Browsing by Subject "ROOT-S(NN)=5.02 TEV"

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  • 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)
    A search has been performed for heavy resonances decaying to ZZ or ZW in 2l2q final states, with two charged leptons (l = e, mu) produced by the decay of a Z boson, and two quarks produced by the decay of a W or Z boson. The analysis is sensitive to resonances with masses in the range from 400 to 4500 GeV. Two categories are defined based on the merged or resolved reconstruction of the hadronically decaying vector boson, optimized for high- and low-mass resonances, respectively. The search is based on data collected during 2016 by the CMS experiment at the LHC in proton-proton collisions with a center-of-mass energy of root s = 13 TeV, corresponding to an integrated luminosity of 35.9 fb(-1). No excess is observed in the data above the standard model background expectation. Upper limits on the production cross section of heavy, narrow spin-1 and spin-2 resonances are derived as a function of the resonance mass, and exclusion limits on the production of W' bosons and bulk graviton particles are calculated in the framework of the heavy vector triplet model and warped extra dimensions, respectively.
  • 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 elliptic azimuthal anisotropy coefficient (upsilon(2)) is measured for charm (D-0) and strange (K-S(0), Lambda, Xi(-), and Omega(-)) hadrons, using a data sample of p + Pb collisions collected by the CMS experiment, at a nucleonnucleon center-of- mass energy of root(NN)-N-s = 8.16 TeV. A significant positive upsilon(2) signal from long- range azimuthal correlations is observed for all particle species in high- multiplicity p + Pb collisions. The measurement represents the first observation of possible long-range collectivity for open heavy flavor hadrons in small systems. The results suggest that charm quarks have a smaller upsilon(2) than the lighter quarks, probably reflecting a weaker collective behavior. This effect is not seen in the larger PbPb collision system at root(NN)-N-s = 5.02 TeV, also presented.
  • Adam, J.; Brucken, E. J.; Chang, B.; Kim, D. J.; Mieskolainen, M. M.; Orava, R.; Rak, J.; Räsänen, S. S.; Saarinen, S.; Slupecki, M.; Snellman, T. W.; Trzaska, W. H.; Vargyas, M.; Viinikainen, J.; The ALICE collaboration (2017)
    At sufficiently high temperature and energy density, nuclear matter undergoes a transition to a phase in which quarks and gluons are not confined: the quark-gluon plasma (QGP)(1). Such an exotic state of strongly interacting quantum chromodynamics matter is produced in the laboratory in heavy nuclei high-energy collisions, where an enhanced production of strange hadrons is observed(2-6). Strangeness enhancement, originally proposed as a signature of QGP formation in nuclear collisions(7), is more pronounced for multi-strange baryons. Several effects typical of heavy-ion phenomenology have been observed in high-multiplicity proton-proton (pp) collisions(8,9), but the enhanced production of multi-strange particles has not been reported so far. Here we present the first observation of strangeness enhancement in high-multiplicity proton-proton collisions. We find that the integrated yields of strange and multi-strange particles, relative to pions, increases significantly with the event charged-particle multiplicity. The measurements are in remarkable agreement with the p-Pb collision results(10,11), indicating that the phenomenon is related to the final system created in the collision. In high-multiplicity events strangeness production reaches values similar to those observed in Pb-Pb collisions, where a QGP is formed.
  • Adam, J.; 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)
    Two-particle angular correlations were measured in pp collisions at root s = 7 TeV for pions, kaons, protons, and lambdas, for all particle/anti-particle combinations in the pair. Data for mesons exhibit an expected peak dominated by effects associated with mini-jets and are well reproduced by general purpose Monte Carlo generators. However, for baryon-baryon and anti-baryon-anti-baryon pairs, where both particles have the same baryon number, a near-side anti-correlation structure is observed instead of a peak. This effect is interpreted in the context of baryon production mechanisms in the fragmentation process. It currently presents a challenge to Monte Carlo models and its origin remains an open question.
  • The ALICE collaboration; Acharya, S.; 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)
    Neutral pion and eta meson invariant differential yields were measured in non-single diffractive p-Pb collisions at root S-NN = 5.02 TeV with the ALICE experiment at the CERN LHC. The analysis combines results from three complementary photon measurements, utilizing the PHOS and EMCal calorimeters and the Photon Conversion Method. The invariant differential yields of pi(0) and eta meson inclusive production are measured near mid-rapidity in a broad transverse momentum range of 0.3 < p(T) < 20 GeV/c and 0.7 < p(T) < 20 GeV/c, respectively. The measured eta/pi(0) ratio increases with p(T) and saturates for p(T) > 4 GeV/c at 0.483 +/- 0.015(stat) +/- 0.015(sys). A deviation from m(T) scaling is observed for p(T) < 2 GeV/c. The measured eta/pi(0) ratio is consistent with previous measurements from proton-nucleus and pp collisions over the full pi range. The measured eta/pi(0) ratio at high p(T) also agrees within uncertainties with measurements from nucleus nucleus collisions. The pi(0) and eta yields in p-Pb relative to the scaled pp interpolated reference, R-pPb, are presented for 0.3 < p(T) < 20 GeV/c and 0.7 < p(T) < 20 GeV/c, respectively. The results are compared with theoretical model calculations. The values of R-pPb are consistent with unity for transverse momenta above 2 GeV/c. These results support the interpretation that the suppressed yield of neutral mesons measured in Pb-Pb collisions at LHC energies is due to parton energy loss in the hot QCD medium.
  • The ALICE collaboration; Acharya, S.; 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 present a measurement of azimuthal correlations between inclusive J/psi and charged hadrons in p-Pb collisions recorded with the ALICE detector at the CERN LHC. The J/psi are reconstructed at forward (p-going, 2.03 <y <3.53) and backward (Pb-going, -4.46 <y <-2.96) rapidity via their mu(+)mu(-) decay channel, while the charged hadrons are reconstructed at mid-rapidity (vertical bar eta vertical bar <1.8). The correlations are expressed in terms of associated charged-hadron yields per W . trigger. A rapidity gap of at least 1.5 units is required between the trigger J/psi and the associated charged hadrons. Possible correlations due to collective effects are assessed by subtracting the associated per-trigger yields in the low-multiplicity collisions from those in the high-multiplicity collisions. After the subtraction, we observe a strong indication of remaining symmetric structures at Delta phi approximate to 0 and Delta phi approximate to pi), similar to those previously found in two-particle correlations at middle and forward rapidity. The corresponding second-order Fourier coefficient (v(2) ) in the transverse momentum interval between 3 and 6 GeV/c is found to be positive with a significance of about 5 sigma. The obtained results are similar to the J/psi v(2) coefficients measured in Pb-Pb collisions at root s(NN) = 5.02 TeV, suggesting a common mechanism at the origin of the J/psi v(2) . (C) 2018 The Author. Published by Elsevier B.V.