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B physics

(summary)

XLVIII International Meeting on Fundamental Physics Benasque, Sep 10

2021

Arantza Oyanguren (IFIC – Valencia)

1

Outline

 Introduction

 The beauty experiments

 Rare B decays

 Semileptonic B decays

 The future

 CKM and CP Violation

 Spectroscopy

2

Introduction

 In the Standard Model of Particle Physics, transitions between different quarks are governed by the CKM mechanism:

t b

u c

d s

Q=+2/3

Q=-1/3



The amplitude of a hadron decay process can be described using Effective Field Theories: Operator Product Expansion (OPE)

Hadronic Matrix Elements

CKM couplings

Wilson Coefficients

( = scale)

q q’

q 3

Hadronic Matrix Elements

CKM Wilson

Coefficients ( = scale)

 ’

Electroweak scale ~ 1/M_W New Physics scale ~ 1/M_NP

C

= C

+ C

C’

= C’

+ C’

Primed C’i  right handed currents:

suppressed in SM

 OPE: a series of effective vertices multiplied by effective coupling constantsCⁱ .

0



0

0

q q’

0

Introduction

couplings

4

Why B decays?

 The b-quark is the heaviest quark forming hadronic bound states (m~4.7 GeV)

 Must decay outside the 3^rd family

 Long lifetime (~1.6 ps)

 Many accessible decay channels (small BR’s)

Flavour oscillations and CP violation

Dominant: bc (favoured) and bu (suppressed)

Rare: Flavour Changing Neutral Current (FCNC): b s,d

Ideal place to probe New Physics effects!

Good for

experimentalists!

Good for theorists!



Type of processes:

5

The beauty experiments

GOLDEN EAGLE

(Aquila Chrysaetos) 2 m wingspan

4-7 kg weight

6

LHCb ATLAS

The LHC experiments

7

● The bb cross section in pp collisions is large, mainly from gluon fusion

~ 300 μb @ √s=7 TeV

~ 600 μb @ √s=13 TeV

b, b

b, b

● The LHCb idea: to build a single-arm forward spectrometer:

~ 4% of the solid angle (2 < η < 5),

~30% of the b hadron production

The b quarks hadronize in B, B_s, B*_(s), b-baryons…

 average B meson momentum ~ 80 GeV

Letter of Intent, 1995

[PRL 118 (2017) 052002]

The LHCb experiment

[JHEP 02 (2021) 023]

8

P_T ~ 1.3-3.8%

IP_~ 25-100m

_P ~ 0.5-1%

IP_~ 15-50 m

|η|<2.4

P_T ~ 0.7-1.5%

IP_~ 25-100m

Very good PID (fake < 0.1%) |η|<2.5 2<η<5

Good PID (fake < 3%)

LHCb,

ATLAS & CMS

The LHC experiments

9

The Belle-II experiment

● Upgrade of the KEK e⁺e^- asymmetric accelerator and the Belle experiment, working at the (4S) (10.54 GeV)

7 GeV

4 GeV

10

The experimental data

3 (Run1) + 6 (Run2) fb^-1 (2011 - 2018)

213 fb^-1 (2019 - 2021)

11

Rare B decays

BEARDED VULTURE

(Gypaetus Barbatus) 2.75 m wingspan

5-7 kg weight

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Rare B decays

● b s,d quark transitions are Flavor Changing Neutral Currents (FCNCs),

 in the SM they only can occur through loops (penguin and box diagrams), excellent probe for physics beyond the SM

Experimentally → leptons/photons with high transverse momenta BR ~ 10^-7

BR ~ 10^-9

b s

W

BR ~ 10^-5

leptonic semileptonic radiative

Theoretically → observables can be calculated in terms of Wilson coefficients

⁺

^-

Ex:

Hadronic uncertainties in decay constants or form factors

13

Rare B decays: B _s  ⁺  ^-

● Very rare decay: FCNC and helicity suppressed BR_SM = 3.66(14) x 10^-9

● Searched for over the last 30 years,

observed by LHCb and CMS [Nature 522 (2015) 68]

● New results by LHCb (Run1+Run2 = 9fb^-1):

12

[arXiv:2108.09283 and 2108.09284v2 [hep-ex]]

‘21

14

Rare B decays: B _s  ⁺  ^-

[CMS PAS BPH-20-003]

● Also measured by ATLAS and CMS (2011-2016 data), combined result*:

* Result from LHCb with partial statistics

Below, but compatible with the SM at 2.1

ATLAS [JHEP04(2019)098]

CMS [JHEP04(2020)188]

LHCb [PRL118(2017)191801]

*

15

Rare B decays: B _d  ⁺  ^-

● Even more rare! (BR_SM ~ 10^-10), still not observed:

* Result from LHCb with partial statistics

[CMS PAS BPH-20-003]

ATLAS [JHEP04(2019)098]

CMS [JHEP04(2020)188]

LHCb [PRL118(2017)191801]

*

16

Rare B decays: B _s  ⁺  ^-

q² = (p_⁺ + p_^-)²

(GeV²)

 Differential decay width: d/dq²

charmonium resonances cc ^-⁺

photon pole

 

SM values (=m

): C

~ - 0.33 C

~ 4.27 C

~ - 4.17

(Everything else small or negligible)

Each q² region probes different processes

C

= C

+ C

(Primed C’_iright handed currents:

suppressed in SM)

B_s mass vesus q² for B_s→⁺^-

J/

(2S)

B_s→⁺^-

Rare B decays: B _s  ⁺  ^-

[arXiv:2105.14007]

m(B_s)

‘21

18

Rare B decays: B _s  ⁺  ^{- ‘21}

[arXiv:2105.14007]

In the q² region 1.1-6 GeV²  3.6 away from SM predictions

Results in other channels:

19





 Angular distribution in B_s ^-⁺ : it depends on q² and three angles









K

B

W

q

 Function of observables related to CP-averages and asymmetries:

F_L , A_FB, S_i, A_i

Rare B decays: B _s  ⁺  ^{- ‘21}

K

[arXiv:2107.13428]

20

Rare B decays: B _s  ⁺  ^{- ‘21}

In general good agreement with SM (no P₅’ observable here), deviations less than 2₂₁

 “Optimized observables”, with form factor cancellations

[JHEP 05 (2013) 137]

Rare B decays: B  K*  ⁺  ^-

~3 local deviation

Negative shift of Re(C₉) preferred over SM hypothesis at level of 2-3

Two new analyses by LHCb with full data:

Angular analysis of B⁺K*⁺⁺^- [PRL 126 (2021) 161802]

Angular analysis of B⁰K*⁰⁺^- [PRL 125 (2020) 011802]

[JHEP 10 (´18) 047]

[PRL 118 (¨17) 111801]

[PLB 781 (¨18) 517]

B⁰K*⁰⁺^-

22

 Experimentally, we perform a double ratio to cancel systematic uncertainties

 In the SM all leptons are expected to behave in the same way

= 1.000 + O(m_²/m_b²)

 Precise theory prediction due to

cancellation of hadronic form factor uncertainties

Rare B decays: R _K

Test of lepton universality:

 Challenge: bremsstrahlung by electrons

23

Rare B decays: R _K

Reconstructed B mass for B⁺→K⁺⁺^- (muons vs electrons) [arXiv:2103.11769]

‘21

B⁺→K⁺⁺^-

B⁺→K⁺e⁺e^-

24

Rare B decays: R _K

Reconstructed B mas for B⁺→K⁺⁺^- (muons vs electrons) [arXiv:2103.11769]

‘21

B⁺→K⁺⁺^-

B⁺→K⁺e⁺e^-

25

Rare B decays: R _K

 Deviation from SM at 3.1   evidence of LFU violation

Results with full LHCb data:

‘21

(1 GeV² < q² < 6 GeV²) [arXiv:2103.11769]

(submitted to Nature Physics)

26

Rare B decays: R _K

 Previous results in other channels:

[JHEP 05 (2020) 040]

[JHEP 08 (2017) 055]

 LHCb measurement in the BK*⁺^- channel, R_K*, with 3fb^-1

 LHCb measurement in the _bpK⁺^- channel, R_pK, with 5fb^-1

[BELLE2-NOTE-PL-2020-014]

 Ongoing R_x analyses with full stat.

 And Belle II entering in the game…

‘

b s W

Rare B decays:  _b  ^‘21

[LHCb-PAPER-2021-03]

 First measurement of the photon polarization in a b-baryon system!

(Expected to be left handed in the SM)

In agreement with SM

28

Rare B decays:  _b   

29

‘21

[arXiv: 2108.07678]

 Constraints from radiative (C7⁽‘⁾):

 Search for other channels: _b^-:

29

Rare B decays

SM

New Physics hypothesis preferred over SM by more than 4 - 5

Main effect on the C^9 coefficient: 4.27^SM -1.1^NP

Triggered models with Z’, leptoquarks (LQ), new fermions and scalars….

J. Matias et al, arXiv:2104.08921

SM

J.M. Camalich et al, arXiv:2103.12738

Global fits (more than 100 observables)

30

Semileptonic B decays

GRIFFON VULTURE

(Gyps Fulvus) 2.6 m wingspan

7-10 kg weight

31

Semileptonic B decays: R _D, R _D*

 Another test of lepton universality (now at tree level):

SM predictions very precise :

Based on HQET form factors:

[H. Na et al., PRD 92 (2015) 054510]

[Fajfer, Kamenic, Nišandižć: PRD85 (2012) 094025]

and experimental measurements (HFLAV) [D.Bigi, Gambino, PRD 94 (2016) 094008]

R(D)_SM=0.299  0.003 R(D*)_SM=0.252  0.003

Ratio of semi-tauonic and semi-muonic branching fractions:

Sensitive to charged Higgs bosons and leptoquarks

(V_cb and form factors (partially) cancel)

32

Semileptonic B decays

Information from the missing mass

squared m_miss²=(P_B-P_D*-P_)² and muon energy

signal normalization

[PRL 115 (2015) 111803]

 Using ^-^-__  Using ⁺⁺^-⁺_

Information from the position of

the pions. Normalized to B⁰D*^-⁺^-⁺ LHCb:  B⁰D*^-⁺ , with ⁺⁺^-⁺(⁰) _

 B⁰D*⁺ ^-_, with ^-^-__ [PRL 115 (2015) 111803]

[PRL 120 (2018) 171802]

 B⁺_cJ/^-⁺ , with with ^-^-__[PRL 120 (2018) 121801]

R(D*) R(J/)

3decay time

[PRL 120 (2018) 121801]

BaBar measured an excess of B⁰D⁽*⁾^-_ (3 away from SM!) [PRD 88 (2013) 072012]

[Nature 546 (2017) 227]

33

Semileptonic B decays

3

 Present global picture of R_D and R_D*

SM

 Average: 3 deviation from SM

 Last results from Belle using semileptonic tags (D and D*) [PRL 124, (2020) 161803]

34

CKM and CP Violation

BARN OWL

(Tyto Alba) 1 m wingspan

0.3 kg weight

35

CKM and CP Violation

 

   

2 3

2 2 2 3

1 1

1 2 1 2











 









 

O A

i A

A i A

V V

V

V V

V

V V

V V

tb ts

td

cb cs

cd

ub us

ud

CKM 



































 

















 The CKM matrix can be parameterized in terms of 4 fundamental parameters:

 Very high level of precision (few %)

 No inconsistencies

 Flavour observables can be expressed as function of these parameters:

Unitary Triangle

‘21

UTfit36

CKM and CP Violation

[LHCb-CONF-2021-001]

 New measurement of the  angle at LHCb:

‘21

The most precise determination from a single experiment!

Fit to 151 observables, 52 parameters Run1+Run2 data (frequentist).

Charm mixing parameters also measured:

37

Spectroscopy

41

EGYPTIAN VULTURE

(Neophron percnopterus) 1.7 m wingspan

2-2.5 kg weight

38

Spectroscopy

 There are several possibilities for combining quarks with color into colorless hadrons, as predicted from the origin of the Quark Model [M. Gell-Mann, PL8 (1964) 214]

 Several of these states have been announced since 1970, but have disappeared with time and new data analysis…

 Important for our understanding of the matter structure and QCD!

39

Spectroscopy

 More than 50 new hadrons discovered in the last decade, most of them by LHCb:

40

Spectroscopy

[PRL 115 (2015) 072001]

Observation of J/ψp Resonances Consistent with Pentaquark States

1263 citations !

41

Spectroscopy

 Hidden-charm tetraquarks [PRL 127 (2021) 082001]

 Hidden-charm pentaquarks:

[PRL 122 (2019) 222001]

42

Spectroscopy

CERN seminar next week:

https://indico.cern.ch/event/1065144/

[LHCb-PAPER-2021-031]

 Doubly-charmed tetraquark 𝑻⁺_𝒄𝒄!

‘21

43

The future

 New detector

 Full software trigger (30MHz)

 Event reconstruction on GPU cards

 + Turbo dedicated trigger scheme

 Installation and commissioning ongoing

 Analysis of Belle II with 5 ab^-1will start to be

competitive with LHCb

SciFi installation ⁴⁴

The future

My message:

 B Physics can be the key for new physics in the coming years

 Great contribution from the Spanish LHCb community and from theorists!

 Missing Spanish ATLAS and CMS

45

Thanks!

46