Inclusive photon multiplicity at forward pseudorapidities in pp and p−-Pb collisions at sNN\sqrt{s_{\rm NN}} = 5.02 TeV with ALICE

Global observables such as the pseudorapidity distributions of particle multiplicities in the final state are crucial to shed light into the physics processes involved in hadronic collisions. In proton$-$lead (p$-$Pb) collisions at Large Hadron Collider (LHC) energies, such measurements provide an important baseline to understand lead$-$lead (Pb$-$Pb) results by disentangling hot nuclear matter effects from the ones due to the cold nuclear matter. Multiplicity measurements can also put constraints on theoretical models describing the initial stages of the collision, e.g., to what degree the nucleon and the nuclei interact as dilute (partons) or dense (CGC-like) fields. The study of inclusive photon multiplicity aims to provide complementary measurements to those obtained with charged particles. In these proceedings, the pseudorapidity distributions of inclusive photons at forward pseudorapidity ($2.3 < \eta_{\rm lab} < 3.9$) in pp and p$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV are presented. The data samples were collected using the Photon Multiplicity Detector (PMD) of ALICE. The multiplicity dependence of photon production in p$-$Pb collisions is presented and a comparison with charged-particle distributions measured at mid-pseudorapidity is shown. The results are also compared with predictions from Monte Carlo event generators.Comment: 5 pages and 3 figure

Measurements of inclusive photons at forward rapidities in p-Pb collisions at sNN\sqrt{s\rm_{NN}} = 5.02 TeV with ALICE

We present multiplicity and pseudorapidity distributions of inclusive photons at forward rapidity in proton-lead (p-Pb) collisions at $\sqrt{s\rm_{NN}}$ = 5.02 TeV using the data obtained from Photon Multiplicity Detector (PMD) of ALICE. The centrality dependence of pseudorapidity distributions of inclusive photons is also studied. Results are compared with the previous ALICE measurements of charged-particle production and with theoretical predictions from Monte Carlo models, DPMJET and HIJING.Comment: Proceedings of The Ninth Annual Conference on Large Hadron Collider Physics - LHCP2021 conference, Date: 7-12 June 202

Jet modification in absence of QGP-medium: the role of multiparton interactions and color reconnection

Recent studies of high-multiplicity events in small collision systems (proton-proton and proton-lead) have drawn research interest towards the possibility of the formation of partonic medium in such systems. One of the important consequences of the formation of dense partonic medium is quenching of high-momentum final-state particles resulting in several experimental observations such as suppression in nuclear modification factor $R_{\rm AA}$, modification of jet shape observable $\rho(r)$, etc. In this work, we study $\rho(r)$ for inclusive charged-particle jets in proton-proton (pp) collisions at $\sqrt{s}$ = 13 TeV using PYTHIA 8 Monash 2013 Monte Carlo simulation and show that the color reconnection (CR) and multiparton interaction (MPI) mechanisms in PYTHIA 8 can also lead to a significant amount of modification of $\rho(r)$ in high-multiplicity events compared to minimum bias events for 10 $<p_{\rm T,\,jet}^{\rm ch}<$ 20 GeV/$c$. The enhanced gluonic contribution in high-multiplicity events is also found to play a role in the observed modification of $\rho(r)$. We notice a direct connection between the number of MPIs and the amount of modification in $\rho(r)$ - the larger the number of MPIs, the larger the amount of modification of $\rho(r)$.Comment: 14 pages, 7 figures, 1 tabl

Initial Stages 2021

Particle production at LHC energies results from the interplay of hard- and soft-QCD processes and is sensitive to non-linear QCD evolution in the initial state. In particular, for p-Pb collisions, one can use the proton to probe the low-$x$ dense gluonic fields of the Pb nuclei. The multiplicity and rapidity dependence of charged- and neutral-particle production, therefore, provides important constraints for initial state models and calculations describing the particle production mechanisms. ALICE has unique coverage at forward rapidity. The Photon Multiplicity Detector can measure neutral-particle production over a kinematic range of $2.3 < \eta < 3.9$. The Forward Multiplicity and the Silicon Pixel Detectors can measure charged particles over a wide range of $-3.4 < \eta < 5.0$. For the first time, results at forward rapidity will be presented for both charged and neutral particles in p-Pb collisions at 5.02 TeV and 8.16 TeV. The multiplicity and centrality dependence will be discussed. In this case, the centrality of the collisions is determined using the energy deposited in the Zero-Degree Calorimeters. Finally, the results will be compared to model calculations based on different particle-production mechanisms and initial conditions in the forward soft-QCD regime, in which perturbative-QCD calculations are impossible

Inclusive photon multiplicity at forward pseudorapidities in pp and p−-Pb collisions at sNN\sqrt{s_{\rm NN}} = 5.02 TeV with ALICE

Global observables such as the pseudorapidity distributions of particle multiplicities in the final state are crucial to shed light into the physics processes involved in hadronic collisions. In proton$-$lead (p$-$Pb) collisions at Large Hadron Collider (LHC) energies, such measurements provide an important baseline to understand lead$-$lead (Pb$-$Pb) results by disentangling hot nuclear matter effects from the ones due to the cold nuclear matter. Multiplicity measurements can also put constraints on theoretical models describing the initial stages of the collision, e.g., to what degree the nucleon and the nuclei interact as dilute (partons) or dense (CGC-like) fields. The study of inclusive photon multiplicity aims to provide complementary measurements to those obtained with charged particles. In these proceedings, the pseudorapidity distributions of inclusive photons at forward pseudorapidity ($2.3 < \eta_{\rm lab} < 3.9$) in pp and p$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV are presented. The data samples were collected using the Photon Multiplicity Detector (PMD) of ALICE. The multiplicity dependence of photon production in p$-$Pb collisions is presented and a comparison with charged-particle distributions measured at mid-pseudorapidity is shown. The results are also compared with predictions from Monte Carlo event generators

Multiplicity dependence of light (anti-)nuclei production in p–Pb collisions at sNN=5.02 TeV

The measurement of the deuteron and anti-deuteron production in the rapidity range −1 < y < 0 as a function of transverse momentum and event multiplicity in p–Pb collisions at √sNN = 5.02 TeV is presented. (Anti-)deuterons are identified via their specific energy loss dE/dx and via their time-of- flight. Their production in p–Pb collisions is compared to pp and Pb–Pb collisions and is discussed within the context of thermal and coalescence models. The ratio of integrated yields of deuterons to protons (d/p) shows a significant increase as a function of the charged-particle multiplicity of the event starting from values similar to those observed in pp collisions at low multiplicities and approaching those observed in Pb–Pb collisions at high multiplicities. The mean transverse particle momenta are extracted from the deuteron spectra and the values are similar to those obtained for p and particles. Thus, deuteron spectra do not follow mass ordering. This behaviour is in contrast to the trend observed for non-composite particles in p–Pb collisions. In addition, the production of the rare 3He and 3He nuclei has been studied. The spectrum corresponding to all non-single diffractive p-Pb collisions is obtained in the rapidity window −1 < y < 0 and the pT-integrated yield dN/dy is extracted. It is found that the yields of protons, deuterons, and 3He, normalised by the spin degeneracy factor, follow an exponential decrease with mass number

Pseudorapidity densities of charged particles with transverse momentum thresholds in pp collisions at √ s = 5.02 and 13 TeV

The pseudorapidity density of charged particles with minimum transverse momentum (pT) thresholds of 0.15, 0.5, 1, and 2 GeV/c is measured in pp collisions at the center of mass energies of √s=5.02 and 13 TeV with the ALICE detector. The study is carried out for inelastic collisions with at least one primary charged particle having a pseudorapidity (η) within 0.8pT larger than the corresponding threshold. In addition, measurements without pT-thresholds are performed for inelastic and nonsingle-diffractive events as well as for inelastic events with at least one charged particle having |η|2GeV/c), highlighting the importance of such measurements for tuning event generators. The new measurements agree within uncertainties with results from the ATLAS and CMS experiments obtained at √s=13TeV.

Nuclear modification factor of light neutral-meson spectra up to high transverse momentum in p–Pb collisions at sNN=8.16 TeV

International audienceNeutral pion (π0) and η meson production cross sections were measured up to unprecedentedly high transverse momenta (pT) in p–Pb collisions at sNN=8.16TeV. The mesons were reconstructed via their two-photon decay channel in the rapidity interval −1.3&lt;y&lt;0.3 in the ranges of 0.4&lt;pT&lt;200 GeV/c and 1.0&lt;pT&lt;50 GeV/c, respectively. The respective nuclear modification factor (RpPb) is presented for pT up to of 200 and 30 GeV/c, where the former was achieved by extending the π0 measurement in pp collisions at s=8TeV using the merged cluster technique. The values of RpPb are below unity for pT&lt;10 GeV/c, while they are consistent with unity for pT&gt;10 GeV/c, leaving essentially no room for final state energy loss. The new data provide strong constraints for nuclear parton distribution and fragmentation functions over a broad kinematic range and are compared to model predictions as well as previous results at sNN=5.02TeV