Inclusive photon production at forward rapidities in proton–proton collisions at $$\mathbf {\sqrt{s}}$$ s = 0.9, 2.76 and 7 TeV

Abstract

The multiplicity and pseudorapidity distributions of inclusive photons have been measured at forward rapidities (2.3 < η < 3.9) in proton-proton collisions at three center-of-mass energies, √ s = 0.9, 2.76 and 7 TeV using the ALICE detector. It is observed that the increase in the average photon multiplicity as a function of beam energy is compatible with both a logarithmic and a power-law dependence. The relative increase in average photon multiplicity produced in inelastic pp collisions at 2.76 and 7 TeV center-of-mass energies with respect to 0.9 TeV are 37.2 ± 0.3 % (stat) ± 8.8 % (sys) and 61.2 ± 0.3 % (stat) ± 7.6 % (sys), respectively. The photon multiplicity distributions for all center-of-mass energies are well described by negative binomial distributions. The multiplicity distributions are also presented in terms of KNO variables. The results are compared to model predictions, which are found in general to underestimate the data at large photon multiplicities, in particular at the highest center-of-mass energy. Limiting fragmentation behavior of photons has been explored with the data, but is not observed in the measured pseudorapidity range.

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

“…Charged particles can be measured over a wide pseudorapidity range (∼ 8 units) of −3.4 < η lab < 5.0 using the Forward Multiplicity Detector (FMD) and the Silicon Pixel Detector (SPD) [9,10]. On the other hand, photon production can be studied over a kinematic range of 2.3 < η lab < 3.9 using the Photon Multiplicity Detector (PMD) [2].…”

“…Various centrality classes are determined by measuring the amplitude of the V0A detector [13,14]. We apply suitable photon-hadron discrimination thresholds based on the number of affected cells and the energy deposition in a cluster produced in the preshower plane of the PMD to obtain the photon rich sample, known as γ-like clusters [2].…”

“…Each element (R mt ) of matrix R corresponds to the probability that an event with true multiplicity t is measured as an event with the measured multiplicity m. A detailed description of the unfolding procedure can be found in Refs. [2,9,16]. The correction of dN γ /dη lab for various centrality classes is performed using the Efficiency-Purity method as described in Ref.…”

“…The MB results are also corrected for trigger and vertex reconstruction efficiencies in a similar way that was followed in Ref. [2]. The trigger and vertex reconstruction efficiencies are estimated to be 98.47% and 99.8% respectively using HIJING.…”

“…Measurements of these observables in p-Pb collisions provide an important baseline to understand lead-lead (Pb-Pb) results by disentangling cold nuclear matter effects from hot nuclear matter effects [1]. The study of inclusive photon multiplicity aims at providing complementary measurements to those of charged particles since the photon production is dominated by the decay of neutral mesons [2].…”