CP violation in beauty decays at LHCb...Lp-p collisions Run 1 (7 8TeV) 2010-2013 3fb 1 Run 2 (13TeV)...

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


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]


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]


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


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)


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 =−0.0364± 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


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 =−0.0364± 0.0012 rad [UTFit]


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


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


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


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]


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)


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!


BACKUP


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)

]


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)]


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



• 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



• 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


Future potential in φs

Diego Martınez Santos


CP violation in beauty decays at LHCb...Lp-p collisions Run 1 (7 8TeV) 2010-2013 3fb 1 Run 2 (13TeV)...

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Transcript of CP violation in beauty decays at LHCb...Lp-p collisions Run 1 (7 8TeV) 2010-2013 3fb 1 Run 2 (13TeV)...