Spin physics with antiprotons

New possibilities arising from the availability at GSI of antiproton beams, possibly polarised, are discussed. The investigation of the nucleon structure can be boosted by accessing in Drell-Yan processes experimental asymmetries related to cross-sections in which the parton distribution functions (PDF) only appear, without any contribution from fragmentation functions; such processes are not affected by the chiral suppression of the transversity function $h_1(x)$. Spin asymmetries in hyperon production and Single Spin Asymmetries are discussed as well, together with further items like electric and magnetic nucleonic form factors and open charm production. Counting rates estimations are provided for each physical case. The sketch of a possible experimental apparatus is proposed.Comment: Presented for the proceedings of ASI "Spin and Symmetry", Prague, July 5-10, 2004, to be published in Czech. J. Phys. 55 (2005

Measurement of differential cross sections for inclusive isolated-photon and photon+jet production in proton-proton collisions at s=13 TeV\sqrt{s} = 13\,\text {TeV}

Measurements of inclusive isolated-photon and photon+jet production in proton–proton collisions at s √ =13TeV s=13TeV are presented. The analysis uses data collected by the CMS experiment in 2015, corresponding to an integrated luminosity of 2.26fb −1 fb−1 . The cross section for inclusive isolated photon production is measured as a function of the photon transverse energy in a fiducial region. The cross section for photon+jet production is measured as a function of the photon transverse energy in the same fiducial region with identical photon requirements and with the highest transverse momentum jet. All measurements are in agreement with predictions from next-to-leading-order perturbative QCD

Measurement of quarkonium production cross sections in pp collisions at root s=13 TeV

Differential production cross sections of prompt J/psi and psi(2S) charmonium and Upsilon(nS) (n = 1, 2, 3) bottomonium states are measured in proton-proton collisions at root s = 13 TeV, with data collected by the CMS detector at the LHC, corresponding to an integrated luminosity of 2.3 fb(-1) for the J/psi and 2.7 fb(-1) for the other mesons. The five quarkonium states are reconstructed in the dimuon decay channel, for dimuon rapidity vertical bar y vertical bar <1.2. The double-differential cross sections for each state are measured as a function of y and transverse momentum, and compared to theoretical expectations. In addition, ratios are presented of cross sections for prompt psi(2S) to J/psi, Upsilon(2S) to Upsilon(1S), and Upsilon(3S) to Upsilon(1S) production. (C) 2018 The Author(s). Published by Elsevier B.V.Peer reviewe

Strange hadron production in pp and pPb collisions at √s_(NN) = 5.02 TeV

The transverse momentum (p_T) distributions of Λ, Ξ⁻, and Ω⁻ baryons, their antiparticles, and K⁰_S mesons are measured in proton-proton (pp) and proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV over a broad rapidity range. The data, corresponding to integrated luminosities of 40.2 nb⁻¹ and 15.6 μb⁻¹ for pp and pPb collisions, respectively, were collected by the CMS experiment. The nuclear modification factor R_(pPb), which is defined as the ratio of the particle yield in pPb collisions and a scaled pp reference, is measured for each particle. A strong dependence on particle species is observed in the p_T range from 2 to 7 GeV, where R_(pPb) for K⁰_S is consistent with unity, while an enhancement ordered by strangeness content and/or particle mass is observed for the three baryons. In pPb collisions, the strange hadron production is asymmetric about the nucleon-nucleon center-of-mass rapidity. Enhancements, which depend on the particle type, are observed in the direction of the Pb beam. The results are compared with predictions from EPOS LHC, which includes parametrized radial flow. The model is in qualitative agreement with the R_(pPb) data, but fails to describe the dependence on particle species in the yield asymmetries measured away from midrapidity in pPb collisions

Measurement of prompt psi(2S) production cross sections in proton-lead and proton-proton collisions at root s(NN)=5.02 TeV

Measurements of prompt ψ(2S) meson production cross sections in proton-lead (pPb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of √sNN = 5.02 TeV are reported. The results are based on pPb and pp data collected by the CMS experiment at the LHC, corresponding to integrated luminosities of 34.6 nb−1 and 28.0 pb−1, respectively. The nuclear modification factor RpPb is measured for prompt ψ(2S) in the transverse momentum range 4 < pT < 30 GeV/c and the center-of-mass rapidity range −2.4 < yCM < 1.93. The results on ψ(2S) RpPb are compared to the corresponding modification factor for prompt J/ψ mesons. The results point to different nuclear effects at play in the production of the excited charmonium state compared to the ground state, in the region of backward rapidity and for pT < 10 GeV/c. © 2019 The Author. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3.Peer reviewe

Constraints on the double-parton scattering cross section from same-sign W boson pair production in proton-proton collisions at root s=8TeV

A first search for same-sign WW production via double-parton scattering is performed based on proton-proton collision data at a center-of-mass energy of 8TeV using dimuon and electron-muon final states. The search is based on the analysis of data corresponding to an integrated luminosity of 19.7 fb(-1). No significant excess of events is observed above the expected single-parton scattering yields. A 95% confidence level upper limit of 0.32 pb is set on the inclusive cross section for same-sign WW production via the double-parton scattering process. This upper limit is used to place a 95% confidence level lower limit of 12.2mb on the effective double-parton cross section parameter, closely related to the transverse distribution of partons in the proton. This limit on the effective cross section is consistent with previous measurements as well as with Monte Carlo event generator predictions.Peer reviewe

Measurement of differential cross sections for inclusive isolated-photon and photon plus jet production in proton-proton collisions at root s=13TeV

Measurements of inclusive isolated-photon and photon+jet production in proton-proton collisions at =13TeV are presented. The analysis uses data collected by the CMS experiment in 2015, corresponding to an integrated luminosity of 2.26fb-1. The cross section for inclusive isolated photon production is measured as a function of the photon transverse energy in a fiducial region. The cross section for photon+jet production is measured as a function of the photon transverse energy in the same fiducial region with identical photon requirements and with the highest transverse momentum jet. All measurements are in agreement with predictions from next-to-leading-order perturbative QCD.Peer reviewe

Measurement of associated Z plus charm production in proton-proton collisions at root s=8TeV

A study of the associated production of a Z boson and a charm quark jet (Z + c), and a comparison to production with a b quark jet (Z + b), in pp collisions at a centre-of-mass energy of 8 TeV are presented. The analysis uses a data sample corresponding to an integrated luminosity of 19.7 fb(-1), collected with the CMS detector at the CERN LHC. The Z boson candidates are identified through their decays into pairs of electrons or muons. Jets originating from heavy flavour quarks are identified using semileptonic decays of c or b flavoured hadrons and hadronic decays of charm hadrons. The measurements are performed in the kinematic region with two leptons with pT(l) > 20 GeV, vertical bar eta(l)vertical bar 25 GeV and vertical bar eta(jet)vertical bar Z + c + X) B(Z -> l(+)l(-)) = 8.8 +/- 0.5 (stat)+/- 0.6 (syst) pb. The ratio of the Z+c and Z+b production cross sections is measured to be sigma(pp -> Z+c+X)/sigma (pp -> Z+b+X) = 2.0 +/- 0.2 (stat)+/- 0.2 (syst). The Z+c production cross section and the cross section ratio are also measured as a function of the transverse momentum of theZ boson and of the heavy flavour jet. The measurements are compared with theoretical predictions.Peer reviewe

The production of isolated photons in PbPb and pp collisions at sNN \sqrt{s_{\mathrm{NN}}} = 5.02 TeV

The transverse energy (E$_{T}^{γ}$) spectra of photons isolated from other particles are measured using proton-proton (pp) and lead-lead (PbPb) collisions at the LHC at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV TeV with integrated luminosities of 27.4 pb$^{-1}$ and 404 μb$^{-1}$ for pp and PbPb data, respectively. The results are presented for photons with 25 <E$_{T}^{γ}$< 200 GeV in the pseudorapidity range |η| < 1.44, and for different centrality intervals for PbPb collisions. Photon production in PbPb collisions is consistent with that in pp collisions scaled by the number of binary nucleon-nucleon collisions, demonstrating that photons do not interact with the quark-gluon plasma. Therefore, isolated photons can provide information about the initial energy of the associated parton in photon+jet measurements. The results are compared with predictions from the next-to-leading-order jetphox generator for different parton distribution functions (PDFs) and nuclear PDFs (nPDFs). The comparisons can help to constrain the nPDFs global fits

Measurement of prompt and nonprompt charmonium suppression in PbPb collisions at 5.02 TeV

The nuclear modification factors of J/psi and psi(2S) mesons are measured in PbPb collisions at a centre-of-mass energy per nucleon pair of root S-NN = 5.02 TeV. The analysis is based on PbPb and pp data samples collected by CMS at the LHC in 2015, corresponding to integrated luminosities of 464 mu b(-1) and 28 pb(-1), respectively. The measurements are performed in the dimuon rapidity range of vertical bar y vertical bar 25 GeV/c is seen with respect to that observed at intermediate p(T). The prompt psi(2S) meson yield is found to be more suppressed than that of the prompt J/psi mesons in the entire p(T) range.Peer reviewe