b-physics at FCC-ee

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b-physics at FCC-ee

Marie-Hélène SCHUNE IJCLab

CNRS/IN2P3 – Université Paris-Saclay

• Context

• Some interesting questions in b-physics and what FCCee could bring

Many thanks to Sébastien Descotes-Genon, Patrick Janot, Stéphane Monteil and Jacques Lefrancois for discussions

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Higgs boson seems quite SM-like

No sign of direct signals of NP particles (gap between SM and NP mass spectra)

Observations

Which are the sources of flavour symmetry

breaking we observed ?

Change of paradigm : not any more theory-driven

b-physics

CP violation and FCNC : sensitive probes of short distance physics 𝐴 𝜓_# → 𝜓_% + 𝑋 = 𝐴_* 𝑐_,-

𝑣^/ + 𝒄_𝐍𝐏

𝜦_𝐍𝐏^𝟐 NP scale and coupling Probes scales >> 1 TeV (depending on c_NP)

FCCee workshop January 2020 2

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Looking back in the mirror : K

_L

à ππ

« The discovery emphasizes, once again, that even almost self evident principles in science cannot be regarded fully valid until they have been critically examined in precise

1961 1964

Cronin and Fich :

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The main current players : B-Factories (Belle2) and LHCb

Belle-II

,

• No hadronization

• Constraint from the other B + beam E

• Quantum correlation

• Clean events

• Trigger fully efficient on B-events

⇒Modes with neutrals, inclusive measurements, high tagging effective efficiency

LHCb

• Gigantic statistics

• All b-hadrons types produced

• Large boost

⇒ Access to tiny BRs, time measurement

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The ideal experimental conditions for b-physics ?

5 10¹² Z⁰ Z^* → 𝑏𝑏 7~ 15%

B_u B_d B_s B_c Λ_b

600 10⁹ 600 10⁹ 150 10⁹ ~1.5 10⁹ 150 10⁹ production : CP symmetric

𝑏𝑏 7

SomeΛ_b polarization ?

Clean e+ e- environment No pile-up, no trigger

ALEPH DELPHI OPAL

−0.49A.B* A.CDE.B/ E.CD

−0.23A./* A.*DE./H E.*I

−0.56A.CB A.*KE./* E.*K

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Some interesting questions in b-

physics and what FCCee could bring

This is obviously as of today, I am not a soothsayer

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The b à s ℓℓ transitions

Relative importance of the different diagrams varies with q²= M²(ℓ⁺ℓ^-)

¯b

d

¯

u/¯c/¯t ¯s

e⁻ e⁺ W⁺

γ/Z⁰

K^∗⁰ B⁰

¯b

d

¯ u/¯c/¯t

¯s

e⁻ e⁺ W⁺

γ/Z⁰

K^∗⁰ B⁰

¯b

d

¯

u/¯c/¯t ¯s

e⁻

e⁺ W⁺

K^∗⁰ B⁰

W⁻ ν^e

ℓ⁺ ℓ^-

?? ?? ??

Rich phenomenology:

o BF (but large theoretical uncertainties due to non-perturbative QCD) o Angular observables

o Ratios of BF (test of Lepton Universality)

A perfect place to

search for NP

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b à s ℓℓ: current situation

B

⁰

→K

^*0

µµ angular analysis: tensions with the SM. Clearly exhibited in

P’5 observable

cc loops : theoretical debate about their impact

but

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R

_Hs

=1 (at 10

^-3

) in the SM

R_K , R_K* , Rφ , R_pK …

0 2 4 6

q² [GeV²/c⁴]

0.6 0.8 1.0 1.2 1.4

RpK

LHCb

arXiv:1912.08139

A coherent picture can be built with the B

⁰

→K

^*0

µµ angular analyses results

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And then ?

• Add more stat

• Change experimental environment

• Measure B⁰→K^*0 ee angular distributions and compare with B⁰→K^*0µµ

Statistics only

systematics wall around 0.5 % ?

R

_Hs

precision in the 1-6 GeV

²

bin

Journal of Physics G: Nuclear and Particle Physics, Volume 46, Number 2 (2018)

2015 2020 2025 2030 2035

Year 0.00

0.05 0.10 0.15 0.20 0.25 0.30

Projecteduncertainty

Belle II RK

Belle II RK⇤

LHCb RK

LHCb RK⇤

LHCb R LHCb RpK

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The challenging part is the modes with the electrons

~ 30% X0 before the magnet

Bremsstrahlung

A light detector is of prime importance !

~0.5 % X0 may be feasible

LEP

~5-10% X0 (Beam pipe, VtxD ..)

LHCb

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But all this with large data samples

B_u B_d B_s B_c Λ_b

FCCee 600 10⁹ 600 10⁹ 150 10⁹ ~1.5 10⁹ 150 10⁹

Belle2 110 10⁹ 110 10⁹ - - -

These huge samples in a clean environment should allow to study b →dℓℓ (factor 20 reduction in rate) B⁰➝ρℓℓ

2011-2016

JHEP 07 (2018) 020

Mass resolution !

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LU tests with tree diagrams

?

e or µ

3.1 σ tension with the SM

But what if a connexion between the 2 Statistics here is not an issue Important to have different experimental conditions

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Search for B

⁰

➝ K* ττ

ILD type detector

Momentum down to 10 MeV σ(PV) = 3 µm

σ(B vtx) = 7µm σ(τ vtx) = 5µm PV B

K

π

τ τ

ππ π

π π π

arXiv:1705.11106

Add π⁰ if possible ?

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Search for B

⁰

➝ K* ττ

Unique place where this can be seen

10¹³Z⁰ and SM BR assumed

BsàDsDsK*

BsàDsK* τν arXiv:1705.11106

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FCCee workshop January 2020

b → cℓ ν and b → uℓ ν

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The knowledge of Vcb is also crucial for tests of CKM and searching for NP in FCNC.

Current precision : V_cb 1.9 %

V_ub 4 %

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V _cb from B _c à τν

b

c

W+

τ⁺

ν Vcb

with NP :

Large missing energy

Use of the other hemisphere

~ 1

B_u B_c

Mass ~5280 MeV ~6275 MeV Lifetime ~1.5 ps ~0.5 ps

⇒ discrimination should be possible

About 20 10⁶ B_càτν with τàe/µ ν produced 1% precision should be

achievable

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Another way to obtain V _cb ?

WW production

₁₀₈ _{WW pairs}

BR(Wà q₁ q₂) = 67%

c-jet b-jet W Vcb

W

b s s d d u c u c u Signal

background

230k

1.7k 127M 6.8M 6.8M 127M Not on the Z⁰ peak

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b c uds Eff b-jet tagger 25%

Eff c-jet tagger 10% 50% 2%

ILD@ILC

Tracking and Vertexing at Future Linear Colliders:

Applications in Flavour Tagging Tomohiko Tanabe (U Tokyo)

IAS Program on High Energy Physics 2017, HKUST

Numbers inspired by:

bTag_c

Very first look !

relative precision on Vcb 0.4 % ? (now 1.5%)

σ(Vcb)/Vcb

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b

c

u c W+

e+/µ⁺ V_ub ν

D⁰

But B_u àD⁰ ℓν and DCS D⁰ decay

B_u B_c

Mass ~5280 MeV ~6275 MeV

Lifetime ~1.5 ps ~0.5 ps

⇒ some discrimination.

Studies to be performed (need a factor

~ 200)

𝐵𝑅 𝐵_O → 𝐷^*ℓ^E𝜈

𝐵𝑅 𝐵_R → 𝐷^*ℓ^E𝜈 ~.0092 Number kindly

provided by Sebastien Descotes-Genon)

N B_U

N B_V = 1.5 600

3.9 10^A/

1.5 10^AH ×.0092~.006

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CP violation in mixing : B _s à D _s ℓ ν

Signal B

_s

à D

_s

ℓ ν with D

_s

à KK π

Backgrounds

ILD type detector

0)

SL(B

-0.02 -0.01 0 0.01A 0.02

) s0 (B SLA

-0.02 -0.01 0 0.01

HFLAV

PDG 2019

B factory average

LHCb

µX

(*)

D(s)

→

0

B(s)

0 D

µX

(*)

D(s)

→

0

B(s)

0 D

muons

0 D

average

× 10 Theory World average

2 = 1 χ

∆

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CP violation in mixing : B _s à D _s ℓ ν

⇒ Statistical uncertainty ~ few 10^-5

But : detection asymmetry to be kept under control Discriminating variables :

lepton p_T

First observation of CP violation in mixing in b- decays accessible ?

S. Monteil @ FCC week Brussels 2019

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CPV in the interference between mixing and decay : B _s à D _s K

Needs to distinguish B_sàD_sK from B_sàD_sπ K/π/p ID is crucial

Mass resolution is crucial for background rejection

Flavour tagging is of prime importance

G. Wilkinson’s talk

High p PID

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JHEP 03 (2018) 059

After PID cuts:

BsàDsK

BsàDsπ

M(DsK)

Tagging performances: But 𝐵𝑅 𝐵_X → 𝐷_X𝜋

𝐵𝑅 𝐵_X → 𝐷_X𝐾 = 𝑉_R\

𝑉_RX

/

~20 LEP B-factories LHCb

ε(1−2η)² ~20-25% ~30% 6%

FCCee should be >~LEP

Hadron PID !

ILD type detector for momentum

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Summary

• 5 10¹² Z⁰ bosons seems to be an ideal place for b-physics

• … but with a well designed detector Tracking and vertexing :

Momentum reconstruction down to 100 MeV σ(PV) = 3 µm

σ(B vtx) = 7µm σ(τ vtx) = 5µm

PID:

Electron/muon up to 45 GeV π/K/p separation over the full kinematical range

e/γ:

resolution : ~3%√E and granularity (transverse and longitudinal)

V0s (K_s and Λ):

Good efficiency and precision important (CPV, B Λ )

G. Wilkinson’s talk

b-physics at FCC-ee