| 1. |
- Abelev, Betty, et al.
(författare)
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Long-range angular correlations on the near and away side in p-Pb collisions at root S-NN=5.02 TeV
- 2013
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 719:1-3, s. 29-41
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Tidskriftsartikel (refereegranskat)abstract
- Angular correlations between charged trigger and associated particles are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV for transverse momentum ranges within 0.5 < P-T,P-assoc < P-T,P-trig < 4 GeV/c. The correlations are measured over two units of pseudorapidity and full azimuthal angle in different intervals of event multiplicity, and expressed as associated yield per trigger particle. Two long-range ridge-like structures, one on the near side and one on the away side, are observed when the per-trigger yield obtained in low-multiplicity events is subtracted from the one in high-multiplicity events. The excess on the near-side is qualitatively similar to that recently reported by the CMS Collaboration, while the excess on the away-side is reported for the first time. The two-ridge structure projected onto azimuthal angle is quantified with the second and third Fourier coefficients as well as by near-side and away-side yields and widths. The yields on the near side and on the away side are equal within the uncertainties for all studied event multiplicity and p(T) bins, and the widths show no significant evolution with event multiplicity or p(T). These findings suggest that the near-side ridge is accompanied by an essentially identical away-side ridge. (c) 2013 CERN. Published by Elsevier B.V. All rights reserved.
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| 2. |
- Abelev, Betty, et al.
(författare)
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Measurement of prompt J/psi and beauty hadron production cross sections at mid-rapidity in pp collisions at root s=7 TeV
- 2012
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; :11
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Tidskriftsartikel (refereegranskat)abstract
- The ALICE experiment at the LHC has studied J/psi production at mid-rapidity in pp collisions at root s = 7 TeV through its electron pair decay on a data sample corresponding to an integrated luminosity L-int = 5.6 nb(-1). The fraction of J/psi from the decay of long-lived beauty hadrons was determined for J/psi candidates with transverse momentum p(t) > 1,3 GeV/c and rapidity vertical bar y vertical bar < 0.9. The cross section for prompt J/psi mesons, i.e. directly produced J/psi and prompt decays of heavier charmonium states such as the psi(2S) and chi(c) resonances, is sigma(prompt J/psi) (p(t) > 1.3 GeV/c, vertical bar y vertical bar < 0.9) = 8.3 +/- 0.8(stat.) +/- 1.1 (syst.)(-1.4)(+1.5) (syst. pol.) mu b. The cross section for the production of b-hadrons decaying to J/psi with p(t) > 1.3 GeV/c and vertical bar y vertical bar < 0.9 is a sigma(J/psi <- hB) (p(t) > 1.3 GeV/c, vertical bar y vertical bar < 0.9) = 1.46 +/- 0.38 (stat.)(-0.32)(+0.26) (syst.) mu b. The results are compared to QCD model predictions. The shape of the p(t) and y distributions of b-quarks predicted by perturbative QCD model calculations are used to extrapolate the measured cross section to derive the b (b) over bar pair total cross section and d sigma/dy at mid-rapidity.
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| 3. |
- Basso, Eduardo, et al.
(författare)
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Nuclear effects in Drell-Yan pair production in high-energy pA collisions
- 2016
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-7998. ; 93:9
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Tidskriftsartikel (refereegranskat)abstract
- The Drell-Yan (DY) process of dilepton pair production off nuclei is not affected by final state interactions, energy loss, or absorption. A detailed phenomenological study of this process is thus convenient for investigation of the onset of initial-state effects in proton-nucleus (pA) collisions. In this paper, we present a comprehensive analysis of the DY process in pA interactions at RHIC and LHC energies in the color dipole framework. We analyze several effects affecting the nuclear suppression, RpA
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| 4. |
- Cepila, Jan, et al.
(författare)
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Theoretical uncertainties in exclusive electroproduction of S-wave heavy quarkonia
- 2019
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:6
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we revise the conventional description of J/ ψ(1 S) , Υ (1 S) , ψ′(2 S) and Υ ′(2 S) elastic photo- and electroproduction off a nucleon target within the color dipole picture and carefully study various sources of theoretical uncertainties in calculations of the corresponding electroproduction cross sections. For this purpose, we test the corresponding predictions using a bulk of available dipole cross section parametrisations obtained from deep inelastic scattering data at HERA. Specifically, we provide the detailed analysis of the energy and hard-scale dependencies of quarkonia yields employing the comprehensive treatment of the quarkonia wave functions in the Schrödinger equation based approach for a set of available c- c¯ and b- b¯ interquark interaction potentials. Besides, we quantify the effect of Melosh spin rotation, the Q2-dependence of the diffractive slope and an uncertainty due to charm and bottom quark mass variations.
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| 5. |
- Goncalves, Victor P., et al.
(författare)
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Drell-Yan process in pA collisions : Path-integral treatment of coherence effects
- 2016
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Ingår i: Physical Review D - Particles, Fields, Gravitation and Cosmology. - 2470-0010. ; 94:11
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we investigate production of Drell-Yan (DY) pairs in proton-nucleus collisions in kinematic regions where the corresponding coherence length does not exceed the nuclear radius, RA, and the quantum coherence effects should be treated with special care. The results for the nucleus-to-nucleon production ratio available in the literature so far are usually based on the assumption of a very long coherence length (LCL) lc RA. Since the onset of coherence effects is controlled by the coherence length lc, we estimated its magnitude in various kinematic regions of the DY process and found that the LCL approximation should not be used at small and medium c.m. collision energies (s 200 GeV) as well as at large dilepton invariant masses. In order to obtain realistic predictions, we computed for the first time the DY cross section using the generalized color dipole approach based on the rigorous Green function formalism, which naturally incorporates the color transparency and quantum coherence effects and hence allows us to estimate the nuclear shadowing with no restrictions on the CL. In addition to the shadowing effect, we studied a complementary effect of initial state interactions (ISI) that causes an additional suppression at large values of the Feynman variable. Numerical results for the nuclear modification factor accounting for the ISI effect and the finite lc are compared to the data available from the fixed-target Fermi National Laboratory measurements and a good agreement has been found. Besides, we present new predictions for the nuclear suppression as a function of dilepton rapidity and invariant mass in the kinematic regions that can be probed by the RHIC collider as well as by the planned AFTER@LHC and LHCb fixed-target experiments.
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| 6. |
- Krelina, Michal, et al.
(författare)
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D-wave effects in diffractive electroproduction of heavy quarkonia from the photon-like V→ QQ¯ transition
- 2020
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 80:2
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Tidskriftsartikel (refereegranskat)abstract
- We analyse the validity of a commonly used identification between structures of the virtual photon γ∗→ QQ¯ and vector meson V→ QQ¯ transitions. In the existing studies of S-wave vector-meson photoproduction in the literature, such an identification is typically performed in the light-front (LF) frame while the radial component of the meson wave function is rather postulated than computed from the first principles. The massive photon-like V→ QQ¯ vertex, besides the S-wave component, also contains an extra D-wave admixture in the QQ¯ rest frame. However, the relative weight of these contributions cannot be justified by any reasonable nonrelativistic QQ¯ potential model. In this work, we investigate the relative role of the D-wave contribution starting from the photon-like quarkonium V→ QQ¯ transition in both frames: in the QQ¯ rest frame (with subsequent Melosh spin transform to the LF frame) and in the LF frame (without Melosh transform). In both cases, we employ the same radial wave functions found in the potential approach. We show that the photon-like transition imposed in the QQ¯ rest frame, with subsequent boosting to the LF frame, leads to significant discrepancies with the experimental data. In the second case, i.e. imposing the photon-like transition straight in the LF frame, we find that the corresponding total J/ ψ(1 S) photoproduction cross sections are very close to those obtained with the “S-wave only” V→ QQ¯ transition, both leading to a good description of the data. However, we find that the “S-wave only” transition leads to a better description of photoproduction data for excited (e.g. ψ′(2 S)) heavy quarkonium states, which represent a more effective tool for study of D-wave effects. Consequently, the predictions for production of excited states based on the photon-like structure of V→ QQ¯ transition should be treated with a great care due to a much stronger sensitivity of the D-wave contribution to the nodal structure of quarkonium wave functions.
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| 7. |
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| 8. |
- Krelina, Michal, et al.
(författare)
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Drell-Yan process in p+Pb collisions at the LHC
- 2016
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Ingår i: Proceedings of Science. - 1824-8039. ; Part F128560
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Tidskriftsartikel (refereegranskat)abstract
- We study the initial-state interactions (non-coherence) and nuclear shadowing (coherence) effects in the Drell-Yan pair production process in p+Pb collisions at the LHC energies. The analysis of the nuclear suppression, RpA < 1, has been performed in the color dipole approach in the large coherence length approximation. The Z0 boson contribution relevant at large dilepton invariant masses has been included. We showed that the initial-state interactions cause a strong suppression at large pT, large dilepton masses and forward rapidities leading to a breakdown of QCD factorisation that can be verified by LHC measurements. The nuclear effects on the correlation function C(Δφ) in azimuthal angle Δφ between dilepton pair and a forward pion have been discussed as well. We predict a characteristic double-peak structure of C(Δφ) for very forward pions and large-mass dilepton pairs.
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| 9. |
- Krelina, Michal, et al.
(författare)
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Spin rotation effects in diffractive electroproduction of heavy quarkonia
- 2019
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:2
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Tidskriftsartikel (refereegranskat)abstract
- In this work we present for the first time the comprehensive study of the Melosh spin rotation effects in diffractive electroproduction of S-wave heavy quarkonia off a nucleon target. Such a study has been performed within the color dipole approach using, as an example and a reference point, two popular parametrizations of the dipole cross section and two potentials describing the interaction between Q and Q¯ and entering in the Schrödinger equation based formalism for determination of the quarkonia wave functions. We find a strong onset of spin rotation effects in 1S charmonium photoproduction which is obviously neglected in present calculations of corresponding cross sections. For photoproduction of radially excited ψ ′ (2 S) these effects are even stronger leading to an increase of the photoproduction cross section by a factor of 2 ÷ 3 depending on the photon energy. Even in production of radially excited Υ ′ (2 S) and Υ ′ ′ (3 S) they can not be neglected and cause the 20–30% enhancement of the photoproduction cross section. Finally, we predict that the spin effects vanish gradually with photon virtuality Q 2 following universality properties in production of different heavy quarkonia as a function of Q2+MV2.
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| 10. |
- Krelina, Michal, et al.
(författare)
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Study of Drell-Yan pair production on nuclear targets
- 2017
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 832:1
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Tidskriftsartikel (refereegranskat)abstract
- Drell-Yan pair production off nuclei is an ideal tool to test the cold nuclear effects occurring before a hard collision since no interaction in the final state is expected, neither energy loss or absorption. We present for the first time a comprehensive study of the nucleus-to-nucleon production ratio (the nuclear modification factor) within the color dipole approach using the Green function formalism which naturally incorporates for the color transparency and quantum coherence effects. We study a different onset of nuclear shadowing in various kinematical regions. At large values of the Feynman variable xF and dilepton invariant mass M we include also a suppression factor due to restrictions caused by the energy conservation induced by multiple initial state interactions (ISI effects). We present a variety of predictions for the nuclear suppression as a function of xF and M that can be verified by experiments at RHIC and LHC. The mixing of coherence effects with ISI effects can be eliminated going to large values of the dilepton invariant mass. Then predictions for the nuclear suppression is a direct manifestation for the onset of net ISI effects that can be verified by the future measurements.
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