LHC

b-C

ON

F-20

13-0

0816

/05/

2013

LHCb-CONF-2013-008May 16, 2013

Study of the J/ψ productioncross-section in proton-lead collisions

at√sNN = 5 TeV

The LHCb collaboration †

Abstract

The production of J/ψ mesons is studied in proton-lead collisions with the LHCbdetector, at a proton-nucleon centre-of-mass energy

√sNN = 5 TeV. The nuclear

attenuation factor is determined and results are compared with theoretical predictions.The analysis is based on a data sample corresponding to an integrated luminosity ofabout 1 nb−1.

† Conference report prepared for the workshop on proton-nucleus collisions at the LHC, ECT*,Trento, 6–10 May 2013. Contact authors: Fanfan Jing, Fanfan.Jing@cern.ch; Michael Schmelling,michael.schmelling@mpi-hd.mpg.de; Burkhard Schmidt, Burkhard.Schmidt@cern.ch; Zhenwei Yang, Zhen-wei.Yang@cern.ch

1 Introduction

The study of proton-nucleus collisions is important for heavy ion physics, as it providesessential input to the understanding of nucleus-nucleus collisions. The program carried outat the LHC on proton-lead collisions with energy per nucleon in the multi-TeV domain,initiated with a short pilot run in September 2012 and continued with a longer run in2013, has motivated many theoretical studies [1–9]. Previous experiments, performed atlower energy per nucleon, have shown that both quarkonium [10] and light hadron [11, 12]production at large rapidity y is highly suppressed in proton-lead collisions with respectto proton-proton collisions. In addition it was found that forward and backward J/ψproduction are different [10,13], where “forward” and “backward” are defined relative tothe direction of the proton beam. This indicates that the nuclear attenuation factor [2]

RpA(y,√sNN) =

1

A

dσpA

dy(y,√sNN)

dσpp

dy(y,√sNN)

(1)

strongly depends on y, where A is the atomic mass number of the nucleus, y is definedas the rapidity with respect to the proton direction in the proton-nucleon centre-of-massframe, and

√sNN is the centre-of-mass energy of the proton-nucleon system.

Despite its asymmetric layout, the LHCb experiment allows measurement of RpA forboth positive and negative rapidities. In proton-proton (pp) collisions the J/ψ productioncross-section, dσpp/dy, is forward-backward symmetric and is determined in the region2.0 < y < 4.5. The production cross-section in proton-lead collisions dσpA/dy for forwardrapidities is measured with the proton beam moving from the interaction point toward thedetector (pA collisions in the following). Data collected with the inverted beam directions(Ap in the following) allow to measure backward production. The measurement of thenuclear attenuation factor as a function of rapidity will be helpful for the interpretation ofcold nuclear effects using different models.

Data were collected with a proton beam energy of 4 TeV and a lead beam energy of1.58 TeV per nucleon, resulting in a centre-of-mass energy of the proton-nucleon systemof 5 TeV. Since the energy of the proton beam is significantly larger than that of thenucleon in the lead beam, the proton-nucleon centre-of-mass system has a rapidity in thelaboratory frame of +0.47 for pA and −0.47 for Ap collisions. This boost results in ashift of the rapidity coverage in the proton-nucleon centre-of-mass system, ranging fromabout 1.5 to 4.0 for pA collisions and from −5.0 to −2.5 for Ap collisions. Throughoutthis document y always indicates the rapidity in the proton-nucleon centre-of-mass system,unless otherwise specified.

In this analysis, in pA collisions the two-dimensional dependence on y and on thetransverse momentum pT of the J/ψ production cross-section is measured. In Ap collisions,due to limited sample size, only the one-dimensional dependence on either y or pT ismeasured.

1

2 Detector, trigger and data set

The LHCb detector [14] is a single-arm forward spectrometer designed for the study ofparticles containing b or c quarks. The detector includes a high precision tracking systemconsisting of a silicon-strip vertex detector (VELO) surrounding the pp interaction region,a large-area silicon-strip detector located upstream of a dipole magnet with a bendingpower of about 4 Tm, and three stations of silicon-strip detectors and straw drift tubesplaced downstream. The combined tracking system has momentum resolution ∆p/pthat varies from 0.4% at 5 GeV/c to 0.6% at 100 GeV/c, and impact parameter resolutionof 20 µm for tracks with high transverse momentum. Charged hadrons are identifiedusing two ring-imaging Cherenkov detectors. Photon, electron and hadron candidates areidentified by a calorimeter system consisting of scintillating-pad and preshower detectors,an electromagnetic calorimeter and a hadronic calorimeter. Muons are identified by asystem composed of alternating layers of iron and multiwire proportional chambers. Thetrigger [15] consists of a hardware stage, based on information from the calorimeter andmuon systems, followed by a software stage which applies a full event reconstruction.

The data set used in this analysis was acquired during the proton-lead run in early2013. The directions of the proton and lead beams were swapped during data takingto produce both pA and Ap collisions. Since the instantaneous luminosity was around5 × 1027 cm−2s−1, five orders of magnitude below the nominal LHCb luminosity for ppcollisions, the trigger thresholds were lowered with respect to the settings used in 2011 and2012 for pp collisions. The requirement on the transverse momenta of muons, for example,was set to pT > 0.6 GeV/c, compared to pT > 1.3 GeV/c during the 2012 pp run.

This analysis is based on data samples corresponding to integrated luminosities of0.75 nb−1 of pA and 0.30 nb−1 of Ap collisions. The luminosities are determined fromonline measurements with an estimated uncertainty of 5%.

Simulated samples based on pp collisions are used to determine acceptance and recon-struction efficiencies. Whenever significant differences are observed in the distributionsof transverse momentum, rapidity and multiplicity between simulated samples and data,the simulated samples are re-weighted to match the data. Figure 1 shows the comparisonof track multiplicity distributions between pA and Ap data for events with exactly onereconstructed primary vertex. It is observed that the track multiplicity in Ap collisionsis significantly larger than that in pA collisions. The track multiplicity in pA collisionsis found to be similar to that in pp events during 2012 high luminosity running, with onaverage around two interactions per event.

3 Event selection

The strategy for the J/ψ production measurement is based on that described in Refs. [16–18].The J/ψ candidates are reconstructed and selected using the J/ψ → µ+µ− channel. Eventswith at least one primary vertex are selected, where the primary vertex is reconstructedfrom at least five tracks in the VELO detector. The J/ψ candidates are formed from trackswith opposite sign charges. The tracks should be identified as muons by the muon detector,

2

track multiplicity0 50 100 150 200 250 300 350 400

pro

bab

ility

-610

-510

-410

-310

-210 Ap pA

= 5 TeVNNspA/Ap PreliminaryLHCb

Figure 1: Comparison of track multiplicity distributions between pA and Ap collisions for eventswith exactly one reconstructed primary vertex. The red triangles represent the Ap collisions,while the blue line indicates the pA collisions. The distributions are not corrected for efficiency.

and the difference between the logarithms of the likelihoods for the muon and the pionhypotheses should be greater than one. A pT above 0.7 GeV/c and a good track fit quality(χ2/ndf < 4) are required for each track. The two muons are required to originate from acommon vertex with a χ2-probability larger than 0.5%. The candidates are kept if theinvariant mass falls in a mass window of ±120 MeV/c2 around the known J/ψ mass [19].To remove duplicate tracks created in the reconstruction, a cut on the Kullback-Leiblerdistance between tracks is applied [20].

4 Determination of the cross-section

The determination of the double-differential production cross-section requires knowledgeof the numbers of prompt J/ψ , J/ψ from b-hadron and background decays in bins ofthe kinematic variables y and pT. This is done by performing a simultaneous fit to thedistributions of the dimuon invariant mass and the pseudo-proper time tz in each kinematicbin. The pseudo-proper time of the J/ψ is defined as

tz =(zJ/ψ − zPV)×MJ/ψ

pz, (2)

where zJ/ψ is the z position of the J/ψ decay vertex, zPV that of the primary vertexrefitted after removing the two muon tracks from the J/ψ candidate, pz the measured J/ψmomentum along the beam axis z, and MJ/ψ the known J/ψ mass. The pseudo-propertime tz is a Lorentz invariant variable which allows us to separate prompt particles fromJ/ψ mesons created in decays of b-hadrons.

The signal dimuon invariant mass distribution in each pT and y bin is modelled bya Crystal Ball (CB) function [21], while the combinatorial background is described by

3

an exponential function. The tz signal distribution is described by the sum of a deltafunction at tz = 0 for the prompt J/ψ and an exponential decay function for the J/ψfrom b component, convolved with a resolution function modelled by a double-Gaussianfunction. The tz background distribution is modelled with an empirical function basedon the shape of the tz distribution that is observed in the J/ψ mass sidebands. All theparameters of the background function are determined from sidebands independently ineach bin of pT and y. These parameters are then fixed in the final simultaneous fits to thedistributions of invariant mass and pseudo-proper time. The total fit function is the sumof the products of the mass and tz fit functions for the signal and background components.Figure 2 shows projections of the fit on mass and tz for a typical bin for both pA and Apdata. The resolutions of the dimuon invariant mass in pA and Ap collisions are consistentwith each other, about 15 MeV, and are both consistent with that in pp collisions.

]2 [MeV/c µ µm3000 3050 3100 3150 3200

)2C

andi

date

s / (

5 M

eV/c

0

200

400

600

800

1000

1200

= 5 TeVNNspA PreliminaryLHCb

<14 GeV/cT

p

2.5< y <3.0

]2 [MeV/c µ µm3000 3050 3100 3150 3200

)2C

andi

date

s / (

5 M

eV/c

0

200

400

600

800

1000

1200

1400

1600

1800

= 5 TeVNNsAp PreliminaryLHCb

<14 GeV/cT

p

3.5−4.0< y <−

[ps]zt-10 -5 0 5 10

Can

dida

tes

/ (0.

2 ps

)

1

10

210

310

410

= 5 TeVNNspA PreliminaryLHCb

<14 GeV/cT

p

2.5< y <3.0

[ps]zt-10 -5 0 5 10

Can

dida

tes

/ (0.

2 ps

)

1

10

210

310

410 = 5 TeVNNsAp

PreliminaryLHCb

<14 GeV/cT

p

3.5−4.0< y <−

Figure 2: Examples for projections of the fit results onto (top) invariant dimuon mass and(bottom) tz in pA (left, 2.5 < y < 3.0) and Ap (right, −4.0 < y < −3.5). The data are integratedover transverse momentum, pT < 14 GeV/c. For the mass projection, the total fitted function isshown (red solid line) together with the signal distribution including J/ψ from b-hadrons (bluedotted line) and background (green dotted line). For the tz projection the total fitted function isshown by the solid red line, the background component is shown as the green hatched area, theprompt signal component by the blue area, the J/ψ from b-hadrons by the solid black line.

Based on the fit result, for each of the two components, namely prompt J/ψ and

4

J/ψ from b, a signal weight factor wi for the ith candidate is obtained with the sPlottechnique [22], using the dimuon invariant mass and tz as separating variables. The sum ofwi over all candidates in a given pT and y bin gives the number of signal candidates in thebin, nsig, while the sum of w2

i gives the variance of nsig. For the event-by-event efficiencycorrection the sum of wi/εi over a given bin leads to the efficiency corrected signal yieldN cor in the bin. The efficiency εi depends on pT and y and includes the geometricalacceptance, trigger and reconstruction efficiencies. The acceptance and reconstructionefficiencies are estimated from the simulated samples mentioned above, while the triggerefficiency is obtained from the data by exploiting a sample of J/ψ events that would stillbe triggered if the J/ψ candidates were removed.

The double differential cross-section for J/ψ production in a given (pT, y) bin is definedas

d2σ

dpTdy=

N cor(J/ψ → µ+µ−)

L × B(J/ψ → µ+µ−)×∆pT ×∆y, (3)

where N cor(J/ψ → µ+µ−) is the efficiency corrected number of J/ψ → µ+µ− signalcandidates in the given bin. In the denominator, L is the integrated luminosity, B(J/ψ →µ+µ−) = (5.93± 0.06)% [19] the branching fraction of the J/ψ → µ+µ− decay, and ∆pT

and ∆y the widths of the pT and y bins. The transverse momentum range pT < 14 GeV/cis divided into 8 bins, with ∆pT = 1 GeV/c for pT < 7 GeV/c and ∆pT = 7 GeV/c for7 < pT < 14 GeV/c. The rapidity bin width is ∆y = 0.5.

5 Systematic uncertainties

Acceptance and reconstruction efficiencies depend not only on the J/ψ kinematics butalso on its polarisation. While measurements [23, 24] in pp collisions indicate that thepolarisation is small, the knowledge about the polarisation of J/ψ production in pAcollisions is limited since no measurements have been performed so far. However, based onthe expectation that the nuclear environment does not enhance polarisation, it is assumedthat the J/ψ mesons are produced with no polarisation. No systematic uncertainty hasbeen assigned to the effect of polarisation in this analysis.

The different contributions to the systematic uncertainties affecting the cross-sectionmeasurement are discussed in the following and summarised in Table 1. The influenceof the fit function used to describe the shape of the dimuon invariant mass distributionis estimated by fitting the invariant mass distribution with the sum of two Crystal Ballfunctions. The total relative difference of 1.8% in the signal yield is taken as systematicuncertainty. The uncertainty of the luminosity determination is estimated to be 5%according to earlier studies [25]. The uncertainty due to reconstruction efficiency ofthe muon tracks is estimated using a data-driven tag-and-probe approach [26] based onpartially reconstructed J/ψ decays. Taking into account the effect of the track multiplicitydifference between proton-ion and proton-proton data, this results in an uncertainty of1.5%. The uncertainties related to the radiative tail, vertexing, track quality and muonidentification are taken from Refs. [16–18], but have been increased conservatively by 30%,

5

Table 1: Relative systematic uncertainties on the differential production cross-section.

Source Systematic uncertainty (%)Correlated between binsMass fits 1.8Tracking efficiency 1.5B(J/ψ → µ+µ−) 1.0Luminosity 5.0tz fit (only for J/ψ from b) 5.0Vertexing, track quality, etc. 3.5Uncorrelated between binsBinning 0.1 to 14

leading to an overall uncertainty of 3.5%. The same has been done for the uncertainty dueto the tz fit procedure, which only affects the component of J/ψ from b. An uncertainty of5% has been conservatively assigned.

Differences in the pT and y spectra between the data and MC can effect the resultbecause of the finite size of the bins. To estimate the size of this effect the total efficiencyhas been checked by doubling the number of bins in pT and rapidity. The relative differencewith respect to the nominal binning, which varies between 0.1% and 14% depending onthe bin, is taken as systematic uncertainty.

6 Results

The measured double differential cross-sections for prompt J/ψ production and J/ψ fromb in pA collisions as a function of pT and y, assuming no J/ψ polarisation, are shown inFig. 3. The single differential cross-sections for prompt J/ψ production and J/ψ from b inpA and Ap collisions as a function of pT and y are displayed in Figs. 4 and 5, respectively.

The integrated cross-sections for prompt J/ψ production and J/ψ from b in pA datasumming over all bins of the analysis, are

σpA(prompt J/ψ ; pT < 14 GeV/c, 1.5 < y < 4.0) = 1028.2± 13.6 (stat.)± 88.6 (syst.) µb,

σpA(J/ψ from b; pT < 14 GeV/c, 1.5 < y < 4.0) = 150.1± 4.2 (stat.)± 12.6 (syst.) µb.

The integrated cross-sections for the prompt J/ψ production and J/ψ from b in Ap data,summing over all bins of the analysis, are

σAp(prompt J/ψ ; pT < 14 GeV/c,−5.0 < y < −2.5)

=1141.9± 49.8 (stat.)± 98.4 (syst.) µb,

σAp(J/ψ from b; pT < 14 GeV/c,−5.0 < y < −2.5)

=119.7± 8.3 (stat.)± 10.0 (syst.) µb.

6

[GeV/c]T

p0 5 10

b/0

.5/(

GeV

/c)]

µd

y [

T/d

pσ2 d

-110

1

10

210

3101.5<y<2.0

2.0<y<2.5

2.5<y<3.0

3.0<y<3.5

3.5<y<4.0

= 5 TeVNNspA PreliminaryLHCb

ψprompt J/

[GeV/c]T

p0 5 10

b/0

.5/(

GeV

/c)]

µd

y [

T/d

pσ2 d

-110

1

10

210

3101.5<y<2.0

2.0<y<2.5

2.5<y<3.0

3.0<y<3.5

3.5<y<4.0

= 5 TeVNNspA PreliminaryLHCb

from bψJ/

Figure 3: Differential cross-sections for (left) prompt J/ψ mesons and (right) J/ψ from b-hadronsas functions of pT in bins of rapidity in pA collisions.

[GeV/c]T

p0 5 10

b/(

GeV

/c)]

µ [

T/d

pσd

1

10

210

310

410 from bψJ/

ψprompt J/ = 5 TeVNNspA PreliminaryLHCb

1.5 < y < 4.0

[GeV/c]T

p0 5 10

b/(

GeV

/c)]

µ [

T/d

pσd

1

10

210

310

410 from bψJ/

ψprompt J/ = 5 TeVNNsAp PreliminaryLHCb

2.5−5.0 < y < −

Figure 4: Differential cross-sections for prompt J/ψ mesons and J/ψ from b-hadrons as functionsof pT in (left) pA and (right) Ap collisions, 1.5 < y < 4.0 for pA and −5.0 < y < −2.5 for Ap.

y1.5 2 2.5 3 3.5 4

b/0

.5]

µ/d

y [

σd

0

100

200

300

400

500

600

700

800

900

1000 from bψJ/

ψprompt J/ = 5 TeVNNspA PreliminaryLHCb

< 14 GeV/cT

p

y−2.5 3 3.5 4 4.5 5

b/0

.5]

µ/d

y [

σd

0

100

200

300

400

500

600

700

800

900

1000 from bψJ/

ψprompt J/ = 5 TeVNNsAp PreliminaryLHCb

< 14 GeV/cT

p

Figure 5: Differential cross-sections fro prompt J/ψ mesons and J/ψ from b-hadrons as functionsof y in (left) pA and (right) Ap collisions, pT < 14 GeV/c.

7

The simultaneous fits to the invariant mass and tz distributions in pA and Ap collisionsgive the fraction of J/ψ from b as a function of pT or y, as shown in Figs. 6 and 7respectively. Figure 8 shows this fraction for pA collision as a function of pT in bins ofy. These results are consistent with those measured in pp collisions with centre-of-massenergies of 2.76, 7 and 8 TeV [16–18].

[GeV/c]T

p0 5 10

fro

m b

ψfr

acti

on

of

J/

0

0.05

0.1

0.15

0.2

0.25

0.3

1.5 < y < 4.0

= 5 TeVNNspA PreliminaryLHCb

[GeV/c]T

p0 5 10

fro

m b

ψfr

acti

on

of

J/

0

0.05

0.1

0.15

0.2

0.25

0.3

2.5−5.0 < y < −

= 5 TeVNNsAp PreliminaryLHCb

Figure 6: Fraction of J/ψ from b-hadron decays as functions of pT in (left) pA and (right) Apcollisions, 1.5 < y < 4.0 for pA and −5.0 < y < −2.5 for Ap.

y1.5 2 2.5 3 3.5 4

fro

m b

ψfr

acti

on

of

J/

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

< 14 GeV/cT

p = 5 TeVNNspA

PreliminaryLHCb

y−2.5 3 3.5 4 4.5 5

fro

m b

ψfr

acti

on

of

J/

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

< 14 GeV/cT

p = 5 TeVNNsAp

PreliminaryLHCb

Figure 7: Fraction of J/ψ from b-hadron decays as functions of y in (left) pA and (right) Apcollisions, pT < 14 GeV/c.

The integrated cross-sections for J/ψ production in pA, Ap and pp collisions can becompared in the common rapidity range of the proton-nucleon system, 2.5 < |y| < 4.0.After integration over this range and the full transverse momentum range, the cross-sectionof prompt J/ψ production in Ap collisions is approximately 50% higher than that in pAcollisions. This result indicates that J/ψ production is less suppressed in the backwardregion of proton-nucleus collisions. The cross-sections of prompt J/ψ production in pAcollisions are about 170 times larger than those in pp collisions at 2.76 TeV [17], and about80 times larger than those in pp collisions at 7 TeV and 8 TeV [16, 18]. For Ap collisions,these numbers are roughly 260 and 130, respectively. Figure 9 shows the cross-sectionsfor prompt J/ψ production scaled by a factor of 1/A in the common rapidity range2.5 < |y| < 4.0 of the proton-nucleon system at different centre-of-mass energies.

8

[GeV/c]T

p0 5 10

fro

m b

ψfr

acti

on

of

J/

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

1.5<y<2.02.0<y<2.52.5<y<3.03.0<y<3.53.5<y<4.0

= 5 TeVNNspA PreliminaryLHCb

Figure 8: Fraction of J/ψ from b-hadron decays as a function of pT in bins of y in pA collisions.

[TeV]NNs0 2 4 6 8 10

b]

µ/A

[ψ

pro

mp

t J/

σ

0

1

2

3

4

5

6

7

8

9

10

2.5 (Ap)−4.0 < y < −2.5 < y < 4.0 (pp,pA)

< 14 GeV/cT

pLHCb Preliminary

pp (Rescaled)

Ap

pA

Figure 9: Cross-sections for prompt J/ψ production scaled by a factor of 1/A and rescaled tothe common rapidity range of the proton-nucleon system, 2.5 < y < 4.0 for pp and pA collisions,and −4.0 < y < −2.5 for Ap collisions. The blue triangles stand for the cross-sections at 2.76, 7and 8 TeV in the same kinematic region. The black line is a linear fit to these three points. Thered square and black dots below the line are the scaled cross-sections in Ap and pA collisions.

The ratio of attenuation factors in the forward (pA) and backward (Ap) regions,rFB(y) ≡ RpA(y)/RAp(−y), defines the forward-backward production asymmetry. Adeviation from unity indicates nuclear effects in proton-nucleus collisions. Figure 10 showsthe ratio rFB as a function of y in the common rapidity range of the proton-nucleon system,together with the theoretical predictions of Ref. [2]. The dots indicate the measurementsfrom data, while the triangles and squares are theoretical predictions taking into accountthe effects of parton energy loss [27,28] in cold nuclear matter with and without saturationeffects [29]. The data are consistent with both predictions, i.e. the current precision is notsufficient to evaluate the importance of saturation effects.

9

Within the kinematic range of this analysis, the J/ψ production cross-section inpp collisions at 5 TeV can be obtained by linear interpolation from previous LHCbmeasurements. This is illustrated in Fig. 9. Taking into account the interpolation error,the nuclear attenuation factor, RpA, is determined in the range of −4.0 < y < −2.5 and2.5 < y < 4.0. Figure 11 shows the comparison with the theoretical predictions of Ref. [2].Within the sizeable uncertainties of the current measurements, the result agrees with thetheoretical predictions.

y2.5 3 3.5 4

(y)

FB

r

0

0.2

0.4

0.6

0.8

1

1.2

1.4

= 5 TeVNNspA/Ap PreliminaryLHCb ψLHCb, prompt J/

E. loss

E. loss + saturation

Figure 10: Forward-backward ratio rFB as a function of rapidity in the range of 2.5 to 4.0 of theproton-nucleon centre-of-mass system. The black dots indicate the data, while the blue trianglesand red squares are theoretical predictions, taking into account the effects of parton energy lossin cold nuclear matter with and without saturation effects [2].

7 Conclusion

The production of J/ψ mesons is studied in proton-lead collisions with the LHCb detectorat a proton-nucleon centre-of-mass energy

√sNN = 5 TeV in the transverse momentum

range of pT < 14 GeV/c and rapidity range 1.5 < y < 4.0 (pA) and −5.0 < y < −2.5(Ap). The nuclear attenuation factor RpA is determined, where the cross-section of J/ψproduction in pp collisions at 5 TeV is interpolated from previous LHCb measurementsat 2.76, 7 and 8 TeV. The forward-backward asymmetry ratio rFB is determined as afunction of rapidity. These preliminary results show good agreement with the theoreticalpredictions in Ref. [2].

10

y-5 0 5

(y)

pA

R

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

= 5 TeVNNspA/Ap PreliminaryLHCb

ψLHCb, prompt J/

E. loss

E. loss + saturation

Figure 11: Attenuation factor RpA determined in data compared to theoretical predictions [2].The black triangles are LHCb measurements, the red solid line is the theoretical prediction basedon parton energy loss effects, the blue dashed line takes additional saturation effects into account.

11

References

[1] J. Albacete et al., Predictions for p+Pb collisions at√sNN = 5 TeV, Int. J. Mod.

Phys. E22 (2013) 1330007, arXiv:1301.3395.

[2] F. Arleo and S. Peigne, Heavy-quarkonium suppression in p-A collisions from partonenergy loss in cold QCD matter, JHEP 03 (2013) 122, arXiv:1212.0434.

[3] A. Adeluyi and T. Nguyen, Coherent photoproduction of ψ and Υ mesons in ultrape-ripheral pPb and PbPb collisions at the CERN Large Hadron Collider at

√sNN =

5 TeV and√sNN = 2.76 TeV, Phys. Rev. C87 (2013) 027901, arXiv:1302.4288.

[4] G. A. Chirilli, B.-W. Xiao, and F. Yuan, Inclusive hadron productions in pA collisions,Phys. Rev. D86 (2012) 054005, arXiv:1203.6139.

[5] D. Kharzeev, E. Levin, and K. Tuchin, Nuclear modification of the J/ψ transversemomentum distributions in high energy pA and AA collisions, arXiv:1205.1554.

[6] J. Lansberg, Upsilon production in pp and pA collisions: from RHIC to the LHC,arXiv:1209.0331.

[7] G. A. Chirilli, High-energy QCD factorization from DIS to pA collisions, Int. J. Mod.Phys. Conf. Ser. 20 (2012) 200, arXiv:1209.1614.

[8] A. Adeluyi and T. Nguyen, Photoproduction of heavy quarks in ultraperipheral pp,pA, and AA collisions at the CERN Large Hadron Collider, arXiv:1210.3327.

[9] F. Arleo, R. Kolevatov, S. Peigne, and M. Rustamova, Centrality and p⊥ de-pendence of J/ψ suppression in proton-nucleus collisions from parton energy loss,arXiv:1304.0901.

[10] FNAL E866/NuSea collaboration, M. Leitch et al., Measurement of J/ψ and ψ′ sup-pression in p-A collisions, Phys. Rev. Lett. 84 (2000) 3256, arXiv:nucl-ex/9909007.

[11] BRAHMS collaboration, I. Arsene et al., Evolution of the nuclear modification factorswith rapidity and centrality in d + Au collisions at

√sNN = 200 GeV, Phys. Rev.

Lett. 93 (2004) 242303, arXiv:nucl-ex/0403005.

[12] PHENIX collaboration, S. Adler et al., Nuclear modification factors for hadrons atforward and backward rapidities in deuteron-gold collisions at

√sNN = 200 GeV,

Phys. Rev. Lett. 94 (2005) 082302, arXiv:nucl-ex/0411054.

[13] PHENIX collaboration, A. Adare et al., Cold nuclear matter effects on J/ψ yields asa function of rapidity and nuclear geometry in d + A collisions at

√sNN = 200 GeV,

Phys. Rev. Lett. 107 (2011) 142301, arXiv:1010.1246.

[14] LHCb collaboration, A. A. Alves Jr. et al., The LHCb detector at the LHC, JINST 3(2008) S08005.

12

[15] R. Aaij et al., The LHCb trigger and its performance in 2011, JINST 8 (2013) P04022,arXiv:1211.3055.

[16] LHCb collaboration, R. Aaij et al., Measurement of J/ψ production in pp collisionsat√s = 7 TeV, Eur. Phys. J. C71 (2011) 1645, arXiv:1103.0423.

[17] LHCb collaboration, R. Aaij et al., Measurement of J/ψ production in pp collisionsat√s = 2.76 TeV, JHEP 02 (2013) 041, arXiv:1212.1045.

[18] LHCb collaboration, R. Aaij et al., Production of J/ψ and Υ mesons in pp collisionsat√s = 8 TeV, arXiv:1304.6977, submitted to JHEP.

[19] Particle Data Group, J. Beringer et al., Review of particle physics, Phys. Rev. D86(2012) 010001.

[20] S. Kullback and R. A. Leibler, On information and sufficiency, Ann. Math. Statist. 22(1951) 79; S. Kullback, Letter to editor: the Kullback-Leibler distance, The AmericanStatistician 41 (1987) 340; the use of the Kullback-Leibler distance is described in M.Needham, Clone track identification using the Kullback-Leibler distance, LHCb-2008-002.

[21] T. Skwarnicki, A study of the radiative cascade transitions between the Upsilon-primeand Upsilon resonances, PhD thesis, Institute of Nuclear Physics, Krakow, 1986,DESY-F31-86-02.

[22] M. Pivk and F. R. Le Diberder, sPlot: a statistical tool to unfold data distributions,Nucl. Instrum. Meth. A555 (2005) 356, arXiv:physics/0402083.

[23] LHCb collaboration, R. Aaij et al., Measurement of J/ψ polarisation in pp collisionsat√s = 7 TeV, LHCb-PAPER-2013-008, in preparation.

[24] ALICE collaboration, B. Abelev et al., J/ψ polarization in pp collisions at√s = 7

TeV, Phys. Rev. Lett. 108 (2012) 082001, arXiv:1111.1630.

[25] LHCb collaboration, First analysis of the pPb pilot run data with LHCb, LHCb-CONF-2012-034.

[26] A. Jaeger et al., Measurement of the track finding efficiency, LHCb-PUB-2011-025.CERN-LHCb-PUB-2011-025.

[27] R. Baier et al., Radiative energy loss of high energy quarks and gluons in a finite-volumequark-gluon plasma, Nucl. Phys. B483 (1997) 291, arXiv:hep-ph/9607355.

[28] B. Zakharov, Radiative energy loss of high-energy quarks in finite-size nuclear matterand quark-gluon plasma, JETP Lett. 65 (1997) 615, arXiv:hep-ph/9704255.

[29] F. Gelis, T. Lappi, and R. Venugopalan, High energy scattering in Quantum Chromo-dynamics, Int. J. Mod. Phys. E16 (2007) 2595, arXiv:0708.0047.

13