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Acharya, S.,Adamová,, D.,Adhya, S.P.,Adler, A.,Adolfsson, J.,Aggarwal, M.M.,Aglieri Rinella, G.,Agnello, M.,Agrawal, N.,Ahammed, Z.,Ahmad, S.,Ahn, S.U.,Aiola, S.,Akindinov, A.,Al-Turany, M.,Alam North-Holland Pub. Co 2019 Physics letters. Section B Vol.798 No.-
<P><B>Abstract</B></P> <P>The ALICE collaboration performed the first rapidity-differential measurement of coherent J / ψ photoproduction in ultra-peripheral Pb–Pb collisions at a center-of-mass energy <SUB> s NN </SUB> = 5.02 TeV. The J / ψ is detected via its dimuon decay in the forward rapidity region ( − 4.0 < y < − 2.5 ) for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 750 μb<SUP>−1</SUP>. The cross section for coherent J / ψ production is presented in six rapidity bins. The results are compared with theoretical models for coherent J / ψ photoproduction. These comparisons indicate that gluon shadowing effects play a role in the photoproduction process. The ratio of <SUP> ψ ′ </SUP> to J / ψ coherent photoproduction cross sections was measured and found to be consistent with that measured for photoproduction off protons.</P>
Adam, J.,Adamová,, D.,Aggarwal, M.M.,Aglieri Rinella, G.,Agnello, M.,Agrawal, N.,Ahammed, Z.,Ahmad, S.,Ahn, S.U.,Aiola, S.,Akindinov, A.,Alam, S.N.,Albuquerque, D.S.D.,Aleksandrov, D.,Alessandro North-Holland Pub. Co 2017 Physics letters. Section B Vol.771 No.-
<P><B>Abstract</B></P> <P>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 <SUB> s NN </SUB> = 2.76 TeV . The transverse momentum ( <SUB> p T </SUB> ) differential production yields at mid-rapidity were used to calculate the nuclear modification factor <SUB> R AA </SUB> in the interval 3 < <SUB> p T </SUB> < 18 GeV/<I>c</I>. The <SUB> R AA </SUB> 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 <SUB> p T </SUB> interval indicates that both charm and beauty quarks lose energy when they traverse the hot medium formed in Pb–Pb collisions at LHC.</P>
Anomalous Evolution of the Near-Side Jet Peak Shape in Pb-Pb Collisions at sNN=2.76 TeV
Adam, J.,Adamová,, D.,Aggarwal, M. M.,Aglieri Rinella, G.,Agnello, M.,Agrawal, N.,Ahammed, Z.,Ahmad, S.,Ahn, S. U.,Aiola, S.,Akindinov, A.,Alam, S. N.,Albuquerque, D. S. D.,Aleksandrov, D.,Aless American Physical Society 2017 Physical review letters Vol.119 No.10
<P>The measurement of two-particle angular correlations is a powerful tool to study jet quenching in a p(T) region inaccessible by direct jet identification. In these measurements pseudorapidity (Delta(eta)) and azimuthal (Delta phi) differences are used to extract the shape of the near-side peak formed by particles associated with a higher p(T) trigger particle (1 < p(T,trig) < 8 GeV/c). A combined fit of the near-side peak and long-range correlations is applied to the data allowing the extraction of the centrality evolution of the peak shape in Pb-Pb collisions at root s(NN) = 2.76 TeV. A significant broadening of the peak in the Delta(eta) direction at low p(T) is found from peripheral to central collisions, which vanishes above 4 GeV/c, while in the Delta(phi) direction the peak is almost independent of centrality. For the 10% most central collisions and 1 < p(T,assoc) < 2 GeV/c, 1 < p(T,trig) < 3 GeV/c a novel feature is observed: a depletion develops around the center of the peak. The results are compared to pp collisions at the same center of mass energy and AMPT model simulations. The comparison to the investigated models suggests that the broadening and the development of the depletion is connected to the strength of radial and longitudinal flow.</P>
Inclusive quarkonium production at forward rapidity in pp collisions at [FORMULA OMISSION] TeV
Adam, J.,Adamová,, D.,Aggarwal, M. M.,Aglieri Rinella, G.,Agnello, M.,Agrawal, N.,Ahammed, Z.,Ahn, S. U.,Aiola, S.,Akindinov, A.,Alam, S. N.,Aleksandrov, D.,Alessandro, B.,Alexandre, D.,Alfaro M Springer Berlin Heidelberg 2016 The European physical journal. C, Particles and fi Vol.76 No.4
<P>We report on the inclusive production cross sections of [FORMULA OMISSION], [FORMULA OMISSION], [FORMULA OMISSION](1S), [FORMULA OMISSION](2S) and [FORMULA OMISSION](3S), measured at forward rapidity with the ALICE detector in [FORMULA OMISSION] collisions at a center-of-mass energy [FORMULA OMISSION] TeV. The analysis is based on data collected at the LHC and corresponds to an integrated luminosity of 1.23 pb[FORMULA OMISSION]. Quarkonia are reconstructed in the dimuon-decay channel. The differential production cross sections are measured as a function of the transverse momentum [FORMULA OMISSION] and rapidity <I>y</I>, over the [FORMULA OMISSION] ranges [FORMULA OMISSION] GeV/<I>c</I> for [FORMULA OMISSION], [FORMULA OMISSION] GeV/<I>c</I> for all other resonances, and for [FORMULA OMISSION]. The cross sections, integrated over [FORMULA OMISSION] and <I>y</I>, and assuming unpolarized quarkonia, are [FORMULA OMISSION] [FORMULA OMISSION]b, [FORMULA OMISSION] [FORMULA OMISSION]b, [FORMULA OMISSION] nb, [FORMULA OMISSION] nb and [FORMULA OMISSION] nb, where the first uncertainty is statistical and the second one is systematic. These values agree, within at most [FORMULA OMISSION], with measurements performed by the LHCb collaboration in the same rapidity range.</P>
Measurement of an Excess in the Yield ofJ/ψat Very LowpTin Pb-Pb Collisions atsNN=2.76 TeV
Adam, J.,Adamová,, D.,Aggarwal, M. M.,Aglieri Rinella, G.,Agnello, M.,Agrawal, N.,Ahammed, Z.,Ahn, S. U.,Aiola, S.,Akindinov, A.,Alam, S. N.,Aleksandrov, D.,Alessandro, B.,Alexandre, D.,Alfaro M American Physical Society 2016 Physical review letters Vol.116 No.22
<P>We report on the first measurement of an excess in the yield of J/psi at very low transverse momentum (pT < 0.3 GeV/c) in peripheral hadronic Pb-Pb collisions at root s(NN) = 2.76 TeV, performed by ALICE at the CERN LHC. Remarkably, the measured nuclear modification factor of J/psi in the rapidity range 2.5 < y < 4 reaches about 7 (2) in the p(T) range 0-0.3 GeV/c in the 70%-90% (50%-70%) centrality class. The J/psi production cross section associated with the observed excess is obtained under the hypothesis that coherent photoproduction of J/psi is the underlying physics mechanism. If confirmed, the observation of J/psi coherent photoproduction in Pb-Pb collisions at impact parameters smaller than twice the nuclear radius opens new theoretical and experimental challenges and opportunities. In particular, coherent photoproduction accompanying hadronic collisions may provide insight into the dynamics of photoproduction and nuclear reactions, as well as become a novel probe of the quark-gluon plasma.</P>
Neutral pion and η meson production at midrapidity in Pb-Pb collisions at sNN=2.76 TeV
Acharya, S.,Acosta, F. T.-.,Adamová,, D.,Adolfsson, J.,Aggarwal, M. M.,Aglieri Rinella, G.,Agnello, M.,Agrawal, N.,Ahammed, Z.,Ahn, S. U.,Aiola, S.,Akindinov, A.,Al-Turany, M.,Alam, S. N.,Albuqu American Physical Society 2018 Physical review. C Vol.98 No.4
<P>Neutral pion and eta meson production in the transverse momentum range 1 < p(T) < 20 GeV/c have been measured at midrapidity by the ALICE experiment at the Large Hadron Collider (LHC) in central and semicentral Pb-Pb collisions at root S-NN = 2.76 TeV. These results were obtained using the photon conversion method as well as the Photon Spectrometer (PHOS) and Electromagnetic Calorimeter detectors. The results extend the upper p(T) reach of the previous ALICE pi(0) measurements from 12 to 20 GeV/c and present the first measurement of eta meson production in heavy-ion collisions at the LHC. The eta/pi(0) ratio is similar for the two centralities and reaches at high p(T) a plateau value of 0.457 +/- 0.013(stat) +/- 0.018(syst) A suppression of similar magnitude for pi(0) and eta meson production is observed in Pb-Pb collisions with respect to their production in pp collisions scaled by the number of binary nucleon-nucleon collisions. We discuss the results in terms of Next to Leading Order (NLO) pQCD predictions and hydrodynamic models. The measurements show a stronger suppression than observed at lower center-of-mass energies in the p T range 6 < p(T) < 10 GeV/c. For p(T) < 3 GeV/c, hadronization models describe the pi(0) results while for the eta some tension is observed.</P>
Flow Dominance and Factorization of Transverse Momentum Correlations in Pb-Pb Collisions at the LHC
Adam, J.,Adamová,, D.,Aggarwal, M. M.,Aglieri Rinella, G.,Agnello, M.,Agrawal, N.,Ahammed, Z.,Ahmad, S.,Ahn, S. U.,Aiola, S.,Akindinov, A.,Alam, S. N.,Albuquerque, D. S. D.,Aleksandrov, D.,Aless American Physical Society 2017 Physical review letters Vol.118 No.16
<P>We present the first measurement of the two-particle transverse momentum differential correlation function, P-2 = <Delta pT Delta p(T)>/ < p(T)>(2), in Pb-Pb collisions at root s(NN) = 2.76 TeV. Results for P-2 are reported as a function of the relative pseudorapidity (Delta eta) and azimuthal angle (Delta phi) between two particles for different collision centralities. The Delta phi dependence is found to be largely independent of Delta eta for broken vertical bar Delta eta broken vertical bar >= 0.9. In the 5% most central Pb-Pb collisions, the two-particle transverse momentum correlation function exhibits a clear double-hump structure around Delta phi=pi (i. e., on the away side), which is not observed in number correlations in the same centrality range, and thus provides an indication of the dominance of triangular flow in this collision centrality. Fourier decompositions of P-2, studied as a function of the collision centrality, show that correlations at broken vertical bar Delta eta broken vertical bar >= 0.9 can be well reproduced by a flow ansatz based on the notion that measured transverse momentum correlations are strictly determined by the collective motion of the system.</P>
Acharya, S.,Adamová,, D.,Adolfsson, J.,Aggarwal, M.M.,Aglieri Rinella, G.,Agnello, M.,Agrawal, N.,Ahammed, Z.,Ahn, S.U.,Aiola, S.,Akindinov, A.,Al-Turany, M.,Alam, S.N.,Albuquerque, D.S.D.,Aleks North-Holland Pub. Co 2018 Physics letters. Section B Vol.783 No.-
<P><B>Abstract</B></P> <P>The ALICE Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high-transverse momentum trigger hadron in p–Pb collisions at <SUB> s NN </SUB> = 5.02 TeV. Jets are reconstructed from charged-particle tracks using the anti- <SUB> k T </SUB> algorithm with resolution parameter R = 0.2 and 0.4. A data-driven statistical approach is used to correct the uncorrelated background jet yield. Recoil jet distributions are reported for jet transverse momentum 15 < p T , jet ch < 50 GeV / c and are compared in various intervals of p–Pb event activity, based on charged-particle multiplicity and zero-degree neutral energy in the forward (Pb-going) direction. The semi-inclusive observable is self-normalized and such comparisons do not require the interpretation of p–Pb event activity in terms of collision geometry, in contrast to inclusive jet observables. These measurements provide new constraints on the magnitude of jet quenching in small systems at the LHC. In p–Pb collisions with high event activity, the average medium-induced out-of-cone energy transport for jets with R = 0.4 and 15 < p T , jet ch < 50 GeV / c is measured to be less than 0.4 GeV / c at 90% confidence, which is over an order of magnitude smaller than a similar measurement for central Pb–Pb collisions at <SUB> s NN </SUB> = 2.76 TeV . Comparison is made to theoretical calculations of jet quenching in small systems, and to inclusive jet measurements in p–Pb collisions selected by event activity at the LHC and in d–Au collisions at RHIC.</P>
First measurement of jet mass in Pb–Pb and p–Pb collisions at the LHC
Acharya, S.,Adamová,, D.,Aggarwal, M.M.,Aglieri Rinella, G.,Agnello, M.,Agrawal, N.,Ahammed, Z.,Ahmad, N.,Ahn, S.U.,Aiola, S.,Akindinov, A.,Alam, S.N.,Albuquerque, D.S.D.,Aleksandrov, D.,Alessan North-Holland Pub. Co 2018 Physics letters. Section B Vol.776 No.-
<P><B>Abstract</B></P> <P>This letter presents the first measurement of jet mass in Pb–Pb and p–Pb collisions at <SUB> s NN </SUB> = 2.76 TeV and <SUB> s NN </SUB> = 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- <SUB> k T </SUB> jet algorithm and resolution parameter R = 0.4 . The jets are measured in the pseudorapidity range | <SUB> η jet </SUB> | < 0.5 and in three intervals of transverse momentum between 60 GeV/<I>c</I> and 120 GeV/<I>c</I>. 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.</P>