Investigation of in-medium effects of charmonia using azimuthal anisotropy and jet fragmentation function in PbPb collisions at √ s NN = 5 . 02 TeV with the CMS experiment

. Quarkonia have been long proposed as the golden probes to study quark-gluon plasma (QGP) in heavy-ion collisions. In this presentation, we present the second-and third-order Fourier coe ffi cients, v 2 and v 3 , for prompt and nonprompt J /ψ mesons in PbPb collisions as functions transverse momentum ( p T ) and PbPb collision centrality. Also, we report the first measurements of v 2 and v 3 for the prompt ψ (2S) mesons in PbPb collisions. The results provide v 2 and v 3 values over the wide studied kinematics regions of transverse momentum and collision centrality.


Introduction
Quarkonia (bound states of a heavy quark and its antiquark such as J/ψ, ψ(2S ), Υ(1S , 2S , 3S ), etc.) are useful probes to study the properties of the quark-gluon plasma (QGP) in heavy ion collisions [1,2].Since heavy quarks are produced via hard parton scattering at early stages of the collisions, they experience the whole space-time evolution of the medium.Azimuthal correlation of these particles can be characterized by the Fourier coefficients (v n ) of the azimuthal distribution.In particular, the second (v 2 ) and the third (v 3 ) order components are sensitive to the initial collision geometry and event-by-event fluctuations, respectively.The azimuthal correlation of quarkonium states are useful in particular to study the quarkonium dynamics and its collectivity inside the QGP [3].In addition, the path-length dependent suppression of quarkonium states could be captured by measurements of quarkonium v 2 values [4].
This conference proceeding reports the measurement of the v 2 and v 3 values for prompt and nonprompt (decayed from b-hadrons) J/ψ mesons, as well as for the prompt ψ(2S) mesons using the scalar product method [5].The data set used in this analysis was collected with the CMS detector in PbPb collisions at √ s NN = 5.02 TeV, corresponding to an integrated luminosity of 1.6 nb −1 .

Analysis procedure
The charmonia are identified using their dimuon decay channel.The separation of the prompt and the nonprompt charmonia relies on the displacement of a secondary µ + µ − vertex relative to the primary collision vertex.The pseudo-proper decay length is defined as ℓ J/ψ = L xyz m J/ψ c/|p µµ |, where L xyz is the distance between the primary and dimuon vertices, m J/ψ is the world average value of the J/ψ meson mass, and p µµ is the dimuon momentum.To extract prompt and nonprompt J/ψ meson yields, the invariant mass spectrum of µ + µ − pairs and their ℓ J/ψ distribution are fitted using a two-dimensional (2D) extended unbinned maximum likelihood fit.For ψ(2S) mesons, the nonprompt component is reduced by placing tight constraints on the ℓ J/ψ distributions.The detailed procedure of the fitting can be found in [6].
The v n (n = 2 and 3) values of J/ψ and ψ(2S) candidates are determined using the scalar product method [5].The event plane angle for the second-and third-order harmonics are defined using Q-vectors in the complex plane Q n = M k=1 ω k e inϕ k , and are obtained using the tracker or hardron forward (HF) calorimeters.Here, k runs over the particles sampled by the subdetector; M is the multiplicity of particles in the tracker or the number of towers for HF; ϕ is the azimuthal angle of the particle or the tower; ω is the weighting factor given by the p T of a particle for the tracker or the transverse energy deposited in an HF tower.In this analysis, three event plane Q-vectors are calculated using the tracker at the mid-pseudorapidity (|η| < 0.75) and the two HF calorimeters covering the forward (3 < η < 5, HF+) and backward (−5 < η < −3, HF−) regions.The v n coefficients for J/ψ or ψ(2S) mesons are obtained as: The subscripts A and B refer to either HF+ or HF−, depending on the rapidity of the J/ψ or ψ(2S) candidate.To avoid autocorrelations, the η gap between the J/ψ or ψ(2S) candidate and the detector used for event plane determination is required to be at least three units of rapidity [5,7,8].For this purpose, HF+ is selected for A (B) when J/ψ and ψ(2S) candidates are produced at negative (positive) rapidity.The ⟨⟩ indicates the real component of the average Q-vector product of all the candidates in a given invariant mass bin.The subscript C denotes the event plane taken from the tracker.The denominator in Eq.( 1) is the correction factor to remove finite resolution effect of the detectors.
To extract the prompt and nonprompt J/ψ meson v n coefficients, the J/ψ candidates are sampled into fine v n intervals.Then, a simultaneous fit of the invariant mass and the ℓ J/ψ distributions, as described above, is performed in each interval.
A different method is used to extract the prompt ψ(2S) meson v n values.The v n values are extracted by a simultaneous fit on the invariant mass and v n distribution of ψ(2S) mesons using a binned χ 2 fit method.The v n distribution is fitted to the following formula:

Results
The measured v 2 and v 3 values for prompt and nonprompt J/ψ mesons in PbPb collisions are shown in Fig. 1 as functions of p T and ⟨N part ⟩, which is the average number of participating nucleons [9].Results for the prompt J/ψ mesons show a flat v 2 for p T > 9 GeV/c, while no clear dependence on p T is found for nonprompt J/ψ mesons.Previous studies from CMS found the J/ψ being produced in large surrounding jet-activity, which suggested the importance of incorporating jet quenching in describin J/ψ suppression in PbPb collisions at high-p T [10].The sizable v 2 of prompt J/ψ mesons at high-p T in Fig. 1 implies the large contribution from path length dependent jet energy loss into the final measured v 2 .The v 2 values for nonprompt J/ψ mesons are found to be smaller than those for prompt J/ψ mesons in the studied kinematic region.This finding indiciates different medium effects for charm and bottom quarks induced by the interaction with the QGP. Figure 2 shows the first v n measurements of the azimuthal anisotropy for prompt ψ(2S) mesons in heavy ion collisions together with the results for prompt J/ψ mesons.The v 2 values are found to be slightly larger for the prompt ψ(2S) than for the prompt J/ψ mesons, especially at higher p T and in peripheral PbPb collisions, although the large uncertainties prevent from making a firm conclusion, with p-values of at best 10%.The v 3 values are found to be consistent with zero in the studied kinematic range.

Summary
The second-order (v 2 ) and third-order (v 3 ) Fourier coefficients of the azimuthal distributions for prompt and nonprompt J/ψ mesons and prompt ψ(2S) mesons are measured in PbPb collisions as functions of transverse momentum (p T ) and ⟨N part ⟩.The v 2 values for prompt and nonprompt J/ψ mesons both indicate a decreasing trend from mid-central towards central collision events.On the other hand, the v 2 is found to be flat for p T > 9 GeV/c for prompt J/ψ mesons, while the dependence on p T is found to be weak for nonprompt J/ψ mesons.The prompt J/ψ meson v 2 values are found to be larger than that of nonprompt J/ψ mesons throughout the studied kinematic region, suggesting different in-medium effects for charm and bottom quarks.The observation of sizable and flattened v 2 values at high p T for prompt J/ψ mesons provides a hint of the contribution of jet quenching to prompt J/ψ meson suppression.The J/ψ v 3 values are reported for the first time separately for prompt and nonprompt components, which are found to be consistent with zero in the measured p T and centrality intervals.The v 2 and v 3 values are also measured for prompt ψ(2S) mesons for the first time  in heavy ion collisions.These J/ψ and ψ(2S) meson measurements provide new insights in the dynamics and in-medium effects of charmonia in heavy ion collisions.

Figure 1 .
Figure 1.The v 2 (upper) and v 3 (lower) values as functions of p T (left) and ⟨N part ⟩ (right) for prompt and nonprompt J/ψ mesons.The results for 3 < p T < 6.5 and 6.5 < p T < 50 GeV/c are studied in the rapidity range of 1.6 < |y| < 2.4 and |y| < 2.4, respectively (left panel).The results for p T bins for the right panel is 6.5-50 GeV/c and rapidity of |y| < 2.4.The vertical bars denote the statistical uncertainties, and the rectangular bands show the systematic uncertainties.

Figure 2 .
Figure 2. The v 2 (upper) and v 3 (lower) values as functions of p T (left) and ⟨N part ⟩ (right) for prompt J/ψ (blue circles) and prompt ψ(2S) (green squares).The results for p T < 6.5 and p T > 6.5 GeV/c are diplayed in the rapidity range of 1.6 < |y| < 2.4 and |y| < 2.4, respectively (left panel).The results for p T bins for the right panel is 6.5-50 GeV/c and rapidity of |y| < 2.4.The vertical bars denote the statistical uncertainties, and the rectangular bands show the systematic uncertainties.