatures of mutational processes that cause base substitutions, small insertions and deletions and structural variation5,6; analyses timings and patterns of tumour evolution7; describes the diverse transcriptional consequences of somatic mutation on splicing, expression levels, fusion genes and promoter activity8,9; and evaluates a range of more-specialized features of cancer genomes8,10–18.
  •  
28.
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29.
  • de Rojas, I., et al. (författare)
  • Common variants in Alzheimer’s disease and risk stratification by polygenic risk scores
  • 2021
  • Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Genetic discoveries of Alzheimer’s disease are the drivers of our understanding, and together with polygenetic risk stratification can contribute towards planning of feasible and efficient preventive and curative clinical trials. We first perform a large genetic association study by merging all available case-control datasets and by-proxy study results (discovery n = 409,435 and validation size n = 58,190). Here, we add six variants associated with Alzheimer’s disease risk (near APP, CHRNE, PRKD3/NDUFAF7, PLCG2 and two exonic variants in the SHARPIN gene). Assessment of the polygenic risk score and stratifying by APOE reveal a 4 to 5.5 years difference in median age at onset of Alzheimer’s disease patients in APOE ɛ4 carriers. Because of this study, the underlying mechanisms of APP can be studied to refine the amyloid cascade and the polygenic risk score provides a tool to select individuals at high risk of Alzheimer’s disease. © 2021, The Author(s).
  •  
30.
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31.
  • Hudson, Lawrence N, et al. (författare)
  • The database of the PREDICTS (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems) project
  • 2017
  • Ingår i: Ecology and Evolution. - : John Wiley & Sons. - 2045-7758. ; 7:1, s. 145-188
  • Tidskriftsartikel (refereegranskat)abstract
    • The PREDICTS project-Projecting Responses of Ecological Diversity In Changing Terrestrial Systems (www.predicts.org.uk)-has collated from published studies a large, reasonably representative database of comparable samples of biodiversity from multiple sites that differ in the nature or intensity of human impacts relating to land use. We have used this evidence base to develop global and regional statistical models of how local biodiversity responds to these measures. We describe and make freely available this 2016 release of the database, containing more than 3.2 million records sampled at over 26,000 locations and representing over 47,000 species. We outline how the database can help in answering a range of questions in ecology and conservation biology. To our knowledge, this is the largest and most geographically and taxonomically representative database of spatial comparisons of biodiversity that has been collated to date; it will be useful to researchers and international efforts wishing to model and understand the global status of biodiversity.
  •  
32.
  • Bellenguez, C, et al. (författare)
  • New insights into the genetic etiology of Alzheimer's disease and related dementias
  • 2022
  • Ingår i: Nature genetics. - : Springer Science and Business Media LLC. - 1546-1718 .- 1061-4036. ; 54:4, s. 412-436
  • Tidskriftsartikel (refereegranskat)abstract
    • Characterization of the genetic landscape of Alzheimer’s disease (AD) and related dementias (ADD) provides a unique opportunity for a better understanding of the associated pathophysiological processes. We performed a two-stage genome-wide association study totaling 111,326 clinically diagnosed/‘proxy’ AD cases and 677,663 controls. We found 75 risk loci, of which 42 were new at the time of analysis. Pathway enrichment analyses confirmed the involvement of amyloid/tau pathways and highlighted microglia implication. Gene prioritization in the new loci identified 31 genes that were suggestive of new genetically associated processes, including the tumor necrosis factor alpha pathway through the linear ubiquitin chain assembly complex. We also built a new genetic risk score associated with the risk of future AD/dementia or progression from mild cognitive impairment to AD/dementia. The improvement in prediction led to a 1.6- to 1.9-fold increase in AD risk from the lowest to the highest decile, in addition to effects of age and the APOE ε4 allele.
  •  
33.
  • Stroth, U., et al. (författare)
  • Progress from ASDEX Upgrade experiments in preparing the physics basis of ITER operation and DEMO scenario development
  • 2022
  • Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 62:4
  • Tidskriftsartikel (refereegranskat)abstract
    • An overview of recent results obtained at the tokamak ASDEX Upgrade (AUG) is given. A work flow for predictive profile modelling of AUG discharges was established which is able to reproduce experimental H-mode plasma profiles based on engineering parameters only. In the plasma center, theoretical predictions on plasma current redistribution by a dynamo effect were confirmed experimentally. For core transport, the stabilizing effect of fast ion distributions on turbulent transport is shown to be important to explain the core isotope effect and improves the description of hollow low-Z impurity profiles. The L-H power threshold of hydrogen plasmas is not affected by small helium admixtures and it increases continuously from the deuterium to the hydrogen level when the hydrogen concentration is raised from 0 to 100%. One focus of recent campaigns was the search for a fusion relevant integrated plasma scenario without large edge localised modes (ELMs). Results from six different ELM-free confinement regimes are compared with respect to reactor relevance: ELM suppression by magnetic perturbation coils could be attributed to toroidally asymmetric turbulent fluctuations in the vicinity of the separatrix. Stable improved confinement mode plasma phases with a detached inner divertor were obtained using a feedback control of the plasma β. The enhanced D α H-mode regime was extended to higher heating power by feedback controlled radiative cooling with argon. The quasi-coherent exhaust regime was developed into an integrated scenario at high heating power and energy confinement, with a detached divertor and without large ELMs. Small ELMs close to the separatrix lead to peeling-ballooning stability and quasi continuous power exhaust. Helium beam density fluctuation measurements confirm that transport close to the separatrix is important to achieve the different ELM-free regimes. Based on separatrix plasma parameters and interchange-drift-Alfvén turbulence, an analytic model was derived that reproduces the experimentally found important operational boundaries of the density limit and between L- and H-mode confinement. Feedback control for the X-point radiator (XPR) position was established as an important element for divertor detachment control. Stable and detached ELM-free phases with H-mode confinement quality were obtained when the XPR was moved 10 cm above the X-point. Investigations of the plasma in the future flexible snow-flake divertor of AUG by means of first SOLPS-ITER simulations with drifts activated predict beneficial detachment properties and the activation of an additional strike point by the drifts.
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34.
  • Meyer, H.F., et al. (författare)
  • Overview of physics studies on ASDEX Upgrade
  • 2019
  • Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
  • Forskningsöversikt (refereegranskat)abstract
    • The ASDEX Upgrade (AUG) programme, jointly run with the EUROfusion MST1 task force, continues to significantly enhance the physics base of ITER and DEMO. Here, the full tungsten wall is a key asset for extrapolating to future devices. The high overall heating power, flexible heating mix and comprehensive diagnostic set allows studies ranging from mimicking the scrape-off-layer and divertor conditions of ITER and DEMO at high density to fully non-inductive operation (q 95 = 5.5, ) at low density. Higher installed electron cyclotron resonance heating power 6 MW, new diagnostics and improved analysis techniques have further enhanced the capabilities of AUG. Stable high-density H-modes with MW m-1 with fully detached strike-points have been demonstrated. The ballooning instability close to the separatrix has been identified as a potential cause leading to the H-mode density limit and is also found to play an important role for the access to small edge-localized modes (ELMs). Density limit disruptions have been successfully avoided using a path-oriented approach to disruption handling and progress has been made in understanding the dissipation and avoidance of runaway electron beams. ELM suppression with resonant magnetic perturbations is now routinely achieved reaching transiently . This gives new insight into the field penetration physics, in particular with respect to plasma flows. Modelling agrees well with plasma response measurements and a helically localised ballooning structure observed prior to the ELM is evidence for the changed edge stability due to the magnetic perturbations. The impact of 3D perturbations on heat load patterns and fast-ion losses have been further elaborated. Progress has also been made in understanding the ELM cycle itself. Here, new fast measurements of and E r allow for inter ELM transport analysis confirming that E r is dominated by the diamagnetic term even for fast timescales. New analysis techniques allow detailed comparison of the ELM crash and are in good agreement with nonlinear MHD modelling. The observation of accelerated ions during the ELM crash can be seen as evidence for the reconnection during the ELM. As type-I ELMs (even mitigated) are likely not a viable operational regime in DEMO studies of 'natural' no ELM regimes have been extended. Stable I-modes up to have been characterised using -feedback. Core physics has been advanced by more detailed characterisation of the turbulence with new measurements such as the eddy tilt angle - measured for the first time - or the cross-phase angle of and fluctuations. These new data put strong constraints on gyro-kinetic turbulence modelling. In addition, carefully executed studies in different main species (H, D and He) and with different heating mixes highlight the importance of the collisional energy exchange for interpreting energy confinement. A new regime with a hollow profile now gives access to regimes mimicking aspects of burning plasma conditions and lead to nonlinear interactions of energetic particle modes despite the sub-Alfvénic beam energy. This will help to validate the fast-ion codes for predicting ITER and DEMO.
  •  
35.
  • Poyatos, R., et al. (författare)
  • Global transpiration data from sap flow measurements: the SAPFLUXNET database
  • 2021
  • Ingår i: Earth System Science Data. - : Copernicus GmbH. - 1866-3508 .- 1866-3516. ; 13:6, s. 2607-2649
  • Tidskriftsartikel (refereegranskat)abstract
    • Plant transpiration links physiological responses of vegetation to water supply and demand with hydrological, energy, and carbon budgets at the land-atmosphere interface. However, despite being the main land evaporative flux at the global scale, transpiration and its response to environmental drivers are currently not well constrained by observations. Here we introduce the first global compilation of whole-plant transpiration data from sap flow measurements (SAPFLUXNET, https://sapfluxnet.creaf.cat/, last access: 8 June 2021). We harmonized and quality-controlled individual datasets supplied by contributors worldwide in a semi-automatic data workflow implemented in the R programming language. Datasets include sub-daily time series of sap flow and hydrometeorological drivers for one or more growing seasons, as well as metadata on the stand characteristics, plant attributes, and technical details of the measurements. SAPFLUXNET contains 202 globally distributed datasets with sap flow time series for 2714 plants, mostly trees, of 174 species. SAPFLUXNET has a broad bioclimatic coverage, with woodland/shrubland and temperate forest biomes especially well represented (80 % of the datasets). The measurements cover a wide variety of stand structural characteristics and plant sizes. The datasets encompass the period between 1995 and 2018, with 50 % of the datasets being at least 3 years long. Accompanying radiation and vapour pressure deficit data are available for most of the datasets, while on-site soil water content is available for 56 % of the datasets. Many datasets contain data for species that make up 90 % or more of the total stand basal area, allowing the estimation of stand transpiration in diverse ecological settings. SAPFLUXNET adds to existing plant trait datasets, ecosystem flux networks, and remote sensing products to help increase our understanding of plant water use, plant responses to drought, and ecohydrological processes. SAPFLUXNET version 0.1.5 is freely available from the Zenodo repository (https://doi.org/10.5281/zenodo.3971689; Poyatos et al., 2020a). The "sapfluxnetr" R package - designed to access, visualize, and process SAPFLUXNET data - is available from CRAN.
  •  
36.
  • Jackura, A., et al. (författare)
  • New analysis of eta pi tensor resonances measured at the COMPASS experiment
  • 2018
  • Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 779, s. 464-472
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a new amplitude analysis of the eta pi D-wave in the reaction pi(-) p -> eta pi(-) p measured by COMPASS. Employing an analytical model based on the principles of the relativistic S-matrix, we find two resonances that can be identified with the a(2)(1320) and the excited a(2)(1700), and perform a comprehensive analysis of their pole positions. For the mass and width of the a(2) we find M = (1307 +/- 1 6) MeV and Gamma=(112 +/- 1 +/- 8) MeV, and for the excited state a(2)' we obtain M = (1720 +/- 10 +/- 60) MeV and Gamma = (280 +/- 10 +/- 70) MeV, respectively.
  •  
37.
  • Adolph, C., et al. (författare)
  • First measurement of the Sivers asymmetry for gluons using SIDIS data
  • 2017
  • Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 772, s. 854-864
  • Tidskriftsartikel (refereegranskat)abstract
    • The Sivers function describes the correlation between the transverse spin of a nucleon and the transverse motion of its partons. For quarks, it was studied in previous measurements of the azimuthal asymmetry of hadrons produced in semi-inclusive deep inelastic scattering of leptons off transversely polarised nucleon targets, and it was found to be non-zero. In this letter the evaluation of the Sivers asymmetry for gluons is presented. The contribution of the photon-gluon fusion subprocess is enhanced by requiring two high transverse-momentum hadrons. The analysis method is based on a Monte Carlo simulation that includes three hard processes: photon-gluon fusion, QCD Compton scattering and the leading-order virtual-photon absorption process. The Sivers asymmetries of the three processes are simultaneously extracted using the LEPTO event generator and a neural network approach. The method is applied to samples of events containing at least two hadrons with large transverse momentum from the COMPASS data taken with a 160 GeV/c muon beam scattered off transversely polarised deuterons and protons. With a significance of about two standard deviations, a negative value is obtained for the gluon Sivers asymmetry. The result of a similar analysis for a Collins-like asymmetry for gluons is consistent with zero. (C) 2017 The Author(s). Published by Elsevier B.V.
  •  
38.
  • Aghasyan, M., et al. (författare)
  • First Measurement of Transverse-Spin-Dependent Azimuthal Asymmetries in the Drell-Yan Process
  • 2017
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 119:11
  • Tidskriftsartikel (refereegranskat)abstract
    • The first measurement of transverse-spin-dependent azimuthal asymmetries in the pion-induced Drell-Yan (DY) process is reported. We use the CERN SPS 190 GeV/c pi(-) beam and a transversely polarized ammonia target. Three azimuthal asymmetries giving access to different transverse-momentum-dependent (TMD) parton distribution functions (PDFs) are extracted using dimuon events with invariant mass between 4.3 GeV/c(2) and 8.5 GeV/c(2). Within the experimental uncertainties, the observed sign of the Sivers asymmetry is found to be consistent with the fundamental prediction of quantum chromodynamics (QCD) that the Sivers TMD PDFs extracted from DY have a sign opposite to the one extracted from semi-inclusive deep-inelastic scattering (SIDIS) data. We present two other asymmetries originating from the pion Boer-Mulders TMD PDFs convoluted with either the nucleon transversity or pretzelosity TMD PDFs. A recent COMPASS SIDIS measurement was obtained at a hard scale comparable to that of these DY results. This opens the way for possible tests of fundamental QCD universality predictions.
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39.
  • Adolph, C., et al. (författare)
  • Azimuthal asymmetries of charged hadrons produced in high-energy muon scattering off longitudinally polarised deuterons
  • 2018
  • Ingår i: European Physical Journal C. - : SPRINGER. - 1434-6044 .- 1434-6052. ; 78:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Single hadron azimuthal asymmetries of positive and negative hadrons produced in muon semi-inclusive deep inelastic scattering off longitudinally polarised deuterons are determined using the 2006 COMPASS data and also combined all deuteron COMPASS data. For each hadron charge, the dependence of the azimuthal asymmetry on the hadron azimuthal angle f is obtained by means of a fiveparameter fitting function that besides a f-independent term includes four modulations predicted by theory: sin f, sin 2f, sin 3f and cos f. The amplitudes of the five terms have been extracted, first, for the hadrons in the whole available kinematic region. In further fits, performed for hadrons from a restricted kinematic region, the f-dependence is determined as a function of one of three variables (Bjorken-x, fractional energy of virtual photon taken by the outgoing hadron and hadron transverse momentum), while disregarding the others. Except thef-independent term, all themodulation amplitudes are very small, and no clear kinematic dependence could be observed within experimental uncertainties.
  •  
40.
  • Adolph, C., et al. (författare)
  • Final COMPASS results on the deuteron spin-dependent structure function g(1)(d) and the Bjorken sum rule
  • 2017
  • Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 769, s. 34-41
  • Tidskriftsartikel (refereegranskat)abstract
    • Final results are presented from the inclusive measurement of deep-inelastic polarised-muon scattering on longitudinally polarised deuterons using a 6LiD target. The data were taken at 160 GeV beam energy and the results are shown for the kinematic range 1 (GeV/c)2 < Q2 < 100 (GeV/c)2 in photon virtuality, 0.004 < x < 0.7 in the Bjorken scaling variable and W > 4GeV/c2 in the mass of the hadronic final state. The deuteron double-spin asymmetry A(1)(d) and the deuteron longitudinal-spin structure function g(1)(d) are presented in bins of x and Q2. Towards lowest accessible values of x, g(1)(d) decreases and becomes consistent with zero within uncertainties. The presented final g(1)(p) values together with the recently published final g(1)(p) values of COMPASS are used to again evaluate the Bjorken sum rule and perform the QCD fit to the g1 world data at next-to-leading order of the strong coupling constant. In both cases, changes in central values of the resulting numbers are well within statistical uncertainties. The flavour singlet axial charge a0, which is identified in the MS renormalisation scheme with the total contribution of quark helicities to the nucleon spin, is extracted at next-to-leading order accuracy from only the COMPASS deuteron data: a0(Q2 = 3 (GeV/c)2) = 0.32 +/- 0.02stat +/- 0.04syst +/- 0.05evol. Together with the recent results on the proton spin structure function g(1)(p), the results on g(1)(d) constitute the COMPASS legacy on the measurements of g1 through inclusive spin-dependent deep inelastic scattering.
  •  
41.
  • Adolph, C., et al. (författare)
  • Leading-order determination of the gluon polarisation from semi-inclusive deep inelastic scattering data
  • 2017
  • Ingår i: European Physical Journal C. - : SPRINGER. - 1434-6044 .- 1434-6052. ; 77:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Using a novel analysis technique, the gluon polarisation in the nucleon is re-evaluated using the longitudinal double-spin asymmetry measured in the cross section of semi-inclusive single-hadron muoproduction with photon virtuality Q(2) > 1 ( GeV/c)(2). The data were obtained by the COMPASS experiment at CERN using a 160 GeV/c polarised muon beam impinging on a polarised (LiD)-Li-6 target. By analysing the full range in hadron transverse momentum p(T), the different pT-dependences of the underlying processes are separated using a neural-network approach. In the absence of pQCD calculations at next-to-leading order in the selected kinematic domain, the gluon polarisation Delta g/g is evaluated at leading order in pQCD at a hard scale of mu(2) = < Q(2) > = 3( GeV/c)(2). It is determined in three intervals of the nucleon momentum fraction carried by gluons, x(g), covering the range 0.04< x(g)< 0.28 and does not exhibit a significant dependence on xg. The average over the three intervals, < Delta g/g > = 0.113 +/- 0.038(stat) +/- 0.036( syst) at < x(g) > approximate to 0.10, suggests that the gluon polarisation is positive in the measured x(g) range.
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42.
  • Adolph, C., et al. (författare)
  • Multiplicities of charged pions and charged hadrons from deep-inelastic scattering of muons off an isoscalar target
  • 2017
  • Ingår i: Physics Letters B. - : ELSEVIER SCIENCE BV. - 0370-2693 .- 1873-2445. ; 764, s. 1-10
  • Tidskriftsartikel (refereegranskat)abstract
    • Multiplicities of charged pions and charged hadrons produced in deep-inelastic scattering were measured in three-dimensional bins of the Bjorken scaling variable x, the relative virtual-photon energy y and the relative hadron energy z. Data were obtained by the COMPASS Collaboration using a 160 GeV muon beam and an isoscalar target ((LiD)-Li-6). They cover the kinematic domain in the photon virtuality Q(2) > 1 (GeV/c) 2, 0.004 < x < 0.4, 0.2 < z < 0.85 and 0.1 < y < 0.7. In addition, a leading-order pQCD analysis was performed using the pion multiplicity results to extract quark fragmentation functions.
  •  
43.
  • Adolph, C., et al. (författare)
  • Sivers asymmetry extracted in SIDIS at the hard scales of the Drell-Yan process at COMPASS
  • 2017
  • Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 770, s. 138-145
  • Tidskriftsartikel (refereegranskat)abstract
    • Eight proton transverse-spin-dependent azimuthal asymmetries are extracted in four regions of the photon virtuality Q(2) from the COMPASS 2010 semi-inclusive hadron measurements in deep inelastic muon nucleon scattering. These Q(2) regions correspond to the four regions of the di-muon mass root Q(2) used in the ongoing analyses of the COMPASS Drell-Yan measurements, which allows for a future direct comparison of the nucleon transverse-momentum-dependent parton distribution functions extracted from these two alternative measurements. In addition, for the azimuthal asymmetries induced by the Sivers transverse-momentum-dependent parton distribution function various two-dimensional kinematic dependences are presented. The integrated Sivers asymmetries are found to be positive with an accutacy that appears to be sufficient to test the sign change of the Sivers function predicted by Quantum Chromodynamics.
  •  
44.
  • Adolphi, C., et al. (författare)
  • Exclusive omega meson muoproduction on transversely polarised protons
  • 2017
  • Ingår i: Nuclear Physics B. - : ELSEVIER SCIENCE BV. - 0550-3213 .- 1873-1562. ; 915, s. 454-475
  • Tidskriftsartikel (refereegranskat)abstract
    • Exclusive production of omega mesons was studied at the COMPASS experiment by scattering 160GeV/c muons off transversely polarised protons. Five single-spin and three double-spin azimuthal asymmetries were measured in the range of photon virtuality 1(GeV/c)(2) < Q(2) < 10(GeV/c)(2), Bjorken scaling variable 0.003 < xBj < 0.3 and transverse momentum squared of the omega meson 0.05(GeV/c)(2) < p(T)(2) < 0.5(GeV/c)(2). The measured asymmetries are sensitive to the nucleon helicity-flip Generalised Parton Distributions (GPD) Et hat are related to the orbital angular momentum of quarks, the chiral-odd GPDs H-T that are related to the transversity Parton Distribution Functions, and the sign of the pi omega transition form factor. The results are compared to recent calculations of a GPD-based model.
  •  
45.
  • Aghasyan, M., et al. (författare)
  • Light isovector resonances in pi(-) p -> pi(-) pi(-) pi(+)p at 190 GeV/c
  • 2018
  • Ingår i: Physical Review D. - : AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 98:9
  • Tidskriftsartikel (refereegranskat)abstract
    • We have performed the most comprehensive resonance-model fit of pi(-)pi(-)pi(+) states using the results of our previously published partial-wave analysis (PWA) of a large data set of diffractive-dissociation events from the reaction pi(-) + p -> pi(-)pi(-)pi(+) +p(recoil) with a 190 GeV/c pion beam. The PWA results, which were obtained in 100 bins of three-pion mass, 0.5 < m(3 pi) < 2.5 GeV/c(2), and simultaneously in 11 bins of the reduced four-momentum transfer squared, 0.1 < t'< 1.0 (GeV/c)(2), are subjected to a resonance-model fit using Breit-Wigner amplitudes to simultaneously describe a subset of 14 selected waves using 11 isovector light-meson states with J(PC) = 0(-+), 1(++), 2(++), 2(-+), 4(++), and spin-exotic 1(-+) quantum numbers. The model contains the well-known resonances pi(1800), a(1)(1260), a(2)(1320), pi(2)(1670), pi(2)(1880), and a(4) (2040). In addition, it includes the disputed pi(1)(1600), the excited states a(1)(1640), a2(1700), and pi(2) (2005), as well as the resonancelike a(1)(1420). We measure the resonance parameters mass and width of these objects by combining the information from the PWA results obtained in the 11 t' bins. We extract the relative branching fractions of the rho(770)pi and f(2)(1270)pi decays of a(2)(1320) and a(4)(2040), where the former one is measured for the first time. In a novel approach, we extract the t' dependence of the intensity of the resonances and of their phases. The t' dependence of the intensities of most resonances differs distinctly from the t' dependence of the nonresonant components. For the first time, we determine the t' dependence of the phases of the production amplitudes and confirm that the production mechanism of the Pomeron exchange is common to all resonances. We have performed extensive systematic studies on the model dependence and correlations of the measured physical parameters.
  •  
46.
  • Aghasyan, M., et al. (författare)
  • Longitudinal double-spin asymmetry A(1)(p) and spin-dependent structure function g(1)(p) of the proton at small values of x and Q(2)
  • 2018
  • Ingår i: Physics Letters B. - : ELSEVIER SCIENCE BV. - 0370-2693 .- 1873-2445. ; 781, s. 464-472
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a precise measurement of the proton longitudinal double-spin asymmetry A(1)(p) and the proton spin-dependent structure function g(1)(P) at photon virtualities 0.006 (GeV/c)(2) < Q(2) < 1 (GeV/c)(2) in the Bjorken x range of 4 x 10(-5) < x < 4 x 10(-2). The results are based on data collected by the COMPASS Collaboration at CERN using muon beam energies of 160 GeV and 200 GeV. The statistical precision is more than tenfold better than that of the previous measurement in this region. In the whole range of x, the measured values of A(1)(p) and g(1)(P) are found to be positive. It is for the first time that spin effects are found at such low values of x.
  •  
47.
  • Aghasyan, M., et al. (författare)
  • Search for muoproduction of X(3872) at COMPASS and indication of a new state (X)over-tilde(3872)
  • 2018
  • Ingår i: Physics Letters B. - : ELSEVIER SCIENCE BV. - 0370-2693 .- 1873-2445. ; 783, s. 334-340
  • Tidskriftsartikel (refereegranskat)abstract
    • We have searched for exclusive production of exotic charmonia in the reaction mu N+ -> mu(+)(J/psi pi(+)pi(-))pi N-+/-' using COMPASS data collected with incoming muons of 160 GeV/c and 200 GeV/c momentum. In the J/psi pi(vertical bar)pi mass distribution we observe a signal with a statistical significance of 4.1 sigma. Its mass and width are consistent with those of the X(3872). The shape of the pi(+)pi(-) mass distribution from the observed decay into J/psi pi(+)pi(-) shows disagreement with previous observations for X(3872). The observed signal may be interpreted as a possible evidence of a new charmonium state. It could be associated with a neutral partner of X(3872) with C=-1 predicted by a tetraquark model. The product of cross section and branching fraction of the decay of the observed state into J/psi pi(+)pi(-) is determined to be 71 +/- 28(stat)+/- 39(syst) pb.
  •  
48.
  • Aghasyan, M., et al. (författare)
  • Transverse-momentum-dependent multiplicities of charged hadrons in muon-deuteron deep inelastic scattering
  • 2018
  • Ingår i: Physical Review D. - : AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 97:3
  • Tidskriftsartikel (refereegranskat)abstract
    • A semi-inclusive measurement of charged hadron multiplicities in deep inelastic muon scattering off an isoscalar target was performed using data collected by the COMPASS Collaboration at CERN. The following kinematic domain is covered by the data: photon virtuality Q(2) > 1 (GeV/c)(2), invariant mass of the hadronic system W > 5 (GeV/c)(2), Bjorken scaling variable in the range 0.003 < x < 0.4, fraction of the virtual photon energy carried by the hadron in the range 0.2 < z < 0.8, and square of the hadron transverse momentum with respect to the virtual photon direction in the range 0.02 (GeV/c)(2) < P-hT(2) < 3 (GeV/c)(2). The multiplicities are presented as a function of P-hT(2) in three-dimensional bins of x, Q(2), z and compared to previous semi-inclusive measurements. We explore the small-P-hT(2) region, i.e. P-hT(2) < 1 (GeV/c)(2), where hadron transverse momenta are expected to arise from nonperturbative effects, and also the domain of larger P-hT(2), where contributions from higher-order perturbative QCD are expected to dominate. The multiplicities are fitted using a single-exponential function at small P-hT(2) to study the dependence of the average transverse momentum < P-hT(2)> on x, Q(2) and z. The power-law behavior of the multiplicities at large P-hT(2) is investigated using various functional forms. The fits describe the data reasonably well over the full measured range.
  •  
49.
  • Akhunzyanov, R., et al. (författare)
  • Transverse extension of partons in the proton probed in the sea-quark range by measuring the DVCS cross section
  • 2019
  • Ingår i: Physics Letters B. - : ELSEVIER SCIENCE BV. - 0370-2693 .- 1873-2445. ; 793, s. 188-194
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on the first measurement of exclusive single-photon muoproduction on the proton by COMPASS using 160 GeV/c polarised mu(+) and mu(-) beams of the CERN SPS impinging on a liquid hydrogen target. We determine the dependence of the average of the measured mu(+) and mu(-) cross sections for deeply virtual Compton scattering on the squared four-momentum transfer t from the initial to the final proton. The slope B of the t-dependence is fitted with a single exponential function, which yields B = (4.3 +/- 0.6(stat) (+0.1)(-0.3)vertical bar(sys)) (GeV/c)(-2). This result can be converted into a transverse extension of partons in the proton,root(r(perpendicular to)(2)) = (0.58 +/- 0.04(stat) (+0.01)(-0.02)vertical bar(sys) +/- 0.04(model)) fm. For this measurement, the average virtuality of the photon mediating the interaction is < Q(2)> = 1.8 (GeV/c)(2) and the average value of the Bjorken variable is < X-Bj > = 0.056.
  •  
50.
  • Adolph, C., et al. (författare)
  • Multiplicities of charged kaons from deep-inelastic muon scattering off an isoscalar target
  • 2017
  • Ingår i: Physics Letters B. - : ELSEVIER SCIENCE BV. - 0370-2693 .- 1873-2445. ; 767, s. 133-141
  • Tidskriftsartikel (refereegranskat)abstract
    • Precise measurements of charged-kaon multiplicities in deep inelastic scattering were performed. The results are presented in three-dimensional bins of the Bjorken scaling variable x, the relative virtual-photon energy y, and the fraction z of the virtual-photon energy carried by the produced hadron. The data were obtained by the COMPASS Collaboration by scattering 160 GeV muons off an isoscalar (LiD)-Li-6 target. They cover the kinematic domain 1 (GeV/c)(2) < Q(2) < 60 (GeV/c)(2) in the photon virtuality, 0.004 < x < 0.4, 0.1 < y < 0.7, 0.20 < z < 0.85, and W > 5 GeV/c(2) in the invariant mass of the hadronic system. The results from the sum of the z-integrated K+ and K- multiplicities at high x point to a value of the non-strange quark fragmentation function larger than obtained by the earlier DSS fit.
  •  
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