Latest results on heavy flavor di-lepton (p-pb and Pb-Pb)

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1 Journal of Physics: Conference Series OPEN ACCESS Latest results on heavy flavor di-lepton (p-pb and Pb-Pb) o cite this article: Dong Ho Moon and the Cms collaboration J. Phys.: Conf. Ser. View the article online for updates and enhancements. Related content - Quarkonium Results in PbPb Collisions at S M Calderón de la Barca Sánchez and the S Collaboration - Quarkonium production in. ev PbPb collisions in S Guillermo Breto Rangel and the Cms collaboration - Heavy flavor and Quarkonia in heavy-ion collisions with the S Hyunchul Kim and the Cms Collaboration his content was downloaded from IP address on //8 at :

2 th Winter Workshop on Nuclear Dynamics (WWND) Journal of Physics: Conference Series () doi:.88/-9/// Latest results on heavy flavor di-lepton (p-pb and Pb-Pb) Dong Ho Moon on behalf of the S collaboration University of Illinois at Chicago dmoon@cern.ch Abstract. he Compact Muon Solenoid (S) has measured various quarkonium states via their decays into muon pairs in, PbPb and collisions at =. and. ev. Quarkonia are especially relevant for studying the quark-gluon plasma since they are produced at early times of the collision and propagate through the medium, maing its evolution. he most recent results on the production of prompt J/ψ in PbPb and the three Υ states in and collisions will be presented.. Introduction One strong signature of the existence for a Quark-Gluon-Plasma (QGP) is quarkonium suression. Recent results from quarkonia measurements performed in S have been found to suort theoretical predictions called the sequential melting scenario [,, ]. Quarkonimum production in heavy-ion collisions is affected by initial effects such as nuclear parton distribution functions (npdfs) [], parton energy loss, and the Cronin effect [, ], and final state effects such as Debye color screening and statistical recombination []. he result of study of the prompt J/ψ azimuthal anisotropy will be reported in this paper. Expected effects contributing to an observed non-zero elliptic anisotropy include recombination of thermalized charm quarks and (or) a path-length difference for absorption of quarkonia traversing the different direction of the almond-shaped hot and dense medium created in midcentral PbPb collisions. his paper also reports the results of bb states produced in proton-lead () collisions. his system is a good reference to understand initial state effects and may allow insight into cold nuclear effects that differ from the suression effects observed in previous measurements [].. Environmental setup and analysis procedure he central feature of the S aaratus is a superconducting solenoid, providing an axial magnetic field of.8. Immersed in the magnetic field are the silicon pixel and strip tracker, the lead-tungstate crystal electromagnetic calorimeter, and the brass/scintillator hadron calorimeter. Muons are measured in gas ionization detectors embedded in the steel return yoke and in the pseudorapidity window η <., with detection planes made of three technologies: Drift ubes, Cathode Strip Chambers, and Resistive Plate Chambers. Matching the muons to the measured in the silicon tracker results in a transverse momentum resolution better than.% for p smaller than GeV/c. A more detailed description of the S detector can be found in Ref. [8]. Content from this work may be used under the terms of the Creative Commons Attribution. licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by Ltd

3 ) ) ) th Winter Workshop on Nuclear Dynamics (WWND) Journal of Physics: Conference Series () doi:.88/-9/// Events / (. GeV/c S Preliminary PbPb L int = b y <.. < p < GeV/c Cent. % =. ev N J/ψ : 8 ± σ = ± MeV/c bkgd + non-prompt Events / (. mm) S Preliminary PbPb =. ev L int = b y <.. < p < GeV/c Cent. % bkgd + non-prompt m (GeV/c ) -... l J/ψ (mm) Figure. Invariant-mass spectra (left) and pseudo-proper decay length distribution (right) of + pairs integrated over centrality. he spectra are integrated over the rapidity range < y <. and the p range. < p < GeV/c. he projections of the two-dimensional fit onto the respective axes are overlaid as solid black lines. he dashed red lines show the fitted contribution of non-prompt J/ψ. he fitted contributions are shown as dotted blue lines [9]. Events / (. GeV/c 8 η <.9 p > GeV/c S =. ev L = nb Events / (. GeV/c 8 η <.9 p > GeV/c S s =. ev L =. pb 8 9 m - (GeV/c ) m - (GeV/c ) + Figure. Invariant mass spectrum in (left) and collisions (right) of + pairs with single muons with p > GeV/c and η <.9. he (black circles) overlaid with the fit (solid blue line). he component of the fit is represented by the dashed blue line []. he. used in the study corresponded to an integrated luminosity of. pb at a center-of-mass energy =. ev. he corresponding integrated luminosity of is nb with a center-of-mass energy =. ev. he direction of the higher-energy proton beam was initially set up to be clockwise, and was reversed after an integrated luminosity of 8 nb of was recorded. As a result of the energy difference of the colliding beams, the nucleon-nucleon center-of-mass in the collisions are not at rest with respect to the laboratory frame. Massless particles emitted at η = in the nucleon-nucleon center-of-mass frame are detected at η = -. (clockwise proton beam) or +. (counterclockwise proton beam) in the laboratory frame. he PbPb used for prompt J/ψ azimuthal anisotropy measurement were collected with a corresponding integrated luminosity of b. he invariant mass spectrum of all + pairs used in the PbPb analysis is shown in the left of Figure. he black curve is an extended unbinned maximum likelihood fit to the spectrum, using the sum of a Crystal Ball (CB) and a Gaussian function for signal, and an exponential for the. o measure the fraction of non-prompt J/ψ (the so called b-fraction), the pseudo-proper decay length l J/ψ, as shown in the right of Figure, is computed as an estimate

4 th Winter Workshop on Nuclear Dynamics (WWND) Journal of Physics: Conference Series () doi:.88/-9/// of the b-fraction decay length by L xy m J/ψ /p. Here, the L xy is defined as, L xy = û S r û S û, () where û is the unit vector in the direction of the J/ψ p and S is the sum of the primary and secondary vertex covariance matrices. In the final step, the invariant mass spectrum of + pairs and their l J/ψ distribution are fitted simultaneously in a two-dimensional (D), extended unbinned maximum likelihood fit. Figure shows the mass spectra for Υ(nS) states in (left) and (right). he yields are extracted from an unbinned maximum likelihood fit to the invariant dimuon mass spectra. he reconstructed mass line shape of each Υ(nS) state is modeled by a CB function, i.e. a Gaussian function with the low-side tail replaced by a power law function describing final-state radiation. Reasonable variations with multiplicity are considered in the systematic uncertainties. he Υ(nS) mass ratios are fixed to the their world average values [], with ground shape is modeled by an exponential function multiplied by an error function and all its parameters are left free in the fit, as in Ref. [].. Results.. Charmonia in PbPb collisions After extracting the prompt J/ψ yields in each rapidity, p, centrality, and φ bin, the v is calculated with a fit of the N J/ψ total dn J/ψ dφ vs φ distributions with the function + v cos( φ). () he N J/ψ total is the yield in φ = /π for each kinematic bin. An example of such fits is given in Figure, for the centrality integrated case. he measured prompt J/ψ v, for -% event centrality, integrated over. < p < GeV/c and y <. is. ±.(stat) ±.(syst), () with a significance for a nonzero v of.8σ. he v results versus centrality, p, and rapidity are shown in Figure. For each of these results, the dependence on one variable is studied by averaging over the other two. A non-zero v is measured in all the kinematic bins studied. he observed anisotropy shows no strong centrality or rapidity dependence when integrated over rapidity and centrality, respectively. In -% centrality events, the result are compatible with a p -independent anisotropy, whether measured at low-p ( < p <. GeV/c) in the forward rapidity interval. < y <., or at high-p (. < p < GeV/c) in rapidity interval y <.... Bottomonia in and collisions he and are further analyzed separately as a function of event activity variables measured in two different rapidity regions. Specifically, the single ratios, Υ(S)/Υ(S) and Υ(S)/Υ(S) are measured in bins of: () E η >, the raw transverse energy deposited in the most forward part of the HF calorimeters at. < η <., and () N η <., the number of charged particles, not including the two muons, with p > MeV/c reconstructed in the tracker at η <. and originating from the same vertex as the Υ. In Figure, for both and, the results are shown as a function of forward transverse energy (E η >, left panel), and as a function of mid-rapidity track multiplicity (N η <., right panel). he difference observed

5 th Winter Workshop on Nuclear Dynamics (WWND) Journal of Physics: Conference Series () doi:.88/-9/// Figure. he φ distribution of high-p (. < p < GeV/c) prompt J/ψ raw yields, measured in the rapidity range y <. and event centrality -%, and normalized by the bin width and the sum of the yields in all four φ bins. he dashed red line in all figures represents the function +v cos( φ) used to extract v [9]... S Preliminary PbPb =. ev L int = b Prompt J/ψ p >. GeV/c y <... S Preliminary PbPb =. ev L int = b Prompt J/ψ Cent. - %.. S Preliminary PbPb =. ev L int = b Prompt J/ψ Cent. - % p >. GeV/c... v. v. y <.. < y <. v.... -% -% -% -. N part -. GeV/c p y Figure. Prompt J/ψ centrality (left), p (middle) and rapidity (right) dependence of v. he boxes represented point-by-point systematic uncertainties. Horizontal bars indicate the bin width [9]. between the Υ states when binning in N η <. can be explained in two oosite ways. If, on one hand, the Υ(S) is systematically produced with more particles than the excited states, it would influence the underlying distribution of charged particles and create an artificial effect when selected in small multiplicity bins. his effect should be sensitive to the underlying multiplicity distribution and would result in a larger correlation if one reduces the size of the multiplicity bins. On the other hand, if the Υ are interacting with the surrounding environment, the Υ(S) is expected, as the most tightly bound state and the one of smallest size, to be less affected than Υ(S) and Υ(S), leading to a decrease of the Υ(nS)/Υ(S) ratios with increasing multiplicity. In either cases, the ratios will continuously decrease from the to to PbPb systems, as a function of event multiplicity. In addition, self-normalized to their activity-integrated values, the individual Υ(nS) yields are calculated. N η <. η <. / N he results are shown in Figure in bins of E η > / E η > (top) and (bottom), for and collisions, where the denominator is average of yields in all events. All the self-normalized cross section ratios increase with increasing forward transverse energy and mid-rapidity particle multiplicity in the event. In the cases where Pb ions are involved, the increase observed in both variables can arise from the increase in the number of nucleon-nucleon collisions. he results are reminiscent of a similar J/ψ measurement made in collisions at ev [].

6 th Winter Workshop on Nuclear Dynamics (WWND) Journal of Physics: Conference Series () doi:.88/-9/// / [ϒ(nS)/ϒ(S)] xpb [ϒ(nS)/ϒ(S)]...8. S =. ev y <.9, L = nb S PbPb =. ev y <., L = b 9% uer limit PRL 9 () p > GeV/c ϒ(nS)/ϒ(S) S s =. ev ϒ(S)/ϒ(S) ϒ(S)/ϒ(S) S =. ev ϒ(S)/ϒ(S) ϒ(S)/ϒ(S) y <.9 ϒ(nS)/ϒ(S) S s =. ev ϒ(S)/ϒ(S) ϒ(S)/ϒ(S) S =. ev ϒ(S)/ϒ(S) ϒ(S)/ϒ(S) y < ϒ (S)/ϒ(S) ϒ(S)/ϒ(S) η > E [GeV] 8 η <. N Figure. (Left) Event activity integrated double ratios of the excited states, Υ(S) and Υ(S), to the ground state, Υ(S) in collisions at =. ev with respect to collisions at s =. ev (circles), compared to the corresponding ratios for PbPb (cross) collisions at =. ev from Ref. [], which used a different set for the normalization. (Middle, Right) Single cross section ratios Υ(S)/Υ(S) and Υ(S)/Υ(S) for y <.9 versus transverse energy measured in. < η <. (left) and number of charged measured in η <. (right), for collisions at s =. ev (open symbols) and collisions at =. ev (closed symbols). In both figures, the error bars indicate the statistical uncertainties, and the boxes represent the point-to-point systematic uncertainties. he global uncertainties on the results are % and 8% for Υ(S)/Υ(S) and Υ(S)/Υ(S), respectively, while in the results they amount to 8% and 9%, respectively [].. Summary We presented the azimuthal anisotropy of prompt J/ψ that shows a.8σ significance for a non-zero v in the centrality -% of high p (>. GeV/c) over rapidity range y <.. No strong centrality, p and rapidity dependence is observed within the measured uncertainties for results that integrate the other variables. his result could give a hint of the path-length dependence of partonic energy loss in a deconfined medium. he results of double ratios [Υ(nS)]/[Υ(S)] /[Υ(nS)]/[Υ(S)] suggests the presence of final-state suression effects in the collisions compared to collisions which affect more strongly the excited states (Υ(S) and Υ(S)) compared to the ground state (Υ(S)). he excited-to-ground-states cross section ratios, Υ(nS)/Υ(S), are found to decrease with increasing charged-particle multiplicity as measured in the η <. interval that contains the region in which the Υ are measured. he self-normalized cross section ratios, Υ(nS)/ Υ(nS) increase with event activity. References []. Matsui and H. Satz, Phys. Lett. B 8 (98) [] S. Digal, P. Petreczky, and H. Satz, Phys. Rev. C () 9 [] A. Mocsy and P. Petreczky, Phys. Rev. Lett 99 () [] R. Vogt, Phys. Rev. C 8 () 9 [] R. Sharma and I. Vitev, Phys. Rev. C 8 () 9 [] F. Arleo and S. Peigne, JHEP () [] S Collaboration, JHEP () [8] S Collaboration, JINS (8) S8 [9] S Collaboration, S Physics Analysis Summary S-HIN () [] S Collaboration, JHEP () [] Particle Data Group Collaboration Phys. Rev. D 8 () [] S Collaboration, Phys. Rev. Lett. 9 () [] ALICE Collaboration, Phys. Rev. Lett. B ()

7 th Winter Workshop on Nuclear Dynamics (WWND) Journal of Physics: Conference Series () doi:.88/-9/// ϒ(S)/ ϒ(S) s =. ev =. ev PbPb =. ev y <. ϒ(S)/ ϒ(S) s =. ev =. ev ϒ(S)/ ϒ(S) s =. ev =. ev ϒ(S) ϒ(S) ϒ(S) ϒ(S) ϒ(S) ϒ(S) S y < η > E η > / E S y < η > E η > / E S y < η > E η > / E ϒ(S)/ ϒ(S) s =. ev =. ev PbPb =. ev y <. ϒ(S)/ ϒ(S) s =. ev =. ev ϒ(S)/ ϒ(S) s =. ev =. ev ϒ(S) ϒ(S) ϒ(S) ϒ(S) ϒ(S) ϒ(S) S y < η <. η <. N / N S y < η <. η <. N / N S y < η <. η <. N / N Figure. he Υ(nS) cross section versus transverse energy measured at < η <. (top row) and versus charged-track multiplicity measured in η <. (bottom row), measured in y <.9 in collisions at s =. ev and collisions at =. ev. For Υ(S), the PbPb at =. ev (open stars) are overlaid. Cross sections and x-axis variables are normalized by their corresponding activity-integrated values. For all points, the abscissae are at the mean value in each bin. he dotted line is a linear function with a slope equal to unity. he error bars indicate the statistical uncertainties, and the boxes represent the point-to-point systematics uncertainties [].