| 1. |
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| 2. |
- Abelev, B., et al.
(författare)
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Charged jet cross sections and properties in proton-proton collisions at root s=7 TeV
- 2015
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 91:11
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Tidskriftsartikel (refereegranskat)abstract
- The differential charged jet cross sections, jet fragmentation distributions, and jet shapes are measured in minimum bias proton-proton collisions at center-of-mass energy root s = 7 TeV using the ALICE detector at the LHC. Jets are reconstructed from charged particle momenta in the midrapidity region using the sequential recombination k(T) and anti-k(T) as well as the SISCone jet finding algorithms with several resolution parameters in the range R = 0.2-0.6. Differential jet production cross sections measured with the three jet finders are in agreement in the transverse momentum (p(T)) interval 20 < p(T)(jet,ch) < 100 GeV/c. They are also consistent with prior measurements carried out at the LHC by the ATLAS Collaboration. The jet charged particle multiplicity rises monotonically with increasing jet p(T), in qualitative agreement with prior observations at lower energies. The transverse profiles of leading jets are investigated using radial momentum density distributions as well as distributions of the average radius containing 80% (< R-80 >) of the reconstructed jet p(T). The fragmentation of leading jets with R = 0.4 using scaled p(T) spectra of the jet constituents is studied. The measurements are compared to model calculations from event generators (PYTHIA, PHOJET, HERWIG). The measured radial density distributions and < R-80 > distributions are well described by the PYTHIA model (tune Perugia-2011). The fragmentation distributions are better described by HERWIG.
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| 3. |
- Abelev, B., et al.
(författare)
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Inclusive photon production at forward rapidities in proton-proton collisions at root s=0.9, 2.76 and 7 TeV
- 2015
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:4
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Tidskriftsartikel (refereegranskat)abstract
- The multiplicity and pseudorapidity distributions of inclusive photons have been measured at forward rapidities (2.3 < eta < 3.9) in proton-proton collisions at three center-of-mass energies, root s = 0.9, 2.76 and 7 TeV using the ALICE detector. It is observed that the increase in the average photon multiplicity as a function of beam energy is compatible with both a logarithmic and a power-law dependence. The relative increase in average photon multiplicity produced in inelastic pp collisions at 2.76 and 7 TeV center-of-mass energies with respect to 0.9 TeV are 37.2 +/- 0.3% (stat) +/- 8.8% (sys) and 61.2 +/- 0.3% (stat) +/- 7.6% (sys), respectively. The photon multiplicity distributions for all center-of-mass energies are well described by negative binomial distributions. The multiplicity distributions are also presented in terms of KNO variables. The results are compared to model predictions, which are found in general to underestimate the data at large photon multiplicities, in particular at the highest center-of-mass energy. Limiting fragmentation behavior of photons has been explored with the data, but is not observed in the measured pseudorapidity range.
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| 4. |
- Abelev, B., et al.
(författare)
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Production of inclusive gamma(1S) and gamma(2S) in p-Pb collisions at, root S-NN=5.02 TeV
- 2015
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 740, s. 105-117
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Tidskriftsartikel (refereegranskat)abstract
- We report on the production of inclusive gamma(1S) and gamma(2S) in p-Pb collisions at root S-NN = 5.02 TeV at the LHC. The measurement is performed with the ALICE detector at backward (-4.46 < ycms < 2.96) and forward (2.03 < ycms <3.53) rapidity down to zero transverse momentum. The production cross sections of the gamma(1S) and gamma(2S) are presented, as well as the nuclear modification factor and the ratio of the forward to backward yields of gamma(1S). A suppression of the inclusive gamma(1S) yield in p-Pb collisions with respect to the yield from pp collisions scaled by the number of binary nucleon-nucleon collisions is observed at forward rapidity but not at backward rapidity. The results are compared to theoretical model calculations including nuclear shadowing or partonic energy loss effects. (C) 2014 The Authors. Published by Elsevier B.V.
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| 5. |
- Abelev, B., et al.
(författare)
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Production of Sigma (1385)(+/-) and Xi (1530)(0) in proton-proton collisions at root s=7 TeV
- 2015
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:1
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Tidskriftsartikel (refereegranskat)abstract
- The production of the strange and double-strange baryon resonances (Sigma (1385)(+/-), Xi (1530)(0)) has been measured at mid-rapidity (vertical bar y vertical bar < 0.5) in proton-proton collisions at root s = 7 TeV with the ALICE detector at the LHC. Transverse momentum spectra for inelastic collisions are compared to QCD-inspired models, which in general underpredict the data. A search for the phi (1860) pentaquark, decaying in the Xi pi channel, has been carried out but no evidence is seen.
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| 6. |
- Abelev, B., et al.
(författare)
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Elliptic flow of identified hadrons in Pb-Pb collisions at root(NN)-N-s=2.76 Tev
- 2015
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; :6
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Tidskriftsartikel (refereegranskat)abstract
- The elliptic flow coefficient (v(2)) of identified particles in Pb-Pb collisions at root s(NN) = 2.76 TeV was measured with the ALICE detector at the Large Hadron Collider (LHC). The results were obtained with the Scalar Product method, a two-particle correlation technique, using a pseudo-rapidity gap of |Delta eta| > 0.9 between the identified hadron under study and the reference particles. The v (2) is reported for pi(+/-), K-+/-, K-S(0), p+(p) over bar, phi, Lambda+(Lambda) over bar, Xi+(Xi) over bar (+) and Omega(-)+(Omega) over bar (+) in several collision centralities. In the low transverse momentum (p(T)) region, p(T) < 3 GeV/c, v(2)(p(T)) exhibits a particle mass dependence consistent with elliptic flow accompanied by the transverse radial expansion of the system with a common velocity field. The experimental data for pi (+/-) and the combined K-+/- and K-S(0) results, are described fairly well by hydrodynamic calculations coupled to a hadronic cascade model (VISHNU) for central collisions. However, the same calculations fail to reproduce the v(2)(p(T)) for p+(p) over bar, phi, Lambda+(Lambda) over bar, Xi+(Xi) over bar (+). For transverse momentum values larger than about 3 GeV/c, particles tend to group according to their type, i.e. mesons and baryons. The present measurements exhibit deviations from the number of constituent quark (NCQ) scaling at the level of +/- 20% for p(T) > 3 GeV/c.
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| 7. |
- Abelev, B., et al.
(författare)
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Multiplicity dependence of jet-like two-particle correlation structures in p-Pb collisions at root s(NN)=5.02 TeV
- 2015
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 741, s. 38-50
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Tidskriftsartikel (refereegranskat)abstract
- Two-particle angular correlations between unidentified 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. The transverse-momentum range 0.7 < p(T),(assoc) < p(T),(trig) < 5.0 GeV/c is examined, to include correlations induced by jets originating from low momentum-transfer scatterings (minijets). The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range vertical bar eta vertical bar < 0.9. The near-side long-range pseudorapidity correlations observed in high-multiplicity p-Pb collisions are subtracted from both near-side short-range and away-side correlations in order to remove the non-jet-like components. The yields in the jet-like peaks are found to be invariant with event multiplicity with the exception of events with low multiplicity. This invariance is consistent with the particles being produced via the incoherent fragmentation of multiple parton-parton scatterings, while the yield related to the previously observed ridge structures is not jet-related. The number of uncorrelated sources of particle production is found to increase linearly with multiplicity, suggesting no saturation of the number of multi-parton interactions even in the highest multiplicity p-Pb collisions. Further, the number scales only in the intermediate multiplicity region with the number of binary nucleon-nucleon collisions estimated with a Glauber Monte-Carlo simulation. (C) 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/).
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| 8. |
- Abelev, B., et al.
(författare)
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Measurement of electrons from semileptonic heavy-flavor hadron decays in pp collisions at root s=2.76 TeV
- 2015
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 91:1
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Tidskriftsartikel (refereegranskat)abstract
- The p(T)-differential production cross section of electrons from semileptonic decays of heavy-flavor hadrons has been measured at midrapidity in proton-proton collisions at root s = 2.76 TeV in the transverse momentum range 0.5 < p(T) < 12 GeV/c with the ALICE detector at the LHC. The analysis was performed using minimum bias events and events triggered by the electromagnetic calorimeter. Predictions from perturbative QCD calculations agree with the data within the theoretical and experimental uncertainties.
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| 9. |
- Abelev, B., et al.
(författare)
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K*(892)(0) and phi(1020) production in Pb-Pb collisions at root s(NN)=2.76 TeV
- 2015
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 91:2
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Tidskriftsartikel (refereegranskat)abstract
- The yields of the K*(892)(0) and phi(1020) resonances are measured in Pb-Pb collisions at root s(NN) = 2.76 TeV through their hadronic decays using the ALICE detector. The measurements are performed in multiple centrality intervals at mid-rapidity (vertical bar y vertical bar < 0.5) in the transverse-momentum ranges 0.3 < p(T) < 5 GeV/c for the K*(892)(0) and 0.5 < p(T) < 5 GeV/c for the phi(1020). The yields of K*(892)(0) are suppressed in central Pb-Pb collisions with respect to pp and peripheral Pb-Pb collisions (perhaps due to rescattering of its decay products in the hadronic medium), while the longer-lived phi(1020) meson is not suppressed. These particles are also used as probes to study the mechanisms of particle production. The shape of the pT distribution of the phi(1020) meson, but not its yield, is reproduced fairly well by hydrodynamic models for central Pb-Pb collisions. In central Pb-Pb collisions at low and intermediate p(T), the p/phi(1020) ratio is flat in p(T), while the p/pi and phi(1020)/pi ratios show a pronounced increase and have similar shapes to each other. These results indicate that the shapes of the p(T) distributions of these particles in central Pb-Pb collisions are determined predominantly by the particle masses and radial flow. Finally, phi(1020) production in Pb-Pb collisions is enhanced, with respect to the yield in pp collisions and the yield of charged pions, by an amount similar to the Lambda and Xi.
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| 10. |
- Adare, A., et al.
(författare)
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Measurements of Elliptic and Triangular Flow in High-Multiplicity He-3 + Au Collisions at root s(NN)=200 GeV
- 2015
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Ingår i: Physical Review Letters. - 1079-7114. ; 115:14
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Tidskriftsartikel (refereegranskat)abstract
- We present the first measurement of elliptic (v(2)) and triangular (v(3)) flow in high-multiplicity He-3 + Au collisions at root s(NN) = 200 GeV. Two-particle correlations, where the particles have a large separation in pseudorapidity, are compared in He-3 + Au and in p + p collisions and indicate that collective effects dominate the second and third Fourier components for the correlations observed in the He-3 + Au system. The collective behavior is quantified in terms of elliptic v(2) and triangular v(3) anisotropy coefficients measured with respect to their corresponding event planes. The v(2) values are comparable to those previously measured in d + Au collisions at the same nucleon-nucleon center-of-mass energy. Comparisons with various theoretical predictions are made, including to models where the hot spots created by the impact of the three He-3 nucleons on the Au nucleus expand hydrodynamically to generate the triangular flow. The agreement of these models with data may indicate the formation of low-viscosity quark-gluon plasma even in these small collision systems.
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| 11. |
- Adare, A., et al.
(författare)
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Search for dark photons from neutral meson decays in p plus p and d plus Au collisions at root s(NN)=200 GeV
- 2015
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 91:3
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Tidskriftsartikel (refereegranskat)abstract
- The standard model (SM) of particle physics is spectacularly successful, yet the measured value of the muon anomalous magnetic moment (g - 2)mu deviates from SM calculations by 3.6 sigma. Several theoretical models attribute this to the existence of a "dark photon," an additional U(1) gauge boson, which is weakly coupled to ordinary photons. The PHENIX experiment at the Relativistic Heavy Ion Collider has searched for a dark photon, U, in pi(0), eta -> gamma e(+)e(-) decays and obtained upper limits of O(2 x 10(-6)) on U-gamma mixing at 90% C.L. for the mass range 30 < m(U) < 90 MeV/c(2). Combined with other experimental limits, the remaining region in the U-gamma mixing parameter space that can explain the (g - 2)(mu) deviation from its SM value is nearly completely excluded at the 90% confidence level, with only a small region of 29 < m(U) < 32 MeV/c(2) remaining.
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| 12. |
- Adare, A., et al.
(författare)
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Measurement of higher cumulants of net-charge multiplicity distributions in Au plus Au collisions at root s(NN)=7.7-200 GeV
- 2016
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 93:1
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Tidskriftsartikel (refereegranskat)abstract
- We report the measurement of cumulants (C-n,n = 1, ..., 4) of the net-charge distributions measured within pseudorapidity (vertical bar eta vertical bar < 0.35) in Au + Au collisions at root s(NN) = 7.7-200 GeV with the PHENIX experiment at the Relativistic Heavy Ion Collider. The ratios of cumulants (e.g., C-1/C-2, C-3/C-1) of the net-charge distributions, which can be related to volume independent susceptibility ratios, are studied as a function of centrality and energy. These quantities are important to understand the quantum-chromodynamics phase diagram and possible existence of a critical end point. The measured values are very well described by expectation from negative binomial distributions. We do not observe any nonmonotonic behavior in the ratios of the cumulants as a function of collision energy. The measured values of C-1/C-2 and C-3/C-1 can be directly compared to lattice quantum-chromodynamics calculations and thus allow extraction of both the chemical freeze-out temperature and the baryon chemical potential at each center-of-mass energy. The extracted baryon chemical potentials are in excellent agreement with a thermal-statistical analysis model.
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| 13. |
- Adare, A., et al.
(författare)
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Centrality dependence of low-momentum direct-photon production in Au plus Au collisions at root s(NN)=200 GeV
- 2015
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 91:6
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Tidskriftsartikel (refereegranskat)abstract
- The PHENIX experiment at RHIC has measured the centrality dependence of the direct photon yield from Au + Au collisions at root s(NN) = 200 GeV down to pT = 0.4 GeV/c. Photons are detected via photon conversions to e(+)e(-) pairs and an improved technique is applied that minimizes the systematic uncertainties that usually limit direct photon measurements, in particular at low pT. We find an excess of direct photons above the N-coll-scaled yield measured in p + p collisions. This excess yield is well described by an exponential distribution with an inverse slope of about 240 MeV/c in the pT range 0.6-2.0 GeV/c. While the shape of the pT distribution is independent of centrality within the experimental uncertainties, the yield increases rapidly with increasing centrality, scaling approximately with N-part(alpha), where alpha = 1.38 +/- 0.03(stat) +/- 0.07(syst).
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| 14. |
- Adare, A., et al.
(författare)
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phi meson production in d plus Au collisions at root s(NN)=200 GeV
- 2015
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 92:4
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Tidskriftsartikel (refereegranskat)abstract
- The PHENIX Collaboration has measured phi meson production in d + Au collisions at root s(NN) = 200 GeV using the dimuon and dielectron decay channels. The phi meson is measured in the forward (backward) d-going (Au-going) direction, 1.2 < y < 2.2 (-2.2 < y < -1.2) in the transverse-momentum (pT) range from 1-7 GeV/c and at midrapidity vertical bar y vertical bar < 0.35 in the p(T) range below 7 GeV/c. The phi meson invariant yields and nuclear-modification factors as a function of p(T), rapidity, and centrality are reported. An enhancement of phi meson production is observed in the Au-going direction, while suppression is seen in the d-going direction, and no modification is observed at midrapidity relative to the yield in p + p collisions scaled by the number of binary collisions. Similar behavior was previously observed for inclusive charged hadrons and open heavy flavor, indicating similar cold-nuclear-matter effects.
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| 15. |
- Adare, A., et al.
(författare)
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Measurement of gamma(1S+2S+3S) production in p plus p and Au plus Au collisions at root sNN=200 GeV
- 2015
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 91:2
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of bottomonium production in heavy-ion and p + p collisions at the Relativistic Heavy Ion Collider (RHIC) are presented. The inclusive yield of the three states, (1S + 2S + 3S), was measured in the PHENIX experiment via electron-positron decay pairs at midrapidity for Au + Au and p + p collisions at root sNN = 200 GeV. The (1S + 2S + 3S) -> e(+)e(-) differential cross section at midrapidity was found to be B(ee)d sigma/dy = 108 +/- 38 (stat) +/- 15 (syst) +/- 11 (luminosity) pb in p + p collisions. The nuclear modification factor in the 30% most central Au + Au collisions indicates a suppression of the total. state yield relative to the extrapolation from p + p collision data. The suppression is consistent with measurements made by STAR at RHIC and at higher energies by the CMS experiment at the Large Hadron Collider.
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| 16. |
- Adare, A., et al.
(författare)
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Systematic study of charged-pion and kaon femtoscopy in Au plus Au collisions at root s(NN)=200 GeV
- 2015
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 92:3
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Tidskriftsartikel (refereegranskat)abstract
- We present a systematic study of charged-pion and kaon interferometry in Au + Au collisions at root s(NN) = 200 GeV. The kaon mean source radii are found to be larger than pion radii in the outward and longitudinal directions for the same transverse mass; this difference increases for more central collisions. The azimuthal-angle dependence of the radii was measured with respect to the second-order event plane and similar oscillations of the source radii were found for pions and kaons. Hydrodynamic models qualitatively describe the similar oscillations of the mean source radii for pions and kaons, but they do not fully describe the transverse-mass dependence of the oscillations.
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| 17. |
- Abe, K., et al.
(författare)
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J-PARC Neutrino Beamline Upgrade Technical Design Report
- 2019
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Rapport (refereegranskat)abstract
- In this document, technical details of the upgrade plan of the J-PARC neutrino beamline for the extension of the T2K experiment are described. T2K has proposed to accumulate data corresponding to 2×1022 protons-on-target in the next decade, aiming at an initial observation of CP violation with 3σ or higher significance in the case of maximal CP violation. Methods to increase the neutrino beam intensity, which are necessary to achieve the proposed data increase, are described.
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| 18. |
- Adare, A, et al.
(författare)
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Measurement of Long-Range Angular Correlation and Quadrupole Anisotropy of Pions and (Anti)Protons in Central d+Au Collisions at sqrt[s_{NN}]=200 GeV.
- 2015
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Ingår i: Physical Review Letters. - 1079-7114. ; 114:19
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Tidskriftsartikel (refereegranskat)abstract
- We present azimuthal angular correlations between charged hadrons and energy deposited in calorimeter towers in central d+Au and minimum bias p+p collisions at sqrt[s_{NN}]=200 GeV. The charged hadron is measured at midrapidity |η|<0.35, and the energy is measured at large rapidity (-3.7<η<-3.1, Au-going direction). An enhanced near-side angular correlation across |Δη|>2.75 is observed in d+Au collisions. Using the event plane method applied to the Au-going energy distribution, we extract the anisotropy strength v_{2} for inclusive charged hadrons at midrapidity up to p_{T}=4.5 GeV/c. We also present the measurement of v_{2} for identified π^{±} and (anti)protons in central d+Au collisions, and observe a mass-ordering pattern similar to that seen in heavy-ion collisions. These results are compared with viscous hydrodynamic calculations and measurements from p+Pb at sqrt[s_{NN}]=5.02 TeV. The magnitude of the mass ordering in d+Au is found to be smaller than that in p+Pb collisions, which may indicate smaller radial flow in lower energy d+Au collisions.
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| 19. |
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| 20. |
- Adare, A., et al.
(författare)
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Charged-pion cross sections and double-helicity asymmetries in polarized p plus p collisions at root s=200 GeV
- 2015
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 91:3
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Tidskriftsartikel (refereegranskat)abstract
- We present midrapidity charged-pion invariant cross sections, the ratio of the pi(-) to pi(+) cross sections and the charge-separated double-spin asymmetries in polarized p + p collisions at root s = p + 200 GeV. While the cross section measurements are consistent within the errors of next-to-leading-order (NLO) perturbative quantum chromodynamics predictions (pQCD), the same calculations overestimate the ratio of the charged-pion cross sections. This discrepancy arises from the cancellation of the substantial systematic errors associated with the NLO-pQCD predictions in the ratio and highlights the constraints these data will place on flavor-dependent pion fragmentation functions. The charge-separated pion asymmetries presented here sample an x range of similar to 0.03-0.16 and provide unique information on the sign of the gluon-helicity distribution.
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| 21. |
- Adare, A., et al.
(författare)
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Cross section for b(b)over-bar production via dielectrons in d plus Au collisions at root s(NN)=200 GeV
- 2015
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 91:1
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Tidskriftsartikel (refereegranskat)abstract
- We report a measurement of e(+)e(-) pairs from semileptonic heavy-flavor decays in d + Au collisions at root s(NN) = 200 GeV. By exploring the mass and transverse-momentum dependence of the yield, the bottom decay contribution can be isolated from charm, and quantified by comparison to PYTHIA and MC@NLO simulations. The resulting b (b) over bar -production cross section is sigma(dAu)(b (b) over bar) = 1.37 +/- 0.28 (stat) +/- 0.46 (syst) mb, which is equivalent to a nucleon-nucleon cross section of sigma(NN)(b (b) over bar) = 3.4 +/- 0.8 (stat) +/- 1.1 ( syst) mu b.
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| 22. |
- Adare, A., et al.
(författare)
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Inclusive cross section and double-helicity asymmetry for pi(0) production at midrapidity in p plus p collisions at root s=510 GeV
- 2016
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 93:1
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Tidskriftsartikel (refereegranskat)abstract
- PHENIX measurements are presented for the cross section and double-helicity asymmetry (A(LL)) in inclusive pi(0) production at midrapidity from p + p collisions at root s = 510 GeV from data taken in 2012 and 2013 at the Relativistic Heavy Ion Collider. The next-to-leading-order perturbative-quantum-chromodynamics theory calculation is in excellent agreement with the presented cross section results. The calculation utilized parton-to-pion fragmentation functions from the recent DSS14 global analysis, which prefer a smaller gluon-to-pion fragmentation function. The pi(0)A(LL) results follow an increasingly positive asymmetry trend with p(T) and root s with respect to the predictions and are in excellent agreement with the latest global analysis results. This analysis incorporated earlier results on pi(0) and jet A(LL) and suggested a positive contribution of gluon polarization to the spin of the proton Delta G for the gluon momentum fraction range x > 0.05. The data presented here extend to a currently unexplored region, down to x similar to 0.01, and thus provide additional constraints on the value of Delta G.
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| 23. |
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| 24. |
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| 25. |
- Delabrouille, J., et al.
(författare)
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Exploring cosmic origins with CORE : Survey requirements and mission design
- 2018
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :4
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Tidskriftsartikel (refereegranskat)abstract
- Future observations of cosmic microwave background (CMB) polarisation have the potential to answer some of the most fundamental questions of modern physics and cosmology, including: what physical process gave birth to the Universe we see today? What are the dark matter and dark energy that seem to constitute 95% of the energy density of the Universe? Do we need extensions to the standard model of particle physics and fundamental interactions? Is the ACDM cosmological scenario correct, or are we missing an essential piece of the puzzle? In this paper, we list the requirements for a future CMB polarisation survey addressing these scientific objectives, and discuss the design drivers of the CORE space mission proposed to ESA in answer to the M5 call for a medium-sized mission. The rationale and options, and the methodologies used to assess the mission's performance, are of interest to other future CMB mission design studies. CORE has 19 frequency channels, distributed over a broad frequency range, spanning the 60-600 GHz interval, to control astrophysical foreground emission. The angular resolution ranges from 2' to 18', and the aggregate CMB sensitivity is about 2 mu K.arcmin. The observations are made with a single integrated focal-plane instrument, consisting of an array of 2100 cryogenically-cooled, linearly-polarised detectors at the focus of a 1.2-m aperture cross-Dragone telescope. The mission is designed to minimise all sources of systematic effects, which must be controlled so that no more than 10(-4) of the intensity leaks into polarisation maps, and no more than about 1% of E-type polarisation leaks into B-type modes. CORE observes the sky from a large Lissajous orbit around the Sun-Earth L2 point on an orbit that offers stable observing conditions and avoids contamination from sidelobe pick-up of stray radiation originating from the Sun, Earth, and Moon. The entire sky is observed repeatedly during four years of continuous scanning, with a combination of three rotations of the spacecraft over different timescales. With about 50% of the sky covered every few days, this scan strategy provides the mitigation of systematic effects and the internal redundancy that are needed to convincingly extract the primordial B-mode signal on large angular scales, and check with adequate sensitivity the consistency of the observations in several independent data subsets. CORE is designed as a near-ultimate CMB polarisation mission which, for optimal complementarity with ground-based observations, will perform the observations that are known to be essential to CMB polarisation science and cannot be obtained by any other means than a dedicated space mission. It will provide well-characterised, highly-redundant multi-frequency observations of polarisation at all the scales where foreground emission and cosmic variance dominate the final uncertainty for obtaining precision CMB science, as well as 2' angular resolution maps of high-frequency foreground emission in the 300-600 GHz frequency range, essential for complementarity with future ground-based observations with large telescopes that can observe the CMB with the same beamsize.
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