JHEP07(2014)103
Published o SISSA by Sp inge
Recei ed:June 4, 2014
Accep ed:June 28, 2014
Published:July 22, 2014
Obse a ion o he Λ0
b→J/ψ pπ−decay
The LHCb collabo a ion
E-mail: [email p o ec ed]
Abs ac : The i s obse a ion o he Cabibbo-supp essed decay Λ
0
b→J/ψ pπ−
is
epo ed using a da a sample o p o on-p o on collisions a 7 and 8 TeV, co esponding
o an in eg a ed luminosi y o 3 b
−1
. A p ominen signal is obse ed and he b anching
ac ion ela i e o he decay mode Λ0
b→J/ψ pK−is de e mined o be
B(Λ0
b→J/ψ pπ−)
B(Λ0
b→J/ψ pK−)= 0.0824 ±0.0025 (s a ) ±0.0042 (sys ).
A sea ch o di ec
CP
iola ion is pe o med. The di e ence in he
CP
asymme ies
be ween hese wo decays is ound o be
ACP (Λ0
b→J/ψ pπ−)−ACP (Λ0
b→J/ψ pK−) = (+5.7±2.4 (s a ) ±1.2 (sys ))%,
which is compa ible wi h CP symme y a he 2.2σle el.
Keywo ds: B physics, CP iola ion, B anching ac ion, Fla o physics, Had on-Had on
Sca e ing
A Xi eP in : 1406.0755
Open Access, Copy igh CERN,
o he bene i o he LHCb Collabo a ion.
A icle unded by SCOAP3.
doi:10.1007/JHEP07(2014)103
JHEP07(2014)103
Con en s
1 In oduc ion 1
2 De ec o and so wa e 2
3 E en selec ion 2
4 Signal and backg ound desc ip ion 4
5CP asymme y 6
6 E iciency co ec ions and sys ema ic unce ain ies 7
7 Resul s and conclusions 9
The LHCb collabo a ion 14
1 In oduc ion
The s udy o
b
-ba yon decays is o conside able in e es bo h o p obe he dynamics o
hea y la ou decay p ocesses and o sea ch o he e ec s o physics beyond he S anda d
Model. Owing o hei non-ze o spin,
b
ba yons p o ide he po en ial o imp o e he limi ed
unde s anding o he helici y s uc u e o he unde lying Hamil onian [1,2].
Beau y ba yons a e copiously p oduced a he LHC, whe e he
Λ0
b
ba yon c oss-sec ion
is abou hal o he size o he
B0
meson p oduc ion in he o wa d egion [
3
,
4
]. The
ATLAS, CMS and LHCb collabo a ions measu ed he
Λ0
b
li e ime [
5
–
8
], and he masses o
he g ound [
8
,
9
] and i s exci ed s a es [
10
]. The
Λ0
b
pola isa ion has been measu ed and
ound o be compa ible wi h ze o [
11
]. The LHCb collabo a ion has s udied
Λ0
b
decays o
cha monium [
11
,
12
], open cha m [
13
,
14
], cha mless s a es [
15
] and inal s a es induced
by elec oweak penguins [
16
]. No e idence o
CP
iola ion has been epo ed in decays
o ba yons. Sea ches wi h
b
-ba yon decays ha e been pe o med wi h he decay channels
Λ0
b→pπ−
,
pK−
[
17
] and
K0
Spπ−
[
15
]. The co esponding heo e ical li e a u e is s ill
limi ed compa ed o ha on Bmeson decays.
The s udy o
b→ccq
decays can be used o cons ain penguin pollu ion in he
de e mina ion o he
CP
- iola ing phases in
B0
and
B0
s
mixing [
18
,
19
]. While decays
o igina ing om he
b→ccs
ansi ions, such as
Λ0
b→J/ψΛ
o
Λ0
b→J/ψpK−
, a e la gely
domina ed by he ee ampli udes, penguins ampli udes a e enhanced in Cabibbo-supp essed
b→ccd ansi ions, such as he Λ0
b→J/ψpπ−decay.
This a icle epo s he i s obse a ion o he
Λ0
b→J/ψpπ−
decay and he de e mina-
ion o i s b anching ac ion ela i e o he Cabibbo- a ou ed mode
Λ0
b→J/ψpK−
. The
– 1 –
JHEP07(2014)103
la e , which was ecen ly obse ed, has been used o ob ain a p ecise measu emen o he
a io o
Λ0
b
o
B0
li e imes [
5
,
12
]. I s absolu e b anching a io is ye o be de e mined. A
measu emen o he
CP
asymme y di e ence be ween he
Λ0
b→J/ψpπ−
and
Λ0
b→J/ψpK−
decays is also epo ed. The analysis is based on a da a sample o p o on-p o on collisions,
co esponding o an in eg a ed luminosi y o 1 b
−1
a a cen e-o -mass ene gy o 7
TeV
and
2 b−1a 8 TeV, collec ed wi h he LHCb de ec o .
2 De ec o and so wa e
The
LHCb
de ec o [
20
] 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
b
o
c
qua 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 p o on-p o on 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 4
Tm
, and h ee s a ions o
silicon-s ip de ec o s and s aw d i ubes [
21
] placed downs eam o he magne . The
combined acking sys em p o ides a momen um measu emen wi h a ela i e unce ain y
ha a ies om 0.4% a low momen um o 0.6% a 100
GeV/c
, and an impac pa ame e
measu emen wi h a esolu ion o 20
µm
o cha ged pa icles wi h la ge ans e se momen-
um,
pT
. Di e en ypes o cha ged had ons a e dis inguished using in o ma ion om wo
ing-imaging Che enko (RICH) de ec o s [
22
]. Pho on, elec on and had on candida es a e
iden i ied 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 i ied by a
sys em composed o al e na ing laye s o i on and mul iwi e p opo ional chambe s [
23
].
The igge [
24
] 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 a ull e en econs uc ion.
Candida e e en s a e i s equi ed o pass he ha dwa e igge , which selec s muons
wi h
pT>
1
.
48
GeV/c
. In he subsequen so wa e igge , a leas one o he candida e
muons is equi ed o be inconsis en wi h o igina ing om any p ima y in e ac ion. Finally,
he muon pai is equi ed o o m a e ex ha is signi ican ly displaced om all p ima y
e ices (PV) and o ha e a mass wi hin 120 MeV/c2o he known J/ψ mass.
In he simula ion, p o on-p o on collisions a e gene a ed using
Py hia
[
25
,
26
] wi h a
speci ic
LHCb
con igu a ion [
27
]. Decays o had onic pa icles a e desc ibed by
E Gen
[
28
],
in which inal s a e adia ion is gene a ed using
Pho os
[
29
]. 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 [30,31] as desc ibed in e . [32].
3 E en selec ion
The
Λ0
b→J/ψpπ−
and
Λ0
b→J/ψpK−
decays a e econs uc ed wi h he
J/ψ
decaying o
wo muons. Cha ge conjuga ion is implied h oughou excep in he de ini ion o he
CP
asymme y.
Candida e
J/ψ →µ+µ−
decays a e econs uc ed om opposi ely cha ged pa icles
passing loose muon-iden i ica ion equi emen s and wi h
pT>
500
MeV/c
. They a e equi ed
– 2 –
JHEP07(2014)103
o o m a good quali y e ex and ha e a mass in he ange [3030
,
3150]
MeV/c2
. This
in e al co esponds o abou eigh imes he
µ+µ−
mass esolu ion a he
J/ψ
mass and
co e s pa o he J/ψ meson adia i e ail.
Candida e
Λ0
b
ba yons a e selec ed om combina ions o
J/ψ
candida es and wo
opposi ely cha ged pa icles, one o which mus be compa ible wi h he p o on hypo hesis.
The p o on candida e is equi ed o ha e a momen um,
p
, la ge han 5
GeV/c
, while he
second cha ged pa icle mus ha e
p >
3
GeV/c
. Bo h pa icles mus ha e
pT>
500
MeV/c
and be inconsis en wi h coming om any PV. All ou cha ged pa icles a e equi ed o be
consis en wi h coming om a common e ex.
The econs uc ed mass and decay ime o he
Λ0
b
candida es a e ob ained om a
kinema ic i [
33
] ha cons ains he mass o he
µ+µ−
pai s o he known
J/ψ
mass and
he
Λ0
b
candida e o o igina e om he PV. I he e en has mul iple PVs, all combina ions a e
conside ed. Candida es a e equi ed o ha e a econs uc ed decay ime la ge han 0
.
2
ps
.
To emo e backg ounds om
Λ0
b→J/ψΛ
decays, candida es ha ha e a
pπ−
mass
wi hin 5
MeV/c2
o he
Λ
ba yon mass a e e oed. To emo e e lec ions om
B0
s→J/ψφ
decays, candida es a e also e oed i he had on-pai mass is less han 1035
MeV/c2
when
applying a K+mass hypo hesis o bo h pa icles.
The emaining candida es a e spli in o samples o
Λ0
b→J/ψpπ−
and
Λ0
b→J/ψpK−
acco ding o he es ima ed p obabili ies ha he cha ged meson candida e is a kaon o a
pion. These p obabili ies a e de e mined using a neu al ne wo k (NN) exploi ing in o ma ion
om he RICH de ec o s, calo ime e and muon sys ems, as well as ack quali y. Pa icles
wi h a la ge pion p obabili y a e ea ed as
Λ0
b→J/ψpπ−
candida es, o he wise hey a e
ea ed as
Λ0
b→J/ψpK−
candida es. In addi ion, he la ge o hese wo p obabili ies is
equi ed o be in excess o 5%. The
Λ0
b
candida es a e equi ed o be in he mass ange
[4900
,
6100]
MeV/c2
. A e his selec ion 4
.
3
×
10
5Λ0
b→J/ψpπ−
and 1
.
9
×
10
5Λ0
b→J/ψpK−
candida es emain.
The selec ion desc ibed abo e is no su icien o isola e he small
Λ0
b→J/ψpπ−
signal om he combina o ial backg ound. The ini ial selec ion is he e o e ollowed by a
mul i a ia e analysis, based on ano he NN [
34
]. The NN classi ie ’s ou pu is used as he
inal selec ion a iable.
The NN is ained en i ely on da a, using he
Λ0
b→J/ψpK−
signal as a p oxy o
he
Λ0
b→J/ψpπ−
decay. The aining is pe o med using hal o he
Λ0
b→J/ψpK−
candida es chosen a andom. The o he hal is used o de ine he no malisa ion sample,
allowing an unbiased measu emen o he
Λ0
b→J/ψpK−
yield. The aining uses signal and
backg ound weigh s de e mined using he
sPlo
echnique [
35
] and ob ained by pe o ming
a maximum likelihood i o he unbinned mass dis ibu ion o he candida es mee ing he
loose selec ion c i e ia.
The i p obabili y densi y unc ion (PDF) is de ined as he sum o he
Λ0
b
signal
componen and he combina o ial backg ound componen s. The pa ame e isa ion o he
indi idual componen s is desc ibed in he nex sec ion.
Se e al e lec ions om
B0
,
B0
s
and
Λ0
b
decays, econs uc ed using misiden i ied
pa icles, mus be accoun ed o in he mass spec um. In o de o a oid he aining being
biased by hese e lec ions, all candida es ha ha e a mass compa ible wi h he
B0
,
B0
s
o
– 3 –
JHEP07(2014)103
Λ0
b
mass a e swapping he
p
and
K
assignmen s wi h any o
π
,
K
, o
p
a e emo ed om
he aining.
The NN classi ie uses in o ma ion abou he candida e kinema ic dis ibu ions, e ex
and ack quali y, impac pa ame e and pa icle iden i ica ion in o ma ion on he p o on.
The mos disc imina ing quan i ies a e he p o on pa icle iden i ica ion p obabili y, he
kinema ic i quali y and he kaon sepa a ion o he PV in his o de . The a iables ha
a e used in he NN a e chosen o a oid co ela ions wi h he econs uc ed
Λ0
b
mass and o
ha e iden ical dis ibu ions in Λ0
b→J/ψpπ−and Λ0
b→J/ψpK−simula ed da a.
Final selec ion equi emen s o he NN classi ie ou pu a e chosen o op imise he
expec ed s a is ical p ecision on he
Λ0
b→J/ψpπ−
signal yield. The expec ed signal and
backg ound yields en e ing he sensi i i y es ima ion a e ob ained om he aining sample
by scaling he numbe o su i ing
Λ0
b→J/ψpK−
candida es by he expec ed yield based
on an assumed b anching ac ion a io o 0
.
1. The expec ed backg ound is ex apola ed
om he numbe o
Λ0
b→J/ψpπ−
candida es in he mass ange [5770
,
6100]
MeV/c2
. A e
applying he inal equi emen on he NN classi ie ou pu , he mul i a ia e selec ion ejec s
99% o he backg ound while keeping 75% o he
Λ0
b→J/ψpK−
signal, ela i e o he
ini ial selec ion.
A e applying he ull selec ion, abou 0
.
1% o he selec ed e en s ha e mo e han one
candida e sha ing a leas one ack, o mo e han one PV ha can be used o de e mine
he kinema ic p ope ies o he candida e. In hese cases one o he candida es o PVs is
used a andom.
4 Signal and backg ound desc ip ion
Fo he candida es passing he NN equi emen s, he yields o
Λ0
b→J/ψpπ−
and
Λ0
b→
J/ψpK−
decays a e de e mined om unbinned maximum likelihood i s o he mass dis-
ibu ions o econs uc ed
Λ0
b
candida es. The PDF is de ined as he sum o a
Λ0
b
signal
componen , a combina o ial backg ound and he sum o se e al e lec ions.
The signal shape is pa ame ised by a Gaussian dis ibu ion wi h powe -law ails on
bo h sides, as indica ed by simula ion. The pa ame e s desc ibing he ails a e aken om
simula ion, while he mean and wid h o he Gaussian a e allowed o a y in he i . The
combina o ial backg ound con ibu ion is desc ibed by an exponen ial unc ion, wi h yield
and slope pa ame e allowed o a y eely.
Se e al peaking backg ounds due o decays o
b
had ons o
J/ψ
mesons and wo cha ged
had ons, whe e one o bo h had ons a e misiden i ied, su i e he selec ion. In his i hey
a e no e oed, unlike in he aining o he NN, excep o candida es consis en wi h he
B0
s→J/ψφ
hypo hesis. Ins ead, hei con ibu ion is modelled by smoo hed non-pa ame ic
unc ions de e mined om simula ed da a. The espec i e yields a e de e mined by swapping
he mass assignmen s o he
p
,
π
and
K
in u n and sea ching o peaks a he
B0
,
B0
s
o
Λ0
b
masses. In he
Λ0
b→J/ψpπ−
i , signi ican backg ounds a e ound om he decays
Λ0
b→J/ψpK−
(wi h
K−
iden i ied as
π−
),
B0→J/ψK+π−
(wi h
K+
iden i ied as
p
), and
B0
s→J/ψK+K−
(wi h one
K
iden i ied as
p
and he o he as
π
). In he
Λ0
b→J/ψpK−
i , he main con ibu ions a e om he decays
B0→J/ψπ+K−
(wi h
π+
iden i ied as
p
),
– 4 –

JHEP07(2014)103
]
2
[MeV/c
-
πpψJ/
m
5500 5600 5700
2
Candida es pe 5 MeV/c
0
200
400
600
800
1000
1200
1400
LHCb Da a
-
πpψJ/→
b
Λ
-
pKψJ/→
b
Λ
B e lec ions
Combina o ial
To al
]
2
[MeV/c
-
pKψJ/
m
5500 5600 5700
2
Candida es pe 5 MeV/c
10
2
10
3
10
Da a
-
pKψJ/→
b
Λ
B e lec ions
Combina o ial
To al
LHCb
Figu e 1
. Dis ibu ion o (le )
J/ψ pπ−
and ( igh )
J/ψ pK−
masses wi h i p ojec ions o e laid.
Fo Λ0
b→J/ψ pK−candida es, only he no malisa ion sample is shown.
B0
s→J/ψK+K−
(wi h
K+
iden i ied as
p
), and
Λ0
b→J/ψpK+
(wi h
K−
and
p
swapped).
These yields a e hen used as Gaussian cons ain s on he no malisa ion o he e lec ion
backg ound shapes. The esul s o he i s a e shown in igu e 1. The con ibu ions o he
e lec ions a e summed, excep o he la ge
Λ0
b→J/ψpK−
e lec ion in he
Λ0
b→J/ψpπ−
i , which is shown sepa a ely.
Low-mass con ibu ions o pa ially econs uc ed
Λ0
b→J/ψpπ−π0
and
Λ0
b→J/ψpK−π0
decays, whe e he
π0
is no conside ed in he combina ion, a e in es iga ed. Adding such a
componen o he i , wi h a mass shape aken om simula ion, esul s in yields compa ible
wi h ze o and does no change he signal yields.
In o al 11 179
±
109
Λ0
b→J/ψpK−
and 2102
±
61
Λ0
b→J/ψpπ−
decays a e ob ained.
The
Λ0
b→J/ψpK−
yield, ha ing been de e mined on he hal o he da a no used in he
aining, is mul iplied by wo, esul ing in a a io o
Λ0
b→J/ψpπ−
o
Λ0
b→J/ψpK−
yields
o 0.0940 ±0.0029.
The shapes used in he mass i a e a ied o de e mine a sys ema ic unce ain y
ela ed o he mass model. No signi ican di e ences a e ound when ying al e na e signal
pa ame e isa ion ha s ill esul in a good i . Changing he peaking backg ounds PDF,
o le ing hei yield ee in he i , change hei ela i e i ac ions, as well as ha o
he combina o ial backg ound, bu does no a ec he signal yields. The combina o ial
backg ound model is changed om an exponen ial o a second-o de polynomial, which
esul s in a
Λ0
b→J/ψpπ−
(
Λ0
b→J/ψpK−
) yield educed by 2.1% (0.3%). These a ia ions
a e added in quad a u e and used o es ima e a sys ema ic unce ain y on he a io o
b anching ac ions.
– 5 –
JHEP07(2014)103
5CP asymme y
The same i p ocedu e is epea ed sepa a ely o ba yon ( agged by a posi i ely cha ged
p o on) and an iba yon candida es. All pa ame e s o he i s a e de e mined again
sepa a ely, excep o he signal shape and he combina o ial backg ound slope, which
a e aken om he i o all candida es. A o al o 1131
±
40
Λ0
b→J/ψpπ−
, 964
±
38
Λ0
b→J/ψpπ+
, 5655
±
77
Λ0
b→J/ψpK−
and 5529
±
76
Λ0
b→J/ψpK+
decays a e ound,
co esponding o he aw asymme ies
A aw(Λ0
b→J/ψpπ−)≡N(Λ0
b→J/ψpπ−)−N(Λ0
b→J/ψpπ+)
N(Λ0
b→J/ψpπ−) + N(Λ0
b→J/ψpπ+)(5.1)
= (+7.9±2.2)%,
A aw(Λ0
b→J/ψpK−) = (+1.1±0.9)%.
The p ocedu e o assess he sys ema ic unce ain ies ela ed o he shape o he mass
dis ibu ion, desc ibed in sec ion 4, is epea ed o de e mine he sensi i i y o he aw
asymme ies. A o al a ia ion o 0.7% is ob ained, which is domina ed by a change in
A aw(Λ0
b→J/ψpπ−) when using a second-o de polynomial backg ound model.
The aw decay- a e asymme y can be decomposed as
A aw(Λ0
b→J/ψph−) = ACP (Λ0
b→J/ψph−) + Ap od(Λ0
b)−A eco(h+) + A eco(p),(5.2)
whe e he e ms on he igh hand side o he equa ion a e he
CP
- iola ing,
Λ0
b
p oduc ion
and econs uc ion asymme ies o he had on
h±
=
π±, K±
and he p o on, espec i ely.
Recons uc ion asymme ies a e de ined ollowing he con en ion
A eco
(
h+
)
≡(h+)−(h−)
(h+)+(h−)
h oughou , whe e

is he econs uc ion e iciency. The p oduc ion asymme y
Ap od
and
he p o on econs uc ion asymme y cancel in he di e ence o he wo asymme ies
∆ACP ≡ ACP (Λ0
b→J/ψpπ−)−ACP (Λ0
b→J/ψpK−)
=A aw(Λ0
b→J/ψpπ−)−A aw(Λ0
b→J/ψpK−) + A eco(π+)−A eco(K+).(5.3)
The kaon and pion asymme ies can be de e mined om he aw asymme y o he
B0→J/ψK∗(892)0decay wi h K∗(892)0→K−π+. I has been measu ed [36] as
A aw(B0→J/ψ K∗(892)0)≡N(B0)−N(B0)
N(B0) + N(B0)= (−1.10 ±0.32 ±0.06)%,(5.4)
whe e he i s unce ain y is s a is ical and he second sys ema ic. I can be decomposed as
A aw(B0→J/ψ K∗(892)0) = ACP (B0→J/ψK∗(892)0)−κAp od(B0) (5.5)
+A eco(π+)−A eco(K+)
≈A eco(π+)−A eco(K+),(5.6)
whe e
κ
is a dilu ion ac o due o
B0
mixing and
Ap od
(
B0
) is he
B0
p oduc ion asymme y,
which is compa ible wi h ze o [
37
]. Unde he assump ion o no
CP
asymme y in he
– 6 –
JHEP07(2014)103
B0→J/ψK∗(892)0
decay and negligible p oduc ion asymme y, his alue can hus be
aken as he combined kaon and pion econs uc ion asymme y, and is consis en wi h
measu emen s in o he decay modes o kaon and pions [37,38].
The di e ence o
CP
asymme ies in he
Λ0
b→J/ψpπ−
and
Λ0
b→J/ψpK−
decays can
hen be ew i en as
∆ACP =A aw(Λ0
b→J/ψpπ−)−A aw(Λ0
b→J/ψpK−) + A aw(B0→J/ψK∗(892)0) (5.7)
= (+5.7±2.4)%,
whe e he unce ain y is s a is ical only.
The kaon and pion momen a in
Λ0
b
decays a e no iden ical o hose in
B0→J/ψK∗(892)0
decays, which could induce di e en de ec o asymme ies in he
Λ0
b
and
B0
modes. This is in es iga ed by weigh ing he
Λ0
b→J/ψpπ−
and
Λ0
b→J/ψpK−
da a o ma ch he pion and kaon momen um dis ibu ions obse ed in
B0→J/ψK∗(892)0
decays. The alue o ∆
ACP
changes by 0.8%, which is assigned as he sys ema ic unce ain y
ela ed o econs uc ion asymme ies.
Local
CP
asymme ies in he Dali z plane a e also sea ched o using he echnique
ou lined in e . [39,40]. No signi ican local asymme ies a e ound.
6 E iciency co ec ions and sys ema ic unce ain ies
The aw quan i ies need o be co ec ed o de e mine he physics quan i ies. The e iciency
o he selec ion equi emen s is s udied wi h simula ion. Some quan i ies a e known no o
be well ep oduced in simula ion, namely he
Λ0
b
ans e se momen um and li e ime, he
pa icle mul iplici y, and he
Λ0
b→J/ψpπ−
and
Λ0
b→J/ψpK−
decay kinema ic p ope ies.
Fo all hese quan i ies he simula ed da a a e weigh ed o ma ch he obse ed dis ibu ions
in da a. They a e ob ained wi h he
sPlo
echnique using he
Λ0
b
candida e mass as he
con ol a iable.
Fo h ee-body
b
-had on decays, bo h he signal decays and he dominan combina o ial
backg ounds popula e egions close o he kinema ic bounda ies o he
J/ψpπ−
and
J/ψpK−
Dali z plo [
41
]. Fo mo e accu a e modelling o hese egions, i is con enien o ans o m
he con en ional Dali z space o a ec angula space (he ea e e e ed o as he squa e
Dali z plo [42]). We ollow he p ocedu e desc ibed in e . [15].
The
Λ0
b→J/ψpπ−
and
Λ0
b→J/ψpK−
decays ha e di e en de ec o accep ance,
econs uc ion and selec ion e iciencies. They a e de e mined om simula ed da a, which
a e weigh ed o ma ch he expe imen al da a. The main di e ences a e induced by
i.
he de ec o accep ance, as he e iciency o
Λ0
b→J/ψpK−
is 6% la ge han ha o
he
Λ0
b→J/ψpπ−
decays due o he lowe kine ic ene gy elease in he o me , which
causes smalle opening angles;
ii.
he econs uc ion and p eselec ion e iciency, which is 4% la ge in
Λ0
b→J/ψpπ−
decays due o he a e age o al and ans e se momen um o he inal s a e pa icles
being la ge han in Λ0
b→J/ψpK−decays;
– 7 –
JHEP07(2014)103
Sou ce BF ∆ACP
Simula ion-based co ec ions 0.913 ±0.040 -
PID 0.960 ±0.010 -
T igge 1.000 ±0.010 -
Λ0
bli e ime 1.000 ±0.001 -
Mass dis ibu ion model 1.000 ±0.021 0.0±0.7%
B0→J/ψK∗(892)0-−1.1±0.3%
De ec ion asymme ies - 0.0±0.8%
To al 0.876 ±0.045 −1.1±1.2 %
Table 1
. Co ec ions and ela ed sys ema ic unce ain ies on he a io o
Λ0
b→J/ψpπ−
o
Λ0
b→J/ψpK−
b anching ac ions (BF) and on he di e ence be ween he
CP
asymme ies ∆
ACP
.
The co ec ions a e mul iplica i e on he b anching ac ion and addi i e o he asymme y.
iii.
he pa icle iden i ica ion equi emen s on he
π−
o
K−
, which a e mo e e icien on
Λ0
b→J/ψpπ−decays by 7%;
i . he φ e o, which emo es 7% (3%) o he Λ0
b→J/ψpK−(J/ψpπ−) signal.
O e all, hese e ec s esul in a u he co ec ion on he a io o b anching ac ions o
Λ0
b→J/ψpπ− o Λ0
b→J/ψpK−decays o 0.913 ±0.040.
The e iciency o pa icle iden i ica ion is no pe ec ly modelled in simula ion. The
kaon and pion iden i ica ion e iciencies a e u he weigh ed a e he kinema ic weigh ing
desc ibed abo e, using a la ge sample o
D∗
- agged
D0→K−π+
decays. The unce ain ies
a e de e mined by a ying he weigh s o he simula ed da a wi hin hei unce ain ies,
yielding a co ec ion o 0
.
960
±
0
.
010. The kinema ic p ope ies o he p o on in he
Λ0
b→J/ψpπ−
and
Λ0
b→J/ψpK−
decays a e ound o be he same. The same applies o
he muons. The e iciencies o p o on and muon iden i ica ion he e o e cancel in he a io
o b anching ac ions, as well as in he CP asymme ies.
The igge e iciency is de e mined using simula ion, which is alida ed using
Λ0
b→
J/ψpK−
decays om da a. Di e ences be ween he
Λ0
b→J/ψpπ−
and
Λ0
b→J/ψpK−
decays e iciencies a e a he pe cen le el and a e assigned as sys ema ic unce ain ies.
The alue o he
Λ0
b
li e ime used in simula ion is aken om e . [
43
], and is 3% lowe
han he cu en mos p ecise measu emen [
5
]. The simula ed da a is weigh ed o accoun
o his and he di e ence is assigned as a sys ema ic unce ain y.
The es ima es o he sys ema ic unce ain ies desc ibed abo e a e summa ised in able 1,
along wi h he o al ob ained by summing hem in quad a u e. The unce ain y on he
a io o b anching ac ions is domina ed by he unce ain y on co ec ions ob ained om
simula ion, mos ly due o he unknown decay kinema ic p ope ies o he
Λ0
b→J/ψpπ−
decay. Fo ∆
ACP
, he mass model dis ibu ion and he de ec ion asymme ies con ibu e
abou equally.
– 8 –
JHEP07(2014)103
D. Hynds
51
, M. Idzik
27
, P. Il en
56
, R. Jacobsson
38
, A. Jaege
11
, J. Jalocha
55
, E. Jans
41
, P. Ja on
39
,
A. Jawahe y
58
, F. Jing
3
, M. John
55
, D. Johnson
55
, C.R. Jones
47
, C. Jo am
38
, B. Jos
38
, N. Ju ik
59
,
M. Kaballo9, S. Kandybei43, W. Kanso6, M. Ka acson38, T.M. Ka bach38, S. Ka odia51,
M. Kelsey59, I.R. Kenyon45, T. Ke el42, B. Khanji20, C. Khu ewa hanakul39, S. Kla e 54,
O. Kochebina7, M. Kolpin11, I. Koma o 39, R.F. Koopman42, P. Koppenbu g41,38, M. Ko ole 32,
A. Kozlinskiy
41
, L. K a chuk
33
, K. K eplin
11
, M. K eps
48
, G. K ocke
11
, P. K oko ny
34
, F. K use
9
,
W. Kucewicz26,o, M. Kucha czyk20,26,38,k, V. Kud ya se 34, K. Ku ek28, T. K a a skheliya31,
V.N. La Thi39, D. Laca e e38, G. La e y54, A. Lai15, D. Lambe 50, R.W. Lambe 42,
E. Lancio i38, G. Lan anchi18, C. Langenb uch38, B. Langhans38, T. La ham48, C. Lazze oni45,
R. Le Gac6, J. an Lee dam41, J.-P. Lees4, R. Le `e e5, A. Le la 32, J. Le an¸cois7, S. Leo23,
O. Le oy
6
, T. Lesiak
26
, B. Le e ing on
11
, Y. Li
3
, M. Liles
52
, R. Lindne
38
, C. Linn
38
, F. Lione o
40
,
B. Liu
15
, G. Liu
38
, S. Lohn
38
, I. Longs a
51
, J.H. Lopes
2
, N. Lopez-Ma ch
39
, P. Lowdon
40
, H. Lu
3
,
D. Lucchesi22,s, H. Luo50, A. Lupa o22, E. Luppi16, , O. Lup on55, F. Mache e 7,
I.V. Machikhiliyan31, F. Maciuc29, O. Mae 30, S. Malde55, G. Manca15,e, G. Mancinelli6,
J. Ma a as5, J.F. Ma chand4, U. Ma coni14, C. Ma in Beni o36, P. Ma ino23,u, R. M¨a ki39,
J. Ma ks11, G. Ma ello i25, A. Ma ens8, A. Ma ´ın S´anchez7, M. Ma inelli41,
D. Ma inez San os42, F. Ma inez Vidal64, D. Ma ins Tos es2, A. Massa e i1, R. Ma e 38,
Z. Ma he38, C. Ma euzzi20, A. Mazu o 16, , M. McCann53, J. McCa hy45, A. McNab54,
R. McNul y
12
, B. McSkelly
52
, B. Meadows
57
, F. Meie
9
, M. Meissne
11
, M. Me k
41
, D.A. Milanes
8
,
M.-N. Mina d4, N. Moggi14, J. Molina Rod iguez60, S. Mon eil5, M. Mo andin22, P. Mo awski27,
A. Mo d`a6, M.J. Mo ello23,u, J. Mo on27, A.-B. Mo is50, R. Moun ain59, F. Muheim50,
K. M¨ulle
40
, R. Mu esan
29
, M. Mussini
14
, B. Mus e
39
, P. Naik
46
, T. Nakada
39
, R. Nandakuma
49
,
I. Nas e a2, M. Needham50, N. Ne i21, S. Neube 38, N. Neu eld38, M. Neune 11, A.D. Nguyen39,
T.D. Nguyen39, C. Nguyen-Mau39, , M. Nicol7, V. Niess5, R. Nie 9, N. Niki in32, T. Nikodem11,
A. No oselo 35, D.P. O’Hanlon48, A. Oblakowska-Mucha27, V. Ob az so 35, S. Ogge o41,
S. Ogil y51, O. Okh imenko44, R. Oldeman15,e, G. Onde wa e 65, M. O landea29,
J.M. O alo a Goicochea2, P. Owen53, A. Oyangu en64, B.K. Pal59, A. Palano13,c, F. Palombo21, ,
M. Palu an18, J. Panman38, A. Papanes is49,38, M. Pappagallo51, C. Pa kes54, C.J. Pa kinson9,45,
G. Passale a17, G.D. Pa el52, M. Pa el53, C. Pa ignani19,j, A. Pazos Al a ez37, A. Pea ce54,
A. Pelleg ino41, M. Pepe Al a elli38, S. Pe azzini14,d, E. Pe ez T igo37, P. Pe e 5,
M. Pe in-Te in
6
, L. Pesca o e
45
, E. Pesen
66
, K. Pe idis
53
, A. Pe olini
19,j
, E. Pica os e Olloqui
36
,
B. Pie zyk4, T. Pilaˇ 48, D. Pinci25, A. Pis one19, S. Play e 50, M. Plo Casasus37, F. Polci8,
A. Poluek o
48,34
, E. Polyca po
2
, A. Popo
35
, D. Popo
10
, B. Popo ici
29
, C. Po e a
2
, E. P ice
46
,
J. P iscianda o39, A. P i cha d52, C. P ou e46, V. Puga ch44, A. Puig Na a o39, G. Punzi23, ,
W. Qian
4
, B. Rachwal
26
, J.H. Rademacke
46
, B. Rako omia amanana
39
, M. Rama
18
, M.S. Rangel
2
,
I. Raniuk43, N. Rauschmay 38, G. Ra en42, S. Reiche 54, M.M. Reid48, A.C. dos Reis1,
S. Riccia di49, S. Richa ds46, M. Rihl38, K. Rinne 52, V. Ri es Molina36, D.A. Roa Rome o5,
P. Robbe
7
, A.B. Rod igues
1
, E. Rod igues
54
, P. Rod iguez Pe ez
54
, S. Roise
38
, V. Romano sky
35
,
A. Rome o Vidal
37
, M. Ro ondo
22
, J. Rou ine
39
, T. Ru
38
, F. Ru ini
23
, H. Ruiz
36
, P. Ruiz Valls
64
,
G. Saba ino25,l, J.J. Sabo ido Sil a37, N. Sagido a30, P. Sail51, B. Sai a15,e,
V. Salus ino Guima aes2, C. Sanchez Mayo domo64, B. Sanma in Sedes37, R. San acesa ia25,
C. San ama ina Rios37, E. San o e i24,l, M. Sapuno 6, A. Sa i18,m, C. Sa iano25,n, A. Sa a24,
D.M. Saunde s46, M. Sa ie16, , D. Sa ina31,32, M. Schille 42, H. Schindle 38, M. Schlupp9,
M. Schmelling10, B. Schmid 38, O. Schneide 39, A. Schoppe 38, M.-H. Schune7, R. Schwemme 38,
B. Sciascia18, A. Sciubba25, M. Seco37, A. Semenniko 31, I. Sepp53, N. Se a40, J. Se ano6,
L. Ses ini22, P. Sey e 11, M. Shapkin35, I. Shapo al16,43, , Y. Shcheglo 30, T. Shea s52,
L. Shekh man34, V. She chenko63, A. Shi es9, R. Sil a Cou inho48, G. Simi22, M. Si endi47,
N. Skidmo e46, T. Skwa nicki59, N.A. Smi h52, E. Smi h55,49, E. Smi h53, J. Smi h47, M. Smi h54,
– 15 –

JHEP07(2014)103
H. Snoek41, M.D. Sokolo 57, F.J.P. Sole 51, F. Soom o39, D. Souza46, B. Souza De Paula2,
B. Spaan9, A. Spa kes50, P. Sp adlin51, F. S agni38, M. S ahl11, S. S ahl11, O. S einkamp40,
O. S enyakin
35
, S. S e enson
55
, S. S oica
29
, S. S one
59
, B. S o aci
40
, S. S acka
23,38
, M. S a iciuc
29
,
U. S aumann
40
, R. S oili
22
, V.K. Subbiah
38
, L. Sun
57
, W. Su cli e
53
, K. Swien ek
27
, S. Swien ek
9
,
V. Sy opoulos42, M. Szczekowski28, P. Szczypka39,38, D. Szila d2, T. Szumlak27, S. T’Jampens4,
M. Teklishyn7, G. Tella ini16, , F. Teube 38, C. Thomas55, E. Thomas38, J. an Tilbu g41,
V. Tisse and4, M. Tobin39, S. Tolk42, L. Tomasse i16, , D. Tonelli38, S. Topp-Joe gensen55,
N. To 55, E. Tou ne ie 4, S. Tou neu 39, M.T. T an39, M. T esch40, A. Tsa ego od se 6,
P. Tsopelas41, N. Tuning41, M. Ubeda Ga cia38, A. Ukleja28, A. Us yuzhanin63, U. Uwe 11,
V. Vagnoni14, G. Valen i14, A. Vallie 7, R. Vazquez Gomez18, P. Vazquez Reguei o37,
C. V´azquez Sie a37, S. Vecchi16, J.J. Vel huis46, M. Vel i17,h, G. Veneziano39, M. Ves e inen11,
B. Viaud
7
, D. Viei a
2
, M. Viei es Diaz
37
, X. Vilasis-Ca dona
36,p
, A. Vollha d
40
, D. Volyanskyy
10
,
D. Voong46, A. Vo obye 30, V. Vo obye 34, C. Voß62, H. Voss10, J.A. de V ies41, R. Waldi62,
C. Wallace
48
, R. Wallace
12
, J. Walsh
23
, S. Wande no h
11
, J. Wang
59
, D.R. Wa d
47
, N.K. Wa son
45
,
D. Websdale53, M. Whi ehead48, J. Wich 38, D. Wiedne 11, G. Wilkinson55, M.P. Williams45,
M. Williams56, F.F. Wilson49, J. Wimbe ley58, J. Wishahi9, W. Wislicki28, M. Wi ek26,
G. Wo mse 7, S.A. Wo on47, S. W igh 47, S. Wu3, K. Wyllie38, Y. Xie61, Z. Xing59, Z. Xu39,
Z. Yang
3
, X. Yuan
3
, O. Yushchenko
35
, M. Zangoli
14
, M. Za e yae
10,b
, L. Zhang
59
, W.C. Zhang
12
,
Y. Zhang3, A. Zhelezo 11, A. Zhokho 31, L. Zhong3and A. Z yagin38
1Cen o B asilei o de Pesquisas F´ısicas (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 ´e de Sa oie, CNRS/IN2P3, Annecy-Le-Vieux, F ance
5Cle mon Uni e si ´e, Uni e si ´e Blaise Pascal, CNRS/IN2P3, LPC, Cle mon -Fe and, F ance
6CPPM, Aix-Ma seille Uni e si ´e, CNRS/IN2P3, Ma seille, F ance
7LAL, Uni e si ´e Pa is-Sud, CNRS/IN2P3, O say, F ance
8LPNHE, Uni e si ´e Pie e e Ma ie Cu ie, Uni e si ´e Pa is Dide o , CNRS/IN2P3, Pa is, F ance
9Fakul ¨a Physik, Technische Uni e si ¨a Do mund, Do mund, Ge many
10 Max-Planck-Ins i u ¨u Ke nphysik (MPIK), Heidelbe g, Ge many
11 Physikalisches Ins i u , Rup ech -Ka ls-Uni e si ¨a Heidelbe g, Heidelbe g, Ge many
12 School o Physics, Uni e si y College Dublin, Dublin, I eland
13 Sezione INFN di Ba i, Ba i, I aly
14 Sezione INFN di Bologna, Bologna, I aly
15 Sezione INFN di Caglia i, Caglia i, I aly
16 Sezione INFN di Fe a a, Fe a a, I aly
17 Sezione INFN di Fi enze, Fi enze, I aly
18 Labo a o i Nazionali dell’INFN di F asca i, F asca i, I aly
19 Sezione INFN di Geno a, Geno a, I aly
20 Sezione INFN di Milano Bicocca, Milano, I aly
21 Sezione INFN di Milano, Milano, I aly
22 Sezione INFN di Pado a, Pado a, I aly
23 Sezione INFN di Pisa, Pisa, I aly
24 Sezione INFN di Roma To Ve ga a, Roma, I aly
25 Sezione INFN di Roma La Sapienza, Roma, I aly
26 Hen yk Niewodniczanski Ins i u e o Nuclea Physics Polish Academy o Sciences, K ak´ow, Poland
27 AGH - Uni e si y o Science and Technology, Facul y o Physics and Applied Compu e Science,
K ak´ow, Poland
28 Na ional Cen e o Nuclea Resea ch (NCBJ), Wa saw, Poland
29
Ho ia Hulubei Na ional Ins i u e o Physics and Nuclea Enginee ing, Bucha es -Magu ele, Romania
30 Pe e sbu g Nuclea Physics Ins i u e (PNPI), Ga china, Russia
– 16 –
JHEP07(2014)103
31 Ins i u e o Theo e ical and Expe imen al Physics (ITEP), Moscow, Russia
32 Ins i u e o Nuclea Physics, Moscow S a e Uni e si y (SINP MSU), Moscow, Russia
33 Ins i u e o Nuclea Resea ch o he Russian Academy o Sciences (INR RAN), Moscow, Russia
34
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
35 Ins i u e o High Ene gy Physics (IHEP), P o ino, Russia
36 Uni e si a de Ba celona, Ba celona, Spain
37 Uni e sidad de San iago de Compos ela, San iago de Compos ela, Spain
38 Eu opean O ganiza ion o Nuclea Resea ch (CERN), Gene a, Swi ze land
39 Ecole Poly echnique F´ed´e ale de Lausanne (EPFL), Lausanne, Swi ze land
40 Physik-Ins i u , Uni e si ¨a Z¨u ich, Z¨u ich, Swi ze land
41 Nikhe Na ional Ins i u e o Suba omic Physics, Ams e dam, The Ne he lands
42 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
43 NSC Kha ki Ins i u e o Physics and Technology (NSC KIPT), Kha ki , Uk aine
44 Ins i u e o Nuclea Resea ch o he Na ional Academy o Sciences (KINR), Kyi , Uk aine
45 Uni e si y o Bi mingham, Bi mingham, Uni ed Kingdom
46 H.H. Wills Physics Labo a o y, Uni e si y o B is ol, B is ol, Uni ed Kingdom
47 Ca endish Labo a o y, Uni e si y o Camb idge, Camb idge, Uni ed Kingdom
48 Depa men o Physics, Uni e si y o Wa wick, Co en y, Uni ed Kingdom
49 STFC Ru he o d Apple on Labo a o y, Didco , Uni ed Kingdom
50 School o Physics and As onomy, Uni e si y o Edinbu gh, Edinbu gh, Uni ed Kingdom
51 School o Physics and As onomy, Uni e si y o Glasgow, Glasgow, Uni ed Kingdom
52 Oli e Lodge Labo a o y, Uni e si y o Li e pool, Li e pool, Uni ed Kingdom
53 Impe ial College London, London, Uni ed Kingdom
54 School o Physics and As onomy, Uni e si y o Manches e , Manches e , Uni ed Kingdom
55 Depa men o Physics, Uni e si y o Ox o d, Ox o d, Uni ed Kingdom
56 Massachuse s Ins i u e o Technology, Camb idge, MA, Uni ed S a es
57 Uni e si y o Cincinna i, Cincinna i, OH, Uni ed S a es
58 Uni e si y o Ma yland, College Pa k, MD, Uni ed S a es
59 Sy acuse Uni e si y, Sy acuse, NY, Uni ed S a es
60
Pon i ´ıcia Uni e sidade Ca ´olica do Rio de Janei o (PUC-Rio), Rio de Janei o, B azil, associa ed o
2
61
Ins i u e o Pa icle Physics, Cen al China No mal Uni e si y, Wuhan, Hubei, China, associa ed o
3
62 Ins i u ¨u Physik, Uni e si ¨a Ros ock, Ros ock, Ge many, associa ed o 11
63 Na ional Resea ch Cen e Ku cha o Ins i u e, Moscow, Russia, associa ed o 31
64 Ins i u o de Fisica Co puscula (IFIC), Uni e si a de Valencia-CSIC, Valencia, Spain, associa ed
o 36
65 KVI - Uni e si y o G oningen, G oningen, The Ne he lands, associa ed o 41
66 Celal Baya Uni e si y, Manisa, Tu key, associa ed o 38
aUni e sidade Fede al do T iˆangulo Minei o (UFTM), Ube aba-MG, B azil
bP.N. Lebede Physical Ins i u e, Russian Academy o Science (LPI RAS), Moscow, Russia
cUni e si `a di Ba i, Ba i, I aly
dUni e si `a di Bologna, Bologna, I aly
eUni e si `a di Caglia i, Caglia i, I aly
Uni e si `a di Fe a a, Fe a a, I aly
gUni e si `a di Fi enze, Fi enze, I aly
hUni e si `a di U bino, U bino, I aly
iUni e si `a di Modena e Reggio Emilia, Modena, I aly
jUni e si `a di Geno a, Geno a, I aly
kUni e si `a di Milano Bicocca, Milano, I aly
lUni e si `a di Roma To Ve ga a, Roma, I aly
mUni e si `a di Roma La Sapienza, Roma, I aly
– 17 –
JHEP07(2014)103
nUni e si `a della Basilica a, Po enza, I aly
oAGH - Uni e si y o Science and Technology, Facul y o Compu e Science, Elec onics and
Telecommunica ions, K ak´ow, Poland
pLIFAELS, La Salle, Uni e si a Ramon Llull, Ba celona, Spain
qUni e si y o U ech , U ech , The Ne he lands
Hanoi Uni e si y o Science, Hanoi, Vie Nam
sUni e si `a di Pado a, Pado a, I aly
Uni e si `a di Pisa, Pisa, I aly
uScuola No male Supe io e, Pisa, I aly
Uni e si `a degli S udi di Milano, Milano, I aly
– 18 –