Rare b-decays Status and prospects

Rare b -decays

Status and prospects

Carlos S´anchez Mayordomo

X CPAN Days Salamanca, Spain 29th October 2018

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Outline

Rare b-decays: introduction Radiative b→sγ

Leptonic b →`<sup>+</sup>`⁻ Semileptonic b→s`<sup>+</sup>`⁻ Future prospects

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Rare b -decays

Flavour Changing Neutral Currents (FCNC) are forbidden at tree-level in the Standard Model (SM)

Sensitive to new particles entering in the loop diagrams Access to much larger scales(compared to direct searches)

b→sγ

b_R(L) W⁻ s_L(R)

γ_L(R) t

Vtb Vts

b→`<sup>+</sup>`⁻ b→s`<sup>+</sup>`⁻

b s

µ⁺ µ⁻ ν

W⁻ W⁺

t

b s

µ⁺ µ⁻ t

γ, Z⁰ W⁻

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Rare b -decays

Effective theory provides a model-independent description H_eff∝V_tbV_ts^∗X

i

C_iOi+C_i⁰O⁰i

Wilson coefficientsCi absorb contributions above the energy scale (can be compared with the SM prediction!)

Relevant operators in rare decays:

O7⁽⁰⁾∝(¯sσ_µνP_L,Rb)F^µν O9⁽⁰⁾∝(¯sγ_µP_L,Rb)(¯`γ<sup>µ</sup>`) O10⁽⁰⁾∝(¯sγ_µP_L,Rb)(¯`γ<sup>µ</sup>γ<sub>5</sub>`)

O⁽S⁰⁾∝(¯sσ_µνP_L,Rb)`<sup>+</sup>`⁻ O⁽P⁰⁾∝(¯sγ_µP_L,Rb)(¯`γ<sub>5</sub>`)

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Rare b -decays

Transition C₇⁽⁰⁾ C₉⁽⁰⁾ C₁₀⁽⁰⁾ C_S,P⁽⁰⁾ b→sγ X

b→`<sup>+</sup>`⁻ X X

b→s`<sup>+</sup>`⁻ X X X

!"#$%&$%$"'$(

J/ψ(1S)

ψ(2S) C7^(!)

C7^(!)C₉^(!) C₉^(!) C10^(!)

4 [m(µ)]² q²

dΓ dq²

)"*(

+,"-(*!.#)"'$(

',"#%!/01,".(&%,2(

)/,3$(,4$"('5)%2(

#5%$.5,6*((

c¯c

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Radiative decays

Sensitive to C

Photon polarization

New physics could modify the photon polarization in b→sγ

Photons are predominantly left-handed in the SM In some models (like LRSM), |A_R/A_L|up to 1/2

JHEP 12 102 (2013)

6/21

Time-dependent B

→ φγ

Time-dependent decay rate:

Γ_(B0

s+ ¯B_s⁰)→φγ(t)∝e^−Γst

cosh (∆Γst/2)−A^∆sinh (∆Γst/2)

2] c ) [MeV/

γ φ ( m

5000 5500 6000

)2cCandidates / (25 MeV/

0 100 200 300 400

500 Data

Model Signal Peaking Missing kaon Combinatorial LHCb

[ps]

t

0 5 10

Ratio of candidates

0 0.05 0.1 0.15 0.2 0.25 0.3

Data Fit SM LHCb

Compatible with SM within2σ

A^∆=−0.98^+0.46_−0.52(stat.)^+0.23_−0.20(syst.)

See C.Remon talk

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Angular B

→ K

e

e

Angular analysis atq² <1 GeV² Virtual photon decaying to e⁺e⁻

Transverse asymmetries are sensitive toC₇⁰

] c2 / [MeV

−) e e+ π− K+ ( m

4800 5000 5200 5400

) 2cCandidates / (30 MeV/

0 5 10 15 20 25

30 Data

Model B⁰→K*0e+e⁻ e− e+ ) X

*0 K

→( B Combinatorial

LHCb

θl cos

-0.5 0 0.5

Candidates / (0.2)

0 10 20 30 40

50 LHCb

θK cos

-1 -0.5 0 0.5 1

Candidates / (0.2)

0 5 10 15 20 25 30 35

40 LHCb

[rad]

0 1 2 φ∼ 3

rad) πCandidates / (0.1

0 5 10 15 20 25 30

35 LHCb

A⁽²⁾_T (q²→0) = 2Re(C7C₇^0∗)

|C7|²+|C₇⁰|² A^Im_T (q²→0) = 2Im(C7C₇^0∗)

|C7|²+|C₇⁰|² Results compatible with SM

A⁽²⁾_T =−0.23±0.23±0.05 A^Im_T = +0.14±0.22±0.05

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Radiative constraints

CurrentC₇⁰ constraints from radiative decays

The combination is consistent with SM

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Leptonic decays

b → `

`

B

→ µ

µ

LHCb measurement with 4.4 fb⁻¹

First observation from a single experiment, 7.8σ B(B_s⁰ →µ⁺µ⁻) = 3.0±0.6^+0.3_−0.2

×10⁻⁹ B(B⁰ →µ⁺µ⁻)<3.4×10⁻¹⁰

Lifetime measurement:

τ(B_s⁰→µ⁺µ⁻) = 2.04±0.44±0.05 ps

Phys. Rev. Lett. 109, 041801 (2012)

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B

→ τ

τ

and leptonic LFV searches

Search ofB_(s)⁰ →τ⁺τ⁻ with 3 fb⁻¹ at LHCb:

B(B_s⁰ →τ⁺τ⁻)<6.8×10⁻³ (95% CL) B(B⁰ →τ⁺τ⁻)<2.1×10⁻³ (95% CL)

Phys. Rev. Lett. 118, 251802 (2017)

Lepton Flavour Violation (LFV) searches (3 fb⁻¹):

Decay BR limit Reference

B_s⁰ →e⁺µ⁻ 6.3×10⁻⁹ JHEP 1803 (2018) 078

B⁰ →e⁺µ⁻ 1.3×10⁻⁹ JHEP 1803 (2018) 078

τ →µµµ 4.7×10⁻⁸ JHEP 02 (2015) 121

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Semileptonic decays

b → s`

`

Differential branching ratios

Several measurements systematically below the SM at lowq²:

B→KµµJHEP 06 (2014) 133 B→K^∗0µµJHEP 04 (2017) 142

B_s⁰→φµµ JHEP 09 (2015) 179

Λ⁰_b →ΛµµJHEP 06 (2015) 115

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Angular observables in B

→ K

µ

µ

Clean observable (form factor independent): JHEP 1305 (2013) 137

P₅⁰ = S₅ pFL(1−FL)

] c4 2/ [GeV q2

0 5 10 15

5'P

−1

−0.5 0 0.5 1

(1S)ψ/J (2S)ψ

LHCb data Belle data

ATLAS data CMS data SM from DHMV SM from ASZB

JHEP 02 (2016) 104

Phys. Rev. Lett. 118,11 (2017) 111801 JHEP 12 (2014) 125

JHEP 10 (2018) 047

Phys. Rev. Lett. B781 (2018) 517-541 Eur. Phys. J. C75 (2015) 8, 382

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Global fit (BRs and angular)

Eur. Phys. J. C77 (2017) 6, 377

14/21

Lepton Flavour Universality (LFU) tests

Ratios are accurately predicted in the SM R_K = B(B⁺→K⁺µ⁺µ⁻)

B(B⁺→K⁺e⁺e⁻) R_K^∗ = B(B⁰ →K^∗0µ⁺µ⁻) B(B⁰ →K^∗0e⁺e⁻)

Results with 3 fb⁻¹ at LHCb:

2.6σ from SM

Phys. Rev. Lett. 113, 151601 (2014)

2.1−2.5σ from SM

JHEP 08 (2017) 055

15/21

Global fit (including LFU)

Global fit including all theb→s`<sup>+</sup>`⁻ observables

Phys. Rev. D 96, 055008 (2017)

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Phase difference in B

→ K

µ

µ

Fit to the full dimuon spectrum: small interference Small interference

B(B⁺ →K⁺µ⁺µ⁻) = (4.37±0.15±0.23)×10⁻⁷ 3σ deviation from SM prediction

Eur. Phys. J. C (2017) 77: 161

17/21

Other results: Λ

→ pπ

µ

µ

First observation ofb→dtransition in baryons

B(Λ⁰_b →pπ⁻µ⁺µ⁻) = (6.9±1.9±1.1)×10⁻⁸ Measurement of the CP asymmetry:

∆A_CP= (−3.5±5.0±0.2)×10⁻² a^T_CP^ˆ−odd= (1.2±5.0±0.7)×10⁻²

JHEP 04 (2017) 029

18/21

Other results: b → d`

`

First evidence ofB⁰_s →K¯^∗0µ⁺µ⁻,3.4σ significance Using 4.4 fb⁻¹ data (2011-2016)

B(B_s⁰ →K¯^∗0µ⁺µ⁻) = (2.9±1.0±0.3)×10⁻⁸

JHEP 07 (2018) 020

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Future prospects

LHCb after Upgrade

Future prospects

Radiative:

Stat. uncertainty below 1% (syst. dominated) Explore b→dγ territory

B_s⁰→µ⁺µ⁻:

σ(B) andσ(τeff) around 2% (syst. dominated) CP(t) analyses

Semileptonic:

Up to 300 fb⁻¹ in HL-LHC

arXiv:1808.08865

20/21

Summary

Rare decays provide clean observables to test the SM

Radiative (C₇⁰ constraints) and leptonic (BRs) are consistent with SM. But still room for NP

Semileptonics: tensions wrt SM

In differential BRs, angular analyses and LFU tests Discrepancies pointing to NP in C₉ (and possiblyC₁₀) Run2 analyses ongoing

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