Browsing by Subject "RAPIDITY"

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  • The ALICE collaboration; Acharya, S.; Adamova, D.; Kim, D. J.; Krizek, F.; Novitzky, Norbert; Onnerstad, B.S.; Parkkila, J. E.; Rak, Jan; Rytkönen, Heidi Maria; Räsänen, Sami; Saarimäki, Oskari Antti Matti; Slupecki, M.; Trzaska, W. H. (2021)
    The prompt production of the charm baryon Lambda(c+) and the A(c)(+)/D-0 production ratios were measured at midrapidity with the ALICE detector in pp and (p)-Pb collisions at root S-NN = 5.02 TeV. These new measurements show a clear decrease of the Lambda(+)(c)/D-0 ratio with increasing transverse momentum (p(T)) in both collision systems in the range 2 < P-T < 12 GeV/c, exhibiting similarities with the light-flavor baryon-tomeson ratios p/pi and Lambda/K-S(0). At low p(T), predictions that include additional color-reconnection mechanisms beyond the leading-color approximation, assume the existence of additional higher-mass charm-baryon states, or include hadronization via coalescence can describe the data, while predictions driven by charmquark fragmentation processes measured in e(+) e(-) and e(-) p collisions significantly underestimate the data. The results presented in this Letter provide significant evidence that the established assumption of universality (colliding-system independence) of parton-to-hadron fragmentation is not sufficient to describe charm-baryon production in hadronic collisions at LHC energies.
  • Adam, J.; Brucken, E. J.; Chang, B.; Hilden, T. E.; Kim, D. J.; Kral, J.; Mieskolainen, M. M.; Orava, R.; Rak, J.; Rasanen, S. S.; Snellman, T. W.; Trzaska, W. H.; The ALICE collaboration (2015)
    We present a measurement of inclusive J/psi production in p-Pb collisions at root S-NN = 5.02 TeV as a function of the centrality of the collision, as estimated from the energy deposited in the Zero Degree Calorimeters. The measurement is performed with the ALICE detector down to zero transverse momentum, p(T), in the backward (-4.46 <y(cms) <-2.96) and forward (2.03 <y(cms) <3.53) rapidity intervals in the dimuon decay channel and in the mid-rapidity region (-1.37 <y(cms) <0.43) in the dielectron decay channel. The backward and forward rapidity intervals correspond to the Pb-going and p-going direction, respectively. The p(T)-differential J/psi production cross section at backward and forward rapidity is measured for several centrality classes, together with the corresponding average p(T) and p(T)(2) values. The nuclear modification factor is presented as a function of centrality for the three rapidity intervals, and as a function of p(T) for several centrality classes at backward and forward rapidity. At mid-and forward rapidity, the J/psi yield is suppressed up to 40% compared to that in pp interactions scaled by the number of binary collisions. The degree of suppression increases towards central p-Pb collisions at forward rapidity, and with decreasing p(T) of the J/psi. At backward rapidity, the nuclear modification factor is compatible with unity within the total uncertainties, with an increasing trend from peripheral to central p-Pb collisions.
  • The CMS collaboration; Sirunyan, A. M.; Eerola, P.; Kirschenmann, H.; Pekkanen, J.; Voutilainen, M.; Havukainen, J.; Heikkilä, J. K.; Järvinen, T.; Karimäki, V.; Kinnunen, R.; Lampén, T.; Lassila-Perini, K.; Laurila, S.; Lehti, S.; Lindén, T.; Luukka, P.; Mäenpää, T.; Siikonen, H.; Tuominen, E.; Tuominiemi, J.; Tuuva, T. (2018)
    The pseudorapidity distributions of dijets as functions of their average transverse momentum (p(T)(ave)) are measured in proton-lead (pPb) and proton-proton (pp) collisions. The data samples were collected by the CMS experiment at the CERN LHC, at a nucleon-nucleon center-of-mass energy of 5.02 TeV. A significant modification of the pPb spectra with respect to the pp spectra is observed in all p(T)(ave) intervals investigated. The ratios of the pPb and pp distributions are compared to next-to-leading order perturbative quantum chromodynamics calculations with unbound nucleon and nuclear parton distribution functions (PDFs). These results give the first evidence that the gluon PDF at large Bjorken x in lead ions is strongly suppressed with respect to the PDF in unbound nucleons.
  • The ALICE collaboration; Acharya, S.; Adamova, D.; Kim, D. J.; Krizek, F.; Parkkila, J. E.; Rak, J.; Rytkönen, Heidi Maria; Räsänen, Sami; Saarimäki, Oskari Antti Matti; Slupecki, M.; Trzaska, W. H.; Zhou, Zhipeng (2021)
    The polarization of inclusive J/psi and Upsilon(1S) produced in Pb-Pb collisions at root s(NN) = 5.02 TeV at the LHC is measured with the ALICE detector. The study is carried out by reconstructing the quarkonium through its decay to muon pairs in the rapidity region 2.5 < y < 4 and measuring the polar and azimuthal angular distributions of the muons. The polarization parameters lambda(theta), lambda(phi) and lambda(theta phi) are measured in the helicity and Collins-Soper reference frames, in the transverse momentum interval 2 < p(T) < 10 GeV/c and p(T) < 15 GeV/c for the J/psi and Upsilon(1S), respectively. The polarization parameters for the J/psi are found to be compatible with zero, within a maximum of about two standard deviations at low p(T), for both reference frames and over the whole p(T) range. The values are compared with the corresponding results obtained for pp collisions at root s = 7 and 8 TeV in a similar kinematic region by the ALICE and LHCb experiments. Although with much larger uncertainties, the polarization parameters for Upsilon(1S) production in Pb-Pb collisions are also consistent with zero. (c) 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
  • Ducloué, B.; Szymanowski, L.; Wallon, S. (2016)
    We study the production of two forward jets with a large interval of rapidity at hadron colliders, which was proposed by Mueller and Navelet as a possible test of the high energy dynamics of QCD, within a complete next-to-leading logarithm framework. We show that using the Brodsky-Lepage-Mackenzie procedure to fix the renormalization scale leads to a very good description of the recent CMS data at the LHC for the azimuthal correlations of the jets. We show that the inclusion of next-to-leading order corrections to the jet vertex significantly reduces the importance of energy-momentum non-conservation which is inherent to the BFKL approach, for an asymmetric jet configuration. Finally, we argue that the double parton scattering contribution is negligible in the kinematics of actual CMS measurements.
  • The ALICE collaboration; Acharya, S.; Adamova, D.; Kim, D. J.; Krizek, F.; Molander, Mikael Andreas; Novitzky, Norbert; Onnerstad, A.; Parkkila, J. E.; Rytkönen, Heidi Maria; Räsänen, Sami; Saarimäki, Oskari Antti Matti; Slupecki, M.; Trzaska, W. H. (2021)
    We report on the inclusive J/psi production cross section measured at the CERN Large Hadron Collider in proton-proton collisions at a center-of-mass energy root s = 13 TeV. The J/psi mesons are reconstructed in the e(+)e(-) decay channel and the measurements are performed at midrapidity (vertical bar y vertical bar < 0.9) in the transverse-momentum interval 0 < p(T) < 40 GeV/c, using a minimum-bias data sample corresponding to an integrated luminosity L-i(nt) = 32.2 nb(-1) and an Electromagnetic Calorimeter triggered data sample with L-i(nt) = 8.3 pb(-1). The p(T)-integrated J/psi production cross section at midrapidity, computed using the minimumbias data sample, is d sigma/dy vertical bar(y) =0 = 8.97 +/- 0.24 (stat) 0.48 (syst) +/- 0.15 (lumi) mu b. An approximate logarithmic dependence with the collision energy is suggested by these results and available world data, in agreement with model predictions. The integrated and p(T)-differential measurements are compared with measurements in pp collisions at lower energies and with several recent phenomenological calculations based on the non-relativistic QCD and Color Evaporation models.
  • The ALICE collaboration; Acharya, S.; Brucken, E. J.; Chang, B.; Hilden, T. E.; Kim, D. J.; Litichevskyi, V.; Mieskolainen, M. M.; Orava, R.; Parkkila, J. E.; Rak, J.; Räsänen, S. S.; Saarinen, S.; Slupecki, M.; Snellman, T. W.; Trzaska, W. H.; Vargyas, M.; Viinikainen, J. (2018)
    Inclusive J/psi production is studied in Xe-Xeinteractions at a centre-of-mass energy per nucleon pair of root s(NN) = 5.44 TeV, using the ALICE detector at the CERN LHC. The J/psi meson is reconstructed via its decay into a muon pair, in the centre-of-mass rapidity interval 2.5 <y <4 and down to zero transverse momentum. In this Letter, the nuclear modification factors R-AA for inclusive J/psi, measured in the centrality range 0-90% as well as in the centrality intervals 0-20% and 20-90% are presented. The R-AA values are compared to previously published results for Pb-Pbcollisions at root s(NN) = 5.02 TeV and to the calculation of a transport model. A good agreement is found between Xe-Xe and Pb-Pbresults as well as between data and the model. (C) 2018 Organisation europeenne pour la recherche nucleaire. Published by Elsevier B.V.
  • Acharya, S.; Brucken, E. J.; Chang, B.; Kim, D. J.; Litichevskyi, V.; Mieskolainen, M. M.; Orava, R.; Rak, J.; Räsänen, S. S.; Snellman, T. W.; Trzaska, W. H.; Viinikainen, J.; The ALICE collaboration (2017)
    We report a precise measurement of the J/psi elliptic flow in Pb-Pb collisions at root s(NN) = 5.02 TeV with the ALICE detector at the LHC. The J/psi mesons are reconstructed at midrapidity (|y| <0.9) in the dielectron decay channel and at forward rapidity (2.5 <y <4.0) in the dimuon channel, both down to zero transverse momentum. At forward rapidity, the elliptic flow v(2) of the J/psi is studied as a function of the transverse momentum and centrality. A positive v(2) is observed in the transverse momentum range 2
  • The ALICE collaboration; Adamová, D.; Brucken, E.J.; Chang, B.; Kim, D.J.; Litichevskyi, V.; Mieskolainen, M.M.; Orava, R.; Rak, J.; Räsänen, S.S.; Saarinen, S.; Slupecki, M.; Snellman, T.W.; Trzaska, W.H.; Vargyas, M.; Viinikainen, J. (2018)
    We report measurements of the inclusive J/psi yield and average transverse momentum as a function of charged-particle pseudorapidity density dNch/d.in p-Pb collisions at root s(NN)= 5.02 TeVwith ALICE at the LHC. The observables are normalised to their corresponding averages in non-single diffractive events. An increase of the normalised J/psi yield with normalised dN(ch)/d(eta), measured at mid-rapidity, is observed at mid-rapidity and backward rapidity. At forward rapidity, a saturation of the relative yield is observed for high charged-particle multiplicities. The normalised average transverse momentum at forward and backward rapidities increases with multiplicity at low multiplicities and saturates beyond moderate multiplicities. In addition, the forward-to-backward nuclear modification factor ratio is also reported, showing an increasing suppression of J/psi production at forward rapidity with respect to backward rapidity for increasing charged-particle multiplicity. (C) 2017 The Author. Published by Elsevier B. V.
  • The CMS collaboration; Sirunyan, A. M.; Eerola, P.; Kirschenmann, H.; Pekkanen, J.; Voutilainen, M.; Järvinen, T.; Karimäki, V.; Kinnunen, R.; Lampén, T.; Lassila-Perini, K.; Lehti, S.; Lindén, T.; Luukka, P.; Tuominen, E.; Tuominiemi, J.; Talvitie, J.; Tuuva, T. (2018)
    Measurements of differential cross sections d sigma/d phi* and double-differential cross sections d(2)sigma/ld phi*d/y/ for inclusive Z boson production are presented using the dielectron and dimuon final states. The kinematic observable phi* correlates with the dilepton transverse momentum but has better resolution, and y is the dilepton rapidity. The analysis is based on data collected with the CMS experiment at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 19.7 fb(-1). The normalised cross section (1/sigma) d sigma/d phi*, within the fiducial kinematic region, is measured with a precision of better than 0.5% for phi* <1. The measurements are compared to theoretical predictions and they agree, typically, within few percent.
  • The CMS collaboration; Eerola, P.; Forthomme, L.; Kirschenmann, H.; Osterberg, K.; Pekkanen, J.; Voutilainen, M.; Garcia, F.; Havukainen, J.; Heikkilä, J. K.; Järvinen, T.; Kinnunen, R.; Lampen, T.; Lassila-Perini, K.; Laurila, S.; Lehti, S.; Linden, T.; Luukka, P.; Mäenpää, T.; Siikonen, H.; Tuominen, E.; Tuominiemi, J.; Tuuva, T.; Karimäki, V.; Sirunyan, A. M. (2020)
    The transverse momentum (P-T) spectra of inclusively produced A c P baryons are measured via the exclusive decay channel Lambda(+)(c) -> pK(-)pi(+) using the CMS detector at the LHC. Spectra are measured as a function of transverse momentum in proton-proton (pp) and lead-lead (PbPb) collisions at a nucleonnucleon center-of-mass energy of 5.02TeV. The measurement is performed within the Lambda(+)(c) rapidity interval vertical bar Y vertical bar <1 in the p(T) range of 5-20GeV/c in pp and 10-20GeV/c in PbPb collisions. The observed yields of Lambda(+)(c) for p(T) of 10-20 GeV/c suggest a suppression in central PbPb collisions compared to pp collisions scaled by the number of nucleon-nucleon (NN) interactions. The Lambda(+)(c)/D-0 production ratio in pp collisions is compared to theoretical models. In PbPb collisions, this ratio is consistent with the result from pp collisions in their common p-r range. (C) 2020 The Author(s). Published by Elsevier B.V.
  • Acharya, S.; Brucken, E. J.; Chang, B.; Kim, D. J.; Litichevskyi, V.; Mieskolainen, M. M.; Orava, R.; Rak, J.; Räsänen, S. S.; Snellman, T. W.; Trzaska, W. H.; Viinikainen, J.; The ALICE collaboration (2017)
    The production of muons from heavy-flavour hadron decays in p-Pb collisions at root s(NN) = 5.02 TeV was studied for 2 <p(T) <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 <y(cms) <3.53 and -4.46 <y(cms) <-2.96, respectively. The production cross sections and nuclear modification factors are presented as a function of transverse momentum (P-T). At forward rapidity, the nuclear modification factor is compatible with unity while at backward rapidity, in the interval 2.5 <p(T) <3.5 GeV/c, it is above unity by more than 2 sigma. The ratio of the forward -to -backward production cross sections is also measured in the overlapping interval 2.96 <|y(cms)| <3.53 and is smaller than unity by 3.7 sigma in 2.5 <p(T) <3.5 GeV/c. The data are described by model calculations including cold nuclear matter effects. (C) 2017 The Author(s). Published by Elsevier B.V.
  • The ALICE collaboration; Acharya, S.; Chang, B.; Kim, D. J.; Krizek, F.; Mieskolainen, M. M.; Orava, R.; Parkkila, J. E.; Rak, J.; Rytkonen, H.; Saarinen, S.; Slupecki, M.; Snellman, T. W.; Trzaska, W. H.; Viinikainen, J.; Zhou, Z. (2019)
    Production cross sections of muons from semi-leptonic decays of charm and beauty hadrons were measured at forward rapidity (2.5 <y <4) in proton-proton (pp) collisions at a centre-of-mass energy root s = 5.02 TeV with the ALICE detector at the CERN LHC. The results were obtained in an extended transverse momentum interval, 2 <p(T)<20 GeV/c, and with an improved precision compared to previous measurements performed in the same rapidity interval at centre-of-mass energies root s = 2.76 and 7 TeV. The p(T)- and y-differential production cross sections as well as the p(T)-differential production cross section ratios between different centre-of-mass energies and different rapidity intervals are described, within experimental and theoretical uncertainties, by predictions based on perturbative QCD.