W and Z boson production in p-Pb collisions at √sNN = 5.02 TeV

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Scaling violation and shadowing corrections at HERA

We study the value of shadowing corrections (SC) in the HERA kinematic region in the Glauber{ Mueller approach. Since the Glauber{Mueller approach was proven in perturbative quantum chromodynamics (QCD) in the double-logarithmic approximation (DLA), we develop the DLA approach for the deep inelastic structure function which takes into account the SC. Our estimates show small SC for F2 in the HERA kinematic region while they turn out to be sizable for the gluon structure function. We compare our estimates with those for gluon distribution in leading order (LO) and next to leading order (NLO) in the DGLAP evolution equations

Hadron Production in the Nucleus Fragmentation Region

The RHIC hadron production data in hadronic collisions at the forward rapidities may hint the evidence of the Color Glass Condensate (CGC). However, in the opposite region, backward rapidities, new effects should be important in order to describe the observables. In this work, the charged hadron and π 0 productions are investigated in the fragmentation region of the nucleus (backward rapidities) considering dAu and pp collisions in the context of the Color Glass Condensate. In the backward rapidity region, only the proton can be treated as a CGC, and the large x nuclear effects need to be considered in order to describe the cross section. The results are shown by means of the nuclear modification ratio comparing the proton-nucleus and proton-proton cross sections and such ratio presents some dependences on the large x nuclear effects

Dielectron production at midrapidity at low transverse momentum in peripheral and semi-peripheral Pb–Pb collisions at √sNN = 5.02 TeV

The first measurement of the e+e − pair production at low lepton pair transverse momentum (pT,ee) and low invariant mass (mee) in non-central Pb–Pb collisions at √ sNN = 5.02 TeV at the LHC is presented. The dielectron production is studied with the ALICE detector at midrapidity (|ηe| < 0.8) as a function of invariant mass (0.4 ≤ mee < 2.7 GeV/c 2 ) in the 50–70% and 70–90% centrality classes for pT,ee < 0.1 GeV/c, and as a function of pT,ee in three mee intervals in the most peripheral Pb–Pb collisions. Below a pT,ee of 0.1 GeV/c, a clear excess of e+e − pairs is found compared to the expectations from known hadronic sources and predictions of thermal radiation from the medium. The mee excess spectra are reproduced, within uncertainties, by different predictions of the photon–photon production of dielectrons, where the photons originate from the extremely strong electromagnetic fields generated by the highly Lorentz-contracted Pb nuclei. Lowest-order quantum electrodynamic (QED) calculations, as well as a model that takes into account the impact-parameter dependence of the average transverse momentum of the photons, also provide a good description of the pT,ee spectra. The measured q hp 2 T,eei of the excess pT,ee spectrum in peripheral Pb–Pb collisions is found to be comparable to the values observed previously at RHIC in a similar phase-space region

J/ψ production at midrapidity in p-Pb collisions at √sNN = 8.16 TeV

The production of inclusive, prompt and non-prompt J/ψ was studied for the first time at midrapidity (−1.37 2 GeV/c. The study of the J/ψ mesons in the dielectron channel used for the first time in ALICE online single-electron triggers from the Transition Radiation Detector, providing a data sample corresponding to an integrated luminosity of 689 ± 13 µb −1 . The proton-proton reference cross section for inclusive J/ψ was obtained based on interpolations of measured data at different centre-of-mass energies and a universal function describing the pT-differential J/ψ production cross sections. The pT-differential nuclear modification factors RpPb of inclusive, prompt, and non-prompt J/ψ are consistent with unity and described by theoretical models implementing only nuclear shadowing

Measurement of inclusive and leading subjet fragmentation in pp and Pb–Pb collisions at √sNN = 5.02 TeV

This article presents new measurements of the fragmentation properties of jets in both proton–proton (pp) and heavy-ion collisions with the ALICE experiment at the Large Hadron Collider (LHC). We report distributions of the fraction zr of transverse momentum carried by subjets of radius r within jets of radius R. Charged-particle jets are reconstructed at midrapidity using the anti-kT algorithm with jet radius R = 0.4, and subjets are reconstructed by reclustering the jet constituents using the anti-kT algorithm with radii r = 0.1 and r = 0.2. In proton–proton collisions, we measure both the inclusive and leading subjet distributions. We compare these measurements to perturbative calculations at next-to-leading logarithmic accuracy, which suggest a large impact of threshold resummation and hadronization effects on the zr distribution. In heavy-ion collisions, we measure the leading subjet distributions, which allow access to a region of harder jet fragmentation than has been probed by previous measurements of jet quenching via hadron fragmentation distributions. The zr distributions enable extraction of the parton-to-subjet fragmentation function and allow for tests of the universality of jet fragmentation functions in the quark–gluon plasma (QGP). We find no significant modification of zr distributions in Pb–Pb compared to pp collisions. However, the distributions are also consistent with a hardening trend for zr < 0.95, as predicted by several jet quenching models. As zr → 1 our results indicate that any such hardening effects cease, exposing qualitatively new possibilities to disentangle competing jet quenching mechanisms. By comparing our results to theoretical calculations based on an independent extraction of the parton-to-jet fragmentation function, we find consistency with the universality of jet fragmentation and no indication of factorization breaking in the QGP

Measurement of ψ(2S) production as a function of charged-particle pseudorapidity density in pp collisions at √s = 13 TeV and p–Pb collisions at √sNN = 8.16 TeV with ALICE at the LHC

Production of inclusive charmonia in pp collisions at center-of-mass energy of √ s = 13 TeV and p–Pb collisions at center-of-mass energy per nucleon pair of √ sNN = 8.16 TeV is studied as a function of charged-particle pseudorapidity density with ALICE. Ground and excited charmonium states (J/ψ, ψ(2S)) are measured from their dimuon decays in the interval of rapidity in the center-of-mass frame 2.5 < ycms < 4.0 for pp collisions, and 2.03 < ycms < 3.53 and −4.46 < ycms < −2.96 for p–Pb collisions. The charged-particle pseudorapidity density is measured around midrapidity (|η| < 1.0). In pp collisions, the measured charged-particle multiplicity extends to about six times the average value, while in p-Pb collisions at forward (backward) rapidity a multiplicity corresponding to about three (four) times the average is reached. The ψ(2S) yield increases with the charged-particle pseudorapidity density. The ratio of ψ(2S) over J/ψ yield does not show a significant multiplicity dependence in either colliding system, suggesting a similar behavior of J/ψ and ψ(2S) yields with respect to charged-particle pseudorapidity density. Results for the ψ(2S) yield and its ratio with respect to J/ψ agree with available model calculations

Central exclusive χc,bproduction at high energy colliders and gluon saturation approach

The central exclusive production of χcand χbat the LHC, RHIC and Tevatron energies is analyzed, using the recent unintegrated parton distribution (UGDs) functions available in the package TMDlib. Comparison with data is performed, which tests the underlying assumptions basing the theoretical approach and it can constrain the unintegrated gluon distribution function at the small-xregion. Predictions for LHC energies using recent UGDs based in CCFM formalism are provided. It is explored the underlying uncertainties on this production as the choice for the unintegrated gluon distribution and factorization scale is done. Moreover, based on the parton saturation model for the gluon distribution, analytical expressions for the rapidity distributions are proposed. The prompt production of J/ψ+γand Υ+γis computed for the first time for LHC energies within the very same formalism used for χproductio

Two-particle transverse momentum correlations in pp and p-Pb collisions at energies available at the CERN Large Hadron Collider

Two-particle transverse momentum differential correlators, recently measured in Pb-Pb collisions at energies available at the CERN Large Hadron Collider (LHC), provide an additional tool to gain insights into particle production mechanisms and infer transport properties, such as the ratio of shear viscosity to entropy density, of the medium created in Pb-Pb collisions. The longitudinal long-range correlations and the large azimuthal anisotropy measured at low transverse momenta in small collision systems, namely pp and p-Pb, at LHC energies resemble manifestations of collective behavior. This suggests that locally equilibrated matter may be produced in these small collision systems, similar to what is observed in Pb-Pb collisions. In this work, the same twoparticle transverse momentum differential correlators are exploited in pp and p-Pb collisions at √s = 7 TeV and √sNN = 5.02 TeV, respectively, to seek evidence for viscous effects. Specifically, the strength and shape of the correlators are studied as a function of the produced particle multiplicity to identify evidence for longitudinal broadening that might reveal the presence of viscous effects in these smaller systems. The measured correlators and their evolution from pp and p-Pb to Pb-Pb collisions are additionally compared to predictions from Monte Carlo event generators, and the potential presence of viscous effects is discussed

Unitarity boundary for deep inelastic structure functions

In this letter we derive the unitarity boundaries in QCD for the deep inelastic structure function in low x kinematic region: the Froissart boundary and a more restricted one, linked with experiment and based on additional assumptions, justified in the leading log approximation of perturbative QCD. The comparison of the unitarity boundaries with the new HERA experimental data gives rise to a challenge for QCD to explain the matching between the deep inelastic scattering and real photoproduction process