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Study of $Upsilon$ production and cold nuclear matter effects in pPb collisions at $sqrt{s_{NN}}=5~mathrm{TeV}$

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 Added by Zhenwei Yang
 Publication date 2014
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and research's language is English




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Production of $Upsilon$ mesons in proton-lead collisions at a nucleon-nucleon centre-of-mass energy $sqrt{s_{NN}}=5 mathrm{TeV}$ is studied with the LHCb detector. The analysis is based on a data sample corresponding to an integrated luminosity of $1.6 mathrm{nb}^{-1}$. The $Upsilon$ mesons of transverse momenta up to $15 mathrm{GeV}/c$ are reconstructed in the dimuon decay mode. The rapidity coverage in the centre-of-mass system is $1.5<y<4.0$ (forward region) and $-5.0<y<-2.5$ (backward region). The forward-backward production ratio and the nuclear modification factor for $Upsilon(1S)$ mesons are determined. The data are compatible with the predictions for a suppression of $Upsilon(1S)$ production with respect to proton-proton collisions in the forward region, and an enhancement in the backward region. The suppression is found to be smaller than in the case of prompt $J/psi$ mesons.



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The production of $psi(2S)$ mesons is studied in dimuon final states using proton-lead collision data collected by the LHCb detector. The data sample corresponds to an integrated luminosity of $1.6~mathrm{nb}^{-1}$. The nucleon-nucleon centre-of-mass energy of the proton-lead collisions is $sqrt{s_{NN}}=5~mathrm{TeV}$. The measurement is performed using $psi(2S)$ mesons with transverse momentum less than $14~mathrm{GeV}/c$ and rapidity $y$ in the ranges $1.5<y<4.0$ and $-5.0<y<-2.5$ in the nucleon-nucleon centre-of-mass system. The forward-backward production ratio and the nuclear modification factor are determined for $psi(2S)$ mesons. Using the production cross-section results of $psi(2S)$ and $J/psi$ mesons from $b$-hadron decays, the $bbar{b}$ cross-section in pPb collisions at $sqrt{s_{NN}}=5~mathrm{TeV}$ is obtained.
The production of $J/psi$ mesons with rapidity $1.5<y<4.0$ or $-5.0<y<-2.5$ and transverse momentum $p_mathrm{T}<14 mathrm{GeV}/c$ is studied with the LHCb detector in proton-lead collisions at a nucleon-nucleon centre-of-mass energy $sqrt{s_{NN}}=5 mathrm{TeV}$. The analysis is based on a data sample corresponding to an integrated luminosity of about $1.6 mathrm{nb}^{-1}$. For the first time the nuclear modification factor and forward-backward production ratio are determined separately for prompt $J/psi$ mesons and $J/psi$ from $b$-hadron decays. Clear suppression of prompt $J/psi$ production with respect to proton-proton collisions at large rapidity is observed, while the production of $J/psi$ from $b$-hadron decays is less suppressed. These results show good agreement with available theoretical predictions. The measurement shows that cold nuclear matter effects are important for interpretations of the related quark-gluon plasma signatures in heavy-ion collisions.
The production of $Upsilon(nS)$ mesons ($n=1,2,3$) in $p$Pb and Pb$p$ collisions at a centre-of-mass energy per nucleon pair $sqrt{s_{NN}}=8.16$ TeV is measured by the LHCb experiment, using a data sample corresponding to an integrated luminosity of 31.8 nb$^{-1}$. The $Upsilon(nS)$ mesons are reconstructed through their decays into two opposite-sign muons. The measurements comprise the differential production cross-sections of the $Upsilon(1S)$ and $Upsilon(2S)$ states, their forward-to-backward ratios and nuclear modification factors, performed as a function of the transverse momentum pt and rapidity in the nucleon-nucleon centre-of-mass frame $y^*$ of the $Upsilon(nS)$ states, in the kinematic range $p_{rm{T}}<25$ GeV/$c$ and $1.5<y^*<4.0$ ($-5.0<y^*<-2.5$) for $p$Pb (Pb$p$) collisions. In addition, production cross-sections for $Upsilon(3S)$ are measured integrated over phase space and the production ratios between all three $Upsilon(nS)$ states are determined. The measurements are compared to theoretical predictions and suppressions for quarkonium in $p$Pb collisions are observed.
58 - Zhaozhong Shi 2018
The study of charm production in heavy-ion collisions is considered an excellent probe for the properties of the hot and dense medium created in heavy-ion collisions. Measurements of D-meson nuclear modification can provide strong constraints into the mechanisms of in-medium energy loss and charm flow in the medium. The measurement of $D^0$ elliptic flow in pPb collisions helps us understand the strength of charm quarks coupling to significantly reduced systems which demonstrate hydrodynamic properties. In this paper, the measurements of the $D^0$ nuclear modification factor in PbPb collisions at 5.02 TeV together with the new measurement of $D^0$ elliptic flow in high multiplicity pPb collisions at 5.02 TeV using the two-particle correlation method will be presented.
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