Production of He-4 and (4) in Pb-Pb collisions at root(NN)-N-S=2.76 TeV at the LHC

Results on the production of He-4 and (4) nuclei in Pb-Pb collisions at root(NN)-N-S = 2.76 TeV in the rapidity range vertical bar y vertical bar <1, using the ALICE detector, are presented in this paper. The rapidity densities corresponding to 0-10% central events are found to be dN/dy4(He) = (0.8 +/- 0.4 (stat) +/- 0.3 (syst)) x 10(-6) and dN/dy4 = (1.1 +/- 0.4 (stat) +/- 0.2 (syst)) x 10(-6), respectively. This is in agreement with the statistical thermal model expectation assuming the same chemical freeze-out temperature (T-chem = 156 MeV) as for light hadrons. The measured ratio of (4)/He-4 is 1.4 +/- 0.8 (stat) +/- 0.5 (syst). (C) 2018 Published by Elsevier B.V.Peer reviewe

First measurement of jet mass in Pb-Pb and p-Pb collisions at the LHC

This letter presents the first measurement of jet mass in Pb–Pb and p–Pb collisions at sNN=2.76 TeV and sNN=5.02 TeV, respectively. Both the jet energy and the jet mass are expected to be sensitive to jet quenching in the hot Quantum Chromodynamics (QCD) matter created in nuclear collisions at collider energies. Jets are reconstructed from charged particles using the anti- kT jet algorithm and resolution parameter R=0.4 . The jets are measured in the pseudorapidity range |ηjet|<0.5 and in three intervals of transverse momentum between 60 GeV/ c and 120 GeV/ c . The measurement of the jet mass in central Pb–Pb collisions is compared to the jet mass as measured in p–Pb reference collisions, to vacuum event generators, and to models including jet quenching. It is observed that the jet mass in central Pb–Pb collisions is consistent within uncertainties with p–Pb reference measurements. Furthermore, the measured jet mass in Pb–Pb collisions is not reproduced by the quenching models considered in this letter and is found to be consistent with PYTHIA expectations within systematic uncertainties.This letter presents the first measurement of jet mass in Pb-Pb and p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV and 5.02 TeV, respectively. Both the jet energy and the jet mass are expected to be sensitive to jet quenching in the hot Quantum Chromodynamics (QCD) matter created in nuclear collisions at collider energies. Jets are reconstructed from charged particles using the anti-$k_{\rm T}$ jet algorithm and resolution parameter $R = 0.4$. The jets are measured in the pseudorapidity range $|\eta_{\rm{jet}}|<0.5$ and in three intervals of transverse momentum between 60 GeV/$c$ and 120 GeV/$c$. The measurement of the jet mass in central Pb-Pb collisions is compared to the jet mass as measured in p-Pb reference collisions, to vacuum event generators, and to models including jet quenching. It is observed that the jet mass in central Pb-Pb collisions is consistent within uncertainties with p-Pb reference measurements. Furthermore, the measured jet mass in Pb-Pb collisions is not reproduced by the quenching models considered in this letter and is found to be consistent with PYTHIA expectations within systematic uncertainties

Measurement of D-meson production at mid-rapidity in pp collisions at √s = 7 TeV

The production cross sections of the prompt charmed mesons D0, D+, D∗+ and D+s were measured at mid-rapidity in proton-proton collisions at a centre-of-mass energy s√=7 TeV with the ALICE detector at the Large Hadron Collider (LHC). D mesons were reconstructed from their decays D0→K−π+, D+→K−π+π+, D∗+→D0π+, D+s→ϕπ+→K−K+π+, and their charge conjugates. With respect to previous measurements in the same rapidity region, the coverage in transverse momentum (pT) is extended and the uncertainties are reduced by a factor of about two. The accuracy on the estimated total cc¯¯ production cross section is likewise improved. The measured pT-differential cross sections are compared with the results of three perturbative QCD calculations

Measurement of D-meson production at mid-rapidity in pp collisions at s=7{\sqrt{s}=7} TeV

The production cross sections for prompt charmed mesons $\mathrm{D^0}$ , $\mathrm{D^+}$ , $\mathrm{D^{*+}}$ and $\mathrm{D_s^+}$ were measured at mid-rapidity in proton–proton collisions at a centre-of-mass energy $\sqrt{s}=7~{\mathrm {TeV}}$ with the ALICE detector at the Large Hadron Collider (LHC). D mesons were reconstructed from their decays $\mathrm{D}^0 \rightarrow \mathrm{K}^-\pi ^+$ , $\mathrm{D}^+\rightarrow \mathrm{K}^-\pi ^+\pi ^+$ , $\mathrm{D}^{*+} \rightarrow \mathrm{D}^0 \pi ^+$ , $\mathrm{D_s^{+}\rightarrow \phi \pi ^+\rightarrow K^-K^+\pi ^+}$ , and their charge conjugates.With respect to previous measurements in the same rapidity region, the coverage in transverse momentum ( $p_\mathrm{T}$ ) is extended and the uncertainties are reduced by a factor of about two. The accuracy on the estimated total $\mathrm{c}{\overline{\mathrm{c}}}$ production cross section is likewise improved. The measured $p_\mathrm{T}$ -differential cross sections are compared with the results of three perturbative QCD calculations

Production of π0 and η mesons up to high transverse momentum in pp collisions at 2.76 TeV

The invariant differential cross sections for inclusive π0 and η mesons at midrapidity were measured in pp collisions at s√=2.76 TeV for transverse momenta 0.4<pT<40 GeV/c and 0.6<pT<20 GeV/c, respectively, using the ALICE detector. This large range in pT was achieved by combining various analysis techniques and different triggers involving the electromagnetic calorimeter (EMCal). In particular, a new single-cluster, shower-shape based method was developed for the identification of high-pT neutral pions, which exploits that the showers originating from their decay photons overlap in the EMCal. The measured cross sections are found to exhibit a similar power-law behavior with an exponent of about 6.3. Next-to-leading-order perturbative QCD calculations differ from the measured cross sections by about 30% for the π0, and between 30-50% for the η meson, while generator-level simulations with PYTHIA 8.2 describe the data to better than 10-30%, except at pT<1 GeV/c. The new data can therefore be used to further improve the theoretical description of π0 and η meson production

Energy dependence of forward-rapidity J/ψ and ψ(2S) production in pp collisions at the LHC

We present results on transverse momentum (pT) and rapidity (y) differential production cross sections, mean transverse momentum and mean transverse momentum square of inclusive J/ψ and ψ(2S) at forward rapidity (2.5 15 GeV/c the non-prompt contribution reaches up to 50% of the total charmonium yield

Energy dependence of forward-rapidity J/ψ\mathrm {J}/\psi and ψ(2S)\psi \mathrm {(2S)} production in pp collisions at the LHC

We present results on transverse momentum ( p_{\mathrm {\textsc {t}}} ) and rapidity ( $y$ ) differential production cross sections, mean transverse momentum and mean transverse momentum square of inclusive $\mathrm {J}/\psi$ and $\psi \mathrm {(2S)}$ at forward rapidity ( $2.515$  GeV/c the non-prompt contribution reaches up to 50% of the total charmonium yield

Production of π0{\pi ^0} and η\eta mesons up to high transverse momentum in pp collisions at 2.76 TeV

The invariant differential cross sections for inclusive $\pi ^{0}$ and $\eta$ mesons at midrapidity were measured in pp collisions at $\sqrt{s}=2.76$  TeV for transverse momenta $0.4<p_{\mathrm {T}}<40$  GeV/c and $0.6<p_{\mathrm {T}}<20$  GeV/c, respectively, using the ALICE detector. This large range in $p_{\mathrm {T}}$ was achieved by combining various analysis techniques and different triggers involving the electromagnetic calorimeter (EMCal). In particular, a new single-cluster, shower-shape based method was developed for the identification of high- $p_{\mathrm {T}}$ neutral pions, which exploits that the showers originating from their decay photons overlap in the EMCal. Above 4 GeV/ $c$ , the measured cross sections are found to exhibit a similar power-law behavior with an exponent of about 6.3. Next-to-leading-order perturbative QCD calculations differ from the measured cross sections by about 30% for the $\pi ^{0}$ , and between 30–50% for the $\eta$ meson, while generator-level simulations with PYTHIA 8.2 describe the data to better than 10–30%, except at $p_{\mathrm {T}}<1$  GeV/ $c$ . The new data can therefore be used to further improve the theoretical description of $\pi ^{0}$ and $\eta$ meson production