Observation of ηc(2S) →pp¯ and search for X(3872) →pp¯ decays

Physics Le e s B 769 (2017) 305–313
Con en s lis s a ailable a ScienceDi ec
Physics Le e s B
www.else ie .com/loca e/physle b
Obse a ion o ηc(2S) →p¯
pand sea ch o X(3872) →p¯
pdecays
.LHCb Collabo a ion
a i c l e i n o a b s a c
A icle his o y:
Recei ed 22 July 2016
Recei ed in e ised o m 23 Feb ua y 2017
Accep ed 23 Ma ch 2017
A ailable online 28 Ma ch 2017
Edi o : M. Dose
The fi s obse a ion o he decay ηc(2S) →p¯
pis epo ed using p o on–p o on collision da a co e-
sponding o an in eg a ed luminosi y o 3.0 b
−1 eco ded by he LHCb expe imen a cen e-o -mass
ene gies o 7 and 8 TeV. The ηc(2S) esonance is p oduced in he decay B+→[c¯
c]K+. The p oduc o
b anching ac ions no malised o ha o he J/ψ in e media e s a e, Rηc(2S), is measu ed o be
Rηc(2S)≡
B(B+→ηc(2S)K+)×B(ηc(2S)→p¯
p)
B(B+→J/ψ K+)×B(J/ψ →p¯
p)=(1.58 ±0.33 ±0.09)×10−2,
whe e he fi s unce ain y is s a is ical and he second sys ema ic. No signals o he decays B+→
X(3872)(→p¯
p)K+and B+→ψ(3770)(→p¯
p)K+a e seen, and he 95% confidence le el uppe limi s on
hei ela i e b anching a ios a e ound o be RX(3872)<0.25 ×10−2and Rψ(3770)<0.10. In addi ion,
he mass di e ences be ween he ηc(1S)and he J/ψ s a es, be ween he ηc(2S)and he ψ(2S)s a es,
and he na u al wid h o he ηc(1S)a e measu ed as
MJ/ψ −Mηc(1S)=110.2±0.5±0.9MeV,
Mψ(2S)−Mηc(2S)=52.5±1.7±0.6MeV,
ηc(1S)=34.0±1.9±1.3MeV.
©2017 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
Cha monium has p o ed o be a ema kable labo a o y o
he s udy o quan um ch omodynamics in he non-pe u ba i e
egime. By compa ing heo e ical p edic ions wi h expe imen al
esul s one can e i y and une he pa ame e s o heo e ical mod-
els in o de o imp o e he accu acy o he p edic ions. In addi ion,
in ecen yea s, many exo ic cha monium-like s a es ha e been ob-
se ed, enewing in e es in cha monium spec oscopy abo e he
open-cha m h eshold [1,2]. The B+→p¯
pK+decay1o e s a clean
en i onmen o s udy in e media e esonances, such as cha mo-
nium and cha monium-like s a es decaying o p¯
p. The p esence o
p¯
pin he final s a e allows in e media e s a es o any quan um
numbe o be s udied.
The fi s adial exci a ion ηc(2S)o he cha monium g ound
s a e ηc(1S)was obse ed a he B ac o ies [3–5] and, o da e,
1The inclusion o cha ge-conjuga e modes is implied h oughou he pape .
only a ew o i s decay modes ha e been obse ed. LHCb has
p e iously measu ed, using da a co esponding o an in eg a ed
luminosi y o 1 b
−1, he decay B+→p¯
pK+and he b anch-
ing ac ions o i s in e media e cha monium con ibu ions. Uppe
limi s on he ηc(2S), X(3872)and X(3915)b anching ac ions
we e also p o ided [6]. The BESIII Collabo a ion has also ecen ly
sea ched o he ηc(2S) →p¯
pdecay in ψ(2S) adia i e ansi-
ions [7], and se an uppe limi on he p oduc o b anching
ac ions B(ψ(3686) →ηc(2S)γ) ×B(ηc(2S) →p¯
p).
The ηc(1S)s a e is he lowes -lying S-wa e spin-single cha -
monium s a e and has been obse ed in a ious p ocesses. The
measu emen s o he ηc(1S)mass and wid h in adia i e cha -
monium ansi ions show a ension wi h hose de e mined in di -
e en p ocesses such as pho on–pho on usion and Bdecays [8].
De ailed in es iga ions o he line shape o he magne ic dipole
ansi ion by he KEDR [9] and CLEO [10] Collabo a ions indi-
ca e ha addi ional ac o s modi y he naï e k3dependence on
he pho on momen um, k, assumed in ea lie measu emen s. This
would a ec he measu emen s o he mass and wid h in adia i e
cha monium ansi ions.
h p://dx.doi.o g/10.1016/j.physle b.2017.03.046
0370-2693/©2017 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.
306 LHCb Collabo a ion / Physics Le e s B 769 (2017) 305–313
In his pape , he fi s obse a ion o ηc(2S) →p¯
pdecay and a
sea ch o ψ(3770) →p¯
pand X(3872) →p¯
pdecays a e epo ed.
The measu emen s o he b anching ac ions a e ela i e o ha o
he B+→J/ψ(→p¯
p)K+decay. Addi ional measu emen s o he
ηc(1S)and ηc(2S)mass and he ηc(1S)wid h a e epo ed. This
new measu emen o he ηc(1S) esonance pa ame e s in exclusi e
B+→[c¯
c]K+decays, whe e [c¯
c]s ands o a gene ic cha monium
esonance, is independen o he abo e-men ioned line-shape com-
plica ions.
2. De ec o and simula ion
The LHCb de ec o [11,12] 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 pp in e ac ion egion, 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 placed downs eam o he mag-
ne . The acking sys em p o ides a measu emen o momen um,
p, o cha ged pa icles wi h a ela i e unce ain y ha a ies om
0.5% a low momen um2 o 1.0% a 200 GeV. The minimum dis-
ance o a ack o a p ima y e ex (PV), he impac pa ame e
(IP), is measu ed wi h a esolu ion o (15 +29/pT)μm, whe e
pTis he componen o he momen um ans e se o he beam,
in GeV. Di e en ypes o cha ged had ons a e dis inguished us-
ing in o ma ion om wo ing-imaging Che enko de ec o s. The
online e en selec ion is pe o med by a igge , which consis s
o a ha dwa e s age, based on in o ma ion om he calo ime e
and muon sys ems, ollowed by a so wa e s age, which applies
ull e en econs uc ion.
A he ha dwa e igge s age, e en s a e equi ed o ha e high
ans e se ene gy in he calo ime e s. Fo had ons, he ans e se
ene gy h eshold is 3.5 GeV. The so wa e igge equi es he
p esence o a wo-, h ee- o ou - ack seconda y e ex wi h
significan displacemen om he p ima y pp in e ac ion e ices.
A leas one cha ged pa icle mus ha e pTla ge han 1.7GeV
and be inconsis en wi h o igina ing om a PV. Amul i a ia e al-
go i hm [13] is used o he iden ifica ion o seconda y e ices
consis en wi h he decay o a bhad on.
Non- esonan B+→p¯
pK+e en s a e simula ed, uni o mly dis-
ibu ed in phase space, as well as esonan modes such as B+→
ηc(2S)(→p¯
p)K+, B+→X(3872)(→p¯
p)K+, B+→ψ(2S)(→
p¯
p)K+and B+→J/ψ(→p¯
p)K+ o op imise he signal selec ion
and o e alua e he a io o he efficiencies o each conside ed
channel wi h espec o he no malisa ion mode. In he simula-
ion, pp collisions a e gene a ed using Py hia 8 [14] wi h a specific
LHCb configu a ion [15]. Decays o had onic pa icles a e desc ibed
by E Gen [16], in which final-s a e adia ion is simula ed us-
ing Pho os [17]. The in e ac ion o he gene a ed pa icles wi h
he de ec o , and i s esponse, a e implemen ed using he Gean 4
oolki [18] as desc ibed in Re . [19].
3. E en selec ion
The selec ion o he B+candida es is done in wo s ages.
Fi s , a selec ion using loose c i e ia o educe he backg ound, is
pe o med, ollowed by a mul i a ia e selec ion. The h ee final-
s a e cha ged pa icles a e equi ed o ha e a ack-fi χ2/nd <3,
whe e nd is he numbe o deg ees o eedom. They mus also
ha e p >1500 MeV, pT>100 MeV, and χ2
IP >1wi h espec o
2Na u al uni s wi h c=1a e used h oughou he pape .
any p ima y e ex in he e en , whe e χ2
IP is defined as he di -
e ence in he e ex-fi χ2o a gi en PV econs uc ed wi h and
wi hou he conside ed ack. Mo eo e , he sum o he ans e se
momen a o he final-s a e pa icles is equi ed o be g ea e han
4500 MeV and he sum o hei momen a is equi ed o be g ea e
han 20 GeV. Pa icle iden ifica ion (PID) equi emen s, based on
he RICH de ec o in o ma ion, a e applied o pand ¯
pcandida es.
The disc imina ing a iables be ween di e en pa icle hypo he-
ses (π, K, p)a e he di e ences be ween log-likelihood alues
 lnLαβunde pa icle hypo heses αand β, espec i ely. The p
and ¯
pcandida es a e equi ed o ha e  ln Lpπ>−5. The econ-
s uc ed B+candida es a e equi ed o ha e an in a ian mass in
he ange 5.08–5.48 GeV. The PV associa ed o each B+candi-
da e is defined o be he one o which he B+candida e has
he smalles χ2
IP. The B+candida e is equi ed o ha e a e ex
fi wi h a χ2/nd <12 and a fligh dis ance g ea e han 3 mm,
aχ2 o he fligh dis ance g ea e han 500, an χ2
IP <10 wi h
espec o he associa ed PV and a pT>1000 MeV. The angle be-
ween he econs uc ed momen um o he B+candida e and he
B+fligh di ec ion (θfl)is equi ed o be θfl>0.632 m ad. The
econs uc ed candida es ha mee he abo e c i e ia a e u he
fil e ed using a Boos ed Decision T ee (BDT) algo i hm [20,21]. The
BDT is ained on a signal sample o simula ed B+→p¯
pK+decays
and a backg ound sample o da a aken om he uppe B+-mass
sideband in he ange 5.34–5.48 GeV. The uppe sideband is ex-
ploi ed o a oid pa ially econs uc ed backg ound mainly due o
B(+,0)→p¯
pK+π(0,−)decays, whe e he pion is no co ec ly e-
cons uc ed, wi h econs uc ed masses smalle han he measu ed
B+mass. The a iables used by he BDT o disc imina e be ween
signal and backg ound candida es a e: he pTo each econs uc ed
ack; he sum o he ans e se momen a o he final-s a e pa -
icles; he sum o hei χ2
IP wi h espec o he p ima y e ex;
he IP o he final-s a e pa icle wi h he highes pT, wi h e-
spec o he p ima y e ex; he numbe o final s a e pa icles
wi h pT>900 GeV/c; he maximum dis ance o closes app oach
be ween any wo o he final-s a e pa icles om he B+decay;
he IP o he B+candida e wi h espec o he p ima y e ex;
he dis ance be ween p ima y and seconda y e ices; cos θfl; he
χ2/nd o he seconda y e ex; a poin ing a iable defined as
Psin θ
Psin θ+ipT,i, whe e Pis he o al momen um o he h ee-pa icle
final s a e, θis he angle be ween he ec o sum o he momen a
o he final-s a e pa icles and he di ec ion o he fligh dis ance
o he B+, wi h ipT,i he sum o he ans e se momen a o
he final-s a e pa icles; and he log likelihood di e ence o each
daugh e be ween he assumed PID hypo hesis and he pion hy-
po hesis. The selec ion c i e ion on he BDT esponse is chosen by
maximising he significance o he χc1→p¯
psignal yield in da a.
The numbe o e en s om his well-known ansi ion p o ides
a con ol sample compa able in size o ha o he ηc(2S). Wi h
his op imisa ion 90% o he B+→p¯
pK+signal candida es a e e-
ained while educing he combina o ial backg ound le el by 83%.
4. In a ian mass spec a and e en yields
An ex ended unbinned maximum likelihood fi is pe o med
o he p¯
pK+in a ian mass dis ibu ion shown in Fig. 1. The
shapes o he di e en con ibu ions a e de e mined om simu-
la ion. The signal peak is pa ame e ised using an Apollonios p ob-
abili y densi y unc ion (PDF) [22]. The yield, mean and esolu ion
a e allowed o a y eely in he fi , while he ail pa ame e s a e
fixed o he alues ob ained om simula ion. The combina o ial
backg ound componen is pa ame e ised by an exponen ial unc-
ion. Pa ially econs uc ed backg ound is pa ame e ised using an
ARGUS PDF [23] con ol ed wi h a Gaussian esolu ion unc ion.
LHCb Collabo a ion / Physics Le e s B 769 (2017) 305–313 307
Fig. 1. In a ian mass spec um o he p¯
pK+candida es. The o al fi cu e and
indi idual fi componen s a e supe imposed on he da a.
The pa ame e s o he ARGUS PDF and o he Gaussian esolu-
ion unc ion a e fixed o he alues ob ained om simula ion. The
misiden ified backg ound due o B+→p¯
pπ+decays, whe e he
cha ged pion is misiden ified as a kaon, is pa ame e ised wi h a
bi u ca ed Gaussian PDF [24] and pa ame e s fixed o he alues
ob ained om simula ion. The yields o pa ially econs uc ed and
misiden ified backg ounds a e de e mined om da a.
The backg ounds obse ed in he p¯
pK+mass dis ibu ion a e
sub ac ed using he sPlo echnique [25] o ex ac he p¯
pmass
spec um in B+→p¯
pK+decays. Signal yields o he esonan
con ibu ions a e hen de e mined om an ex ended unbinned
maximum likelihood fi o he p¯
pmass spec um. To imp o e
he p¯
pin a ian mass esolu ion, he fi o he B+decay e -
ex is pe o med wi h he B+mass cons ained o he known
alue [8] and he B+candida e poin ing o he PV [26]. The p¯
p
mass spec um is also used o de e mine he mass di e ences
MJ/ψ −Mηc(1S)and Mψ(2S)−Mηc(2S)and he na u al wid h o
he ηc(1S)s a e. In o de o ha e accu a e mass measu emen s,
acalib a ion is applied o he momen a o he final-s a e pa icles.
La ge samples o B+→J/ψ K+decays wi h J/ψ →μ+μ−a e
used o calib a e he momen um scale o he spec ome e [27].
Possible eflec ions due o B+→p¯
→p¯
pK+decays a e in es-
iga ed using simula ions, which show ha no na ow s uc u es
a e induced in he p¯
pspec um. Six cha monium esonances a e
included in he nominal fi o he p¯
pin a ian mass spec um:
ηc(1S), J/ψ, χc0, χc1, ηc(2S)and ψ(2S). Al e na i e fi s including
he ψ(3770)o he X(3872) esonances a e pe o med in o de
o es ima e uppe limi s on hei b anching ac ions. The J/ψ
and ψ(2S)peaks a e pa ame e ised wi h a double Gaussian PDF.
The ηc(1S), ηc(2S), χc0and ψ(3770)shapes a e modelled wi h a
ela i is ic B ei –Wigne PDF con ol ed wi h a Gaussian PDF. The
X(3872)and he χc1a e desc ibed wi h a Gaussian PDF since hei
na u al wid h is much smalle han mass esolu ion. Due o he
B+mass cons ain in he e ex fi , he p¯
pmass esolu ion is e -
ec i ely cons an in he en i e p¯
pspec um. The mass esolu ion
pa ame e , common o all he cha monium s a es, is ound o be
σp¯
p=(4.3 ±0.4)MeV, in good ag eemen wi h he simula ions.
The masses o he χc0, χc1, X(3872), ψ(3770)and X(3915)s a es
a e fixed o he known alues [8]. The J/ψ and ψ(2S)peak po-
si ions (MJ/ψ and Mψ(2S)), he mass di e ences (MJ/ψ −Mηc(1S)
and Mψ(2S)−Mηc(2S)), and he na u al wid h o he ηc(1S)s a e
(ηc(1S)) a e ee pa ame e s and a e ob ained om he fi o he
da a. A Gaussian cons ain o he a e age alue o he na u al
wid h o he ηc(2S)is applied [8]. The p¯
pnon- esonan compo-
nen is assumed o ha e no ela i e o bi al angula momen um,
J=0. The fi includes a possible in e e ence e ec be ween he
ηc(1S)s a e and he J=0 non- esonan componen . The ampli-
ude is gi en by |A|2=|Anon- es + e
iδAηc(1S)|2, whe e Anon- es
is he ampli ude o he non- esonan componen , Aηc(1S)is he
ampli ude o he ηc(1S)s a e, δis he phase di e ence and a
no malisa ion ac o . The shape o he non- esonan componen in
he p¯
pmass spec um ollows a phase-space dis ibu ion [8]. The
fi esul is shown in Fig. 2. A zoom o he fi esul in he ange
3.55–4.00 GeV is shown by he inse in Fig. 2.
Using Wilks’ heo em [28], he s a is ical significance o he
ηc(2S)signal is compu ed om he change in he bes fi like-
lihood when omi ing he signal unde sc u iny, 2ln(LS+B/LB),
whe e LS+Band LBa e he likelihoods om he nominal fi and
om he fi wi hou he ηc(2S)signal componen , espec i ely.
The s a is ical significance o he ηc(2S)signal is ound o be
6.4 s anda d de ia ions. No e idence o he ψ(3770)and X(3872)
esonances is ound. The signal yields a e epo ed in Table 1.
Fig. 2. In a ian mass spec um o he p¯
pcandida es. Backg ound in he B+→p¯
pK+dis ibu ion is sub ac ed using he sPlo echnique as desc ibed in he ex . The o al
fi cu e is supe imposed. A zoom o he fi esul in he ange 3.55–4.00 GeV is shown by he inse .
308 LHCb Collabo a ion / Physics Le e s B 769 (2017) 305–313
Table 1
Signal yields om he fi o he p¯
pmass spec-
um in B+→p¯
pK+decays. The fi ac ions o
he ηc(1S)and he non- esonan componen in he
J=0ampli ude a e 25% and 65% espec i ely. The
fi ac ions do no include unce ain ies due o he
ambigui ies in he ela i e phase o he in e e ing
ampli udes. Unce ain ies a e s a is ical only.
S a e Signal yield
ηc(1S)+non- es. 11246 ±119
J/ψ 6721 ±93
χc084±22
χc195±16
ηc(2S)106±22
ψ(2S)588 ±30
ψ(3770)−6±9
X(3872)−14±8
5. Efficiencies and sys ema ic unce ain ies
The b anching ac ion o he B+→[c¯
c](→p¯
p)K+decay o a
specific [c¯
c] esonance ela i e o ha o he J/ψ is gi en by
R[c¯
c]≡
B(B+→[c¯
c]K+)×B([c¯
c]→p¯
p)
B(B+→J/ψ K+)×B(J/ψ →p¯
p)
=N([c¯
c])
N(J/ψ) ×J/ψ
c¯
c
,(1)
whe e N([c¯
c]) ≡N(B+→[c¯
c](→p¯
p)K+)and N(J/ψ) ≡N(B+→
J/ψ(→p¯
p)K+)a e he numbe s o decays and J/ψ /c¯
cis he
o al efficiency a io. The o al efficiency is he p oduc o he
de ec o geome ical accep ance, he igge efficiency, he econ-
s uc ion and selec ion efficiency, he PID efficiency, and he BDT
classifie efficiency. The a io o he efficiencies be ween he signal
and he no malising J/ψ channels is de e mined using simula ed
samples. To accoun o any disc epancy be ween da a and simula-
ion, he PID efficiencies o kaons and p o ons a e calib a ed om
da a samples o D∗+ →D0(→K−π+)π+and Λ0→pπ−decays.
Fo each simula ed candida e, i s PID alue is eplaced by a alue
ex ac ed andomly om he co esponding PID cu es de e mined
om con ol samples. The selec ion is hen applied o he PID-
co ec ed simula ed sample o es ima e he efficiency.
Sys ema ic unce ain ies o igina e om he de e mina ion o
he signal yields, efficiencies, selec ion p ocedu e and b anching
ac ions. Since he final s a e is common o all conside ed de-
cays, mos o he sys ema ic unce ain ies cancel in he a ios.
Impe ec knowledge o he in a ian mass dis ibu ions o he
signal and backg ound causes sys ema ic unce ain ies in he signal
yield de e mina ion, he mass di e ence and wid h measu emen s.
The con ibu ion om he fi model is s udied by using al e na-
i e shapes o he B+componen , o he [c¯
c]s a es and o he
backg ound. Fo he B+signal shape, a Gaussian PDF wi h powe -
law ails on bo h sides and he sum o wo Gaussian PDFs wi h
powe -law ails a e used as al e na i es o he Apollonios PDF. The
combina o ial backg ound componen in he p¯
pK+in a ian mass
is pa ame e ised using a linea PDF. The e ec o emo ing he
peaking backg ound due o misiden ified B+→p¯
pπ+decays is
in es iga ed by checking he a ia ion o he a io o he b anch-
ing ac ions by including o neglec ing his componen in he fi .
Inco ec modelling o he pa ially econs uc ed backg ound can
also in oduce a sys ema ic unce ain y. This is es ima ed by e-
mo ing he p¯
pK+in a ian mass fi ange below 5.20 GeV in
o de o exclude i s con ibu ion. In he fi o he p¯
pspec um,
o he J/ψ signal, he Apollonios PDF is used as an al e na i e
o he sum o wo Gaussian PDFs. The ange o he p¯
pin a ian
mass spec um is also a ied. The sys ema ic unce ain y due o
he a ia ion o he fi ange gi es a negligible con ibu ion o he
Table 2
Sys ema ic unce ain ies in uni s o 10−4on he ηc(2S), X(3872)and ψ(3770)
b anching ac ion measu emen s ela i e o ha o he J/ψ. The efficiency con-
ibu ion includes bo h he PID efficiency a ia ion and he s a is ical e o due o
he fini e size o he simula ed samples.
ηc(2S)X(3872)ψ(3770)
Fi 5 3 5
BDT 8 2 11
Efficiency 2 1 1
To al 9 4 12
Table 3
Sys ema ic unce ain ies on he mass di e ences MJ/ψ −Mηc(1S), Mψ(2S)−Mηc(2S)
and he ηc(1S)measu emen s. The sys ema ic unce ain y associa ed o he mo-
men um scale calib a ion is negligible o he o al wid h ηc(1S)measu emen .
MJ/ψ −Mηc(1S)
[MeV]
Mψ(2S)−Mηc(2S)
[MeV]
ηc(1S)
[MeV]
Fi 0.90 0.10 1.20
BDT 0.21 0.55 0.40
Momen um scale 0.03 0.06 –
To al 0.92 0.56 1.27
b anching ac ion measu emen while i is he la ges con ibu-
ion o he MJ/ψ −Mηc(1S)di e ence. The la ges a ia ion in he
a io o he b anching ac ions due o he fi model is assigned as
he co esponding sys ema ic unce ain y.
Possible biases ela ed o he signal selec ion c i e ia a e in es-
iga ed by a ying he BDT equi emen and by checking he e ec
on he b anching ac ion a io and on he efficiency a io, a e ac-
coun ing o s a is ical fluc ua ions. The maximum a ia ion in he
a io o he yields o he maximum a ia ion in he mass di e ence
and wid h measu emen s a e conside ed as an es ima e o he co -
esponding sou ce o sys ema ic unce ain y. In addi ion, a ia ions
in he p ocedu e used o de e mine he PID efficiency and he un-
ce ain y due o he fini e size o he simula ed samples, lead o an
unce ain y on he efficiency a io in he b anching ac ions e al-
ua ion. The o al sys ema ic unce ain ies on he ela i e b anching
ac ion measu emen s, de e mined by adding he indi idual con-
ibu ions in quad a u e, a e lis ed in Table 2.
The significance, including sys ema ic unce ain ies, o he sig-
nals is de e mined by con ol ing he p ofile likelihoods used in
he yield de e mina ions wi h a Gaussian wi h a wid h equal o
he size o he sys ema ic unce ain ies ha a ec he yield. F om
he modified p ofile likelihood he significance o he ηc(2S)signal
is ound o be 6.0 s anda d de ia ions. The uppe limi s a 90% and
95% confidence le el on he X(3872)and ψ(3770) a io o b anch-
ing ac ions a e de e mined om in eg a ing he p ofile likelihood
unc ions including sys ema ic unce ain y.
The measu emen s o he mass di e ences MJ/ψ −Mηc(1S)and
Mψ(2S)−Mηc(2S)and he na u al wid h o he ηc(1S)s a e a e
u he a ec ed by he unce ain y in he momen um scale calib a-
ion. This sys ema ic unce ain y is small o he mass di e ences
and negligible (< 0.003 MeV) o he na u al wid h. Table 3 sum-
ma ises he sys ema ic unce ain ies on he measu emen o he
MJ/ψ −Mηc(1S), Mψ(2S)−Mηc(2S)mass di e ences and on he
ηc(1S)na u al wid h.
6. Resul s and conclusions
A sea ch o he ηc(2S), ψ(3770)and X(3872)con ibu ions
in B+→p¯
pK+decays is pe o med using da a co esponding o
an in eg a ed luminosi y o 3.0 b
−1 eco ded a cen e-o -mass
ene gies o √s=7TeVand 8TeV. The b anching ac ions a e de-
e mined using he B+→J/ψ(→p¯
p)K+decay as no malisa ion
channel. The ηc(2S) →p¯
pdecay is obse ed o he fi s ime wi h
LHCb Collabo a ion / Physics Le e s B 769 (2017) 305–313 309
a o al significance o 6.0 s anda d de ia ions. The ela i e b anch-
ing ac ion is measu ed o be
Rηc(2S)=(1.58 ±0.33 ±0.09)×10−2,
whe e he fi s unce ain y is s a is ical and he second sys em-
a ic. Fo he B+→X(3872)(→p¯
p)K+and he B+→ψ(3770)(→
p¯
p)K+decays, he uppe limi s a 90 (95)% confidence le el a e
Rψ(3770)<9(10)×10−2,
RX(3872)<0.20(0.25)×10−2.
The isible b anching ac ion calcula ed using he alue o
B(B+→J/ψ K+) ×B(J/ψ →p¯
p) =(2.2 ±0.1) ×10−6[8] is de-
e mined o be
B(B+→ηc(2S)K+)×B(ηc(2S)→p¯
p)
=(3.47 ±0.72 ±0.20 ±0.16)×10−8,
whe e he las unce ain y is due o he unce ain y on B(B+→
J/ψ K+) ×B(J/ψ →p¯
p).
The di e ences be ween MJ/ψ and Mηc(1S)and be ween
Mψ(2S)and Mηc(2S)a e measu ed o be
MJ/ψ −Mηc(1S)=110.2±0.5±0.9MeV,
Mψ(2S)−Mηc(2S)=52.5±1.7±0.6MeV.
The na u al wid h o he ηc(1S)is ound o be
ηc(1S)=34.0±1.9±1.3MeV.
In con as o he de e mina ions using adia i e decays, hese
mass and wid h de e mina ions do no depend on he knowledge
o he line shapes o he magne ic dipole ansi ion.
Acknowledgemen s
We exp ess ou g a i ude o ou colleagues in he CERN ac-
cele a o depa men s o he excellen pe o mance o he LHC.
We hank he echnical and adminis a i e s a a he LHCb in-
s i u es. We acknowledge suppo om CERN and om he na-
ional agencies: CAPES, CNPq, FAPERJ and FINEP (B azil); NSFC
(China); CNRS/IN2P3 (F ance); BMBF, DFG and MPG (Ge many);
INFN (I aly); FOM and NWO (The Ne he lands); MNiSW and NCN
(Poland); MEN/IFA (Romania); MinES and FANO (Russia); MinECo
(Spain); SNSF and SER (Swi ze land); NASU (Uk aine); STFC (Uni ed
Kingdom); NSF (USA). We acknowledge he compu ing esou ces
ha a e p o ided by CERN, IN2P3 (F ance), KIT and DESY (Ge -
many), INFN (I aly), SURF (The Ne he lands), PIC (Spain), G idPP
(Uni ed Kingdom), RRCKI and Yandex LLC (Russia), CSCS (Swi ze -
land), IFIN-HH (Romania), CBPF (B azil), PL-GRID (Poland) and OSC
(USA). We a e indeb ed o he communi ies behind he mul i-
ple open sou ce so wa e packages on which we depend. Indi id-
ual g oups o membe s ha e ecei ed suppo om A H Foun-
da ion (Ge many), EPLANET, Ma ie Skłodowska-Cu ie Ac ions and
ERC (Eu opean Union), Conseil Géné al de Hau e-Sa oie, Labex
ENIGMASS and OCEVU, Région Au e gne (F ance), RFBR and Yan-
dex LLC (Russia), GVA, Xun aGal and GENCAT (Spain), He chel
Smi h Fund, The Royal Socie y, Royal Commission o he Exhibi-
ion o 1851 and he Le e hulme T us (Uni ed Kingdom).
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M. Pa el 54, C. Pa ignani 15,∗,e, A. Pea ce55,50, A. Pelleg ino 42, G. Penso 26,k, M. Pepe Al a elli 39,
S. Pe azzini 39, P. Pe e 5, L. Pesca o e 46, K. Pe idis 47, A. Pe olini 20,h, A. Pe o 66, M. Pe uzzo 22,q,
E. Pica os e Olloqui 37, B. Pie zyk 4, M. Pikies 27, D. Pinci 26, A. Pis one20, A. Piucci 12, S. Play e 51,
M. Plo Casasus 38, T. Poikela 39, F. Polci 8, A. Poluek o 49,35, I. Polyako 60, E. Polyca po 2, G.J. Pome y 47,
A. Popo 36, D. Popo 11,39, B. Popo ici 30, C. Po e a 2, E. P ice 47, J.D. P ice 53, J. P iscianda o 38,
A. P i cha d 53, C. P ou e 47, V. Puga ch 45, A. Puig Na a o 40, G. Punzi 24,p, W. Qian 56, R. Quagliani 7,47,
B. Rachwal 27, J.H. Rademacke 47, M. Rama 24, M. Ramos Pe nas 38, M.S. Rangel 2, I. Raniuk 44,
G. Ra en 43, F. Redi 54, S. Reiche 10, A.C. dos Reis1, C. Remon Alepuz 68, V. Renaudin 7, S. Riccia di 50,
S. Richa ds 47, M. Rihl 39, K. Rinne 53,39, V. Ri es Molina 37, P. Robbe 7,39, A.B. Rod igues 1,
E. Rod igues 58, J.A. Rod iguez Lopez 64, P. Rod iguez Pe ez 55, A. Rogozhniko 67, S. Roise 39,
V. Romano skiy 36, A. Rome o Vidal 38, J.W. Ronayne 13, M. Ro ondo 23, M.S. Rudolph 60, T. Ru 39,
P. Ruiz Valls 68, J.J. Sabo ido Sil a 38, E. Sadykho 32, N. Sagido a 31, B. Sai a 16, , V. Salus ino Guima aes 2,
C. Sanchez Mayo domo 68, B. Sanma in Sedes 38, R. San acesa ia 26, C. San ama ina Rios 38,
M. San ima ia 19, E. San o e i 25,j, A. Sa i19,k, C. Sa iano 26,s, A. Sa a25, D.M. Saunde s 47,
D. Sa ina 32,33, S. Schael 9, M. Schellenbe g 10, M. Schille 39, H. Schindle 39, M. Schlupp 10,
M. Schmelling 11, T. Schmelze 10, B. Schmid 39, O. Schneide 40, A. Schoppe 39, K. Schube 10,
M. Schubige 40, M.-H. Schune 7, R. Schwemme 39, B. Sciascia 19, A. Sciubba 26,k, A. Semenniko 32,
A. Se gi 46, N. Se a 41, J. Se ano 6, L. Ses ini 23, P. Sey e 21, M. Shapkin 36, I. Shapo al 17,44,g,
Y. Shcheglo 31, T. Shea s 53, L. Shekh man 35, V. She chenko 66, A. Shi es 10, B.G. Siddi 17,
R. Sil a Cou inho 41, L. Sil a de Oli ei a 2, G. Simi 23,o, M. Si endi 48, N. Skidmo e 47, T. Skwa nicki 60,
E. Smi h 54, I.T. Smi h 51, J. Smi h 48, M. Smi h 55, H. Snoek 42, M.D. Sokolo 58, F.J.P. Sole 52, D. Souza 47,
B. Souza De Paula 2, B. Spaan 10, P. Sp adlin 52, S. S idha an 39, F. S agni 39, M. S ahl 12, S. S ahl 39,
P. S e ko 40, S. S e ko a 54, O. S einkamp 41, S. S emmle 12, O. S enyakin 36, S. S e enson 56, S. S oica 30,
S. S one 60, B. S o aci 41, S. S acka 24, , M. S a iciuc 30, U. S aumann 41, L. Sun 58, W. Su cli e 54,
K. Swien ek 28, V. Sy opoulos 43, M. Szczekowski 29, T. Szumlak 28, S. T’Jampens 4, A. Taydugano 6,
T. Tekampe 10, G. Tella ini 17,g, F. Teube 39, C. Thomas 56, E. Thomas 39, J. an Tilbu g 42,
V. Tisse and 4, M. Tobin 40, S. Tolk 48, L. Tomasse i 17,g, D. Tonelli 39, S. Topp-Joe gensen 56, F. To iello 60,
E. Tou nefie 4, S. Tou neu 40, K. T abelsi 40, M. T aill 52, M.T. T an 40, M. T esch 41, A. T iso ic 39,
A. Tsa ego od se 6, P. Tsopelas 42, A. Tully 48, N. Tuning 42, A. Ukleja29, A. Us yuzhanin 67,66, U. Uwe 12,
C. Vacca 16,39, , V. Vagnoni 15,39, S. Vala 39, G. Valen i 15, A. Vallie 7, R. Vazquez Gomez 19,
P. Vazquez Reguei o 38, S. Vecchi 17, M. an Veghel 42, J.J. Vel huis 47, M. Vel i 18, , G. Veneziano 40,
A. Venka eswa an 60, M. Ve ne 5, M. Ves e inen 12, B. Viaud 7, D. Viei a 1, M. Viei es Diaz 38,
X. Vilasis-Ca dona 37,m, V. Volko 33, A. Vollha d 41, B. Voneki 39, D. Voong 47, A. Vo obye 31,
312 LHCb Collabo a ion / Physics Le e s B 769 (2017) 305–313
V. Vo obye 35, C. Voß 65, J.A. de V ies 42, C. Vázquez Sie a 38, R. Waldi 65, C. Wallace 49, R. Wallace 13,
J. Walsh 24, J. Wang 60, D.R. Wa d 48, H.M. Wa k 53, N.K. Wa son 46, D. Websdale 54, A. Weiden41,
M. Whi ehead 39, J. Wich 49, G. Wilkinson 56,39, M. Wilkinson 60, M. Williams 39, M.P. Williams 46,
M. Williams 57, T. Williams 46, F.F. Wilson 50, J. Wimbe ley 59, M. Winn 4, J. Wishahi 10, W. Wislicki 29,
M. Wi ek 27, G. Wo mse 7, S.A. Wo on 48, K. W aigh 52, S. W igh 48, K. Wyllie 39, Y. Xie 63, Z. Xing 60,
Z. Xu 40, Z. Yang 3, H. Yin 63, J. Yu 63, X. Yuan 35, O. Yushchenko 36, M. Zangoli 15, K.A. Za ebski 46,
M. Za e yae 11,c, L. Zhang 3, Y. Zhang 7, Y. Zhang 62, A. Zhelezo 12, Y. Zheng 62, A. Zhokho 32,
V. Zhuko 9, 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 Sezione INFN di 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 Sezione INFN di Milano Bicocca, Milano, I aly
22 Sezione INFN 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 Budke Ins i u e o Nuclea Physics (SB RAS) and No osibi sk S a e Uni e si y, No osibi sk, Russia
36 Ins i u e o High Ene gy Physics (IHEP), P o ino, Russia
37 ICCUB, Uni e si a de Ba celona, Ba celona, Spain
38 Uni e sidad de San iago de Compos ela, San iago de Compos ela, Spain
39 Eu opean O ganiza ion o Nuclea Resea ch (CERN), Gene a, Swi ze land
40 Ecole Poly echnique Fédé ale de Lausanne (EPFL), Lausanne, Swi ze land
41 Physik-Ins i u , Uni e si ä Zü ich, Zü ich, Swi ze land
42 Nikhe Na ional Ins i u e o Suba omic Physics, Ams e dam, The Ne he lands
43 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
44 NSC Kha ki Ins i u e o Physics and Technology (NSC KIPT), Kha ki , Uk aine
45 Ins i u e o Nuclea Resea ch o he Na ional Academy o Sciences (KINR), Kyi , Uk aine
46 Uni e si y o Bi mingham, Bi mingham, Uni ed Kingdom
47 H.H. Wills Physics Labo a o y, Uni e si y o B is ol, B is ol, Uni ed Kingdom
48 Ca endish Labo a o y, Uni e si y o Camb idge, Camb idge, Uni ed Kingdom
49 Depa men o Physics, Uni e si y o Wa wick, Co en y, Uni ed Kingdom
50 STFC Ru he o d Apple on Labo a o y, Didco , Uni ed Kingdom
51 School o Physics and As onomy, Uni e si y o Edinbu gh, Edinbu gh, Uni ed Kingdom
52 School o Physics and As onomy, Uni e si y o Glasgow, Glasgow, Uni ed Kingdom
53 Oli e Lodge Labo a o y, Uni e si y o Li e pool, Li e pool, Uni ed Kingdom
54 Impe ial College London, London, Uni ed Kingdom
55 School o Physics and As onomy, Uni e si y o Manches e , Manches e , Uni ed Kingdom
56 Depa men o Physics, Uni e si y o Ox o d, Ox o d, Uni ed Kingdom
57 Massachuse s Ins i u e o Technology, Camb idge, MA, Uni ed S a es
58 Uni e si y o Cincinna i, Cincinna i, OH, Uni ed S a es
59 Uni e si y o Ma yland, College Pa k, MD, Uni ed S a es
60 Sy acuse Uni e si y, Sy acuse, NY, Uni ed S a es
61 Pon i ícia Uni e sidade Ca ólica do Rio de Janei o (PUC-Rio), Rio de Janei o, B azil w
62 Uni e si y o Chinese Academy o Sciences, Beijing, China x
63 Ins i u e o Pa icle Physics, Cen al China No mal Uni e si y, Wuhan, Hubei, China x
64 Depa amen o de Fisica, Uni e sidad Nacional de Colombia, Bogo a, Colombia y
65 Ins i u ü Physik, Uni e si ä Ros ock, Ros ock, Ge many z
66 Na ional Resea ch Cen e Ku cha o Ins i u e, Moscow, Russia aa
LHCb Collabo a ion / Physics Le e s B 769 (2017) 305–313 313
67 Yandex School o Da a Analysis, Moscow, Russia aa
68 Ins i u o de Fisica Co puscula (IFIC), Uni e si a de Valencia-CSIC, Valencia, Spain ab
69 Van Swinde en Ins i u e, Uni e si y o G oningen, G oningen, The Ne he lands ac
*Co esponding au ho s.
E-mail add esses: obe a.ca [email p o ec ed] (R. Ca dinale), [email p o ec ed]h (C. Pa ignani).
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.
wAssocia ed o Uni e sidade Fede al do Rio de Janei o (UFRJ), Rio de Janei o, B azil.
xAssocia ed o Cen e o High Ene gy Physics, Tsinghua Uni e si y, Beijing, China.
yAssocia 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.
zAssocia ed o Physikalisches Ins i u , Rup ech -Ka ls-Uni e si ä Heidelbe g, Heidelbe g, Ge many.
aa Associa ed o Ins i u e o Theo e ical and Expe imen al Physics (ITEP), Moscow, Russia.
ab Associa ed o ICCUB, Uni e si a de Ba celona, Ba celona, Spain.
ac Associa ed o Nikhe Na ional Ins i u e o Suba omic Physics, Ams e dam, The Ne he lands.