Prompt and nonprompt J/ψ production and nuclear modification in pPb collisions at √sNN = 8.16 TeV

Physics Le e s B 774 (2017) 159–178
Con en s lis s a ailable a ScienceDi ec
Physics Le e s B
www.else ie .com/loca e/physle b
P omp and nonp omp J/ψ p oduc ion and nuclea modifica ion in
pPb collisions a √sNN =8.16 TeV
.LHCb Collabo a ion
a i c l e i n oa b s a c
A icle his o y:
Recei ed 22 June 2017
Recei ed in e ised o m 19 Sep embe
2017
Accep ed 19 Sep embe 2017
A ailable online 22 Sep embe 2017
Edi o : L. Rolandi
The p oduc ion o J/ψ mesons is s udied in p o on-lead collisions a he cen e-o -mass ene gy pe
nucleon pai √sNN =8.16 TeV wi h he LHCb de ec o a he LHC. The double di e en ial c oss-sec ions
o p omp and nonp omp J/ψ p oduc ion a e measu ed as a unc ion o he J/ψ ans e se momen um
and apidi y in he nucleon–nucleon cen e-o -mass ame. Fo wa d- o-backwa d a ios and nuclea
modifica ion ac o s a e de e mined. The esul s a e compa ed wi h heo e ical calcula ions based on
collinea ac o isa ion using nuclea pa on dis ibu ion unc ions, on he colou glass condensa e o on
cohe en ene gy loss models.
©2017 The Au ho . Published by Else ie B.V. This is an open access a icle unde he CC BY license
(h p://c ea i ecommons.o g/licenses/by/4.0/). Funded by SCOAP3.
1. In oduc ion
The p oduc ion o J/ψ mesons, and mo e gene ally o qua ko-
nium s a es, has been conside ed as a sensi i e p obe o colou
sc eening in a ho and dense medium since he p oposal by Ma -
sui and Sa z in 1986 [1] o he supp ession o he J/ψ meson
p oduc ion in hea y-ion collisions as a sign o deconfinemen . The
heo e ical unde s anding o he bound-s a e dynamics o qua ko-
nium by means o la ice QCD and e ec i e field heo ies has
p og essed subs an ially in he las 30 yea s. In hea y-ion colli-
sions, he eme ging pic u e indica es s ong modifica ions o he
qua konium bound-s a e cha ac e is ics [2]. Expe imen ally, mea-
su emen s a he SPS, RHIC and LHC e ealed in e es ing pa -
e ns [3]. In pa icula , an addi ional low ans e se momen um
(pT) componen o J/ψ p oduc ion was obse ed in PbPb colli-
sions a he LHC [4–8]. This obse a ion had been p edic ed as a
sign o cha monium o igina ing om unbound cha m qua ks, gen-
e a ed ei he du ing he li e ime o he deconfined medium [9] o
a he phase bounda y [10].
The limi ed unde s anding o nuclea phenomena un ela ed o
deconfinemen , commonly called cold nuclea ma e (CNM) e -
ec s, es ic s he abili y o phenomenological models o desc ibe
he expe imen al da a on J/ψ p oduc ion in PbPb collisions. The
size o CNM e ec s can be quan ified by measu emen s in p o on-
nucleus o deu e on-nucleus collisions, which ha e been pu sued
a fixed a ge expe imen s as well as a RHIC and LHC [3]. The
ea u e o CNM d awing he highes a en ion o p o on-lead col-
lisions a he LHC is he modifica ion o he gluon flux coupling o
he cha m qua k pai . This modifica ion is o en ea ed wi hin a
collinea pa on dis ibu ion amewo k employing nuclea pa on
dis ibu ion unc ions (nPDFs) [11–15]. A low longi udinal mo-
men um ac ions xca ied by he pa on, calcula ions wi hin he
colou glass condensa e (CGC) e ec i e field heo y, desc ibing he
sa u a ion egime o QCD [16,17], a e equen ly employed. Se e al
calcula ions ha e been pu sued o quan i y nuclea modifica ions
o J/ψ p oduc ion in he collinea amewo k [18–21] o in he
CGC amewo k [22–24]. I has o be no ed ha he low-xgluon
con en o he nucleus is la gely uncons ained by expe imen al
da a a pe u ba i e scales. In addi ion, small-angle gluon adia ion
aking in o accoun in e e ence be ween ini ial and final s a e a-
dia ion, called cohe en ene gy loss, was p oposed as he dominan
nuclea modifica ion o qua konium p oduc ion in p o on-lead col-
lisions [25]. The disc imina ion be ween hese phenomena is a
s ong mo i a ion o he s udy o he p oduc ion o qua konium
as a ha d-scale p obe o QCD a high densi y.
The expe imen al esul s on J/ψ p oduc ion in p o on-lead col-
lisions based on he 2013 da a samples a √sNN =5 TeV published
by he LHC expe imen s ALICE, ATLAS, CMS and LHCb [26–31] can
be quali a i ely desc ibed by implemen a ions o he app oaches
desc ibed abo e in he kinema ic applicabili y ange o he calcu-
la ions [18–21,23–25]. No conclusion on he dominan mechanism
o nuclea modifica ion o J/ψ p oduc ion could be d awn.
The measu emen o an addi ional supp ession o he exci ed
s a e ψ(2S)by ALICE [32,33] and LHCb [34] in p o on-lead colli-
sions a √sNN =5 TeV and by PHENIX a RHIC [35,36] in a ious
collision sys ems a √sNN =0.2 TeV canno be explained by he
modifica ion o he gluon flux o by cohe en ene gy loss because
i would a ec he J/ψ and he ψ(2S)s a es in a simila way.
These measu emen s mo i a ed calcula ions in ol ing had onic
and pa onic in e ac ions influencing he e olu ion o he c¯
cpai
a e he fi s in e ac ion [37,38] o p o on(deu e on)-nucleus col-
lisions. Al hough he impac on J/ψ p oduc ion is gene ally small
h ps://doi.o g/10.1016/j.physle b.2017.09.058
0370-2693/©2017 The Au ho . Published by Else ie B.V. This is an open access a icle unde he CC BY license (h p://c ea i ecommons.o g/licenses/by/4.0/). Funded by
SCOAP3.
160 LHCb Collabo a ion / Physics Le e s B 774 (2017) 159–178
in hese models, i can be significan in apidi y anges wi h la ge
pa icle densi ies.
The measu emen o he nonp omp J/ψ p oduc ion p o ides
access o he p oduc ion o beau y had ons. The modifica ion o
hei kinema ic dis ibu ions in nucleus–nucleus collisions ca -
ies aluable in o ma ion abou he c ea ed ma e [3]. Simi-
la ly o di ec cha monium p oduc ion, he p oduc ion o beau y
had ons can be subjec o CNM e ec s al e ing he in e p e a ion
o nucleus–nucleus collision da a. Such e ec s can be p ecisely
measu ed in p o on-lead collisions.
The measu emen s o he p oduc ion o p omp J/ψ and non-
p omp J/ψ mesons, called J/ψ- om-b-had ons in he ollowing,
p esen ed in his le e a e impo an ing edien s o he unde -
s anding o he imp in s o deconfinemen in nucleus–nucleus col-
lisions. They a e based on la ge in eg a ed luminosi ies and on
highe collision ene gies han he ini ial measu emen s wi h he
2013 p o on-lead da a sample by he LHCb expe imen a √sNN =
5TeV[27].
2. De ec o , da a sample and obse ables
The LHCb de ec o [39,40] is a single-a m o wa d spec ome-
e co e ing he pseudo apidi y ange 2 <η<5, designed o he
s udy o pa icles con aining bo cqua ks. The de ec o includes
a high-p ecision acking sys em consis ing o a silicon-s ip e -
ex de ec o su ounding he in e ac ion egion [41], a la ge-a ea
silicon-s ip de ec o loca ed ups eam o a dipole magne wi h
a bending powe o abou 4Tm, and h ee s a ions o silicon-
s ip de ec o s and s aw d i ubes [42] placed downs eam o
he magne . The acking sys em p o ides a measu emen o mo-
men um o cha ged pa icles wi h a ela i e unce ain y ha a ies
om 0.5% a low momen um o 1.0% a 200 GeV/c. The minimum
dis ance o a ack o a p ima y e ex (PV), he impac pa ame-
e , is measu ed wi h a esolu ion o (15 +29/pT)μm, whe e pT
is he ans e se momen um in he LHCb ame, in GeV/c. Di e -
en ypes o cha ged had ons a e dis inguished using in o ma ion
om wo ing-imaging Che enko de ec o s [43]. Pho ons, elec-
ons and had ons a e iden ified by a calo ime e sys em consis ing
o scin illa ing-pad and p eshowe de ec o s, an elec omagne ic
calo ime e and a had onic calo ime e . Muons a e iden ified by a
sys em composed o al e na ing laye s o i on and mul iwi e p o-
po ional chambe s [44].
This analysis is based on da a acqui ed du ing he 2016 LHC
hea y-ion un, whe e p o ons and
208Pb ions we e colliding a a
cen e-o -mass ene gy pe nucleon pai o √sNN =8.16 TeV. Since
he ene gy pe nucleon in he p o on beam is la ge han in he
lead beam, he nucleon–nucleon cen e-o -mass sys em has a a-
pidi y in he labo a o y ame o 0.465 (−0.465), when he p o on
(lead) beam a els om he e ex de ec o owa ds he muon
chambe s. Consequen ly, he LHCb de ec o co e s wo di e en
accep ance egions:
1. 1.5 <y∗<4.0 when he p o on beam a els om he e ex
de ec o owa ds he muon chambe s,
2. −5.0 <y∗<−2.5 when he p o on beam a els om he
muon chambe s owa ds he e ex de ec o ,
whe e y∗is he apidi y in he cen e-o -mass ame o he col-
liding nucleons, wi h espec o he p o on beam di ec ion. In
his le e , he fi s configu a ion is deno ed pPb and he second
one Pbp. The da a samples co espond o an in eg a ed luminosi y
o 13.6 ±0.3 nb−1o pPb collisions and 20.8 ±0.5 nb−1o Pbp
collisions. The ins an aneous luminosi y o he majo i y o he
eco ded e en s anges be ween 0.5 and 1.0 ×1029 cm−2s−1. This
luminosi y co esponds on a e age o abou 0.1 o ewe collisions
pe bunch c ossing.
In his le e , we desc ibe he measu emen o he double-
di e en ial p oduc ion c oss-sec ions o J/ψ mesons as a unc ion
o pTand y∗in he anges 0 <pT<14 GeV/cand 1.5 <y∗<4.0
o pPb and −5.0 <y∗<−2.5 o Pbp. The measu emen is pe -
o med sepa a ely o p omp J/ψ mesons, i.e. p oduced di ec ly
in he ini ial ha d sca e ing o om he decay o an exci ed cha -
monium s a e p oduced di ec ly, and o J/ψ mesons coming om
he decay o a long-li ed b-had on, ei he di ec ly o ia an exci ed
cha monium s a e.
Nuclea e ec s a e quan ified by he nuclea modifica ion ac o ,
RpPb,
RpPb(pT,y∗)≡1
A
d2σpPb(pT,y∗)/dpTdy∗
d2σpp(pT,y∗)/dpTdy∗,(1)
whe e A =208 is he mass numbe o he Pb ion, d2σpPb(pT, y∗)/
dpTdy∗ he J/ψ p oduc ion c oss-sec ion in pPb o Pbpcollisions
and d2σpp(pT, y∗)/dpTdy∗ he J/ψ e e ence p oduc ion c oss-
sec ion in pp collisions a he same nucleon–nucleon cen e-o -
mass ene gy. The de e mina ion o he e e ence c oss-sec ion is
desc ibed in Sec. 5.1. In he absence o nuclea e ec s, he nuclea
modifica ion ac o is equal o uni y.
In addi ion o he nuclea modifica ion ac o , he obse able
RFB quan ifies he ela i e o wa d- o-backwa d p oduc ion a es.
The o wa d- o-backwa d a io is measu ed as he a io o c oss-
sec ions in he posi i e and nega i e y∗accep ances e alua ed in
he same absolu e y∗ alue anges,
RFB(pT,y∗)≡d2σpPb(pT,+y∗)/dpTdy∗
d2σpPb(pT,−y∗)/dpTdy∗.(2)
3. E en selec ion and c oss-sec ion de e mina ion
The J/ψ p oduc ion c oss-sec ion measu emen ollows he ap-
p oach desc ibed in Re . [45]. The double di e en ial J/ψ p oduc-
ion c oss-sec ion in each kinema ic bin o pTand y∗is compu ed
as
d2σ
dpTdy∗=N(J/ψ →μ+μ−)
L× o ×B(J/ψ →μ+μ−)×pT×y∗,(3)
whe e N(J/ψ →μ+μ−)is he numbe o econs uc ed p omp
J/ψ o J/ψ- om-b-had ons signal mesons,  o is he o al de-
ec ion efficiency in he gi en kinema ic bin, B(J/ψ →μ+μ−) =
(5.961 ±0.033)%[46] is he b anching ac ion o he decay
J/ψ →μ+μ−,pT=1GeV/cand y∗=0.5a e he bin wid hs
and Lis he in eg a ed luminosi y. The luminosi y is de e mined
wi h a an de Mee scan, which was pe o med o bo h beam
configu a ions. The luminosi y de e mina ion ollows closely he
app oach desc ibed in Re . [47].
3.1. Selec ion
An online e en selec ion is pe o med by a igge sys em con-
sis ing o a ha dwa e s age, which, o his analysis, selec s e en s
con aining a leas one muon wi h pTla ge han 500 MeV/c, ol-
lowed by a so wa e s age. In he fi s s age o he so wa e igge ,
wo muon acks wi h pT>500 MeV/ca e equi ed o o m a J/ψ
candida e wi h in a ian mass Mμ+μ−>2.5GeV/c2. In he second
s age, J/ψ candida es wi h an in a ian mass wi hin 120 MeV/c2
o he known alue o he J/ψ mass [46] a e selec ed.
In be ween he wo so wa e s ages, he alignmen and cali-
b a ion o he de ec o is pe o med in nea eal- ime [48]. The
LHCb Collabo a ion / Physics Le e s B 774 (2017) 159–178 161
same alignmen and calib a ion is p opaga ed o he offline econ-
s uc ion, ensu ing consis en and high-quali y pa icle iden ifica-
ion (PID) in o ma ion be ween he online and offline p ocessings.
The iden ical pe o mance o he online and offline econs uc ions
o e s he oppo uni y o pe o m physics analyses di ec ly using
candida es econs uc ed in he igge [49,50] as well as s o ing
all econs uc ed pa icles in he e en [51]. The p esen analysis
exploi s his ea u e o he fi s ime in p o on-lead collisions and
is using he online econs uc ion.
A he analysis s age, each e en is equi ed o ha e a leas
one PV econs uc ed om a leas ou acks measu ed in he
e ex de ec o . Fo e en s wi h mul iple PVs, he PV ha has he
smalles χ2
IP wi h espec o he J/ψ candida e is chosen. He e,
χ2
IP is defined as he di e ence be ween he e ex-fi χ2cal-
cula ed wi h he J/ψ meson candida e included in o excluded
om he PV fi . Each iden ified muon ack is equi ed o ha e
pT>750 MeV/c, 2 <η<5 and o ha e a good-quali y ack fi .
The wo muon acks o he J/ψ candida e mus o m a good-
quali y e ex, ep esen ing a igh e selec ion compa ed o he
so wa e igge equi emen .
3.2. De e mina ion o signal yields
The econs uc ed e ex o he J/ψ mesons o igina ing om
b-had on decays ends o be sepa a ed om he PVs. These J/ψ
mesons can hus be dis inguished om p omp J/ψ mesons by
exploi ing he pseudo p ope ime defined as
z≡(zJ/ψ −zPV)×MJ/ψ
pz
,(4)
whe e zJ/ψ and zPV a e he coo dina es along he beam axis o
he J/ψ decay e ex posi ion and o he PV posi ion, pzis he
zcomponen o he J/ψ momen um and MJ/ψ he known J/ψ
mass. The yields o J/ψ signal candida es, o he p omp and
J/ψ- om-b-had ons ca ego ies, a e de e mined om a simul a-
neous wo-dimensional unbinned maximum likelihood fi o hei
in a ian mass and pseudo p ope ime dis ibu ions, pe o med
independen ly o each (pT, y∗)bin.
In he fi unc ion, he in a ian -mass dis ibu ion o he signal
is desc ibed by a C ys al Ball unc ion [52], and he combina o-
ial backg ound by an exponen ial unc ion. The zdis ibu ion o
p omp J/ψ is desc ibed by a Di ac δ- unc ion δ( z), and ha o
J/ψ- om-b-had ons by an exponen ial unc ion o z>0. Bo h
o hem a e con ol ed wi h a iple-Gaussian esolu ion unc ion,
modelled om simula ion samples o ake in o accoun he e -
ex esolu ion. The backg ound zdis ibu ion is desc ibed by an
empi ical unc ion de i ed om he shape obse ed in he J/ψ
uppe mass sideband, 3200 <Mμ+μ−<3250 MeV/c2. This back-
g ound comes om muons o semilep onic b- and c-had on decays
and om pions and kaons decaying in he de ec o . The dis ibu-
ion is pa ame e ised as a sum o a Di ac δ- unc ion and o fi e
exponen ial unc ions, h ee o posi i e z alues and wo o neg-
a i e z alues, con ol ed wi h he sum o wo Gaussian unc ions.
An example o he in a ian mass and he pseudo p ope ime
dis ibu ions o one (pT, y∗)bin is shown in Fig. 1 o he pPb
and Pbpsamples, whe e he one-dimensional p ojec ions o he
fi esul a e d awn on he dis ibu ions. The wid h o he Gaus-
sian pa o he C ys al Ball unc ion a ies as a unc ion o pT
be ween 10 MeV/c2(15 MeV/c2) and 15 MeV/c2(33 MeV/c2) in
he lowes (highes ) apidi y bins in he labo a o y ame in bo h
beam configu a ions. Due o he apidi y shi s be ween he labo-
a o y ame and he nucleon–nucleon cen e-o -mass ames, he
wo examples do no co espond o he same apidi y ange in he
labo a o y while hey a e in he same |y∗| ange and, in his exam-
ple, he mass esolu ion in he Pbpconfigu a ion is di e en om
he one in he pPb configu a ion.
3.3. Efficiencies
The o al de ec ion efficiency,  o , is he p oduc o he geo-
me ical accep ance, and he efficiencies o cha ged ack econ-
s uc ion, pa icle iden ifica ion, candida e and igge selec ions.
Samples o simula ed e en s a e used o e alua e hese efficien-
cies excep o he pa icle iden ifica ion, which is de e mined in a
da a-d i en app oach. In he simula ion, pPb and Pbpminimum-
bias collisions a e gene a ed using he Epos e en gene a o uned
wi h he LHC model [53]. The J/ψ →μ+μ−signal candida es a e
gene a ed sepa a ely, wi h he Py hia8 gene a o [54] in pp col-
lisions wi h beams ha ing momen a equal o he momen a pe
nucleon o he pand Pb beams. They a e hen me ged wi h he
Epos minimum bias collisions o build he samples ou o which
he efficiencies a e compu ed. The decays o had ons a e gene -
a ed by E Gen [55], in which final-s a e elec omagne ic adia ion
is gene a ed wi h Pho os [56]. The in e ac ion o he pa icles wi h
he de ec o , and he de ec o esponse, a e implemen ed using he
Gean 4 oolki [57] as desc ibed in Re . [58].
The cha ged- ack econs uc ion efficiency is fi s e alua ed in
simula ion and is co ec ed using a da a-d i en ag-and-p obe ap-
p oach. Fo his pu pose, J/ψ candida es a e o med wi h one
ully- econs uc ed “ ag” ack and one “p obe” ack econs uc ed
pa ially wi h a subse o he acking sub-de ec o s and bo h iden-
ified as muons [59] in da a and in simula ion. The a io o he
single ack efficiencies om his ag-and-p obe app oach is used
as a co ec ion ac o . These co ec ion ac o s o each ack a e
hen applied o he signal candida es in he simula ion o ob ain
he in eg a ed efficiency in e e y kinema ic bin. The ag-and-p obe
co ec ion e alua ion is elying on he pPb and he Pbpda a sam-
ples, since he la ge acking calib a ion samples in pp collisions
a e limi ed in de ec o occupancy by an addi ional selec ion c i e-
ion on igge le el.
The muon iden ifica ion efficiency is de e mined o each ack
in da a wi h a ag-and-p obe me hod [60] aking in o accoun he
efficiency a ia ions as unc ion o ack momen um, pseudo apid-
i y and de ec o occupancy. Calib a ion samples o J/ψ mesons
a e selec ed applying a igh iden ifica ion c i e ion on one o he
muons and no iden ifica ion equi emen s o he second muon.
Howe e , he sizes o he calib a ion samples collec ed in pPb and
Pbpcollisions a e limi ed. The efficiency is hus e alua ed using
he calib a ion samples collec ed in pp collisions, aking in o ac-
coun he di e en de ec o occupancies be ween pp, pPb and Pbp
collisions, since his pa ame e a ec s he muon iden ifica ion pe -
o mance. The J/ψ simula ion is weigh ed wi h he efficiencies
de e mined pe ack in da a in o de o compu e he muon iden-
ifica ion efficiency in bins o J/ψ pTand y∗.
The ha dwa e and so wa e igge efficiencies ob ained om
he simula ion a e alida ed by compa ing hem wi h he efficien-
cies measu ed in con ol da a samples eco ded wi h minimum
and unbiased igge equi emen s, and con aining J/ψ candida es.
The o al efficiency in each (pT, y∗)bin,  o , is ound o be
he same o p omp J/ψ and J/ψ- om-b-had ons wi hin unce -
ain ies and is aken o be iden ical o he wo componen s. I
is shown in Fig. 2 o pPb and Pbpcollision da a, as a unc ion
o he J/ψ pTin he di e en apidi y bins. The unce ain ies a e
he quad a ic sums o he s a is ical unce ain ies and he unce -
ain ies associa ed o he da a-d i en co ec ions and alida ions,
desc ibed in he ollowing sec ion.
162 LHCb Collabo a ion / Physics Le e s B 774 (2017) 159–178
Fig. 1. (le ) In a ian mass and ( igh ) pseudo p ope ime dis ibu ions o J/ψ candida es in he bin 6 <pT<7GeV/cand 3.5 <|y∗| <4.0 o he ( op) pPb and (bo om)
Pbpsamples espec i ely. The black ci cles wi h e o ba s ep esen he LHCb da a. The p ojec ion o he esul o he fi desc ibed in he ex is d awn on each dis ibu ion:
he ed solid line is he o al fi unc ion, he blue dashed line is he p omp J/ψ signal componen , he pu ple solid line is he J/ψ- om-b-had ons signal componen and
he g een dashed line is he combina o ial backg ound componen .
Fig. 2. To al J/ψ de ec ion efficiency,  o , as a unc ion o he J/ψ pTin di e en y∗bins o (le ) pPb and ( igh ) Pbp.
4. Sys ema ic unce ain ies
The sys ema ic unce ain ies on he c oss-sec ion o p omp
J/ψ and J/ψ- om-b-had ons a e summa ised in Table 1 and
desc ibed in he ollowing. The o al de ec ion efficiency  o o
p omp J/ψ and J/ψ- om-bis ound o be equal wi hin he
s a is ical p ecision o he simula ion and all sys ema ic unce ain-
ies apply bo h o p omp J/ψ and J/ψ- om-b. Accep ance and
econs uc ion efficiencies o he J/ψ ec o meson depend on
i s pola isa ion a p oduc ion. The ALICE and he LHCb measu e-
men s in pp collisions [61,62] indica e a pola isa ion consis en
wi h ze o in mos o he kinema ic egion o he analysis p e-
LHCb Collabo a ion / Physics Le e s B 774 (2017) 159–178 163
Fig. 3. P oduc ion c oss-sec ion o ( op le ) p omp J/ψ in pPb, ( op igh ) J/ψ- om-b-had ons in pPb, (bo om le ) p omp J/ψ in Pbpand (bo om igh )
J/ψ- om-b-had ons in Pbp. The da a poin s a e placed a he cen e o he pTbins, he ho izon al e o ba s indica e he bin wid hs and he e ical e o ba s he
o al unce ain ies, calcula ed as quad a ic sums o he s a is ical and sys ema ic unce ain ies.
Table 1
Summa y o ela i e sys ema ic unce ain ies in pPb and Pbpon he c oss-sec ion o
p omp J/ψ and J/ψ- om-b-had ons. Unce ain ies ha a e compu ed bin-by-bin
a e exp essed as anges gi ing he minimum o maximum alues. The las column
indica es he co ela ion be ween bins wi hin he same beam configu a ion.
Sou ce pPb PbpCommen
Signal model 1.3% 1.3% co ela ed
Muon iden ifica ion 2.0%–11.0% 2.1%–15.3% co ela ed
T acking 3.0%–8.0% 5.9%–26.5% co ela ed
Ha dwa e igge 1.0%–10.9% 1.0%–7.4% co ela ed
So wa e igge 2.0% 2.0% co ela ed
Simula ion s a is ics 0.4%–7.0% 0.4%–26.2% unco ela ed
B(J/ψ →μ+μ−)0.05% 0.05% co ela ed
Luminosi y 2.6% 2.5% co ela ed
Pola isa ion – – no conside ed
sen ed in his le e . In his analysis, i is assumed ha he J/ψ
mesons a e p oduced wi h no pola isa ion in pPb and Pbpcolli-
sions a √sNN =8.16 TeV. No sys ema ic unce ain y is assigned
o he e ec s o pola isa ion.
The unce ain y on he J/ψ-meson yields, ela ed o he mod-
elling o he signal mass shape in he simul aneous mass and zfi ,
is s udied using an al e na i e fi model. In his model, he signal
mass shape is desc ibed by he sum o a C ys al Ball unc ion and
o a Gaussian unc ion. The ela i e di e ence o he signal yields
be ween he nominal and al e na i e fi s amoun s o 1.3%, which
is aken as a ully co ela ed sys ema ic unce ain y be ween bins.
The unce ain y associa ed o he shape o he zdis ibu ion is
negligible.
The unce ain y on he muon iden ifica ion has mul iple con-
ibu ions. The s a is ical unce ain y o he efficiencies is de i ed
om he calib a ion sample. The impac o he fini e binning in
muon momen um, pseudo apidi y and de ec o occupancy on he
efficiencies is es ima ed by a ying he binning scheme. Finally, an
unce ain y due o he me hod o de e mine he numbe o signal
candida es in he calib a ion samples is also conside ed. The o al
sys ema ic unce ain y due o hese h ee sou ces a ies be ween
2% and 15%. I is assumed o be ully co ela ed be ween bins. This
assump ion is alid o neighbou ing bins in accep ance. The bias
in oduced by his assump ion in he e alua ion o he o al sys-
ema ic unce ain y on in eg a ed quan i ies is negligible.
The da a-d i en co ec ions o he ack econs uc ion effi-
ciency ca y unce ain ies ela ed o he s a is ical unce ain ies
o he da a, domina ing in mos bins. In addi ion, a sys ema ic
unce ain y is ela ed o a po en ial bias o he selec ion c i e ia
which a e necessa y o ob ain a good signal o e backg ound a-
io o he de e mina ion o he efficiency co ec ions. A sys ema ic
unce ain y ela ed o he me hod is applied simila ly o pp colli-
sions and amoun s o 0.8% pe ack [59]. The o al unce ain y
ela ed o cha ged ack econs uc ion a ies om 3.0% o 8.0%
o pPb and 5.9% o 26.5% o Pbp, co ela ed be ween bins. The
unce ain y in he Pbpcase is la ge due o he smalle signal
o e backg ound a io o he pa ially econs uc ed candida es
used in he da a-d i en ag-and-p obe me hod compa ed o he
pPb case. The assump ion on he co ela ion is alid o neigh-
bou ing bins. The in oduced bias in he e alua ion o he o al
sys ema ic unce ain y on in eg a ed quan i ies is negligible. The
la ges unce ain ies appea a low ack momen a and hence low
J/ψ pT.
The igge efficiency is de e mined in da a and in simula ion
by he da a-d i en me hod desc ibed in he p e ious sec ion and in
Re . [49]. The unce ain ies ela ed o he igge a e es ima ed by
compa ing he esul s in simula ion and in da a. The unce ain y
on he ha dwa e igge efficiency is ound o a y be ween 1%
and 11%, and he unce ain y on he so wa e igge efficiency is

164 LHCb Collabo a ion / Physics Le e s B 774 (2017) 159–178
es ima ed o amoun o 2%. The igge unce ain ies a e assumed
o be ully co ela ed be ween bins.
The fini e size o he simula ion e en sample used o he e -
ficiency de e mina ion in oduces a sys ema ic unce ain y, which
a ies be ween 0.4% and 26.2% be ween he kinema ic bins o he
pPb and he Pbpsimula ion. The la ges ela i e alues appea
a high pTand la ge apidi ies and do no domina e he o e -
all unce ain ies. They di e be ween he pPb and Pbpcase due
o he di e en apidi y co e age in he cen e-o -mass sys em.
The b anching ac ion con ibu es o he c oss-sec ion unce ain y
wi h 0.05%. The luminosi y measu emen unce ain y amoun s o
2.6% in pPb and o 2.5% in Pbpcollisions. The unce ain y on all
o he applied selec ions is ound o be negligible based on compa -
isons be ween da a and simula ion signal dis ibu ions o selec ion
and kinema ics a iables.
5. Resul s
5.1. C oss-sec ions
The measu ed double-di e en ial c oss-sec ions o p omp J/ψ
and J/ψ- om-b-had ons in he pPb and Pbpda a samples a e
shown in Fig. 3, as a unc ion o pT o he conside ed y∗bins. The
nume ical alues a e p esen ed in Appendices A.1–A.4. The o al
c oss-sec ions, in eg a ed o e he measu emen anges, amoun o
σp omp J/ψ (1.5<y∗<4.0,pT<14 GeV/c)
=1625 ±4±117μb,
σJ/ψ- om-b-had ons(1.5<y∗<4.0,pT<14 GeV/c)
=276 ±2±20μb,
σp omp J/ψ (−5.0<y∗<−2.5,pT<14 GeV/c)
=1692 ±4±182μb,
σJ/ψ- om-b-had ons(−5.0<y∗<−2.5,pT<14 GeV/c)
=209 ±1±22μb,
whe e he fi s unce ain ies a e s a is ical and he second sys em-
a ic.
The ac ion o J/ψ- om-b-had ons, b, is de i ed om he
c oss-sec ion measu emen s. The ac ion bis defined as
b(pT,y∗)≡(5)
d2σJ/ψ- om-b-had ons/dpTdy∗
d2σp omp J/ψ /dpTdy∗+d2σJ/ψ- om-b-had ons/dpTdy∗.
Mos o he sys ema ic unce ain ies cancel in he de e mina ion
o b, which can hus be measu ed p ecisely. The alues o bas a
unc ion o pTin he di e en y∗bins a e shown in Fig. 4 o pPb
and Pbpand lis ed in Appendices A.5 and A.6. The alues o b
measu ed in pp collisions a a cen e-o -mass ene gy o 8TeV[63],
a e shown on he same figu e o compa ison. The di e ences ha
appea be ween he measu emen s pe o med in he wo collision
sys ems indica e, pa icula ly a low pT, di e en nuclea modifi-
ca ions o p omp J/ψ and b-qua k p oduc ion.
The ocus o his publica ion is he quan ifica ion o he nuclea
e ec s, compa ing in pa icula he J/ψ p oduc ion in p o on-lead
collisions wi h ha in pp collisions a he same ene gy. Follow-
ing he same app oach as in he p e ious LHCb publica ion on
J/ψ p oduc ion in pPb collisions a √sNN =5TeV[27], a pp
e e ence c oss-sec ion a √s=8.16 TeV is de e mined om an in-
e pola ion o he LHCb c oss-sec ion measu emen s a 7TeV[64],
8TeV[63] and 13 TeV [45]. The ex ac ed e e ence c oss-sec ion is
in ag eemen wi h he measu ed c oss-sec ion a √s=8TeV. Fo
Fig. 4. F ac ion o J/ψ- om-b-had ons, b, as a unc ion o pT o ( om op
o bo om) 1.5 <|y∗| <2.0, 2.0 <|y∗| <2.5, 2.5 <|y∗| <3.0, 3.0 <|y∗| <3.5,
3.5 <|y∗| <4.0, 4.0 <|y∗| <4.5and 4.5 <|y∗| <5.0. The da a poin s a e placed a
he cen e o he pTbins, he ho izon al e o ba s indica e he bin wid hs and he
e ical e o ba s he o al unce ain ies, calcula ed as quad a ic sums o he s a is-
ical and sys ema ic unce ain ies. Blue ci cles a e o pPb collisions, ed squa es o
Pbpcollisions and black iangles o pp collisions a 8TeV aken om Re . [63].
he edges o he apidi y ange in pPb collisions (1.5 <y∗<2.0)
and in Pbpcollisions (4.5 <y∗<5.0), which a e no co e ed by
he measu emen s in pp collisions, an ex apola ion is used based
on he expe imen al measu emen s. The in e pola ion and he ex-
apola ion me hods we e alida ed wi h ALICE and LHCb da a and
a e desc ibed in Re . [65].
The c oss-sec ion as a unc ion o y∗, in eg a ed o e pTin he
ange 0 <pT<14 GeV/cin pPb and Pbpcollisions, is shown in
Fig. 5. The c oss-sec ion is compa ed wi h he e e ence c oss-
sec ion o p omp J/ψ and J/ψ- om-b-had ons p oduc ion in
pp collisions a √s=8.16 TeV, mul iplied by he Pb mass numbe
A =208. The o al ela i e unce ain ies on he pp c oss-sec ion
ange be ween 3% and 11% and a e la ges in he bins based on ex-
apola ions. The c oss-sec ions as a unc ion o pT, in eg a ed o e
he ange 1.5 <y∗<4.0 o pPb and −5.0 <y∗<−2.5 o Pbp,
and he co esponding scaled pp c oss-sec ions a e ep esen ed in
Fig. 6. In his case, he o al ela i e unce ain ies on he pp e e -
ence c oss-sec ion a y be ween 3% and 18%.
LHCb Collabo a ion / Physics Le e s B 774 (2017) 159–178 165
Fig. 5. Absolu e p oduc ion c oss-sec ions o (le ) p omp J/ψ and ( igh ) J/ψ- om-b-had ons, as a unc ion o y∗, in eg a ed o e he ange 0 <pT<14 GeV/c. The black
ci cles a e he pPb and Pbp alues and he ed open squa es he alues o pp collisions a he same ene gy, mul iplied by he Pb mass numbe A =208. The ho izon al
e o ba s a e he bin wid hs and e ical e o ba s he o al unce ain ies.
Fig. 6. Absolu e p oduc ion c oss-sec ions o ( op le ) p omp J/ψ in pPb, ( op igh ) p omp J/ψ in Pbp, (bo om le ) J/ψ- om-b-had ons in Pbpand (bo om le )
J/ψ- om-b-had ons in Pbp, as a unc ion o pTand in eg a ed o e he apidi y ange o he analysis. The black ci cles a e he pPb and Pbp alues and he ed open
squa es he alues o pp collisions a he same ene gy, mul iplied by he Pb mass numbe A =208, in eg a ed o e he same apidi y anges. The ho izon al e o ba s a e
he bin wid hs and e ical e o ba s he o al unce ain ies.
5.2. Nuclea modifica ion ac o s
The nuclea modifica ion ac o RpPb defined in Eq. (1) is com-
pu ed om he p omp J/ψ and J/ψ- om-b-had ons p oduc ion
c oss-sec ions in pp and pPb o Pbpcollisions. The sys ema ic
unce ain ies a e assumed o be unco ela ed be ween he mea-
su emen s in p o on-lead and in pp collisions. The nuclea modi-
fica ion ac o s o p omp J/ψ and J/ψ- om-b-had ons p oduc-
ion as unc ions o pTo y∗, in eg a ing o e he o he a iable,
a e shown in Figs. 7 and 8, espec i ely. The nume ical alues a e
a ailable in Appendix B. The esul s a √sNN =5TeV[27] a e also
depic ed on Fig. 8 and a e in good ag eemen wi h he new and
mo e p ecise esul s a √sNN =8.16 TeV.
A o wa d apidi y, 1.5 <y∗<4.0, a s ong supp ession o
up o 50% is obse ed in he case o p omp J/ψ p oduc ion
a low pT(Fig. 7). This beha iou esul s in a s ong supp es-
sion in he nuclea modifica ion ac o as a unc ion o apidi y
shown in Fig. 8. Wi h inc easing pT, RpPb app oaches uni y and
he supp ession is s onge a mo e o wa d apidi ies. The p o-
duc ion o J/ψ- om-b-had ons is also supp essed compa ed o
166 LHCb Collabo a ion / Physics Le e s B 774 (2017) 159–178
Fig. 7. J/ψ nuclea modifica ion ac o , RpPb, in eg a ed o e y∗in he analysis ange, as a unc ion o pT o ( op le ) p omp J/ψ in pPb, (bo om le ) J/ψ- om-b-had ons
in pPb, ( op igh ) p omp J/ψ in Pbpand (bo om igh ) J/ψ- om-b-had ons in Pbp. Ho izon al e o ba s a e he bin wid hs, e ical e o ba s he o al unce ain ies.
The black ci cles a e he alues measu ed in his le e and he colou ed a eas he heo e ical p edic ions om he models de ailed in he ex wi h hei unce ain ies.
Fig. 8. J/ψ nuclea modifica ion ac o , RpPb, in eg a ed o e pTin he ange 0 <pT<14 GeV/c, as a unc ion o y∗ o (le ) p omp J/ψ and ( igh ) J/ψ- om-b-had ons.
The ho izon al e o ba s a e he bin wid hs and e ical e o ba s he o al unce ain ies. The black ci cles a e he alues measu ed in his le e , he ed squa es he alues
measu ed a
√sNN =5TeV om Re . [27] and he colou ed a eas he heo e ical compu a ions om he models de ailed in he ex , wi h hei unce ain ies.
ha in pp collisions a o wa d apidi ies, al hough o a lesse de-
g ee, as shown in Fig. 8. No dependence as a unc ion o apidi y
can be obse ed wi hin he expe imen al unce ain ies. The depen-
dence as a unc ion o he ans e se momen um is weake o
J/ψ- om-b-had ons compa ed o p omp J/ψ, bu he nuclea
modifica ion ac o is also app oaching uni y a high ans e se
momen um.
A backwa d apidi y, −5.0 <y∗<−2.5, a weake supp ession
o p omp J/ψ p oduc ion a low pTis obse ed, o up o 25%.
Simila ly o he o wa d- apidi y egion, he supp ession is weak-
ening and he nuclea modifica ion ac o is app oaching alues
consis en wi h uni y a high ans e se momen um. The nuclea
modifica ion ac o as a unc ion o apidi y shows a weak supp es-
sion wi h no isible apidi y dependence wi hin expe imen al un-
ce ain ies. The nuclea modifica ion ac o o J/ψ- om-b-had ons
a backwa d apidi y is consis en wi h uni y o e he ull kine-
ma ic egion.
The measu emen s o p omp J/ψ nuclea modifica ion ac o s
a e compa ed in Figs. 7 and 8wi h h ee g oups o calcula ions:
LHCb Collabo a ion / Physics Le e s B 774 (2017) 159–178 167
1. collinea ac o isa ion using di e en nPDFs [66,67] (labelled
“HELAC-Onia wi h EPS09LO”, “HELAC-Onia wi h nCTEQ15” and
“HELAC-Onia wi h EPS09NLO” on he figu es),
2. CGC e ec i e field heo y in he dilu e-dense app oxima ion
aking in o accoun he dense na u e o he Pb nucleus, bu
app oxima ing he p o on as a dilu e pa on sou ce [24,68] (la-
belled “CGC”),
3. cohe en ene gy loss calcula ing he impac o low angle co-
he en gluon adia ion du ing he c ossing o he nucleus [25]
(labelled “Ene gy Loss”).
The CGC calcula ions [24,68] desc ibe well he beha iou o he
p omp J/ψ da a a o wa d apidi y. A backwa d apidi y, his
app oach is no a ailable due o he b eakdown o he dilu e ap-
p oxima ion o he pa ons in he p o on. The unce ain ies ake
in o accoun he a ia ion o he cha m-qua k mass and he ac-
o isa ion scale. These unce ain ies la gely cancel in his a io o
c oss-sec ions. The collinea calcula ions a e based on he HELAC-
Onia e en gene a o [66,67], uned o ep oduce p omp J/ψ
c oss-sec ion measu emen s in pp collision [21] and combined
wi h di e en se s o nPDFs: nCTEQ15 [14] and EPS09 a leading
(LO) and a nex - o-leading o de (NLO) [12]. Howe e , he la ge
unce ain ies e eal he missing expe imen al cons ain s on he
gluon densi y in he nucleus a low xp obed by he measu emen s
in he LHCb de ec o accep ance. A backwa d apidi ies, he expe -
imen al poin s a e ound a he lowe bound o sligh ly below he
heo e ical unce ain y bands and exhibi a di e en apidi y shape
om he calcula ions. The cohe en ene gy loss model [25] is able
o p o ide he o e all shape o he supp ession, bu o e es ima es
he expe imen al da a a o wa d apidi ies. The unce ain y o his
calcula ion eflec s he allowed a ia ion o he pa ame e isa ion o
pp da a used in he model and he allowed a ia ion o he only
ee model pa ame e om fi s o o he measu emen s.
The measu emen s o J/ψ- om-b-had ons nuclea modifica-
ion ac o s a e compa ed in Figs. 7 and 8wi h a pe u ba i e QCD
calcula ion a fixed-o de nex - o-leading-loga i hms (FONLL) [69,
70] coupled wi h he EPS09 nPDF se a nex - o-leading o de [12]
(labelled “FONLL wi h EPS09NLO” on he figu es). The displayed
unce ain ies co espond o he unce ain ies om he nPDF, which
a e o simila size o o smalle han he o al expe imen al unce -
ain ies. The pTdependence o he expe imen al da a is desc ibed
wi hin unce ain ies by he model. Howe e , he calcula ion ends
o show la ge nuclea modifica ion ac o s han he da a. This
endency is confi med by he nuclea modifica ion ac o as a unc-
ion o apidi y, whe e he mos p ecise expe imen al da a poin s
a e below he model unce ain y band. Fu he mo e, a backwa d
apidi y, he slope o he heo e ical cu e is no seen in he ex-
pe imen al da a.
Finally, ecen measu emen s ha e shown ha long- ange col-
lec i e e ec s, which ha e p e iously been obse ed in ela i ely
la ge nucleus–nucleus collision sys ems, may also be p esen in
smalle collision sys ems a la ge cha ged-pa icle mul iplici es
[71–74]. I hese e ec s ha e a hyd odynamic o igin, momen-
um aniso opies a he qua k le el can a ise and may mod-
i y he dis ibu ion o obse ed hea y-qua k had ons [75]. How-
e e , he expec ed magni ude o hese e ec s on p omp J/ψ
o J/ψ- om-b-had ons p oduc ion has no ye been calcula ed.
Since he measu emen s in his le e a e in eg a ed o e cha ged-
pa icle mul iplici y, po en ial modifica ions in high-mul iplici y
e en s a e dilu ed.
5.3. Fo wa d- o-backwa d a ios
Figs. 9 and 10 show he o wa d- o-backwa d a io, RFB, o
he p oduc ion o p omp J/ψ and J/ψ- om-b-had ons, in he
o e lapping accep ance be ween he wo beam configu a ions, as
unc ions o ans e se momen um and apidi y, espec i ely. The
nume ical esul s a e lis ed in Appendix C. In he RFB a io, mos
o he sys ema ic unce ain ies cancel. The measu emen s o RFB
a √sNN =5TeV[27] a e compa ed wi h he measu emen s a
8.16 TeV and a e ound o be in ag eemen . They a e compa ed
wi h he heo e ical compu a ions based on collinea ac o isa ion
wi h di e en nPDFs desc ibed in he p e ious sec ion.
The calcula ions wi h di e en nPDFs do no ully co e he ex-
pe imen al poin s wi hin unce ain ies in pa icula a low pTwi h
he excep ion o he EPS09LO combina ion, which has conside -
ably la ge unce ain ies. Howe e , a de ailed analysis o heo e ical
co ela ions in he pT-dependen RFB may be in e es ing o u-
u e s udies in o de o quan i y mo e p ecisely he disc epancies.
The cohe en ene gy loss calcula ion is compa ed wi h he apid-
i y dependence o he expe imen al da a poin s in Fig. 10. I shows
wi hin i s small unce ain ies a sligh ly di e en slope om he
expe imen al da a poin s and p edic s la ge alues in he bin a
smalles |y∗|.
The RFB a io o J/ψ- om-b-had ons in Fig. 9 shows a ising
end as a unc ion o ans e se momen um s a ing om a alue
0.7 a low pT owa ds alues consis en wi h uni y a high pT. The
apidi y dependence o RFB in Fig. 10 is consis en wi h a fla be-
ha iou wi h a cen al alue o 0.8.
6. Conclusions
The di e en ial p oduc ion c oss-sec ions o p omp J/ψ and
J/ψ- om-b-had ons in pPb and Pbpcollisions a
√sNN =8.16 TeV
a e measu ed in he ange 0 <pT<14 GeV/c. The nuclea mod-
ifica ion ac o s a e simila o he findings a a collision ene gy
o √sNN =5TeV, bu wi h inc eased p ecision hanks o 10 and
40 imes la ge da a se s in pPb and Pbpcollisions, espec i ely.
A supp ession o p omp J/ψ p oduc ion compa ed o pp colli-
sions o up o 50% (25%) in pPb (Pbp) a he lowes ans e se
momen um is obse ed. In bo h configu a ions, he nuclea mod-
ifica ion ac o app oaches uni y asymp o ically a he highes pT.
Theo e ical calcula ions o he nuclea modifica ion ac o based
on collinea ac o isa ion wi h di e en nuclea pa on dis ibu-
ion unc ions, cohe en ene gy loss as well as he colou glass
condensa e model can accoun o he majo i y o he obse ed
dependences. Fo he fi s ime, beau y-had on p oduc ion is mea-
su ed p ecisely down o pT=0a he LHC in pPb and Pbp
collisions. In pPb, a weak supp ession a he lowes ans e se
momen a is obse ed, whe eas in Pbpno significan de ia ion
om uni y in he nuclea modifica ion ac o is ound. This weak
modifica ion o beau y p oduc ion in p o on-ion collisions is an
impo an ing edien o he in es iga ion o he modifica ions
o beau y p oduc ion in hea y-ion collisions. Al hough he p e-
sen ed measu emen s ha e imp o ed p ecision, i is no possible
o single ou he main nuclea modifica ion mechanism be ween
di e en phenomenological app oaches o cha monium p oduc-
ion in p o on-lead collisions a he TeV scale. This measu e-
men o J/ψ p oduc ion is he fi s s ep owa ds measu emen s
o o he cha monium s a es as well as complemen a y obse -
ables like D ell–Yan p oduc ion, o imp o e he unde s anding o
quan um ch omodynamics a low xand in dense nuclea en i on-
men s.
Acknowledgemen s
We hank G. B uno, B. Ducloué, H. Shao, J.-Ph. Lansbe g and
F. A léo o p o iding heo e ical p edic ions o J/ψ p oduc ion
in pPb and Pbpcollisions in he LHCb accep ance ange. We ex-
p ess ou g a i ude o ou colleagues in he CERN accele a o de-
174 LHCb Collabo a ion / Physics Le e s B 774 (2017) 159–178
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M. Pa el 55, C. Pa ignani 15,e, A. Pea ce40, A. Pelleg ino 43, G. Penso 26, M. Pepe Al a elli 40, S. Pe azzini 40,
P. Pe e 5, L. Pesca o e 41, K. Pe idis 48, A. Pe olini 20,h, A. Pe o 68, M. Pe uzzo 22,q,
E. Pica os e Olloqui 38, B. Pie zyk 4, M. Pikies 27, D. Pinci 26, A. Pis one20,h, A. Piucci 12, V. Placin a 30,
S. Play e 52, M. Plo Casasus 39, T. Poikela 40, F. Polci 8, M. Poli Lene 19, A. Poluek o 50,36, I. Polyako 61,
E. Polyca po 2, G.J. Pome y 48, S. Ponce 40, A. Popo 37, D. Popo 11,40, S. Posla skii 37, C. Po e a 2,
E. P ice 48, J. P iscianda o 39, C. P ou e 48, V. Puga ch 46, A. Puig Na a o 42, H. Pullen 57, G. Punzi 24,p,
W. Qian 50, R. Quagliani 7,48, B. Quin ana 5, B. Rachwal 28, J.H. Rademacke 48, M. Rama 24,
M. Ramos Pe nas 39, M.S. Rangel 2, I. Raniuk 45,†, F. Ra niko 35, G. Ra en 44, M. Ra onel Salzgebe 40,
M. Reboud 4, F. Redi 55, S. Reiche 10, A.C. dos Reis1, C. Remon Alepuz 70, V. Renaudin 7, S. Riccia di 51,
S. Richa ds 48, M. Rihl 40, K. Rinne 54, V. Ri es Molina 38, P. Robbe 7, A.B. Rod igues 1, E. Rod igues 59,
J.A. Rod iguez Lopez 66, P. Rod iguez Pe ez 56,†, A. Rogozhniko 35, S. Roise 40, A. Rollings 57,
V. Romano skiy 37, A. Rome o Vidal 39, J.W. Ronayne 13, M. Ro ondo 19, M.S. Rudolph 61, T. Ru 40,
P. Ruiz Valls 70, J. Ruiz Vidal 70, J.J. Sabo ido Sil a 39, E. Sadykho 32, N. Sagido a 31, B. Sai a 16, ,
V. Salus ino Guima aes 1, D. Sanchez Gonzalo 38, C. Sanchez Mayo domo 70, B. Sanma in Sedes 39,
R. San acesa ia 26, C. San ama ina Rios 39, M. San ima ia 19, E. San o e i 25,j, G. Sa pis 56, A. Sa i 26,
C. Sa iano 26,s, A. Sa a 25, D.M. Saunde s 48, D. Sa ina 32,33, S. Schael 9, M. Schellenbe g 10,
M. Schille 53, H. Schindle 40, M. Schlupp 10, M. Schmelling 11, T. Schmelze 10, B. Schmid 40,
O. Schneide 41, A. Schoppe 40, H.F. Sch eine 59, K. Schube 10, M. Schubige 41, M.-H. Schune 7,
R. Schwemme 40, B. Sciascia 19, A. Sciubba 26,k, A. Semenniko 32, A. Se gi 47, N. Se a 42, J. Se ano 6,
L. Ses ini 23, P. Sey e 40, M. Shapkin 37, I. Shapo al 45, Y. Shcheglo 31, T. Shea s 54, L. Shekh man 36,w,
V. She chenko 68, B.G. Siddi 17,40, R. Sil a Cou inho 42, L. Sil a de Oli ei a 2, G. Simi 23,o, S. Simone 14,d,
M. Si endi 49, N. Skidmo e 48, T. Skwa nicki 61, E. Smi h 55, I.T. Smi h 52, J. Smi h 49, M. Smi h 55,
l. Soa es La a 1, M.D. Sokolo 59, F.J.P. Sole 53, B. Souza De Paula 2, B. Spaan 10, P. Sp adlin 53,
S. S idha an 40, F. S agni 40, M. S ahl 12, S. S ahl 40, P. S e ko 41, S. S e ko a 55, O. S einkamp 42,
S. S emmle 12, O. S enyakin 37, H. S e ens 10, S. S one 61, B. S o aci 42, S. S acka 24,p, M.E. S amaglia 41,
M. S a iciuc 30, U. S aumann 42, L. Sun 64, W. Su cli e 55, K. Swien ek 28, V. Sy opoulos 44,
LHCb Collabo a ion / Physics Le e s B 774 (2017) 159–178 177
M. Szczekowski 29, T. Szumlak 28, M. Szymanski 63, S. T’Jampens 4, A. Taydugano 6, T. Tekampe 10,
G. Tella ini 17,g, F. Teube 40, E. Thomas 40, J. an Tilbu g 43, M.J. Tilley 55, V. Tisse and 4, M. Tobin 41,
S. Tolk 49, L. Tomasse i 17,g, D. Tonelli 24, S. Topp-Joe gensen 57, F. To iello 61,
R. Tou inho Jadallah Aoude 1, E. Tou nefie 4, M. T aill 53, M.T. T an 41, M. T esch 42, A. T iso ic 40,
A. Tsa ego od se 6, P. Tsopelas 43, A. Tully 49, N. Tuning 43, A. Ukleja29, A. Us yuzhanin 35, U. Uwe 12,
C. Vacca 16, , A. Vagne 69, V. Vagnoni 15,40, A. Valassi 40, S. Vala 40, G. Valen i 15, R. Vazquez Gomez 19,
P. Vazquez Reguei o 39, S. Vecchi 17, M. an Veghel 43, J.J. Vel huis 48, M. Vel i 18, , G. Veneziano 57,
A. Venka eswa an 61, T.A. Ve lage 9, M. Ve ne 5, M. Ves e inen 57, J.V. Viana Ba bosa 40, B. Viaud 7,
D. Viei a 63, M. Viei es Diaz 39, H. Viemann 67, X. Vilasis-Ca dona 38,m, M. Vi i 49, V. Volko 33,
A. Vollha d 42, B. Voneki 40, A. Vo obye 31, V. Vo obye 36,w, C. Voß 9, J.A. de V ies 43,
C. Vázquez Sie a 39, R. Waldi 67, C. Wallace 50, R. Wallace 13, J. Walsh 24, J. Wang 61, D.R. Wa d 49,
H.M. Wa k 54, N.K. Wa son 47, D. Websdale 55, A. Weiden42, M. Whi ehead 40, J. Wich 50,
G. Wilkinson 57,40, M. Wilkinson 61, M. Williams 56, M.P. Williams 47, M. Williams 58, T. Williams 47,
F.F. Wilson 51, J. Wimbe ley 60, M.A. Winn 7,∗, J. Wishahi 10, W. Wislicki 29, M. Wi ek 27, G. Wo mse 7,
S.A. Wo on 49, K. W aigh 53, K. Wyllie 40, Y. Xie 65, Z. Xu 4, Z. Yang 3, Z. Yang 60, Y. Yao 61, H. Yin 65,
J. Yu 65, X. Yuan 61, O. Yushchenko 37, K.A. Za ebski 47, M. Za e yae 11,c, L. Zhang 3, Y. Zhang 7,
A. Zhelezo 12, Y. Zheng 63, X. Zhu 3, V. Zhuko 33, J.B. Zonne eld 52, S. Zucchelli 15
1Cen o B asilei o de Pesquisas Físicas (CBPF), Rio de Janei o, B azil
2Uni e sidade Fede al do Rio de Janei o (UFRJ), Rio de Janei o, B azil
3Cen e o High Ene gy Physics, Tsinghua Uni e si y, Beijing, China
4LAPP, Uni e si é Sa oie Mon -Blanc, CNRS/IN2P3, Annecy-Le-Vieux, F ance
5Cle mon Uni e si é, Uni e si é Blaise Pascal, CNRS/IN2P3, LPC, Cle mon -Fe and, F ance
6CPPM, Aix-Ma seille Uni e si é, CNRS/IN2P3, Ma seille, F ance
7LAL, Uni e si é Pa is-Sud, CNRS/IN2P3, O say, F ance
8LPNHE, Uni e si é Pie e e Ma ie Cu ie, Uni e si é Pa is Dide o , CNRS/IN2P3, Pa is, F ance
9I. Physikalisches Ins i u , RWTH Aachen Uni e si y, Aachen, Ge many
10 Fakul ä Physik, Technische Uni e si ä Do mund, Do mund, Ge many
11 Max-Planck-Ins i u ü Ke nphysik (MPIK), Heidelbe g, Ge many
12 Physikalisches Ins i u , Rup ech -Ka ls-Uni e si ä Heidelbe g, Heidelbe g, Ge many
13 School o Physics, Uni e si y College Dublin, Dublin, I eland
14 Sezione INFN di Ba i, Ba i, I aly
15 Sezione INFN di Bologna, Bologna, I aly
16 Sezione INFN di Caglia i, Caglia i, I aly
17 Uni e si a e INFN, Fe a a, Fe a a, I aly
18 Sezione INFN di Fi enze, Fi enze, I aly
19 Labo a o i Nazionali dell’INFN di F asca i, F asca i, I aly
20 Sezione INFN di Geno a, Geno a, I aly
21 Uni e si a & INFN, Milano-Bicocca, Milano, I aly
22 Sezione di Milano, Milano, I aly
23 Sezione INFN di Pado a, Pado a, I aly
24 Sezione INFN di Pisa, Pisa, I aly
25 Sezione INFN di Roma To Ve ga a, Roma, I aly
26 Sezione INFN di Roma La Sapienza, Roma, I aly
27 Hen yk Niewodniczanski Ins i u e o Nuclea Physics Polish Academy o Sciences, K aków, Poland
28 AGH – Uni e si y o Science and Technology, Facul y o Physics and Applied Compu e Science, K aków, Poland
29 Na ional Cen e o Nuclea Resea ch (NCBJ), Wa saw, Poland
30 Ho ia Hulubei Na ional Ins i u e o Physics and Nuclea Enginee ing, Bucha es -Magu ele, Romania
31 Pe e sbu g Nuclea Physics Ins i u e (PNPI), Ga china, Russia
32 Ins i u e o Theo e ical and Expe imen al Physics (ITEP), Moscow, Russia
33 Ins i u e o Nuclea Physics, Moscow S a e Uni e si y (SINP MSU), Moscow, Russia
34 Ins i u e o Nuclea Resea ch o he Russian Academy o Sciences (INR RAN), Moscow, Russia
35 Yandex School o Da a Analysis, Moscow, Russia
36 Budke Ins i u e o Nuclea Physics (SB RAS), No osibi sk, Russia
37 Ins i u e o High Ene gy Physics (IHEP), P o ino, Russia
38 ICCUB, Uni e si a de Ba celona, Ba celona, Spain
39 Uni e sidad de San iago de Compos ela, San iago de Compos ela, Spain
40 Eu opean O ganiza ion o Nuclea Resea ch (CERN), Gene a, Swi ze land
41 Ins i u e o Physics, Ecole Poly echnique Fédé ale de Lausanne (EPFL), Lausanne, Swi ze land
42 Physik-Ins i u , Uni e si ä Zü ich, Zü ich, Swi ze land
43 Nikhe Na ional Ins i u e o Suba omic Physics, Ams e dam, The Ne he lands
44 Nikhe Na ional Ins i u e o Suba omic Physics and VU Uni e si y Ams e dam, Ams e dam, The Ne he lands
45 NSC Kha ki Ins i u e o Physics and Technology (NSC KIPT), Kha ki , Uk aine
46 Ins i u e o Nuclea Resea ch o he Na ional Academy o Sciences (KINR), Kyi , Uk aine
47 Uni e si y o Bi mingham, Bi mingham, Uni ed Kingdom
48 H.H. Wills Physics Labo a o y, Uni e si y o B is ol, B is ol, Uni ed Kingdom
49 Ca endish Labo a o y, Uni e si y o Camb idge, Camb idge, Uni ed Kingdom
50 Depa men o Physics, Uni e si y o Wa wick, Co en y, Uni ed Kingdom
51 STFC Ru he o d Apple on Labo a o y, Didco , Uni ed Kingdom
52 School o Physics and As onomy, Uni e si y o Edinbu gh, Edinbu gh, Uni ed Kingdom
53 School o Physics and As onomy, Uni e si y o Glasgow, Glasgow, Uni ed Kingdom
178 LHCb Collabo a ion / Physics Le e s B 774 (2017) 159–178
54 Oli e Lodge Labo a o y, Uni e si y o Li e pool, Li e pool, Uni ed Kingdom
55 Impe ial College London, London, Uni ed Kingdom
56 School o Physics and As onomy, Uni e si y o Manches e , Manches e , Uni ed Kingdom
57 Depa men o Physics, Uni e si y o Ox o d, Ox o d, Uni ed Kingdom
58 Massachuse s Ins i u e o Technology, Camb idge, MA, Uni ed S a es
59 Uni e si y o Cincinna i, Cincinna i, OH, Uni ed S a es
60 Uni e si y o Ma yland, College Pa k, MD, Uni ed S a es
61 Sy acuse Uni e si y, Sy acuse, NY, Uni ed S a es
62 Pon i ícia Uni e sidade Ca ólica do Rio de Janei o (PUC-Rio), Rio de Janei o, B azil x
63 Uni e si y o Chinese Academy o Sciences, Beijing, China y
64 School o Physics and Technology, Wuhan Uni e si y, Wuhan, China y
65 Ins i u e o Pa icle Physics, Cen al China No mal Uni e si y, Wuhan, Hubei, China y
66 Depa amen o de Fisica, Uni e sidad Nacional de Colombia, Bogo a, Colombia z
67 Ins i u ü Physik, Uni e si ä Ros ock, Ros ock, Ge many aa
68 Na ional Resea ch Cen e Ku cha o Ins i u e, Moscow, Russia ab
69 Na ional Resea ch Tomsk Poly echnic Uni e si y, Tomsk, Russia ab
70 Ins i u o de Fisica Co puscula , Cen o Mix o Uni e sidad de Valencia – CSIC, Valencia, Spain ac
71 Van Swinde en Ins i u e, Uni e si y o G oningen, G oningen, The Ne he lands ad
*Co esponding au ho .
E-mail add ess: [email p o ec ed]h (M.A. Winn).
aUni e sidade Fede al do T iângulo Minei o (UFTM), Ube aba-MG, B azil.
bLabo a oi e Lep ince-Ringue , Palaiseau, F ance.
cP.N. Lebede Physical Ins i u e, Russian Academy o Science (LPI RAS), Moscow, Russia.
dUni e si à di Ba i, Ba i, I aly.
eUni e si à di Bologna, Bologna, I aly.
Uni e si à di Caglia i, Caglia i, I aly.
gUni e si à di Fe a a, Fe a a, I aly.
hUni e si à di Geno a, Geno a, I aly.
iUni e si à di Milano Bicocca, Milano, I aly.
jUni e si à di Roma To Ve ga a, Roma, I aly.
kUni e si à di Roma La Sapienza, Roma, I aly.
lAGH -Uni e si y o Science and Technology, Facul y o Compu e Science, Elec onics and Telecommunica ions, K aków, Poland.
mLIFAELS, La Salle, Uni e si a Ramon Llull, Ba celona, Spain.
nHanoi Uni e si y o Science, Hanoi, Vie Nam.
oUni e si à di Pado a, Pado a, I aly.
pUni e si à di Pisa, Pisa, I aly.
qUni e si à degli S udi di Milano, Milano, I aly.
Uni e si à di U bino, U bino, I aly.
sUni e si à della Basilica a, Po enza, I aly.
Scuola No male Supe io e, Pisa, I aly.
uUni e si à di Modena e Reggio Emilia, Modena, I aly.
Iligan Ins i u e o Technology (IIT), Iligan, Philippines.
wNo osibi sk S a e Uni e si y, No osibi sk, Russia.
xAssocia ed o Uni e sidade Fede al do Rio de Janei o (UFRJ), Rio de Janei o, B azil.
yAssocia ed o Cen e o High Ene gy Physics, Tsinghua Uni e si y, Beijing, China.
zAssocia ed o LPNHE, Uni e si é Pie e e Ma ie Cu ie, Uni e si é Pa is Dide o , CNRS/IN2P3, Pa is, F ance.
aa Associa ed o Physikalisches Ins i u , Rup ech -Ka ls-Uni e si ä Heidelbe g, Heidelbe g, Ge many.
ab Associa ed o Ins i u e o Theo e ical and Expe imen al Physics (ITEP), Moscow, Russia.
ac Associa ed o ICCUB, Uni e si a de Ba celona, Ba celona, Spain.
ad Associa ed o Nikhe Na ional Ins i u e o Suba omic Physics, Ams e dam, The Ne he lands.
†Deceased.