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Register a new userMeasurements of long-range near-side angular correlations in $sqrt{s_{text{NN}}}=5$TeV proton-lead collisions in the forward region
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Two-particle angular correlations are studied in proton-lead collisions at a nucleon-nucleon centre-of-mass energy of $sqrt{s_{text{NN}}}=5$TeV, collected with the LHCb detector at the LHC. The analysis is based on data recorded in two beam configurations, in which either the direction of the proton or that of the lead ion is analysed. The correlations are measured in the laboratory system as a function of relative pseudorapidity, $Deltaeta$, and relative azimuthal angle, $Deltaphi$, for events in different classes of event activity and for different bins of particle transverse momentum. In high-activity events a long-range correlation on the near side, $Deltaphi approx 0$, is observed in the pseudorapidity range $2.0<eta<4.9$. This measurement of long-range correlations on the near side in proton-lead collisions extends previous observations into the forward region up to $eta=4.9$. The correlation increases with growing event activity and is found to be more pronounced in the direction of the lead beam. However, the correlation in the direction of the lead and proton beams are found to be compatible when comparing events with similar absolute activity in the direction analysed.
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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 photo-production of $J/psi$ mesons at low transverse momentum is studied in peripheral lead-lead collisions collected by the LHCb experiment at a centre-of-mass energy per nucleon pair of 5 TeV, corresponding to an integrated luminosity of 210 $rm{mu b}^{-1}$. The $J/psi$ candidates are reconstructed through the prompt decay into two muons of opposite charge in the rapidity region of $2.0<y<4.5$. The results significantly improve previous measurements and are compared to the latest theoretical prediction.
The momentum correlation between protons and lambda particles emitted from central Pb+Pb collisions at sqrt(s_{NN}) = 17.3 GeV was studied by the NA49 experiment at the CERN SPS. A clear enhancement is observed for small relative momenta (q_{inv} < 0.2 GeV). By fitting a theoretical model, which uses the strong interaction between the proton and the lambda in a given pair, to the measured data a value for the effective source size is deduced. Assuming a static Gaussian source distribution we derive an effective radius parameter of R_G = 3.02 pm 0.20$(stat.)^{+0.44}_{-0.16}(syst.) fm.
Dihadron angular correlations in $d$+Au collisions at $sqrt{s_{rm NN}}=200$ GeV are reported as a function of the measured zero-degree calorimeter neutral energy and the forward charged hadron multiplicity in the Au-beam direction. A finite correlated yield is observed at large relative pseudorapidity ($Deltaeta$) on the near side (i.e. relative azimuth $Deltaphisim0$). This correlated yield as a function of $Deltaeta$ appears to scale with the dominant, primarily jet-related, away-side ($Deltaphisimpi$) yield. The Fourier coefficients of the $Deltaphi$ correlation, $V_{n}=langlecos nDeltaphirangle$, have a strong $Deltaeta$ dependence. In addition, it is found that $V_{1}$ is approximately inversely proportional to the mid-rapidity event multiplicity, while $V_{2}$ is independent of it with similar magnitude in the forward ($d$-going) and backward (Au-going) directions.
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