Despite the f$_0$(980) hadron having been discovered half a century ago, the question about its quark content has not been settled: it might be an ordinary quark-antiquark ($\mathrm{q\bar{q}}$) meson, a tetraquark ($\mathrm{q\bar{q}q\bar{q}}$) exotic state, a kaon-antikaon ($\mathrm{K\bar{K}}$) molecule, or a quark-antiquark-gluon ($\mathrm{q\bar{q}g}$) hybrid. This paper reports strong evidence that the f$_0$(980) state is an ordinary $\mathrm{q\bar{q}}$ meson, inferred from the scaling of elliptic anisotropies ($v_2$) with the number of constituent quarks ($n_\mathrm{q}$), as empirically established using conventional hadrons in relativistic heavy ion collisions. The f$_0$(980) state is reconstructed via its dominant decay channel f$_0$(980) $\to$$\pi^+\pi^-$, in proton-lead collisions recorded by the CMS experiment at the LHC, and its $v_2$ is measured as a function of transverse momentum ($p_\mathrm{T}$). It is found that the $n_q$ = 2 ($\mathrm{q\bar{q}}$ state) hypothesis is favored over $n_q$ = 4 ($\mathrm{q\bar{q}q\bar{q}}$ or $\mathrm{K\bar{K}}$ states) by 7.7, 6.3, or 3.1 standard deviations in the $p_\mathrm{T}$$\lt$ 10, 8, or 6 GeV/$c$ ranges, respectively, and over $n_\mathrm{q}$ = 3 ($\mathrm{q\bar{q}g}$ hybrid state) by 3.5 standard deviations in the $p_\mathrm{T}$$\lt$ 8 GeV/$c$ range. This result represents the first determination of the quark content of the f$_0$(980) state, made possible by using a novel approach, and paves the way for similar studies of other exotic hadron candidates.
The elliptic flow, $v_{2}$, for $f_0(980)$ as a function of $p_{T}$ in pPb collision at 8.16 TeV.
The elliptic flow after nonflow subtraction, $v_{2}^{sub}$, for $f_0(980)$ as a function of $p_{T}$ in pPb collision at 8.16 TeV.
The elliptic flow after nonflow subtraction, $v_{2}^{sub}/2$, for $f_0(980)$ as a function of $<KE_{T}>/2$ in pPb collision at 8.16 TeV.
The azimuthal anisotropy of $\Upsilon$(1S) mesons in high-multiplicity proton-lead collisions is studied using data collected by the CMS experiment at a nucleon-nucleon center-of-mass energy of 8.16 TeV. The $\Upsilon$(1S) mesons are reconstructed using their dimuon decay channel. The anisotropy is characterized by the second Fourier harmonic coefficients, found using a two-particle correlation technique, in which the $\Upsilon$(1S) mesons are correlated with charged hadrons. A large pseudorapidity gap is used to suppress short-range correlations. Nonflow contamination from the dijet background is removed using a low-multiplicity subtraction method, and the results are presented as a function of $\Upsilon$(1S) transverse momentum. The azimuthal anisotropies are smaller than those found for charmonia in proton-lead collisions at the same collision energy, but are consistent with values found for $\Upsilon$(1S) mesons in lead-lead interactions at a nucleon-nucleon center-of-mass energy of 5.02 TeV.
The $p_{\mathrm{T}}$ dependent $v_{2}^{\textrm{sub}}$ values of $\Upsilon(1S)$ mesons measured in the high-multiplicity region of $70 \leq N^{\text{offline}}_{\text{trk}} < 300$, where a low-multiplicity region of $N^{\text{offline}}_{\text{trk}} < 50$ is used to estimate and correct for the dijet contribution.
The $p_{\mathrm{T}}$ dependent $v_{2}^{\textrm{sub}}$ values of $\Upsilon(1S)$ mesons measured in the high-multiplicity region of $70 \leq N^{\text{offline}}_{\text{trk}} < 300$, where a low-multiplicity region of $N^{\text{offline}}_{\text{trk}} < 50$ is used to estimate and correct for the dijet contribution.
Measurements of the second Fourier harmonic coefficient ($v_2$) of the azimuthal distributions of prompt and nonprompt D$^0$ mesons produced in pp and pPb collisions are presented. Nonprompt D$^0$ mesons come from beauty hadron decays. The data samples are collected by the CMS experiment at nucleon-nucleon center-of-mass energies of 13 and 8.16 TeV, respectively. In high multiplicity pp collisions, $v_2$ signals for prompt charm hadrons are reported for the first time, and are found to be comparable to those for light-flavor hadron species over a transverse momentum ($p_\mathrm{T}$) range of 2-6 GeV. Compared at similar event multiplicities, the prompt D$^0$ meson $v_2$ values in pp and pPb collisions are similar in magnitude. The $v_2$ values for open beauty hadrons are extracted for the first time via nonprompt D$^0$ mesons in pPb collisions. For $p_\mathrm{T}$ in the range of 2-5 GeV, the results suggest that $v_2$ for nonprompt D$^0$ mesons are smaller than those for prompt D$^0$ mesons. These new measurements indicate a positive charm hadron $v_2$ in pp collisions and suggest a mass dependence in $v_2$ between charm and beauty hadrons in the pPb system. These results provide insights into the origin of heavy-flavor quark collectivity in small systems.
Results of elliptic flow, corrected for short range correlations, for prompt neutral D mesons, as a function of transverse momenta for $|y_{lab}|< 1$, with $N^{offline}_{trk} \geq 100$ in pp collisions at 13 TeV.
Results of elliptic flow, corrected for short range correlations, for prompt neutral D mesons, as a function of multiplicity for $|y_{lab}|< 1$, with 2$ < p_{T} < $4 GeV in pp collisions at 13 TeV.
Results of elliptic flow, corrected for short range correlations, for prompt neutral D mesons, as a function of multiplicity for $|y_{lab}|< 1$, with 4$ < p_{T} < $6 GeV in pp collisions at 13 TeV.
A measurement of the elliptic flow ($v_2$) of prompt J/$\psi$ mesons in high-multiplicity pPb collisions is reported using data collected by the CMS experiment at a nucleon-nucleon center-of-mass energy $\sqrt{s_\mathrm{NN}} =$ 8.16 TeV. Prompt J/$\psi$ mesons decaying into two muons are reconstructed in the rapidity region in the nucleon-nucleon center-of-mass frame ($y_\mathrm{cm}$), corresponding to either $-$2.86 $\lt y_{\mathrm{cm}} <$ $-$1.86 or 0.94 $\lt y_{\mathrm{cm}} <$ 1.94. The average $v_2$ result from the two rapidity ranges is reported over the transverse momentum (p$_\mathrm{T}$) range from 0.2 to 10 GeV. Positive $v_2$ values are observed for the prompt J/$\psi$ meson, as extracted from long-range two-particle correlations with charged hadrons, for 2 $\lt p_{\mathrm{T}}<$ 8 GeV. The prompt J/$\psi$ results are compared with previous CMS measurements of elliptic flow for open charm mesons (D$^0$) and strange hadrons. From these measurements, constraints can be obtained on the collective dynamics of charm quarks produced in high-multiplicity events arising from small systems.
The elliptic flow, $v_2$, for prompt $\mathrm{J}/\psi$ mesons as a function of $p_{\mathrm{T}}$ in pPb collision at 8.16 TeV.
The elliptic flow corrected for residual jet correlations, $v_2^{\mathrm{sub}}$, for prompt $\mathrm{J}/\psi$ mesons as a function of $p_{\mathrm{T}}$ in pPb collision at 8.16 TeV.
The elliptic flow per constituent quark corrected for residual jet correlations, $v_2^{\mathrm{sub}}/n_q$, for prompt $\mathrm{J}/\psi$ mesons as a function of transverse kinetic energy per constituent quark in pPb collision at 8.16 TeV.
The elliptic azimuthal anisotropy coefficient ($v_2$) is measured for charm (D$^0$) and strange (K$_\mathrm{S}^0$, $\Lambda$, $\Xi^-$, and $\Omega^-$) hadrons, using a data sample of pPb collisions collected by the CMS experiment, at a nucleon-nucleon center-of-mass energy $\sqrt{s_{_\mathrm{NN}}} =$ 8.16 TeV. A significant positive $v_2$ signal from long-range azimuthal correlations is observed for all particle species in high-multiplicity pPb 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 $v_2$ than the lighter quarks, probably reflecting a weaker collective behavior. This effect is not seen in the larger PbPb collision system at $\sqrt{s_{_\mathrm{NN}}} =$ 5.02 TeV, also presented.
The elliptic flow, $v_{2}$, for $K^{0}_{S}$ as a function of $p_{T}$ in pPb collision at 8.16 TeV.
The elliptic flow, $v_{2}$, for $\Lambda$ as a function of $p_{T}$ in pPb collision at 8.16 TeV.
The elliptic flow, $v_{2}$, for $\Xi^{-}$ as a function of $p_{T}$ in pPb collision at 8.16 TeV.
Multi-particle cumulants and corresponding Fourier harmonics are measured for azimuthal angle distributions of charged particles in $pp$ collisions at $\sqrt{s}$ = 5.02 and 13 TeV and in $p$+Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV, and compared to the results obtained for low-multiplicity Pb+Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. These measurements aim to assess the collective nature of particle production. The measurements of multi-particle cumulants confirm the evidence for collective phenomena in $p$+Pb and low-multiplicity Pb+Pb collisions. On the other hand, the $pp$ results for four-particle cumulants do not demonstrate collective behaviour, indicating that they may be biased by contributions from non-flow correlations. A comparison of multi-particle cumulants and derived Fourier harmonics across different collision systems is presented as a function of the charged-particle multiplicity. For a given multiplicity, the measured Fourier harmonics are largest in Pb+Pb, smaller in $p$+Pb and smallest in $pp$ collisions. The $pp$ results show no dependence on the collision energy, nor on the multiplicity.
$c_2\{4\}$ cumulants for reference particles with 0.3 $< p_T <$ 3.0 GeV selected according to $M_{ref}$ (EvSel_$M_{ref}$) for pp collisions at $\sqrt{s}$= 5.02 TeV.
$c_2\{4\}$ cumulants for reference particles with 0.3 $< p_T <$ 3.0 GeV selected according to $M_{ref}$ (EvSel_$M_{ref}$) for pp collisions at $\sqrt{s}$= 13 TeV.
$c_2\{4\}$ cumulants for reference particles with 0.3 $< p_T <$ 3.0 GeV selected according to $M_{ref}$ (EvSel_$M_{ref}$) for pPb collisions at $\sqrt{ s_{NN} }$= 5.02 TeV.
Measurements of two- and multi-particle angular correlations in pp collisions at sqrt(s) = 5, 7, and 13 TeV are presented as a function of charged-particle multiplicity. The data, corresponding to integrated luminosities of 1.0 inverse picobarn (5 TeV), 6.2 inverse picobarns (7 TeV), and 0.7 inverse picobarns (13 TeV), were collected using the CMS detector at the LHC. The second-order (v[2]) and third-order (v[3]) azimuthal anisotropy harmonics of unidentified charged particles, as well as v[2] of K0 short and Lambda/anti-Lambda particles, are extracted from long-range two-particle correlations as functions of particle multiplicity and transverse momentum. For high-multiplicity pp events, a mass ordering is observed for the v[2] values of charged hadrons (mostly pions), K0 short, and Lambda/anti-Lambda, with lighter particle species exhibiting a stronger azimuthal anisotropy signal below pt of about 2 GeV/c. For 13 TeV data, the v[2] signals are also extracted from four- and six-particle correlations for the first time in pp collisions, with comparable magnitude to those from two-particle correlations. These observations are similar to those seen in pPb and PbPb collisions, and support the interpretation of a collective origin for the observed long-range correlations in high-multiplicity pp collisions.
The second-order Fourier coefficients, $V_{2\Delta}(2, |\Delta\eta| > 2)$, as a function of $N_{offline}^{trk}$ for charged particles.
The second-order Fourier coefficients, $V_{2\Delta}(2, |\Delta\eta| > 2)$, as a function of $N_{offline}^{trk}$ for charged particles, after correcting for back-to-back jet correlations, estimated from the 10 $\leq$ $N_{offline}^{trk}$ < 20 range.
The second-order Fourier coefficients, $V_{3\Delta}(2, |\Delta\eta| > 2)$, as a function of $N_{offline}^{trk}$ for charged particles.
Correlations induced by quantum statistics are sensitive to the spatio-temporal extent as well as dynamics of particle emitting sources in heavy-ion collisions. In addition, such correlations can be used to search for the presence of a coherent component of pion production. Two and three-pion correlations of same and mixed-charge are measured at low relative momentum to estimate the coherent fraction of charged pions in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV at the LHC with ALICE. The genuine three-pion quantum statistics correlation is found to be suppressed relative to the two-pion correlation based on the assumption of fully chaotic pion emission. The suppression is observed to decrease with triplet momentum. The observed suppression at low triplet momentum may correspond to a coherent fraction in charged pion emission of 23% $\pm$ 8%.
C2 versus qinv for same-charge pions in six kT intervals. 0-5% centrality.
C2 versus qinv for mixed-charge pions in six kT intervals. 0-5% centrality.
C2 versus qinv for same-charge pions in six kT intervals. 45-50% centrality.
Angular correlations between unidentified charged trigger particles and various species of charged associated particles (unidentified particles, pions, kaons, protons and antiprotons) are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV in the transverse-momentum range $0.3 < p_{\rm T} < 4$ GeV/$c$. The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range $|\eta_{\rm lab}|<0.8$. Fourier coefficients are extracted from the long-range correlations projected onto the azimuthal angle difference and studied as a function of $p_{\rm T}$ and in intervals of event multiplicity. In high-multiplicity events, the second-order coefficient for protons, $v_2^p$, is observed to be smaller than that for pions, $v_2^\pi$, up to about $p_{\rm T} = 2$ GeV/$c$. To reduce correlations due to jets, the per-trigger yield measured in low-multiplicity events is subtracted from that in high-multiplicity events. A two-ridge structure is obtained for all particle species. The Fourier decomposition of this structure shows that the second-order coefficients for pions and kaons are similar. The $v_2^p$ is found to be smaller at low $p_{\rm T}$ and larger at higher $p_{\rm T}$ than $v_2^pi$, with a crossing occurring at about 2 GeV. This is qualitatively similar to the elliptic-flow pattern observed in heavy-ion collisions. A mass ordering effect at low transverse momenta is consistent with expectations from hydrodynamic model calculations assuming a collectively expanding system.
The Fourier coefficients V2(2PC,sub) extracted for all charged particles as a function of PT from the correlation in the 0-20% multiplicity class after subraction of the correlation from the 60-100% event class.
The Fourier coefficients V2(2PC,sub) extracted for charged pions as a function of PT from the correlation in the 0-20% multiplicity class after subraction of the correlation from the 60-100% event class.
The Fourier coefficients V2(2PC,sub) extracted for charged kaons as a function of PT from the correlation in the 0-20% multiplicity class after subraction of the correlation from the 60-100% event class.
The directed flow of charged particles at mid-rapidity is measured in Pb-Pb collisions at $\sqrt{s_\rm{NN}}=2.76$ TeV relative to the collision symmetry plane defined by the spectator nucleons. A negative slope of the rapidity-odd directed flow component with approximately 3 times smaller magnitude than found at the highest RHIC energy is observed. This suggests a smaller longitudinal tilt of the initial system and disfavors the strong fireball rotation predicted for the LHC energies. The rapidity-even directed flow component is measured for the first time with spectators and found to be independent of pseudorapidity with a sign change at transverse momenta $p_{\rm T}$ between $1.2$ and $1.7$ GeV/$c$. Combined with the observation of a vanishing rapidity-even $p_{\rm T}$ shift along the spectator deflection this is strong evidence for dipole-like initial density fluctuations in the overlap zone of the nuclei. Similar trends in the rapidity-even directed flow and the estimate from two-particle correlations at mid-rapidity, which is larger by about a factor of 40, indicate a weak correlation between fluctuating participant and spectator symmetry planes. These observations open new possibilities for investigation of the initial conditions in heavy-ion collisions with spectator nucleons.
Correlation between x components of the Q-vector of projectile (Qpx) and target (Qtx) spectators, MEAN(QpxQtx).
Correlation between y components of the Q-vector of projectile (Qpy) and target (Qty) spectators, MEAN(QpyQty).
Correlation between x and y components of the Q-vector of projectile (Qpx) and target (Qty) spectators, MEAN(QpxQty).
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