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Register a new userStudies of dijet transverse momentum balance and pseudorapidity distributions in pPb collisions at sqrt(s[NN]) = 5.02 TeV
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The CMS Collaboration
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Dijet production has been measured in pPb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV. A data sample corresponding to an integrated luminosity of 35 inverse nanobarns was collected using the Compact Muon Solenoid detector at the Large Hadron Collider. The dijet transverse momentum balance, azimuthal angle correlations, and pseudorapidity distributions are studied as a function of the transverse energy in the forward calorimeters (ETHFfour). For pPb collisions, the dijet transverse momentum ratio and the width of the distribution of dijet azimuthal angle difference are comparable to the same quantities obtained from a simulated pp reference and insensitive to ETHFfour. In contrast, the mean value of the dijet pseudorapidity is found to change monotonically with increasing ETHFfour, indicating a correlation between the energy emitted at large pseudorapidity and the longitudinal motion of the dijet frame. The pseudorapidity distribution of the dijet system in minimum bias pPb collisions is compared with next-to-leading-order perturbative QCD predictions obtained from both nucleon and nuclear parton distribution functions, and the data more closely match the latter.
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The almost hermetic coverage of CMS is used to measure the distribution of transverse energy as a function of pseudo-rapidity for pPb collisions at $sqrt{s_{NN}} = 5.02$ TeV. For minimum bias collisions $(1/N)~dE_T/deta$ reaches 23 GeV which implies an $E_T$ per participant pair comparable to that of peripheral PbPb collisions at $sqrt{s_{NN}} = 2.76$ TeV. The centrality dependence of transverse energy production has been studied using centrality measures defined in three different angular regions. There is a strong auto-correlation between $(1/N)~dE_T/deta$ and the $eta$ range used to define centrality %both for data and the EPOS-LHC and HIJING event generators. The centrality dependence of the data is much stronger for $eta$ values on the lead side than the proton side and shows significant differences from that predicted by either event generator.
The transverse momentum ($p_text{T}$) distribution for inclusive neutral pions in the very forward rapidity region has been measured, with the Large Hadron Collider forward detector (LHCf), in proton--lead collisions at nucleon-nucleon center-of-mass energies of $sqrt{s_{NN}} = 5.02$TeV at the LHC. The $p_text{T}$ spectra obtained in the rapidity range $-11.0 < y_text{lab} < -8.9$ and $0 < p_text{T} < 0.6$GeV (in the detector reference frame) show a strong suppression of the production of neutral pions after taking into account ultra-peripheral collisions. This leads to a nuclear modification factor value, relative to the interpolated $p_text{T}$ spectra in proton-proton collisions at $sqrt{s} = 5.02$TeV, of about 0.1--0.4. This value is compared with the predictions of several hadronic interaction Monte Carlo simulations.
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.
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.
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.
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