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Possibility for $J/Ψ$ suppression in high multiplicity proton-proton collisions at $\sqrt{s_{NN}}=7\,$TeV  [PDF]
Thomas Lang,Marcus Bleicher
Physics , 2013, DOI: 10.1103/PhysRevC.87.024907
Abstract: We study $J/\Psi$ absorption in high multiplicity proton-proton (pp) collisions at $\sqrt {s_{NN}}=7\,$TeV. We predict a modification of the $J/\Psi$-yield within the UrQMD transport approach, where explicit interactions of the $J/\Psi$ with the surrounding comovers and a prehadronic phase with adjusted cross sections and $J/\Psi$ melting is included. We present the analog of the nuclear modification factor in pp collisions at various charged particle multiplicities. It turns out that $J/\Psi$-Mesons may be suppressed towards higher particle multiplicities in pp collisions at LHC energies.
Open charm production in high multiplicity proton-proton events at the LHC  [PDF]
E. G. Ferreiro,C. Pajares
Physics , 2015,
Abstract: We present the dependence of $D$ production on the charged particle multiplicity in proton-proton collisions at LHC energies. We show that, in a framework of source coherence, the open charm production exhibits a growth with the multiplicity which is stronger than linear in the high density domain. This departure from linearity was previously observed in the $J/\psi$ inclusive data from proton-proton collisions at 7 TeV and was successfully described in our approach. Our assumption, the existence of coherence effects present in proton-proton collisions at high energy, applies for high multiplicity proton-proton collisions in the central rapidity region and should affect any hard observable.
Open heavy flavour and J/psi production in proton-proton collisions measured with the ALICE experiment at LHC  [PDF]
Claudio Geuna
Physics , 2012,
Abstract: Open heavy flavour and J/psi production are powerful tools to test pQCD calculations in proton-proton collisions in the new LHC energy regime. In addition, they provide the necessary reference for the ALICE heavy-ion program. The ALICE experiment at the LHC collected proton-proton collisions at sqrt{s} = 7 and 2.76 TeV in 2010 and 2011. We report here the latest results of open heavy flavour and J/psi production at both mid- and forward-rapidity via their various hadronic and leptonic decay channels. These include, among other topics, the first LHC result on J/psi polarization, multiplicity dependence of the J/psi production, D-meson measurement down to low transverse momentum and J/psi production from B-hadron decays. Comparisons with different theoretical models will be discussed as well.
Measurement of charm and beauty production at central rapidity versus charged-particle multiplicity in proton-proton collisions at $\mathbf{\sqrt{\textit s}}=7$ TeV  [PDF]
ALICE Collaboration
Physics , 2015, DOI: 10.1007/JHEP09(2015)148
Abstract: Prompt D meson and non-prompt J/$\psi$ yields are studied as a function of the multiplicity of charged particles produced in inelastic proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=7$ TeV. The results are reported as a ratio between yields in a given multiplicity interval normalised to the multiplicity-integrated ones (relative yields). They are shown as a function of the multiplicity of charged particles normalised to the average value for inelastic collisions (relative charged-particle multiplicity). D$^0$, D$^+$ and D$^{*+}$ mesons are measured in five $p_{\rm T}$ intervals from 1 to 20 GeV/$c$ and for $|y|<0.5$ via their hadronic decays. The D-meson relative yield is found to increase with increasing charged-particle multiplicity. For events with multiplicity six times higher than the average multiplicity of inelastic collisions, a yield enhancement of a factor about 15 relative to the multiplicity-integrated yield in inelastic collisions is observed. The yield enhancement is independent of transverse momentum within the uncertainties of the measurement. The D$^0$-meson relative yield is also measured as a function of the relative multiplicity at forward pseudorapidity. The non-prompt J/$\psi$, i.e. the B hadron, contribution to the inclusive J/$\psi$ production is measured in the di-electron decay channel at central rapidity. It is evaluated for $p_{\rm T}>1.3$ GeV/$c$ and $|y|<0.9$, and extrapolated to $p_{\rm T}>0$. The fraction of non-prompt J/$\psi$ in the inclusive J/$\psi$ yields shows no dependence on the charged-particle multiplicity at central rapidity. Charm and beauty hadron relative yields exhibit a similar increase with increasing charged-particle multiplicity. The measurements are compared to PYTHIA 8, EPOS 3 and percolation calculations.
Impact of the Nuclear Modification of the Gluon Densities on J/Psi production in pPb collisions at sqrt(s_NN) = 5 TeV  [PDF]
E. G. Ferreiro,F. Fleuret,J. P. Lansberg,A. Rakotozafindrabe
Physics , 2013, DOI: 10.1103/PhysRevC.88.047901
Abstract: We update our previous studies of nuclear-matter effects on J/Psi production in proton-nucleus for the recent LHC pPb runs at sqrt(s_NN)=5 TeV. We have analysed the effects of the modification of the gluon PDFs in nucleus, using an exact kinematics for a 2->2 process, namely g+g->J/Psi+g as expected from LO pQCD. This allows to constrain the transverse-momentum while computing the nuclear modification factor for different rapidities, unlike with the usual simplified kinematics. Owing to the absence of measurement in pp collisions at the same sqrt(s_NN) and owing to the expected significant uncertainties in yield interpolations which would hinder definite interpretations of nuclear modification factor --R_pPb--, we have derived forward-to-backward and central-to-peripheral yield ratios in which the unknown proton-proton yield cancel. These have been computed without and with a transverse-momentum cut, e.g. to comply with the ATLAS and CMS constraints in the central-rapidity region.
Multiplicity Dependence of Pion, Kaon, Proton and Lambda Production in p-Pb Collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV  [PDF]
ALICE Collaboration
Physics , 2013, DOI: 10.1016/j.physletb.2013.11.020
Abstract: In this Letter, comprehensive results on ${\rm\pi}^\pm$, K$^\pm$, K$^0_S$, p, $\rm\bar{p}$, $\rm \Lambda$ and $\rm \bar{\Lambda}$ production at mid-rapidity ($0 < y_{\rm cms} < 0.5$) in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ 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 $p_{\rm T}$ distributions are compared to results at lower energy and with predictions based on QCD-inspired and hydrodynamic models.
Coherent photoproduction of $\psi$ and $\Upsilon$ mesons in ultraperipheral pPb and PbPb collisions at the CERN LHC
Adeluyi, Adeola;Nguyen, Trang
High Energy Physics - Phenomenology , 2013,
Abstract: Exclusive photoproduction of vector mesons in the perturbative two-gluon exchange formalism depends significantly on nucleon and nuclear gluon distributions. In the present study we calculate total cross sections and rapidity distributions of $J/\psi(1s)$, $\psi(2s)$, $\Upsilon(1s)$, $\Upsilon(2s)$, and $\Upsilon(3s)$ in ultraperipheral proton-lead (pPb) and lead-lead (PbPb) collisions at the CERN Large Hadron Collider (LHC) at $\sqrt{s_{_{NN}}}=5$ TeV and $\sqrt{s_{_{NN}}}=2.76$ TeV respectively. Effects of gluon shadowing are investigated and potentials for constraining nuclear gluon modifications are discussed.
Measurement of the multiplicity dependence of charm production in proton--proton collisions at \sqrt{s}=7 TeV with the ALICE experiment at the CERN-LHC  [PDF]
Aamer Wali Rauf,for the ALICE Collaboration
Physics , 2013,
Abstract: Potential of the charm quark as a probe to study the Quark-Gluon Plasma (QGP) is best harnessed when its production mechanisms are disentangled from its propagation through the QGP. Proton-proton (pp) collisions help us to study charmed hadron production mechanisms. The measurement of D-meson yields in pp collisions as a function of the multiplicity of produced particles allows one to gain some insight into the processes occurring in the collision at a microscopic level. Here, the preliminary results are presented from this measurement at \sqrt{s} = 7 TeV. The analysis strategy, the applied corrections, and the determination of the systematic uncertainties are described. The preliminary results are presented and compared with those from a similar, published, measurement of J/\psi production.
Quarkonium production measurements with the ALICE detector at the LHC  [PDF]
Ginés Martínez García for the ALICE Collaboration
Physics , 2011, DOI: 10.1088/0954-3899/38/12/124034
Abstract: In this new energy regime, quarkonium provides a unique probe to study the properties of the high-density, strongly interacting system formed in the early stages of high-energy heavy-ion collisions. In ALICE, quarkonium states are reconstructed down to p_T=0 via their mu+mu- decay channel in the muon spectrometer (2.5
Quarkonia production in proton-lead collisions at LHCb  [PDF]
Yiming Li
Physics , 2014,
Abstract: The production of $J/\psi$ and $\Upsilon$ mesons decaying into dimuon final state is studied at the LHCb experiment, with rapidity in the range of (1.5, 4.0) or (-5.0, -2.5) in proton-lead collisions at a nucleon-nucleon centre-of-mass energy $\sqrt{s_{NN}}$ = 5 TeV, based on a data sample corresponding to an integrated luminosity of 1.6 /fb. The nuclear modification factor and forward-backward production ratio are determined for prompt $J/\psi$, $J/\psi$ from b-hadron decay and $\Upsilon(1S)$ mesons in study of the cold nuclear matter effects.
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