332 research outputs found
Observation of Λ Hyperon Local Polarization in p-Pb Collisions at √sNN=8.16 TeV
No full textThe polarization of the Λ and ̄Λ hyperons along the beam direction has been measured in proton-lead (p-Pb) collisions at a center-of-mass energy per nucleon pair of 8.16 TeV. The data were obtained with the CMS detector at the LHC and correspond to an integrated luminosity of 186.0±6.5 nb−1
. A significant azimuthal dependence of the hyperon polarization, characterized by the second-order Fourier sine coefficient Pz,s2, is observed. The Pz,s2 values decrease as a function of charged particle multiplicity, but increase with transverse momentum. A hydrodynamic model that describes the observed Pz,s2 values in nucleus-nucleus collisions by introducing vorticity effects does not reproduce either the sign or the magnitude of the p-Pb results. These observations pose a challenge to the current theoretical implementation of spin polarization in heavy ion collisions and offer new insights into the origin of spin polarization in hadronic collisions at LHC energies
Observation of Λ Hyperon Local Polarization in p-Pb Collisions at =8.16 TeV
No full textThe polarization of the Λ and hyperons along the beam direction has been measured in proton-lead (p-Pb) collisions at a center-of-mass energy per nucleon pair of 8.16 TeV. The data were obtained with the CMS detector at the LHC and correspond to an integrated luminosity of 186.0 6.5 nb. A significant azimuthal dependence of the hyperon polarization, characterized by the second-order Fourier sine coefficient P, is observed. The P values decrease as a function of charged particle multiplicity, but increase with transverse momentum. A hydrodynamic model that describes the observed P values in nucleus-nucleus collisions by introducing vorticity effects does not reproduce either the sign or the magnitude of the p-Pb results. These observations pose a challenge to the current theoretical implementation of spin polarization in heavy ion collisions and offer new insights into the origin of spin polarization in hadronic collisions at LHC energies
Observation of Λ Hyperon Local Polarization in <i>p</i>-pb Collisions at √<i>s</i><sub>nn</sub>=8.16 Tev
No full textThe polarization of the Lambda and (Lambda) over bar hyperons along the beam direction has been measured in proton-lead (p-Pb) collisions at a center-of-mass energy per nucleon pair of 8.16 TeV. The data were obtained with the CMS detector at the LHC and correspond to an integrated luminosity of 186.0 +/- 6.5 nb(-1). A significant azimuthal dependence of the hyperon polarization, characterized by the second-order Fourier sine coefficient P-z,P-s2, is observed. The P-z,P-s2 values decrease as a function of charged particle multiplicity, but increase with transverse momentum. A hydrodynamic model that describes the observed P-z,P-s2 values in nucleus-nucleus collisions by introducing vorticity effects does not reproduce either the sign or the magnitude of the p-Pb results. These observations pose a challenge to the current theoretical implementation of spin polarization in heavy ion collisions and offer new insights into the origin of spin polarization in hadronic collisions at LHC energies.LPHE-L
Evidence for Similar Collectivity of High Transverse-Momentum Particles in p-Pb and Pb-Pb Collisions
No full textCharged hadron elliptic anisotropies (v2
) are presented over a wide transverse momentum (pT
) range for proton-lead (pPb
) and lead-lead (PbPb) collisions at nucleon-nucleon center-of-mass energies of 8.16 and 5.02 TeV, respectively. The data were recorded by the CMS experiment and correspond to integrated luminosities of 186 and 0.607 nb−1
for the pPb
and PbPb systems, respectively. A four-particle cumulant analysis is performed using subevents separated in pseudorapidity to effectively suppress noncollective effects. At high pT
(pT>8 GeV
), significant positive v2
values that are similar between pPb
and PbPb collisions at comparable charged particle multiplicities are observed. This observation suggests a common origin for the multiparticle collectivity for high-pT
particles in the two systems
Observation of the Charged-Particle Multiplicity Dependence of σψ(2S)/σJ/ψ in p -Pb Collisions at 8.16 TeV
No full textBound states of charm and anticharm quarks, known as charmonia, have a rich spectroscopic structure that can be used to probe the dynamics of hadron production in high-energy hadron collisions. Here, the cross section ratio of excited (Formula presented) and ground state (Formula presented) vector mesons is measured as a function of the charged-particle multiplicity in proton-lead ((Formula presented)) collisions at a center-of-mass (CM) energy per nucleon pair of 8.16 TeV. The data corresponding to an integrated luminosity of (Formula presented) were collected using the CMS detector. The ratio is measured separately for prompt and nonprompt charmonia in the transverse momentum range (Formula presented) and in four rapidity ranges spanning (Formula presented). For the first time, a statistically significant multiplicity dependence of the prompt cross section ratio is observed in proton-nucleus collisions. There is no clear rapidity dependence in the ratio. The prompt measurements are compared with a theoretical model which includes interactions with nearby particles during the evolution of the system. These results provide additional constraints on hadronization models of heavy quarks in nuclear collisions
Observation of double <i>J</i>/ψ meson production in <i>p</i>Pb collisions at √<i>s</i><sub>NN</sub>=8.16 TeV
No full textThe first observation of the concurrent production of two J/psi mesons in proton-nucleus collisions is presented. The analysis is based on a proton-lead (pPb) data sample recorded at a nucleon-nucleon center-of-mass energy of 8.16 TeV by the CMS experiment at the CERN LHC and corresponding to an integrated luminosity of 174.6 nb(-1). The two J/psi mesons are reconstructed in their mu(+)mu(-) decay channels with transverse momenta p(T) > 6.5 GeV and rapidity vertical bar y vertical bar J/psi J/psi +X process is observed with a significance of 5.3 standard deviations. The measured inclusive fiducial cross section, using the four-muon channel alone, is sigma(pPb (-> J/psi J/psi + X) = 22.0 +/- 8.9(stat) +/- 1.5(syst) nb. A fit of the data to the expected rapidity separation for pairs of J/psi mesons produced in single (SPS) and double (DPS) parton scatterings yields sigma(pPb)(SPS) (-> J/psi J/psi + X) = 16.5 +/- 10.8(stat) +/- 0.1(syst) nb and sigma(pPb)(DPS) (-> J/psi J/psi + X) = 5.4 +/- 6.2(stat) +/- 0.4(syst) nb, respectively. This latter result can he transformed into a lower hound on the effective DPS cross section, closely related to the squared average interparton transverse separation in the collision, of sigma(eff) > 1.0 mb at 95% confidence level.LPHE-L
Search for a Neutral Gauge Boson with Nonuniversal Fermion Couplings in Vector Boson Fusion Processes in Proton-Proton Collisions at s=13 TeV
No full textThe first search for a heavy neutral spin-1 gauge boson (Z0) with nonuniversal fermion couplings
produced via vector boson fusion processes and decaying to tau leptons or W bosons is presented. The
analysis is performed using LHC data at ffiffiffi
s
p 1⁄4 13 TeV, collected from 2016 to 2018 with the CMS
experiment and corresponding to an integrated luminosity of 138 fb−1. The data are consistent with the
standard model predictions. Upper limits are set on the product of the cross section for production of the Z0
boson and its branching fraction to ττ or WW. The presence of a Z0 boson decaying to τþτ− (WþW−) is
excluded for masses up to 2.45(1.60) TeV, depending on the Z0 boson coupling to standard model weak
bosons, and assuming a Z0 → τþτ− (WþW−) branching fraction of 50
Search for Nuclear Modifications of B+ Meson Production in p-Pb Collisions at √sNN=8.16 TeV
No full textDetermination of the spin and parity of all-charm tetraquarks
No full textThe traditional quark model1,2 accounts for the existence of baryons, such as protons and neutrons, which consist of three quarks, as well as mesons, composed of a quark–antiquark pair. Only recently has substantial evidence started to accumulate for exotic states composed of four or five quarks and antiquarks3. The exact nature of their internal structure remains uncertain4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28–29. Here we report the first measurement of quantum numbers of the recently discovered family of three all-charm tetraquarks30, 31–32, using data collected by the CMS experiment at the Large Hadron Collider from 2016 to 2018 (refs. 33,34). The angular analysis techniques developed for the discovery and characterization of the Higgs boson35, 36–37 have been applied to the new exotic states. Here we show that the quantum numbers for parity P and charge conjugation C symmetries are found to be +1. The spin J of these exotic states is determined to be consistent with 2ħ, while 0ħ and 1ħ are excluded at 95% and 99% confidence levels, respectively. The JPC = 2++ assignment implies particular configurations of constituent spins and orbital angular momenta, which constrain the possible internal structure of these tetraquarks
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