Search results for "COLLISIONS"

Correlated Event-by-Event Fluctuations of Flow Harmonics in Pb-Pb Collisions at √sNN = 2.76 TeV

2016

We report the measurements of correlations between event-by-event fluctuations of amplitudes of anisotropic flow harmonics in nucleus-nucleus collisions, obtained for the first time using a new analysis method based on multiparticle cumulants in mixed harmonics. This novel method is robust against systematic biases originating from nonflow effects and by construction any dependence on symmetry planes is eliminated. We demonstrate that correlations of flow harmonics exhibit a better sensitivity to medium properties than the individual flow harmonics. The new measurements are performed in Pb-Pb collisions at the center-of-mass energy per nucleon pair of √=2.76  TeV sNN p ¼ 2.76 TeV by the ALI…

Forward-backward multiplicity correlations in pp collisions at √s = 0.9, 2.76 and 7 TeV

2015

The strength of forward-backward (FB) multiplicity correlations is measured by the ALICE detector in proton-proton (pp) collisions at √ s = 0.9, 2.76 and 7 TeV. The measurement is performed in the central pseudorapidity region (|η| 0.3 GeV/c. Two separate pseudorapidity windows of width (δη) ranging from 0.2 to 0.8 are chosen symmetrically around η = 0. The multiplicity correlation strength (bcorr) is studied as a function of the pseudorapidity gap (ηgap) between the two windows as well as the width of these windows. The correlation strength is found to decrease with increasing ηgap and shows a non-linear increase with δη. A sizable increase of the correlation strength with the collision en…

Observation of the rare B(s)(0) + decay from the combined analysis of CMS and LHCb data.

2015

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported licence.-- et al.

Search for supersymmetry in events with photons, bottom quarks, and missing transverse momentum in proton-proton collisions at a centre-of-mass energ…

2013

A search has been performed for the experimental signature of an isolated photon with high transverse momentum, at least one jet identified as originating from a bottom quark, and high missing transverse momentum. Such a final state may originate from supersymmetric models with gauge-mediated supersymmetry breaking in events in which one of a pair of higgsino-like neutralinos decays into a photon and a gravitino while the other decays into a Higgs boson and a gravitino. The search is performed using the full dataset of 7 TeV proton–proton collisions recorded with the ATLAS detector at the LHC in 2011, corresponding to an integrated luminosity of 4.7 fb−1. A total of 7 candidate events are o…

Measurement of the production of high-pT electrons from heavy-flavour hadron decays in Pb–Pb collisions at √sNN = 2.76 TeV

2017

Electrons from heavy-flavour hadron decays (charm and beauty) were measured with the ALICE detector in Pb–Pb collisions at a centre-of-mass of energy √sNN = 2.76 TeV. The transverse momentum (pT) differential production yields at mid-rapidity were used to calculate the nuclear modification factor RAA in the interval 3 < pT < 18 GeV/c. The RAA shows a strong suppression compared to binary scaling of pp collisions at the same energy (up to a factor of 4) in the 10% most central Pb–Pb collisions. There is a centrality trend of suppression, and a weaker suppression (down to a factor of 2) in semi-peripheral (50–80%) collisions is observed. The suppression of electrons in this broad pT interval …

Production of muons from heavy-flavour hadron decays in p–Pb collisions at √sNN = 5.02 TeV

2017

The production of muons from heavy-flavour hadron decays in p–Pb collisions at √sNN = 5.02 TeV was studied for 2 < pT < 16 GeV/c with the ALICE detector at the CERN LHC. The measurement was performed at forward (p-going direction) and backward (Pb-going direction) rapidity, in the ranges of rapidity in the centre-of-mass system (cms) 2.03 < ycms < 3.53 and −4.46 < ycms < −2.96, respectively. The production cross sections and nuclear modification factors are presented as a function of transverse momentum (pT). At forward rapidity, the nuclear modification factor is compatible with unity while at backward rapidity, in the interval 2.5 < pT < 3.5 GeV/c, it is above unity by more than 2σ. The r…

Spatially dependent parton distribution functions and hard processes in nuclear collisions

2014

Measurement of emission-angle anisotropy via long-range angular correlations with high-pT hadrons in d+Au and p+p collisions at √sNN = 200 GeV

2018

We present measurements of two-particle angular correlations between high-transverse-momentum (2 < pT < 11 GeV/c) π0 observed at midrapidity (|η| < 0.35) and particles produced either at forward (3.1 <η< 3.9) or backward (−3.7 <η< −3.1) rapidity in d + Au and p + p collisions at √sNN = 200 GeV. The azimuthal angle correlations for particle pairs with this large rapidity gap in the Au-going direction exhibit a characteristic structure that persists up to pT ≈ 6 GeV/c and which strongly depends on collision centrality, which is a similar characteristic to the hydrodynamical particle flow in A + A collisions. The structure is absent in the d-going direction as well as in p + p collisions, in t…

Measurement of J/ψ at forward and backward rapidity in p+p, p+Al, p+Au, and 3He+Au collisions at √sNN=200 GeV

2020

Charmonium is a valuable probe in heavy-ion collisions to study the properties of the quark gluon plasma, and is also an interesting probe in small collision systems to study cold nuclear matter effects, which are also present in large collision systems. With the recent observations of collective behavior of produced particles in small system collisions, measurements of the modification of charmonium in small systems have become increasingly relevant. We present the results of J/Psi measurements at forward and backward rapidity in various small collision systems, p + p, p + Al, p + Au, and He-3+Au, at root s(NN) = 200 GeV. The results are presented in the form of the observable RAB, the nuc…

Centrality and pseudorapidity dependence of the charged-particle multiplicity density in Xe–Xe collisions at √sNN = 5.44 TeV

2019

In this Letter, the ALICE Collaboration presents the first measurements of the charged-particle multiplicity density, dNch/dη, and total charged-particle multiplicity, Ntot ch , in Xe–Xe collisions at a centre-of-mass energy per nucleon–nucleon pair of √sNN = 5.44 TeV. The measurements are performed as a function of collision centrality over a wide pseudorapidity range of −3.5 < η < 5. The values of dNch/dη at mid-rapidity and Ntot ch for central collisions, normalised to the number of nucleons participating in the collision (Npart) as a function of √sNN follow the trends established in previous heavy-ion measurements. The same quantities are also found to increase as a function of Npart, a…