Modification of charged-particle jets in event-shape engineered Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5$ TeV

The ALICE collaboration Acharya, Shreyasi ; Adamova, Dagmar ; Aglieri Rinella, Gianluca ; et al.
Phys.Lett.B 851 (2024) 138584, 2024.
Inspire Record 2681682 DOI 10.17182/hepdata.150418

Charged-particle jet yields have been measured in semicentral Pb$-$Pb collisions at center-of-mass energy per nucleon-nucleon collision $\sqrt{s_{\rm NN}} = 5$ TeV with the ALICE detector at the LHC. These yields are reported as a function of the jet transverse momentum, and further classified by their angle with respect to the event plane and the event shape, characterized by ellipticity, in an effort to study the path-length dependence of jet quenching. Jets were reconstructed at midrapidity from charged-particle tracks using the anti-$k_{\rm T}$ algorithm with resolution parameters $R =$ 0.2 and 0.4, with event-plane angle and event-shape values determined using information from forward scintillating detectors. The results presented in this letter show that, in semicentral Pb$-$Pb collisions, there is no significant difference between jet yields in predominantly isotropic and elliptical events. However, out-of-plane jets are observed to be more suppressed than in-plane jets. Further, this relative suppression is greater for low transverse momentum ($<$ 50 GeV/$c$) $R =$ 0.2 jets produced in elliptical events, with out-of-plane to in-plane jet-yield ratios varying up to 5.2$\sigma$ between different event-shape classes. These results agree with previous studies indicating that jets experience azimuthally anisotropic suppression when traversing the QGP medium, and can provide additional constraints on the path-length dependence of jet energy loss.

6 data tables

Charged-particle jet yields, R=0.2

Charged-particle jet yields, R=0.4

q2-large/q2-small, R=0.2

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Version 2
Enhanced deuteron coalescence probability in jets

The ALICE collaboration Acharya, Shreyasi ; Adamova, Dagmar ; Adler, Alexander ; et al.
Phys.Rev.Lett. 131 (2023) 042301, 2023.
Inspire Record 2601274 DOI 10.17182/hepdata.141173

The transverse-momentum ($p_{\rm T}$) spectra and coalescence parameters $B_2$ of (anti)deuterons are measured in pp collisions at $\sqrt{s} = 13$ TeV for the first time in and out of jets. In this measurement, the direction of the leading particle with the highest $p_{\rm T}$ in the event ($p_{\rm T}^{\rm{ lead}} > 5$ GeV/$c$) is used as an approximation for the jet axis. The event is consequently divided into three azimuthal regions and the jet signal is obtained as the difference between the Toward region, that contains jet fragmentation products in addition to the underlying event (UE), and the Transverse region, which is dominated by the UE. The coalescence parameter in the jet is found to be approximately a factor of 10 larger than that in the underlying event. This experimental observation is consistent with the coalescence picture and can be attributed to the smaller average phase-space distance between nucleons inside the jet cone as compared to the underlying event. The results presented in this Letter are compared to predictions from a simple nucleon coalescence model, where the phase space distributions of nucleons are generated using PYTHIA 8 with the Monash 2013 tuning, and to predictions from a deuteron production model based on ordinary nuclear reactions with parametrized energy-dependent cross sections tuned on data. The latter model is implemented in PYTHIA 8.3. Both models reproduce the observed large difference between in-jet and out-of-jet coalescence parameters, although the almost flat trend of the $B^{\rm Jet}_2$ is not reproduced by the models, which instead give a decreasing trend.

6 data tables

Transverse momentum spectra for the transverse azimuthal regions. Events with a leading track with PT>5 GEV at midrapidity are selected. The spectrum is shown in Figure 1 (left panel).

Transverse momentum spectra for the toward azimuthal regions. Events with a leading track with PT>5 GEV at midrapidity are selected. The spectrum is shown in Figure 1 (left panel).

Transverse momentum spectra for the away azimuthal regions. Events with a leading track with PT>5 GEV at midrapidity are selected. The spectrum is shown in Figure 1 (left panel).

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K$^{*}$(892)$^{\pm}$ resonance production in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV

The ALICE collaboration Acharya, Shreyasi ; Adamova, Dagmar ; Aglieri Rinella, Gianluca ; et al.
CERN-EP-2023-176, 2023.
Inspire Record 2692205 DOI 10.17182/hepdata.150017

The production of K$^*$(892)$^\pm$ meson resonance is measured at midrapidity ($|y|<0.5$) in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV using the ALICE detector at the LHC. The resonance is reconstructed via its hadronic decay channel K$^*$(892)$^\pm \rightarrow \rm{K^0_S \pi^\pm}$. The transverse momentum distributions are obtained for various centrality intervals in the $p_{\rm T}$ range of 0.4-16 GeV/$c$. The reported measurements of integrated yields, mean transverse momenta, and particle yield ratios are consistent with previous ALICE measurements for K$^*$(892)$^0$. The $p_{\rm T}$-integrated yield ratio 2K$^*$(892)$^\pm$/($\rm{K^+ + K^-}$) in central Pb-Pb collisions shows a significant suppression (9.3$\sigma$) relative to pp collisions. Thermal model calculations overpredict the particle yield ratio. Although both simulations consider the hadronic phase, only HRG-PCE accurately represents the measurements, whereas MUSIC+SMASH tends to overpredict them. These observations, along with the kinetic freeze-out temperatures extracted from the yields of light-flavored hadrons using the HRG-PCE model, indicate a finite hadronic phase lifetime, which increases towards central collisions. The $p_{\rm T}$-differential yield ratios 2K$^*$(892)$^\pm$/($\rm{K^+ + K^-}$) and 2K$^*$(892)$^\pm$/($\rm{\pi^+ + \pi^-}$) are suppressed by up to a factor of five at $p_{\rm T}<2$ GeV/$c$ in central Pb-Pb collisions compared to pp collisions at $\sqrt{s} =$ 5.02 TeV. Both particle ratios and are qualitatively consistent with expectations for rescattering effects in the hadronic phase. The nuclear modification factor shows a smooth evolution with centrality and is below unity at $p_{\rm T}>8$ GeV/$c$, consistent with measurements for other light-flavored hadrons. The smallest values are observed in most central collisions, indicating larger energy loss of partons traversing the dense medium.

17 data tables

$p_{\rm T}$-distributions of $\rm{K}^{*}$ (average of particle and anti-particle) meson measured in Pb-Pb collisions at \sqrt{s_{NN}}$ = 5.02 TeV for 0-10\% centrality.

$p_{\rm T}$-distributions of $\rm{K}^{*}$ (average of particle and anti-particle) meson measured in Pb-Pb collisions at \sqrt{s_{NN}}$ = 5.02 TeV for 10-20\% centrality.

$p_{\rm T}$-distributions of $\rm{K}^{*}$ (average of particle and anti-particle) meson measured in Pb-Pb collisions at \sqrt{s_{NN}}$ = 5.02 TeV for 20-40\% centrality.

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Skewness and kurtosis of mean transverse momentum fluctuations at the LHC energies

The ALICE collaboration Acharya, Shreyasi ; Adamova, Dagmar ; Aglieri Rinella, Gianluca ; et al.
Phys.Lett.B 850 (2024) 138541, 2024.
Inspire Record 2692420 DOI 10.17182/hepdata.147284

The first measurements of skewness and kurtosis of mean transverse momentum ($\langle p_\mathrm{T}\rangle$) fluctuations are reported in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV, Xe$-$Xe collisions at $\sqrt{s_\mathrm{NN}}$$=$ 5.44 TeV and pp collisions at $\sqrt{s} = 5.02$ TeV using the ALICE detector. The measurements are carried out as a function of system size $\langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle_{|\eta|<0.5}^{1/3}$, using charged particles with transverse momentum ($p_\mathrm{T}$) and pseudorapidity ($\eta$), in the range $0.2 < p_\mathrm{T} < 3.0$ GeV/$c$ and $|\eta| < 0.8$, respectively. In Pb$-$Pb and Xe$-$Xe collisions, positive skewness is observed in the fluctuations of $\langle p_\mathrm{T}\rangle$ for all centralities, which is significantly larger than what would be expected in the scenario of independent particle emission. This positive skewness is considered a crucial consequence of the hydrodynamic evolution of the hot and dense nuclear matter created in heavy-ion collisions. Furthermore, similar observations of positive skewness for minimum bias pp collisions are also reported here. Kurtosis of $\langle p_\mathrm{T}\rangle$ fluctuations is found to be in good agreement with the kurtosis of Gaussian distribution, for most central Pb$-$Pb collisions. Hydrodynamic model calculations with MUSIC using Monte Carlo Glauber initial conditions are able to explain the measurements of both skewness and kurtosis qualitatively from semicentral to central collisions in Pb--Pb system. Color reconnection mechanism in PYTHIA8 model seems to play a pivotal role in capturing the qualitative behavior of the same measurements in pp collisions.

9 data tables

Standardized skewness of $\langle p_\mathrm{T}\rangle$ as a function of $\langle\mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle^{1/3}_{|\eta|<0.5}$ in pp collisions at $\sqrt{s}$ = 5.02 TeV.

Standardized skewness of $\langle p_\mathrm{T}\rangle$ as a function of $\langle\mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle^{1/3}_{|\eta|<0.5}$ in Xe$-$Xe collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV.

Standardized skewness of $\langle p_\mathrm{T}\rangle$ as a function of $\langle\mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle^{1/3}_{|\eta|<0.5}$ in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV.

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First measurement of the $|t|$-dependence of incoherent J/$\psi$ photonuclear production

The ALICE collaboration Acharya, Shreyasi ; Adamova, Dagmar ; Adler, Alexander ; et al.
CERN-EP-2023-080, 2023.
Inspire Record 2658375 DOI 10.17182/hepdata.146880

The first measurement of the cross section for incoherent photonuclear production of J/$\psi$ vector meson as a function of the Mandelstam $|t|$ variable is presented. The measurement was carried out with the ALICE detector at midrapidity, $|y|<0.8$, using ultra-peripheral collisions of Pb nuclei at a centre-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV. This rapidity interval corresponds to a Bjorken-$x$ range $(0.3$$-$$1.4)\times 10^{-3}$. Cross sections are reported in five $|t|$ intervals in the range $0.04<|t|<1$~GeV$^2$ and compared to the predictions of different models. Models that ignore quantum fluctuations of the gluon density in the colliding hadron predict a $|t|$-dependence of the cross section much steeper than in data. The inclusion of such fluctuations in the same models provides a better description of the data.

1 data table

|t|-dependence of incoherent J/Psi photonuclear production cross section in Pb-Pb UPCs measured at midrapidity, |y| < 0.8


Pseudorapidity dependence of anisotropic flow and its decorrelations using long-range multiparticle correlations in Pb-Pb and Xe-Xe collisions

The ALICE collaboration Acharya, Shreyasi ; Adamova, Dagmar ; Adler, Alexander ; et al.
Phys.Lett.B 850 (2024) 138477, 2024.
Inspire Record 2679248 DOI 10.17182/hepdata.146722

The pseudorapidity dependence of elliptic ($v_2$), triangular ($v_3$), and quadrangular ($v_4$) flow coefficients of charged particles measured in Pb-Pb collisions at a centre-of-mass energy per nucleon pair of $\sqrt{s_{\rm NN}}=5.02$ TeV and in Xe-Xe collisions at $\sqrt{s_{\rm NN}}=5.44$ TeV with ALICE at the LHC are presented. The measurements are performed in the pseudorapidity range $-3.5 < \eta < 5$ for various centrality intervals using two- and multi-particle cumulants with the subevent method. The flow probability density function (p.d.f.) is studied with the ratio of flow coefficient $v_2$ calculated with four- and two-particle cumulant, and suggests that the variance of flow p.d.f. is independent of pseudorapidity. The decorrelation of the flow vector in the longitudinal direction is probed using two-particle correlations. The results measured with respect to different reference regions in pseudorapidity exhibit differences, argued to be a result of saturating decorrelation effect above a certain pseudorapidity separation, in contrast to previous publications which assign this observation to non-flow effects. The results are compared to $3+1$ dimensional hydrodynamic and the AMPT transport model calculations. Neither of the models is able to simultaneously describe the pseudorapidity dependence of measurements of anisotropic flow and its fluctuations. The results presented in this work highlight shortcomings in our current understanding of initial conditions and subsequent system expansion in the longitudinal direction. Therefore, they provide input for its improvement.

15 data tables

$v_{2}\{2\}$ versus $\eta$ for $x^{\pm}$ in $\mathrm{Pb}-\mathrm{Pb}$ at $\sqrt{s_{\mathrm{NN}}}=5.023\,\mathrm{Te\!V}$

$v_{3}\{2\}$ versus $\eta$ for $x^{\pm}$ in $\mathrm{Pb}-\mathrm{Pb}$ at $\sqrt{s_{\mathrm{NN}}}=5.023\,\mathrm{Te\!V}$

$v_{4}\{2\}$ versus $\eta$ for $x^{\pm}$ in $\mathrm{Pb}-\mathrm{Pb}$ at $\sqrt{s_{\mathrm{NN}}}=5.023\,\mathrm{Te\!V}$

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Femtoscopic correlations of identical charged pions and kaons in pp collisions at $\sqrt{s}=13$ TeV with event-shape selection

The ALICE collaboration Acharya, Shreyasi ; Adamova, Dagmar ; Aglieri Rinella, Gianluca ; et al.
Phys.Rev.C 109 (2024) 024915, 2024.
Inspire Record 2709104 DOI 10.17182/hepdata.146805

Collective behavior has been observed in high-energy heavy-ion collisions for several decades. Collectivity is driven by the high particle multiplicities that are produced in these collisions. At the Large Hadron Collider (LHC), features of collectivity have also been seen in high-multiplicity proton-proton collisions that can attain particle multiplicities comparable to peripheral Pb-Pb collisions. One of the possible signatures of collective behavior is the decrease of femtoscopic radii extracted from pion and kaon pairs emitted from high-multiplicity collisions with increasing pair transverse momentum. This decrease can be described in terms of an approximate transverse mass scaling. In the present work, femtoscopic analyses are carried out by the ALICE collaboration on charged pion and kaon pairs produced in pp collisions at $\sqrt{s}=13$ TeV from the LHC to study possible collectivity in pp collisions. The event-shape analysis method based on transverse sphericity is used to select for spherical versus jet-like events, and the effects of this selection on the femtoscopic radii for both charged pion and kaon pairs are studied. This is the first time this selection method has been applied to charged kaon pairs. An approximate transverse-mass scaling of the radii is found in all multiplicity ranges studied when the difference in the Lorentz boost for pions and kaons is taken into account. This observation does not support the hypothesis of collective expansion of hot and dense matter that should only occur in high-multiplicity events. A possible alternate explanation of the present results is based on a scenario of common emission conditions for pions and kaons in pp collisions for the multiplicity ranges studied.

74 data tables
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Prompt and non-prompt J$/\psi$ production at midrapidity in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

The ALICE collaboration Acharya, Shreyasi ; Adamova, Dagmar ; Aglieri Rinella, Gianluca ; et al.
JHEP 02 (2024) 066, 2024.
Inspire Record 2692201 DOI 10.17182/hepdata.146723

The transverse momentum ($p_{\rm T}$) and centrality dependence of the nuclear modification factor $R_{\rm AA}$ of prompt and non-prompt J$/\psi$, the latter originating from the weak decays of beauty hadrons, have been measured by the ALICE collaboration in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV. The measurements are carried out through the ${\rm e}^{+}{\rm e}^{-}$ decay channel at midrapidity ($|y| < 0.9$) in the transverse momentum region $1.5 < p_{\rm T} < 10$ GeV/$c$. Both prompt and non-prompt J$/\psi$ measurements indicate a significant suppression for $p_{\rm T} >$ 5 GeV/$c$, which becomes stronger with increasing collision centrality. The results are consistent with similar LHC measurements in the overlapping $p_{\rm T}$ intervals, and cover the kinematic region down to $p_{\rm T}$ = 1.5 GeV/$c$ at midrapidity, not accessible by other LHC experiments. The suppression of prompt J$/\psi$ in central and semicentral collisions exhibits a decreasing trend towards lower transverse momentum, described within uncertainties by models implementing J$/\psi$ production from recombination of c and $\overline{\rm c}$ quarks produced independently in different partonic scatterings. At high transverse momentum, transport models including quarkonium dissociation are able to describe the suppression for prompt J$/\psi$. For non-prompt J$/\psi$, the suppression predicted by models including both collisional and radiative processes for the computation of the beauty-quark energy loss inside the quark$-$gluon plasma is consistent with measurements within uncertainties.

16 data tables

Non-prompt J/$\psi$ fraction as a function of transverse momentum in Pb-Pb at 5.02 TeV, centrality 0-10%

Non-prompt J/$\psi$ fraction as a function of transverse momentum in Pb-Pb at 5.02 TeV, centrality 10-30%

Non-prompt J/$\psi$ fraction as a function of transverse momentum in Pb-Pb at 5.02 TeV, centrality 30-50%

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Measurement of spin-orbital angular momentum interactions in relativistic heavy-ion collisions

The ALICE collaboration Acharya, Shreyasi ; Adamova, Dagmar ; Adler, Alexander ; et al.
Phys.Rev.Lett. 125 (2020) 012301, 2020.
Inspire Record 1762362 DOI 10.17182/hepdata.127978

The first evidence of spin alignment of vector mesons ($K^{*0}$ and $\phi$) in heavy-ion collisions at the Large Hadron Collider (LHC) is reported. The spin density matrix element $\rho_{00}$ is measured at midrapidity ($|y| <$ 0.5) in Pb-Pb collisions at a center-of-mass energy ($\sqrt{s_{\rm NN}}$) of 2.76 TeV with the ALICE detector. $\rho_{00}$ values are found to be less than 1/3 (1/3 implies no spin alignment) at low transverse momentum ($p_{\rm T} <$ 2 GeV/$c$) for $K^{*0}$ and $\phi$ at a level of 3$\sigma$ and 2$\sigma$, respectively. No significant spin alignment is observed for the $K^0_S$ meson (spin = 0) in Pb-Pb collisions and for the vector mesons in $pp$ collisions. The measured spin alignment is unexpectedly large but qualitatively consistent with the expectation from models which attribute it to a polarization of quarks in the presence of angular momentum in heavy-ion collisions and a subsequent hadronization by the process of recombination.

28 data tables

$cos\theta^{*}$ distribution of $\rm{K}^{*0}$ (average of particle and anti-particle) meson w.r.t. Event Plane in transverse momentum range 0.8-1.2 GeV/$c$ measured in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV.

$cos\theta^{*}$ distribution of $\phi$ meson w.r.t. Event Plane in transverse momentum range 0.5-0.7 GeV/$c$ measured in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV.

$cos\theta^{*}$ distribution of $\rm{K}^{*0}$ (average of particle and anti-particle) meson w.r.t. Production Plane in transverse momentum range 0.4-1.2 GeV/$c$ measured in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV.

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Measurements of inclusive J/$\psi$ production at midrapidity and forward rapidity in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

The ALICE collaboration Acharya, Shreyasi ; Adamova, Dagmar ; Adler, Alexander ; et al.
Phys.Lett.B 849 (2024) 138451, 2024.
Inspire Record 2648616 DOI 10.17182/hepdata.146644

The measurements of the inclusive J/$\psi$ yield at midrapidity ($\left | y \right | < 0.9$) and forward rapidity (2.5 $< y <$ 4) in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with the ALICE detector at the LHC are reported. The inclusive J/$\psi$ production yields and nuclear modification factors, $R_{\rm AA}$, are measured as a function of the collision centrality, J/$\psi$ transverse momentum ($p_{\rm T}$), and rapidity. The J/$\psi$ average transverse momentum and squared transverse momentum ($\langle p_{\mathrm{T}}\rangle$ and $\langle p_{\mathrm{T}}^{\mathrm{2}}\rangle$) are evaluated as a function of the centrality at midrapidity. Compared to the previous ALICE publications, here the entire Pb$-$Pb collisions dataset collected during the LHC Run 2 is used, which improves the precision of the measurements and extends the $p_{\rm T}$ coverage. The $p_{\rm T}$-integrated $R_{\rm AA}$ shows a hint of an increasing trend towards unity from semicentral to central collisions at midrapidity, while it is flat at forward rapidity. The $p_{\rm T}$-differential $R_{\rm AA}$ shows a strong suppression at high $p_{\rm T}$ with less suppression at low $p_{\rm T}$ where it reaches a larger value at midrapidity compared to forward rapidity. The ratio of the $p_{\rm T}$-integrated yields of J/$\psi$ to those of D$^{0}$ mesons is reported for the first time for the central and semicentral event classes at midrapidity. Model calculations implementing charmonium production via the coalescence of charm quarks and antiquarks during the fireball evolution (transport models) or in a statistical approach with thermal weights are in good agreement with the data at low $p_{\rm T}$. At higher $p_{\rm T}$, the data are well described by transport models and a model based on energy loss in the strongly-interacting medium produced in nuclear collisions at the LHC.

14 data tables

Inclusive J$/psi$ invariant yield as a function of pT in Pb-Pb collisions at $\sqrt{{s}_{NN}}$ = 5.02 TeV for 0-10% centrality interval and |y|< 0.9. The given systematic uncertainties are the total systematic ones and are mostly considered as fully correlated over pT.;

Inclusive J$/psi$ invariant yield as a function of pT in Pb-Pb collisions at $\sqrt{{s}_{NN}}$ = 5.02 TeV for 30-50% centrality interval and |y|< 0.9. The given systematic uncertainties are the total systematic ones and are mostly considered as fully correlated over pT.;

Inclusive J$/psi$ invariant yield as a function of pT in Pb-Pb collisions at $\sqrt{{s}_{NN}}$ = 5.02 TeV for 0-20% centrality interval and 2.5 < y < 4. The given systematic uncertainties are the total systematic ones. It contains the correlated uncertainties over pT which amount to 1.69%. ;

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