CP violation in beauty decays at LHCb
Veronika Chobanova on behalf of the LHCb collaboration
XIV International Conference on Heavy Quarks and LeptonsYamagata, 28 May 2018
LHCb experiment
LHCb detector designed for decays of hadrons with a bor c quarks
• Excellent time resolution 〈σt〉 ≈ 45 fs
• Momentum resolution 0.5− 1%
• B flavour tagging efficiency ≈ 4%
• PID efficiencies > 95%
∫L p-p collisions
Run 1 (7−8 TeV)
2010-2013 3 fb−1
Run 2 (13 TeV)
2015-now 4 fb−1
[2008 JINST 3 S08005]
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 1
LHCb experiment
More on LHCb prospects in Preema Pais’ talk on Fri at 15:15
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 2
CPV in b → ccs transitions
13/ 69
Now come 2 complications:1 B0
s → J/ψKK : superposition of 4 polarized final states 0,⊥, ‖,SParameter Value
φ0s −0.045 ± 0.053 ± 0.007
φ‖s − φ0
s −0.018 ± 0.043 ± 0.009φ⊥s − φ
0s −0.014 ± 0.035 ± 0.006
φSs − φ
0s 0.015 ± 0.061 ± 0.021
|λ0| 1.012 ± 0.058 ± 0.013|λ‖/λ0| 1.02 ± 0.12 ± 0.05|λ⊥/λ0| 0.97 ± 0.16 ± 0.01|λS/λ0| 0.86 ± 0.12 ± 0.04
Mixing induced (φs) and direct CPV parameters (λ) are measured.So far, no φs polarization-dependence measured [LHCb, PRL 114, 041801 (2015)]
2 Decay b → ccs involves not only tree, but also gluonic, electroweak penguins,exchange and penguin annihilation topologies!What we measured in B0
s→ J/ψφ is φs = −2βs + ∆φpengs + ∆φNP
s .Mandatory to control ∆φpeng
s to claim NP!
Tree
Bq
J/ψ
X
W
b
q
q
c
c
q′
Penguin
Bq
J/ψ
XW
b
q q
q′
c
c
u, c, t
Colour SingletExchange
Exchange
B0q J/ψ
X
W
b
q c
c
q′
q′Colour SingletExchange
Penguin-Annihilation
B0q
J/ψ
X
W
b
q
q′
q′
c
c
u,c,t Colour Singlet
Exchange
Olivier Leroy (CPPM) Prospects for CPV and mixing in neutral B 13 July 2016 13 / 32q
b
b
q
u,c,t
t,c,u
±W ±Wq0B q
0B
*tqV tbV
tqV*tbV
|BL,H〉 = p|B0〉 ± q|B0〉
• Access to SM parameters and NP through direct and mixing-induced CPviolation in b → ccs decays, e.g. B0 → J/ψK0
S and B0s → J/ψφ
• Tree-dominated processes, small penguin contributions (T P > E,PA)
• Precise SM predictions
q0B
q0
B
f
q/p
fA
fA
λf =q
p
Af
Af
CPV due to mixing-decay interference whenarg(λf ) 6= 0
arg(λJ/ψK
0S
) = 2β + ∆βpeng
+ ∆βNP
arg(λJ/ψφ ) ≡ φs = −2βs + ∆φpengs + ∆φ
NPs
2βSM
= (47.48+2.26−1.96)
2βSMs = (2.122± 0.037)
CKMFitter
β≡arg
(−VcdV
∗cb
VtdV∗tb
)βs≡arg
(−VtsV
∗tb
VcsV∗cb
)Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 3
Measurement of β
• β is the most precisely measured angle of the Unitarity triangle
• CPV measurement in time-dependent decay rates of b → ccs transitions
Γ(
B0 → f
)− Γ
(B
0 → f)
Γ(
B0 → f
)+ Γ
(B
0 → f) =
Sf sin(∆mt)− Cf cos(∆mt)
cosh(∆Γt/2) + A∆Γ
sinh(∆Γt/2)
∆Γ = 0≈ Sf sin(∆mt)− Cf cos(∆mt)
Sccs ≡2I(λccs )
1 + |λccs |2≈ sin(2β) Cccs ≡
1− |λccs |2
1 + |λccs |2
sin 2βSMccs = 0.740
+0.020−0.025 [CKMFitter]
sin 2βSMccs = 0.724± 0.028 [UTFit]
sin 2βccs = 0.699± 0.017 [HFLAV]
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 4
Measurement of β
• “Golden mode” B0 → J/ψK0S, a CP final state
• LHCb B0 → J/ψ [µµ]K0S in Run I (3 fb−1)
→ Excellent decay time resolution ≈ 45 fs
→ Effective tagging efficiency ≈ 3%
→ Main systematicsSCP : background tagging asymmetryCCP : ∆m knowledge
SJ/ψ [µµ]K
0S
= +0.731± 0.035(stat)± 0.020(syst)
CJ/ψ [µµ]K
0S
= −0.038± 0.032(stat)± 0.005(syst)
LHCb 3 fb−1
[PRL 115 031601 (2015)]
• Additional modesB0 → J/ψ [ee]K0
S and B0 → ψ(2S)[µµ]K0S
improve uncertainty on β by ≈ 20%
S[cc]K
0S
= +0.760± 0.034
C[cc]K
0S
= −0.017± 0.029
LHCb 3 fb−1
[JHEP 11 (2017) 170]
[PRL 115 031601 (2015)]
B0 → J/ψ [µµ]K0S
[JHEP 11 (2017) 170]
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 5
Prospects of β
σstat(S(J/ψK0S)) now 50 ab
−1
Belle II 0.029 0.005
now 50 fb−1
300 fb−1
LHCb 0.035 0.006 0.003
• LHCb Run I precision close to that of B factories
• Both Belle II and LHCb Upgrade will achieve highstatistical precision
→ Ultimate precision systematics dominated
• Belle IISCP Vertexing and time resolutionCCP Tag-side interference
• LHCbSCP Background tagging asym. should scaledown but difficult to predictCCP ∆m precision, expected to improve
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 6
Measurement of φs
q
b
b
q
u,c,t
t,c,u
±W ±Wq0B q
0B
*tqV tbV
tqV*tbV
b
g
s b
g
sd
d
• Neutral B mesons very sensitive in the mixingto new sources of flavour violation, e.g. gluinobox in SUSY
• B0s → J/ψ [µ−µ+]K+K− is the “golden mode” for φs
→ Also measurement ofΓs =
ΓH+ΓL2
, ∆Γs = ΓL − ΓH , ∆ms = mH −mL
φs =−2βs + ∆φpengs + ∆φ
NPs
−2βSMs =−0.0370± 0.0006 rad [CKMFitter]
−2βSMs =−0.0364± 0.0012 rad [UTFit]
φccss =−0.021± 0.031 rad [HFLAV]
LHCb measurements in two regions in M(KK) with full LHC Run I data of 3 fb−1
• M(KK) < 1.05 GeV/c2[PRL 114, 041801 (2015)]
Dominated by B0s → J/ψφ, small contribution from KK S wave
• M(KK) > 1 GeV/c2[JHEP 08 (2017) 037]
Rich resonant structure in KK, including φ, S wave, φ(1680), f ′2 (1525)
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 7
φs from B0s → J/ψKK for M(KK) < 1.05GeV/c2 | LHCb [PRL 114, 041801 (2015)]
• B0s → J/ψKK is an admixture of CP-even and CP-odd eigenstates
φ: CP-even(A0+A‖)+CP-odd(A⊥)
S wave: CP-odd (AS)
→ Use angular distribution (helicity angles) to disentangle CP-evenand CP-odd components
Nsig ≈ 96× 103
CP evenCP oddS wave
−2βSMs =−0.0370± 0.0006 rad [CKMFitter]
−2βSMs =−0.0364± 0.0012 rad [UTFit]
φs = −0.058± 0.049± 0.006 rad∆Γs = 0.0805±0.0091±0.0032 ps−1
Main systematic uncertaintyAngular acceptance (MC size):±0.004 rad
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 8
φs from B0s → J/ψKK for M(KK) > 1GeV/c2 | LHCb [JHEP 08 (2017) 037]
Nsig ≈ 31× 103
• LHCb with 3 fb−1
• Determine resonant structure and φs , Γs and∆Γs in fit to M(KK)
≈ 10% f ′2 (1525) and S-wave each
• Main systematic uncertainty
Resonance modelling: ±0.0236 mrad
• Combination with B0s → J/ψφ improves φs
precision by over 7%
B → J/ψKK, M(KK) > 1.05 GeV
φs = 0.119± 0.107± 0.034 rad
|λ| = 0.994± 0.018± 0.006
∆Γs = 0.066± 0.018± 0.010 ps−1
Combination with LHCb Run I B → J/ψφ
φs = −0.025± 0.045± 0.008 rad
|λ| = 0.978± 0.013± 0.003
∆Γs = 0.0813± 0.0073± 0.0036 ps−1
−2βSMs =−0.0370± 0.0006 rad [CKMFitter]
−2βSMs =−0.0364± 0.0012 rad [UTFit]
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 9
φs in b → ccs: Combination
LHCb measurements also in B0s → J/ψππ , B0
s → ψ(2S)φ and B0s → DsDs
Exp. Mode Lumi φs [rad]
LHCb J/ψKK 3 fb−1 −0.058± 0.049± 0.006 [PRL 114, 041801 (2015)]
J/ψKK HM 3 fb−1
+0.119± 0.107± 0.034 [JHEP 08 (2017) 037]
J/ψππ 3 fb−1 −0.070± 0.068± 0.008 [PLB 736 (2014) 186]
ψ(2S)φ 3 fb−1
+0.23+0.29−0.28 ± 0.02 [PLB 762 (2016) 253]
D+s D−s 3 fb
−1+0.02± 0.17± 0.02 [PRL 113, 211801 (2014)]
ATLAS J/ψφ 19.2 fb−1 −0.098± 0.084± 0.040 [JHEP 1608 (2016) 147]
CMS J/ψφ 19.7 fb−1 −0.075± 0.097± 0.031 [PLB 757 (2016) 97]
Average −0.021± 0.031 [HFLAV]
Theory −0.0370± 0.0006 [CKMFitter]
• B0s → J/ψKK gives the lowest
uncertainties
• LHCb dominates world average
• Results consistent with SM predictionbut still a lot of room for NP
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 10
φs prospects
• LHCb to measire φs in additional modes with more data
B0s → J/ψ [e+e−]KK
B0s → J/ψη [γγ ] - no angular analysis needed because B0
s → VP but worse resolution [PLB762 (2016) 484-492]
B0s → ηcφ - also B0
s → VP, first observation by LHCb [JHEP 1707 (2017) 021]
• σstat(φs) ≈ 0.003 rad at 300 fb−1 (vs current σth(φs) = 0.0006 rad)
]-1L [fb0 50 100 150 200 250 300
(ra
d)S
TA
T) sφ(σ
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
sensitivitys
φφψ J/→ 0
sBKK (high mass)ψ J/→ 0
sBππψ J/→ 0
sB(2S)KKψ → 0
sB
sDs D→ 0sB
sc all c0sB
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 11
Controlling the penguin pollution in β and φs
• With increasing precision crucial to understand penguin pollution
• Can use U-spin and SU(3) related modes, where penguin not suppressed, to determine its sizeS. Faller, R. Fleischer, M. Jung, T. Mannel [arXiv:0809.0842]
1 b → ccs amplitude (i = 0, ‖,⊥):
A′i (b → ccs) =(
1− λ2
2
)A′i[1 + εa′i e
iθ′e iγ]
2 b → ccd amplitude:
Ai (b → ccd) = −λAi
[1 + aie
iθe iγ]
a′i e
iθ′: “Penguin/Tree ratio” in
b → ccs
aieiθ
: “Penguin/Tree ratio“ inb → ccd
λ ≡ |Vus | ≈ 0.225, ε ≡ λ2
1−λ2 ≈ 0.054, γ unitarity triangle angle
3 SU(3): a′i = ai , θ′i = θi ; extract ∆φpeng
s (ai , θi )/∆βpeng (ai , θi ) from fit to CP parameters and BF
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 12
Controlling the penguin pollution in β
• B0s → J/ψK0
S an excellent candidate - same topology as B0 → J/ψK0S
• LHCb measurement with 3 fb−1[JHEP06(2015)131]
A∆Γ(B0s → J/ψK
0S) = +0.49
+0.77−0.65(stat)± 0.06(syst)
C(B0s → J/ψK
0S) = −0.28± 0.41(stat)± 0.08(syst)
S(B0s → J/ψK
0S) = −0.08± 0.40(stat)± 0.08(syst)
• B0 → J/ψπ0 another good candidate, thoughcontains PA and E [Belle, PRL 93, 261801]
→ PA and E can be studied further inB0
s → J/ψπ0 though very challenging
• B+ → J/ψK+ and B+ → J/ψπ+ provideadditional information with Adir
CP
[LHCb PRD 95 (2017) 052005], [LHCb JHEP 03 (2017) 036]
∆2βpeng = (−1.10+0.70−0.85)
K. De Bruyn, R. Fleischer[JHEP 03 (2015) 145]
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 13
Controlling the penguin pollution in φs
13/ 69
Now come 2 complications:1 B0
s → J/ψKK : superposition of 4 polarized final states 0,⊥, ‖,SParameter Value
φ0s −0.045 ± 0.053 ± 0.007
φ‖s − φ0
s −0.018 ± 0.043 ± 0.009φ⊥s − φ
0s −0.014 ± 0.035 ± 0.006
φSs − φ
0s 0.015 ± 0.061 ± 0.021
|λ0| 1.012 ± 0.058 ± 0.013|λ‖/λ0| 1.02 ± 0.12 ± 0.05|λ⊥/λ0| 0.97 ± 0.16 ± 0.01|λS/λ0| 0.86 ± 0.12 ± 0.04
Mixing induced (φs) and direct CPV parameters (λ) are measured.So far, no φs polarization-dependence measured [LHCb, PRL 114, 041801 (2015)]
2 Decay b → ccs involves not only tree, but also gluonic, electroweak penguins,exchange and penguin annihilation topologies!What we measured in B0
s→ J/ψφ is φs = −2βs + ∆φpengs + ∆φNP
s .Mandatory to control ∆φpeng
s to claim NP!
Tree
Bq
J/ψ
X
W
b
q
q
c
c
q′
Penguin
Bq
J/ψ
XW
b
q q
q′
c
c
u, c, t
Colour SingletExchange
Exchange
B0q J/ψ
X
W
b
q c
c
q′
q′Colour SingletExchange
Penguin-Annihilation
B0q
J/ψ
X
W
b
q
q′
q′
c
c
u,c,t Colour Singlet
Exchange
Olivier Leroy (CPPM) Prospects for CPV and mixing in neutral B 13 July 2016 13 / 32Determine ∆φpeng
s from SU(3)-related modes, where penguin unsuppressedS. Faller, R. Fleischer, T. Mannel [arXiv:0810.4248]
• B0 → J/ψρ (BF, C, S)
• B0s → J/ψK∗ (BF, C), has no PA and E
φs penguin pollution of J/ψφLHCb with 3 fb−1 (J/ψK∗+J/ψρ)[JHEP11(2015)082],[PLB742(2015)38-49]
Consistent with zero
∆φ0s = 0.000+0.011
−0.009(stat)+0.009−0.004(syst)
∆φ‖s = 0.001+0.010−0.014(stat)± 0.008(syst)
∆φ⊥s = 0.003+0.010−0.014(stat)± 0.008(syst)
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 14
Summary
• β will remain the most precisely measured angle of the unitarity triangle
→ Ultimate precision depends on assuring excellent detector performance, e.g. flavour tagging at LHCbUpgrade, and measuring precisely the physics parameters (∆Γ, ∆m...)
• φs will continue to be dominated by B0s → J/ψKK, at LHCb modes with neutrals and electrons to be
added
• Penguin pollution to be determined with increased precision in U-spin and SU(3)-related modes both byLHCb and Belle II
Thanks for your attention!
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 15
BACKUP
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 16
d4Γ(B0s → J/ψφ)
dt dΩ∝
10∑i=1
hk(t)fk(Ω), B0s flavour dependent↓ ↓
hk(t) = Nke−Γs t
[ak cosh(
1
2∆Γst) + bk sinh(
1
2∆Γst)±ck cos(
1
2∆mst)±dk sin(
1
2∆mst)
]
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 17
φs from B0s → J/ψKK
• First measured by CDF and D0
• Measurements by ATLAS, CMS and LHCb from LHC Run I
LHC Run I B0s → J/ψKK measurements
Experiment√s Int. luminosity
ATLAS 7− 8 TeV 19.2 fb−1[JHEP 08 (2016) 147], [PRD 90, 052007 (2014)]
CMS 8 TeV 19.7 fb−1[PLB 757, 97 (2016)]
LHCb 7− 8 TeV 3 fb−1[PRL 114, 041801 (2015)], [PRL 108, 101803 (2012)]
Tagging power Tagging category Time res.
εtag (1− 2ω)2
ATLAS 1.49± 0.02% OS (µ, e, b-jet) 97 fs [PLB 757, 97 (2016)]
CMS 1.307± 0.032% OS (µ, e) 78 fs [JHEP 08, 147 (2016)]
LHCb 3.73± 0.15% OS (µ, e, K) + SS (K) 46 fs [PRL 114, 041801 (2015)]
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 18
Measurement of φs
φs accessed in B0s decay time distribution
aCP(t) ≡Γ(B0
s → f )− Γ(B0s → f )
Γ(B0s → f ) + Γ(B0
s → f )= ηf sin(φs) sin(∆mst)
aCP(t) ≈ e−12
∆m2sσ
2t (1− 2ω) ηf sin(φs) sin(∆mst)
e−12
∆m2sσ
2t Decay time with finite resolution σt
ηf CP eigenvalue
(1− 2ω) Flavour tagging with mistag probability ω
Two types of taggingPV
SV
𝑏 → 𝑐
𝑏 → 𝑋𝑙−
SV
𝑐 → 𝑠
same side
opposite side
𝑏
𝑏
𝐽/𝜓
𝐾∗0
𝑑
𝑑𝑢
𝜋+
𝑥
𝑙−
𝐾+
𝐵0
ℎ𝑏
SS pion
SS kaon (for 𝘉0𝘴 )
OS muon
OS electron
OS kaon
OS vertex charge
→ Same-side tagging:B0
s flavour from charge of kaonoriginating from primary vertex
—————————
→ Opposite-side tagging:B0
s flavour from charge of kaon, muon orelectron originating from a secondaryvertex
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 19
φs from B0s → J/ψKK for M(KK) < 1.05GeV/c2 | LHCb [PRL 114, 041801 (2015)]
• Penguin contribution possibly different for eachpolarisation
• Compare results with assigning different φis for
i = 0,⊥, ‖, S→ Measure λi = |λi |e−iφ
is
• Result consistent with nominal fit, i.e. nopolarisation dependency
CP evenCP oddS wave
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 20
φs from B0s → J/ψKK for M(KK) < 1.05GeV/c2 | LHCb [PRL 114, 041801 (2015)]
• LHCb measurement with 3 fb−1
• Subtract background with sWeights determined from fit to M(J/ψKK)
→ Fit to MC to subtract peaking backgroundsB0
d → J/ψKπ (∼ 1700 events) and Λb → J/ψpK− (∼ 5000 events)
→ Fit to the data to subtract the combinatorial background
Nsig ≈ 96× 103
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 21
Future potential in φs
Diego Martınez Santos
Veronika Chobanova CPV in beauty decays at LHCb XIV HQL 22