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Measurement of quark- and gluon-like jet fractions using jet charge in PbPb and pp collisions at 5.02 TeV

The CMS collaboration Sirunyan, Albert M ; Tumasyan, Armen ; Adam, Wolfgang ; et al.
JHEP 07 (2020) 115, 2020.
Inspire Record 1789224 DOI 10.17182/hepdata.88294

The momentum-weighted sum of the electric charges of particles inside a jet, known as jet charge, is sensitive to the electric charge of the particle initiating the parton shower. This paper presents jet charge distributions in $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV lead-lead (PbPb) and proton-proton (pp) collisions recorded with the CMS detector at the LHC. These data correspond to integrated luminosities of 404 $\mu$b$^{-1}$ and 27.4 pb$^{-1}$ for PbPb and pp collisions, respectively. Leveraging the sensitivity of the jet charge to fundamental differences in the electric charges of quarks and gluons, the jet charge distributions from simulated events are used as templates to extract the quark- and gluon-like jet fractions from data. The modification of these jet fractions is examined by comparing pp and PbPb data as a function of the overlap of the colliding Pb nuclei (centrality). This measurement tests the color charge dependence of jet energy loss due to interactions with the quark-gluon plasma. No significant modification between different centrality classes and with respect to pp results is observed in the extracted fractions of quark- and gluon-like jet fractions.

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Unfolded jet charge measurements for the $p_{T}$-weighting factor $\kappa = 0.5$ and a minimum track $p_{T}$ of 1 GeV for inclusive jets in pp and PbPb data. The PbPb results are shown for different centrality regions.

The standard deviation of the jet charge distributions with different track $p_{T}$ thresholds and $\kappa$ value of 0.5 for pp collisions and in the various event centrality bins for PbPb collisions compared with the PYTHIA6 prediction.

The standard deviation of the jet charge distributions with different track $p_{T}$ thresholds and $\kappa$ value of 0.3 for pp collisions and in the various event centrality bins for PbPb collisions compared with the PYTHIA6 prediction.

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Dependence on pseudorapidity and centrality of charged hadron production in PbPb collisions at a nucleon-nucleon centre-of-mass energy of 2.76 TeV

The CMS collaboration Chatrchyan, Serguei ; Khachatryan, Vardan ; Sirunyan, Albert M ; et al.
JHEP 08 (2011) 141, 2011.
Inspire Record 919733 DOI 10.17182/hepdata.58223

A measurement is presented of the charged hadron multiplicity in hadronic PbPb collisions, as a function of pseudorapidity and centrality, at a collision energy of 2.76 TeV per nucleon pair. The data sample is collected using the CMS detector and a minimum-bias trigger, with the CMS solenoid off. The number of charged hadrons is measured both by counting the number of reconstructed particle hits and by forming hit doublets of pairs of layers in the pixel detector. The two methods give consistent results. The charged hadron multiplicity density dN(ch)/d eta, evaluated at eta=0 for head-on collisions, is found to be 1612 +/- 55, where the uncertainty is dominated by systematic effects. Comparisons of these results to previous measurements and to various models are also presented.

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The measured charged hadron multiplicity density as a function of the centrality.

The measured charged hadron multiplicity density divided by Npart/2 as a function of the pseudorapidity in 4 centrality bins.

The measured charged hadron multiplicity density at pseudorapidiy=0 divided by Npart/2 as a function of the number of participants.


Jet properties in PbPb and pp collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV

The CMS collaboration Sirunyan, Albert M ; Tumasyan, Armen ; Adam, Wolfgang ; et al.
JHEP 05 (2018) 006, 2018.
Inspire Record 1658057 DOI 10.17182/hepdata.83196

Modifications of the properties of jets in PbPb collisions, relative to those in pp collisions, are studied at a nucleon-nucleon center-of-mass energy of $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV via correlations of charged particles with the jet axis in relative pseudorapidity ($\Delta \eta$), relative azimuth ($\Delta \phi$), and relative angular distance from the jet axis $\Delta \mathrm{r} = \sqrt{{(\Delta\eta)^{2}+(\Delta\phi)^{2}}}$. This analysis uses data collected with the CMS detector at the LHC, corresponding to integrated luminosities of 404 $\mu$b$^{-1}$ and 27.4 pb$^{-1}$ for PbPb and pp collisions, respectively. Charged particle number densities, jet fragmentation functions, and jet shapes are presented as a function of PbPb collision centrality and charged-particle track transverse momentum, providing a differential description of jet modifications due to interactions with the quark-gluon plasma.

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The distribution of jet-correlated charged-particle tracks with $|{\Delta\phi}|<1.0$ as a function of $\Delta\eta$ in pp and PbPb collisions. The PbPb results are shown for different centrality regions.

The difference between the PbPb and pp measurements from Table 1.

The distribution of jet-correlated charged-particle tracks with $|{\Delta\eta}|<1.0$ as a function of $\Delta\phi$ in pp and PbPb collisions. The PbPb results are shown for different centrality regions.

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Multiplicity and transverse momentum dependence of charge-balance functions in pPb and PbPb collisions at LHC energies

The CMS collaboration Tumasyan, Armen ; Adam, Wolfgang ; Andrejkovic, Janik Walter ; et al.
JHEP 08 (2024) 148, 2024.
Inspire Record 2679254 DOI 10.17182/hepdata.135972

Measurements of the charge-dependent two-particle angular correlation function in proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy of $\sqrt{s_\mathrm{NN}}$ = 8.16 TeV and lead-lead (PbPb) collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV are reported. The pPb and PbPb data sets correspond to integrated luminosities of 186 nb$^{-1}$ and 0.607 nb$^{-1}$, respectively, and were collected using the CMS detector at the CERN LHC. The charge-dependent correlations are characterized by balance functions of same- and opposite-sign particle pairs. The balance functions, which contain information about the creation time of charged particle pairs and the development of collectivity, are studied as functions of relative pseudorapidity ($\Delta \eta$) and relative azimuthal angle ($\Delta \phi$), for various multiplicity and transverse momentum ($p_\mathrm{T}$) intervals. A multiplicity dependence of the balance function is observed in $\Delta \eta$ and $\Delta \phi$ for both systems. The width of the balance functions decreases toward high-multiplicity collisions in the momentum region $\lt$ 2 GeV, for pPb and PbPb results. Integrals of the balance functions are presented in both systems, and a mild dependence of the charge-balancing fractions on multiplicity is observed. No multiplicity dependence is observed at higher transverse momentum. The data are compared with HYDJET, HIJING and AMPT generator predictions, none of which capture completely the multiplicity dependence seen in the data. The comparison of results with different center-of-mass energies suggest that the balance functions become narrower at higher energies, which is consistent with the idea of delayed hadronization and the effect of radial flow.

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$\Delta\eta$ projection of balance function in low $p_{T}$ in 0-10% centrality

$\Delta\eta$ projection of balance function in low $p_{T}$ in 30-40% centrality

$\Delta\eta$ projection of balance function in low $p_{T}$ in 70-80% centrality

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Higher-order moments of the elliptic flow distribution in PbPb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV

The CMS collaboration Tumasyan, Armen ; Adam, Wolfgang ; Andrejkovic, Janik Walter ; et al.
JHEP 2024 (2024) 106, 2024.
Inspire Record 2724506 DOI 10.17182/hepdata.132638

The hydrodynamic flow-like behavior of charged hadrons in high-energy lead-lead collisions is studied through multiparticle correlations. The elliptic anisotropy values based on different orders of multiparticle cumulants, $v_{2}\{2k\}$, are measured up to the tenth order ($k$ = 5) as functions of the collision centrality at a nucleon-nucleon center-of-mass energy of $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV. The data were recorded by the CMS experiment at the LHC and correspond to an integrated luminosity of 0.607 nb$^{-1}$. A hierarchy is observed between the coefficients, with $v_{2}\{2\} > v_{2}\{4\} \gtrsim v_{2}\{6\} \gtrsim v_{2}\{8\} \gtrsim v_{2}\{10\}$. Based on these results, centrality-dependent moments for the fluctuation-driven event-by-event $v_{2}$ distribution are determined, including the skewness, kurtosis and, for the first time, superskewness. Assuming a hydrodynamic expansion of the produced medium, these moments directly probe the initial-state geometry in high-energy nucleus-nucleus collisions.

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The $v_2\{2k\}$ ($k = 1, ..., 5$) values as functions of centrality in PbPb collisions at $\sqrt{s_{NN}}=5.02~\textrm{Te}\textrm{V}$. The measurement is performed with charged particles within the acceptance region.

The relative differences $(v_2\{2k\}-v_2\{10\})/v_2\{10\}$ ($k = 1, ..., 4$) as functions of centrality in PbPb collisions at $\sqrt{s_{NN}}=5.02~\textrm{Te}\textrm{V}$. The measurement is performed with charged particles within the acceptance region.

The $h_1$ and the $h_2$ hydrodynamic probes as functions of centrality in PbPb collisions at $\sqrt{s_{NN}}=5.02~\textrm{Te}\textrm{V}$. The measurement is performed with charged particles within the acceptance region.

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Long-range two-particle correlations of strange hadrons with charged particles in pPb and PbPb collisions at LHC energies

The CMS collaboration Khachatryan, Vardan ; Sirunyan, Albert M ; Tumasyan, Armen ; et al.
Phys.Lett.B 742 (2015) 200-224, 2015.
Inspire Record 1315947 DOI 10.17182/hepdata.66784

Measurements of two-particle angular correlations between an identified strange hadron (K0S or Lambda/anti-Lambda) and a charged particle, emitted in pPb collisions, are presented over a wide range in pseudorapidity and full azimuth. The data, corresponding to an integrated luminosity of approximately 35 inverse nanobarns, were collected at a nucleon-nucleon center-of-mass energy (sqrt(s[NN])) of 5.02 TeV with the CMS detector at the LHC. The results are compared to semi-peripheral PbPb collision data at sqrt(s[NN]) = 2.76 TeV, covering similar charged-particle multiplicities in the events. The observed azimuthal correlations at large relative pseudorapidity are used to extract the second-order (v[2]) and third-order (v[3]) anisotropy harmonics of K0S and Lambda/anti-Lambda particles. These quantities are studied as a function of the charged-particle multiplicity in the event and the transverse momentum of the particles. For high-multiplicity pPb events, a clear particle species dependence of v[2] and v[3] is observed. For pt < 2 GeV, the v[2] and v[3] values of K0S particles are larger than those of Lambda/anti-Lambda particles at the same pt. This splitting effect between two particle species is found to be stronger in pPb than in PbPb collisions in the same multiplicity range. When divided by the number of constituent quarks and compared at the same transverse kinetic energy per quark, both v[2] and v[3] for K0S particles are observed to be consistent with those for Lambda/anti-Lambda particles at the 10% level in pPb collisions. This consistency extends over a wide range of particle transverse kinetic energy and event multiplicities.

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The elliptic flow v2(2, $|\Delta\eta| > 2$) extracted for all charged particles as a function of $p_{T}$ from the correlation in the $N_{offline}^{trk}$ < 35 multiplicity class in pPb.

The elliptic flow v2(2, $|\Delta\eta| > 2$) extracted for all charged particles as a function of $p_{T}$ from the correlation in the 35 $\leq N_{offline}^{trk}$ < 60 multiplicity class in pPb.

The elliptic flow v2(2, $|\Delta\eta| > 2$) extracted for all charged particles as a function of $p_{T}$ from the correlation in the 60 $\leq N_{offline}^{trk}$ < 120 multiplicity class in pPb.

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Version 2
Charged-particle nuclear modification factors in PbPb and pPb collisions at sqrt(s[NN)]=5.02 TeV

The CMS collaboration Khachatryan, Vardan ; Sirunyan, Albert M ; Tumasyan, Armen ; et al.
JHEP 04 (2017) 039, 2017.
Inspire Record 1496050 DOI 10.17182/hepdata.77101

The spectra of charged particles produced within the pseudorapidity window abs(eta) < 1 at sqrt(s[NN]) = 5.02 TeV are measured using 404 inverse microbarns of PbPb and 27.4 inverse picobarns of pp data collected by the CMS detector at the LHC in 2015. The spectra are presented over the transverse momentum ranges spanning 0.5 < pt < 400 GeV in pp and 0.7 < pt < 400 GeV in PbPb collisions. The corresponding nuclear modification factor, R[AA], is measured in bins of collision centrality. The R[AA] in the 5% most central collisions shows a maximal suppression by a factor of 7-8 in the pt region of 6-9 GeV. This dip is followed by an increase, which continues up to the highest pt measured, and approaches unity in the vicinity of pt = 200 GeV. The R[AA] is compared to theoretical predictions and earlier experimental results at lower collision energies. The newly measured pp spectrum is combined with the pPb spectrum previously published by the CMS Collaboration to construct the pPb nuclear modification factor, R[pA], up to 120 GeV. For pt > 20 GeV, R[pA] exhibits weak momentum dependence and shows a moderate enhancement above unity.

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Charged-particle per-event yields measured in 0-5% PbPb centrality class.

Charged-particle per-event yields measured in 0-5% PbPb centrality class.

Charged-particle per-event yields measured in 5-10% PbPb centrality class.

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Measurement of long-range near-side two-particle angular correlations in pp collisions at sqrt(s) = 13 TeV

The CMS collaboration Khachatryan, Vardan ; Sirunyan, Albert M ; Tumasyan, Armen ; et al.
Phys.Rev.Lett. 116 (2016) 172302, 2016.
Inspire Record 1397173 DOI 10.17182/hepdata.73192

Results on two-particle angular correlations for charged particles produced in pp collisions at a center-of-mass energy of 13 TeV are presented. The data were taken with the CMS detector at the LHC and correspond to an integrated luminosity of about 270 inverse nanobarns. The correlations are studied over a broad range of pseudorapidity (abs(eta) < 2.4) and over the full azimuth (phi) as a function of charged particle multiplicity and transverse momentum (pt). In high-multiplicity events, a long-range (abs(Delta eta) > 2.0), near-side (Delta phi approximately 0) structure emerges in the two-particle Delta eta-Delta phi correlation functions. The magnitude of the correlation exhibits a pronounced maximum in the range 1.0 < pt < 2.0 GeV/c and an approximately linear increase with the charged particle multiplicity, with an overall correlation strength similar to that found in earlier pp data at sqrt(s) = 7 TeV. The present measurement extends the study of near-side long-range correlations up to charged particle multiplicities of N[ch] approximately 180, a region so far unexplored in pp collisions. The observed long-range correlations are compared to those seen in pp, pPb, and PbPb collisions at lower collision energies.

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Correlated yield obtained with the ZYAM procedure as a function of $|\Delta\Phi|$, averaged over 2 $<|\Delta\eta|<$ 4 in for 0.1 $<p_{T}<$ 1.0 $GeV/c$ and $N_{offline}^{trk}<$ 35 bins for pp data at $\sqrt =$ 13 $TeV$. The $p_{T}$ selection applies to both particles in the pair. Only statistical uncertainties are given. The subtracted ZYAM constant is given ($C_{ZYAM}$).

Correlated yield obtained with the ZYAM procedure as a function of $|\Delta\Phi|$, averaged over 2 $<|\Delta\eta|<$ 4 in for 0.1 $<p_{T}<$ 1.0 $GeV/c$ and $N_{offline}^{trk}<$ 35 bins for pp data at $\sqrt =$ 7 $TeV$. The $p_{T}$ selection applies to both particles in the pair. Only statistical uncertainties are given. The subtracted ZYAM constant is given ($C_{ZYAM}$).

Correlated yield obtained with the ZYAM procedure as a function of $|\Delta\Phi|$, averaged over 2 $<|\Delta\eta|<$ 4 in for 1.0 $<p_{T}<$ 2.0 $GeV/c$ and $N_{offline}^{trk}<$ 35 bins for pp data at $\sqrt =$ 13 $TeV$. The $p_{T}$ selection applies to both particles in the pair. Only statistical uncertainties are given. The subtracted ZYAM constant is given ($C_{ZYAM}$).

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Observation of correlated azimuthal anisotropy Fourier harmonics in pp and pPb collisions at the LHC

The CMS collaboration Sirunyan, Albert M ; Tumasyan, Armen ; Adam, Wolfgang ; et al.
Phys.Rev.Lett. 120 (2018) 092301, 2018.
Inspire Record 1626103 DOI 10.17182/hepdata.79667

The azimuthal anisotropy Fourier coefficients ($v_n$) in 8.16 TeV pPb data are extracted via long-range two-particle correlations as a function of event multiplicity and compared to corresponding results in pp and PbPb collisions. Using a four-particle cumulant technique, $v_n$ correlations are measured for the first time in pp and pPb collisions. The $v_2$ and $v_4$ coefficients are found to be positively correlated in all collision systems. For high multiplicity pPb collisions an anticorrelation of $v_2$ and $v_3$ is observed, with a similar correlation strength as in PbPb data at the same multiplicity. The new correlation results strengthen the case for a common origin of the collectivity seen in pPb and PbPb collisions in the measured multiplicity range.

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The $v_{n}$ result from 2-particle correlation as a function of multiplicity ($N_{trk}^{offline}$) in PbPb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV. Results after low-multiplicity subtraction are denoted as $v_{n}^{sub}$.

The $v_{n}$ result from 2-particle correlation as a function of multiplicity ($N_{trk}^{offline}$) in pPb collisions at $\sqrt{s_{NN}}$ = 8.16 TeV. Results after low-multiplicity subtraction are denoted as $v_{n}^{sub}$.

The $v_{4}$ result from 2-particle correlation as a function of multiplicity ($N_{trk}^{offline}$) in pp collisions at $\sqrt{s}$ = 13.00 TeV. Results after low-multiplicity subtraction are denoted as $v_{4}^{sub}$.

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Evidence for collective multi-particle correlations in pPb collisions

The CMS collaboration Khachatryan, Vardan ; Sirunyan, Albert M ; Tumasyan, Armen ; et al.
Phys.Rev.Lett. 115 (2015) 012301, 2015.
Inspire Record 1345262 DOI 10.17182/hepdata.67530

The second-order azimuthal anisotropy Fourier harmonics, v2, are obtained in pPb and PbPb collisions over a wide pseudorapidity (eta) range based on correlations among six or more charged particles. The pPb data, corresponding to an integrated luminosity of 35 inverse nanobarns, were collected during the 2013 LHC pPb run at a nucleon-nucleon center-of-mass energy of 5.02 TeV by the CMS experiment. A sample of semi-peripheral PbPb collision data at sqrt(s[NN])= 2.76 TeV, corresponding to an integrated luminosity of 2.5 inverse microbarns and covering a similar range of particle multiplicities as the pPb data, is also analyzed for comparison. The six- and eight-particle cumulant and the Lee-Yang zeros methods are used to extract the v2 coefficients, extending previous studies of two- and four-particle correlations. For both the pPb and PbPb systems, the v2 values obtained with correlations among more than four particles are consistent with previously published four-particle results. These data support the interpretation of a collective origin for the previously observed long-range (large Delta[eta]) correlations in both systems. The ratios of v2 values corresponding to correlations including different numbers of particles are compared to theoretical predictions that assume a hydrodynamic behavior of a pPb system dominated by fluctuations in the positions of participant nucleons. These results provide new insights into the multi-particle dynamics of collision systems with a very small overlapping region.

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The cumulant $c_2\{6\}$ extracted for all charged particles with $0.3 < p_T < 3.0$ GeV/c as a function of $N_{trk}^{offline}$ in PbPb collisions.

The cumulant $c_2\{8\}$ extracted for all charged particles with $0.3 < p_T < 3.0$ GeV/c as a function of $N_{trk}^{offline}$ in PbPb collisions.

The cumulant $c_2\{6\}$ extracted for all charged particles with $0.3 < p_T < 3.0$ GeV/c as a function of $N_{trk}^{offline}$ in pPb collisions.

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