Moon, Dong Ho

Raics, Péter

Trócsányi, Zoltán

Ujvári, Balázs

Journal of Physics Conference Series

English

University of Debrecen Electronic Archive

Journal of Physics: Conference Series
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Latest results on heavy flavor di-lepton (p-Pb and
Pb-Pb)
To cite this article: Dong Ho Moon and the CMS collaboration 2014 J. Phys.: Conf. Ser. 535 012023
 
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This content was downloaded from IP address 193.6.136.39 on 28/04/2020 at 13:39
Latest results on heavy flavor di-lepton (p-Pb and
Pb-Pb)
Dong Ho Moon on behalf of the CMS collaboration
University of Illinois at Chicago
E-mail: dmoon@cern.ch
Abstract. The Compact Muon Solenoid (CMS) has measured various quarkonium states via
their decays into muon pairs in pp, PbPb and pPb collisions at
√
sNN = 2.76 and 5.02 TeV.
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, mapping its evolution. The
most recent results on the production of prompt J/ψ in PbPb and the three Υ states in pp and
pPb collisions will be presented.
1. Introduction
One strong signature of the existence for a Quark-Gluon-Plasma (QGP) is quarkonium
suppression. Recent results from quarkonia measurements performed in CMS have been found
to support theoretical predictions called the sequential melting scenario [1, 2, 3]. Quarkonimum
production in heavy-ion collisions is affected by initial effects such as nuclear parton distribution
functions (nPDFs) [4], parton energy loss, and the Cronin effect [5, 6], and final state effects
such as Debye color screening and statistical recombination [1].
The 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 mid-
central PbPb collisions.
This paper also reports the results of bb states produced in proton-lead (pPb) collisions. This
system is a good reference to understand initial state effects and may allow insight into cold
nuclear effects that differ from the suppression effects observed in previous measurements [7].
2. Environmental setup and analysis procedure
The central feature of the CMS apparatus is a superconducting solenoid, providing an axial
magnetic field of 3.8 T. 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| < 2.4, with detection planes made of three technologies:
Drift Tubes, Cathode Strip Chambers, and Resistive Plate Chambers. Matching the muons to
the tracks measured in the silicon tracker results in a transverse momentum resolution better
than 1.5% for pT smaller than 100 GeV/c. A more detailed description of the CMS detector
can be found in Ref. [8].
30th Winter Workshop on Nuclear Dynamics (WWND2014) IOP Publishing
Journal of Physics: Conference Series 535 (2014) 012023 doi:10.1088/1742-6596/535/1/012023
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 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 IOP Publishing Ltd 1
)2 (GeV/cµµm
2.6 2.7 2.8 2.9 3 3.1 3.2 3.3 3.4 3.5
 )2
Ev
en
ts 
/ (
 0
.0
2 
Ge
V/
c
0
500
1000
1500
2000
2500
3000
CMS Preliminary
 = 2.76 TeVNNsPbPb  
-1bµ = 150 intL
|y| < 2.4
 < 30 GeV/cT6.5 < p
Cent. 0-100%
 177±: 8525 ψJ/N
2 1 MeV/c± = 35 σ
data
total fit
bkgd + non-prompt
background
 (mm)ψJ/l
-1 -0.5 0 0.5 1 1.5 2
Ev
en
ts 
/ (
0.
03
5 
m
m
)
1
10
210
310
410
CMS Preliminary
 = 2.76 TeVNNsPbPb  
-1bµ = 150 intL |y| < 2.4
 < 30 GeV/cT6.5 < p
Cent. 0-100%
data
total fit
bkgd + non-prompt
background
Figure 1. Invariant-mass spectra (left) and pseudo-proper decay length distribution (right)
of µ+µ− pairs integrated over centrality. The spectra are integrated over the rapidity range 0
< |y| < 2.4 and the pT range 6.5 < pT < 30 GeV/c. The projections of the two-dimensional fit
onto the respective axes are overlaid as solid black lines. The dashed red lines show the fitted
contribution of non-prompt J/ψ. The fitted background contributions are shown as dotted blue
lines [9].
)2 (GeV/c-µ+µm
7 8 9 10 11 12 13 14
 
)
2
E v
e n
t s
 /  
(  0
. 0 5
 G
e V
/ c
0
200
400
600
800
1000
1200
1400  = 5.02 TeVNNsCMS pPb 
-1L = 31 nb
data
total fit
background
| < 1.93
CM
µη|
 > 4 GeV/cµ
T
p
)2 (GeV/c-µ+µm
7 8 9 10 11 12 13 14
 
)
2
E v
e n
t s
 /  
(  0
. 0 5
 G
e V
/ c
0
100
200
300
400
500
600
700
800
 = 2.76 TeVsCMS pp 
-1L = 5.4 pb
data
total fit
background
| < 1.93µ
CM
η|
 > 4 GeV/cµ
T
p
Figure 2. Invariant mass spectrum in pPb (left) and pp collisions (right) of µ+µ− pairs with
single muons with pµT > 4 GeV/c and |ηµCM | < 1.93. The data (black circles) overlaid with the
fit (solid blue line). The background component of the fit is represented by the dashed blue
line [10].
The pp. data used in the study corresponded to an integrated luminosity of 5.4 pb−1 at a
center-of-mass energy
√
sNN = 2.76 TeV. The corresponding integrated luminosity of pPb data
is 31 nb−1 with a center-of-mass energy
√
sNN = 5.02 TeV. The direction of the higher-energy
proton beam was initially set up to be clockwise, and was reversed after an integrated luminosity
of 18 nb−1 of data was recorded. As a result of the energy difference of the colliding beams, the
nucleon-nucleon center-of-mass in the pPb collisions are not at rest with respect to the laboratory
frame. Massless particles emitted at |ηCM | = 0 in the nucleon-nucleon center-of-mass frame are
detected at η = -0.465 (clockwise proton beam) or +0.465 (counterclockwise proton beam) in
the laboratory frame. The PbPb data used for prompt J/ψ azimuthal anisotropy measurement
were collected with a corresponding integrated luminosity of 150 µb−1.
The invariant mass spectrum of all µ+µ− pairs used in the PbPb analysis is shown in the left
of Figure 1. The 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 background. To measure the fraction of non-prompt J/ψ (the so called b-fraction), the
pseudo-proper decay length lJ/ψ, as shown in the right of Figure 1, is computed as an estimate
30th Winter Workshop on Nuclear Dynamics (WWND2014) IOP Publishing
Journal of Physics: Conference Series 535 (2014) 012023 doi:10.1088/1742-6596/535/1/012023
2
of the b-fraction decay length by LxymJ/ψ/pT . Here, the Lxy is defined as,
Lxy =
uˆTS−1~r
uˆTS−1uˆ
, (1)
where uˆ is the unit vector in the direction of the J/ψ pT and S is the sum of the primary and
secondary vertex covariance matrices. In the final step, the invariant mass spectrum of µ+µ−
pairs and their lJ/ψ distribution are fitted simultaneously in a two-dimensional (2D), extended
unbinned maximum likelihood fit.
Figure 2 shows the mass spectra for Υ(nS) states in pp (left) and pPb (right). The yields
are extracted from an unbinned maximum likelihood fit to the invariant dimuon mass spectra.
The 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.
The Υ(nS) mass ratios are fixed to the their world average values [11], 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. [12].
3. Results
3.1. Charmonia in PbPb collisions
After extracting the prompt J/ψ yields in each rapidity, pT , centrality, and ∆φ bin, the v2 is
calculated with a fit of the 1
N
J/ψ
total
dNJ/ψ
dφ vs ∆φ distributions with the function
1 + 2v2cos(2∆φ). (2)
The N
J/ψ
total is the yield in ∆φ = 2/pi for each kinematic bin. An example of such fits is given
in Figure 3, for the centrality integrated case. The measured prompt J/ψ v2, for 10-60% event
centrality, integrated over 6.5 < pT < 30 GeV/c and |y| < 2.4 is
0.054± 0.013(stat)± 0.006(syst), (3)
with a significance for a nonzero v2 of 3.8σ. The v2 results versus centrality, pT , and rapidity
are shown in Figure 4. For each of these results, the dependence on one variable is studied by
averaging over the other two. A non-zero v2 is measured in all the kinematic bins studied. The
observed anisotropy shows no strong centrality or rapidity dependence when integrated over
rapidity and centrality, respectively. In 10-60% centrality events, the result are compatible with
a pT -independent anisotropy, whether measured at low-pT ( 3 < pT < 6.5 GeV/c) in the forward
rapidity interval 1.6 < |y| < 2.4, or at high-pT (6.5 < pT < 30 GeV/c) in rapidity interval |y| <
2.4.
3.2. Bottomonia in pp and pPb collisions
The pp and pPb data are further analyzed separately as a function of event activity variables
measured in two different rapidity regions. Specifically, the single ratios, Υ(2S)/Υ(1S) and
Υ(3S)/Υ(1S) are measured in bins of: (1) E
|η|>4
T , the raw transverse energy deposited in the
most forward part of the HF calorimeters at 4.0 < |η| < 5.2, and (2) N |η|<2.4tracks , the number
of charged particles, not including the two muons, with pT > 400MeV/c reconstructed in the
tracker at |η| <2.4 and originating from the same vertex as the Υ. In Figure 5, for both pp and
pPb, the results are shown as a function of forward transverse energy (E
|η|>4
T , left panel), and
as a function of mid-rapidity track multiplicity (N
|η|<2.4
tracks , right panel). The difference observed
30th Winter Workshop on Nuclear Dynamics (WWND2014) IOP Publishing
Journal of Physics: Conference Series 535 (2014) 012023 doi:10.1088/1742-6596/535/1/012023
3
Figure 3. The ∆φ distribution of high-pT (6.5 < pT < 30 GeV/c) prompt J/ψ raw yields,
measured in the rapidity range |y| < 2.4 and event centrality 10-50%, and normalized by the bin
width and the sum of the yields in all four ∆φ bins. The dashed red line in all figures represents
the function 1+2v2cos(2∆φ) used to extract v2 [9].
partN
0 50 100 150 200 250 300
2v
-0.05
0
0.05
0.1
0.15
0.2
0.25
CMS Preliminary
 = 2.76 TeVNNsPbPb  
-1bµ = 150 intL
ψPrompt J/
 > 6.5 GeV/c
T
p
|y| < 2.4
30-60% 20-30% 10-20%
 GeV/c
T
p
0 5 10 15 20 25 30
2v
-0.05
0
0.05
0.1
0.15
0.2
0.25
|y| < 2.4
1.6 < |y| < 2.4
CMS Preliminary
 = 2.76 TeVNNsPbPb  
-1bµ = 150 intL
ψPrompt J/
Cent. 10 - 60 %
|y|
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4
2v
-0.05
0
0.05
0.1
0.15
0.2
0.25
CMS Preliminary
 = 2.76 TeVNNsPbPb  
-1bµ = 150 intL
ψPrompt J/
Cent. 10 - 60 %
 > 6.5 GeV/c
T
p
Figure 4. Prompt J/ψ centrality (left), pT (middle) and rapidity (right) dependence of v2.
The boxes represented point-by-point systematic uncertainties. Horizontal bars indicate the bin
width [9].
between the Υ states when binning in N
|η|<2.4
tracks can be explained in two opposite ways. If, on one
hand, the Υ(1S) 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. This 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(1S)
is expected, as the most tightly bound state and the one of smallest size, to be less affected than
Υ(2S) and Υ(3S), leading to a decrease of the Υ(nS)/Υ(1S) ratios with increasing multiplicity.
In either cases, the ratios will continuously decrease from the pp to pPb 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. The results are shown in Figure 6 in bins of E
|η|>4
T /〈E|η|>4T 〉 (top) and
N
|η|<2.4
tracks /〈N |η|<2.4tracks 〉 (bottom), for pp and pPb 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. The pp results are reminiscent of a similar J/ψ measurement made
in pp collisions at 7 TeV [13].
30th Winter Workshop on Nuclear Dynamics (WWND2014) IOP Publishing
Journal of Physics: Conference Series 535 (2014) 012023 doi:10.1088/1742-6596/535/1/012023
4
(1S)ϒ(2S)/ϒ (1S)ϒ(3S)/ϒ
p p
( 1 S
) ]
ϒ
( n S
) /
ϒ
 
/  [
x P
b
( 1 S
) ]
ϒ
( n S
) /
ϒ [
0
0.2
0.4
0.6
0.8
1
1.2
1.4
 > 4 GeV/cµ
T
p
 = 5.02 TeVNNsCMS pPb 
-1| < 1.93, L = 31 nb
CM
|y
 = 2.76 TeVNNsCMS PbPb 
-1bµ| < 2.4, L = 150 
CM
|y
95% upper limit
PRL 109 (2012) 222301
 [GeV]|>4η|TE
0 5 10 15 20 25 30 35 40
( 1 S
)
ϒ
( n S
) /
ϒ
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
| < 1.93
CM
|y
 = 5.02 TeVNNsCMS pPb 
(1S)ϒ(2S)/ϒ 
(1S)ϒ(3S)/ϒ 
 = 2.76 TeVsCMS pp 
(1S)ϒ(2S)/ϒ 
(1S)ϒ(3S)/ϒ 
|<2.4η|
tracksN
0 20 40 60 80 100 120 140
( 1 S
)
ϒ
( n S
) /
ϒ
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
|< 1.93
CM
|y
 = 5.02 TeVNNsCMS pPb 
(1S)ϒ(2S)/ϒ 
(1S)ϒ(3S)/ϒ 
 = 2.76 TeVsCMS pp 
(1S)ϒ(2S)/ϒ 
(1S)ϒ(3S)/ϒ 
Figure 5. (Left) Event activity integrated double ratios of the excited states, Υ(2S) and Υ(3S),
to the ground state, Υ(1S) in pPb collisions at
√
sNN = 5.02 TeV with respect to pp collisions
at
√
s = 2.76 TeV (circles), compared to the corresponding ratios for PbPb (cross) collisions
at
√
sNN = 2.76 TeV from Ref. [12], which used a different dataset for the pp normalization.
(Middle, Right) Single cross section ratios Υ(2S)/Υ(1S) and Υ(3S)/Υ(1S) for |yCM | < 1.93
versus transverse energy measured in 4.0 < |η| < 5.2 (left) and number of charged tracks
measured in |η| < 2.4 (right), for pp collisions at √s = 2.76 TeV (open symbols) and pPb
collisions at
√
sNN = 5.02 TeV (closed symbols). In both figures, the error bars indicate the
statistical uncertainties, and the boxes represent the point-to-point systematic uncertainties.
The global uncertainties on the pp results are 7% and 8% for Υ(2S)/Υ(1S) and Υ(3S)/Υ(1S),
respectively, while in the pPb results they amount to 8% and 9%, respectively [10].
4. Summary
We presented the azimuthal anisotropy of prompt J/ψ that shows a 3.8σ significance for a
non-zero v2 in the centrality 10-60% of high pT (>6.5 GeV/c) over rapidity range |y| < 2.4.
No strong centrality, pT and rapidity dependence is observed within the measured uncertainties
for results that integrate the other variables. This result could give a hint of the path-length
dependence of partonic energy loss in a deconfined medium.
The results of double ratios [Υ(nS)]/[Υ(1S)]pPb/[Υ(nS)]/[Υ(1S)]pp suggests the presence of
final-state suppression effects in the pPb collisions compared to pp collisions which affect more
strongly the excited states (Υ(2S) and Υ(3S)) compared to the ground state (Υ(1S)). The
excited-to-ground-states cross section ratios, Υ(nS)/Υ(1S), are found to decrease with increasing
charged-particle multiplicity as measured in the |η| <2.4 interval that contains the region in
which the Υ are measured. The self-normalized cross section ratios, Υ(nS)/〈Υ(nS)〉 increase
with event activity.
References
[1] T. Matsui and H. Satz, Phys. Lett. B 178 (1986) 416
[2] S. Digal, P. Petreczky, and H. Satz, Phys. Rev. C 64 (2001) 904015
[3] A. Mocsy and P. Petreczky, Phys. Rev. Lett 99 (2007) 211602
[4] R. Vogt, Phys. Rev. C 81 (2010) 044903
[5] R. Sharma and I. Vitev, Phys. Rev. C 87 (2013) 044905
[6] F. Arleo and S. Peigne, JHEP 03 (2013) 122
[7] CMS Collaboration, JHEP 1205 (2012) 063
[8] CMS Collaboration, JINST 3 (2008) S08004
[9] CMS Collaboration, CMS Physics Analysis Summary CMS-HIN-12-001 (2012)
[10] CMS Collaboration, JHEP 04 (2014) 103
[11] Particle Data Group Collaboration Phys. Rev. D 86 (2012) 010001
[12] CMS Collaboration, Phys. Rev. Lett. 109 (2012) 222301
[13] ALICE Collaboration, Phys. Rev. Lett. B 712 (2012) 165
30th Winter Workshop on Nuclear Dynamics (WWND2014) IOP Publishing
Journal of Physics: Conference Series 535 (2014) 012023 doi:10.1088/1742-6596/535/1/012023
5
〉|>4η|TE〈/
|>4η|
TE
0 0.5 1 1.5 2 2.5 3 3.5 4
〉
( 1 S
)
ϒ 〈
( 1 S
) /
ϒ
0
1
2
3
4
5
6
7
CMS
| < 1.93
CM
|y
〉(1S)ϒ〈
(1S)ϒ
| < 2.4
CM
|y
 = 2.76 TeVspp 
 = 5.02 TeVNNspPb 
 = 2.76 TeVNNsPbPb 
〉|>4η|TE〈/
|>4η|
TE
0 0.5 1 1.5 2 2.5 3 3.5 4
〉
( 2 S
)
ϒ 〈
( 2 S
) /
ϒ
0
1
2
3
4
5
6
7
CMS
| < 1.93
CM
|y
〉(2S)ϒ〈
(2S)ϒ
 = 2.76 TeVspp 
 = 5.02 TeVNNspPb 
〉 |>4η|T E〈/
|>4η|
TE
0 0.5 1 1.5 2 2.5 3 3.5 4
〉
( 3 S
)
ϒ 〈
( 3 S
) /
ϒ
0
1
2
3
4
5
6
7
CMS
| < 1.93
CM
|y
〉(3S)ϒ〈
(3S)ϒ
 = 2.76 TeVspp 
 = 5.02 TeVNNspPb 
〉|<2.4η|
tracksN〈/
|<2.4η|
tracksN
0 0.5 1 1.5 2 2.5 3 3.5 4
〉
( 1 S
)
ϒ 〈
( 1 S
) /
ϒ
0
1
2
3
4
5
6
7
CMS
| < 1.93
CM
|y
〉(1S)ϒ〈
(1S)ϒ
| < 2.4
CM
|y
 = 2.76 TeVspp 
 = 5.02 TeVNNspPb 
 = 2.76 TeVNNsPbPb 
〉|<2.4η|
tracksN〈/
|<2.4η|
tracksN
0 0.5 1 1.5 2 2.5 3 3.5 4
〉
( 2 S
)
ϒ 〈
( 2 S
) /
ϒ
0
1
2
3
4
5
6
7
CMS
| < 1.93
CM
|y
〉(2S)ϒ〈
(2S)ϒ
 = 2.76 TeVspp 
 = 5.02 TeVNNspPb 
〉 |<2.4η|
tracks N〈/
|<2.4η|
tracksN
0 0.5 1 1.5 2 2.5 3 3.5 4
〉
( 3 S
)
ϒ 〈
( 3 S
) /
ϒ
0
1
2
3
4
5
6
7
CMS
| < 1.93
CM
|y
〉(3S)ϒ〈
(3S)ϒ
 = 2.76 TeVspp 
 = 5.02 TeVNNspPb 
Figure 6. The Υ(nS) cross section versus transverse energy measured at 4 < |η| < 5.2 (top
row) and versus charged-track multiplicity measured in |η| < 2.4 (bottom row), measured in
|yCM | < 1.93 in pp collisions at
√
s = 2.76 TeV and pPb collisions at
√
sNN = 5.02 TeV. For
Υ(1S), the PbPb data at
√
sNN = 2.76 TeV (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. The dotted line is a linear function with a slope
equal to unity. The error bars indicate the statistical uncertainties, and the boxes represent the
point-to-point systematics uncertainties [10].
30th Winter Workshop on Nuclear Dynamics (WWND2014) IOP Publishing
Journal of Physics: Conference Series 535 (2014) 012023 doi:10.1088/1742-6596/535/1/012023
6


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

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

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