Lepton flavour universality violating B decays in trees

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Lepton flavour universality violating B decays in trees

Adam Morris

To cite this version:

Lepton flavour universality violating B decays in trees

Adam Morris

Aix Marseille Univ, CNRS/IN2P3, CPPM

XIII Meeting on B Physics Marseille, 2nd October, 2018

Introduction

Introduction

Lepton Flavour Universality (LFU):

• In SM, electroweak couplings of charged leptons are identical (universal).

• Difference between e, — and fi should therefore only be driven by mass.

• Test: ratios of branching fractions to final states differing by lepton flavour. LFU tests with tree-level b-hadron decays:

R(X

) =

B(X

→ X

fi



)

B(X

→ X

‘



)

:

• ‘+_{: average e}+_{& —}+_{or just —}+

b c q Xb Xc W+ e+_=—+_=fi+ 

Introduction

Introduction

In this talk:

• BaBar R(D)–R(D∗) hadronic tag, leptonic fi

• Belle R(D)–R(D∗) hadronic tag, leptonic fi

• Belle R(D∗) semileptonic tag, leptonic fi

• LHCb R(D∗) muonic fi

• LHCb R(J= ) muonic fi

• Belle R(D∗) 1-prong hadronic fi (+ fi polarisation)

• LHCb R(D∗_{) 3-prong hadronic fi}

Predictions:

• R(D) = 0:299 ± 0:003[HFLAV Summer 2018] • R(D∗) = 0:258 ± 0:005[HFLAV Summer 2018]

• R(J= ) ∈ [0:25; 0:28][PLB452 (1999) 120, arXiv:0211021, PRD73 (2006) 054024, PRD74 (2006) 074008]

Leptonic fi modes

Leptonic fi modes

Leptonic fi modes

Introduction to B-factory measurements

B-factory measurements: R(D(∗)) = B(B → D (∗)_fi−_ fi) [B(B → D(∗)_e−_ e) + B(B → D(∗)—−—)]=2 • Use fi−→ e−_ efi and fi−→ —−—fi so

normalisation modes have same visible final states

• Charged and neutral B and D(∗) _mesons

• D and D∗ reconstructed in many final states

+ µ 0 D 0 B p PV p τ ν τ+ − → * 0 D B + K − * D µ ν 0 D 0 B p PV p µ ν µ+ − → * 0 _D B + K + µ µ ν − * D

BaBar: R(D)–R(D∗ ) hadronic tag PRL 109, 101802 (2012) and PRD 88, 072012 (2013)

BaBar R(D)–R(D∗_{) with hadronic tag}

• Reconstruct hadronic decays of other B (=Btag)

+ D(∗) _{+ ‘(=e,—)}

• Yields determined from 2D fit:

• m2 miss≡ |Pe+e−− PBtag− PD(∗)− P‘|2 • |p∗ ‘| ≡ momentum of ‘ in B frame R(D) = 0:440 ± 0:058 (stat) ± 0:042 (syst) R(D∗) = 0:332 ± 0:024 (stat) ± 0:018 (syst) • R(D) 2:0ff above SM • R(D∗) 2:7ff above SM • Combination 3:4ff from SM [PRL 109, 101802 (2012)]

Belle: R(D)–R(D∗ ) hadronic tag PRD 92, 072014 (2015)

Belle R(D)–R(D∗_{) with hadronic tag}

• Reconstruct hadronic decays of other B (=Btag)

+ D(∗) _{+ ‘(=e,—)}

• Yields determined from simultaneous 1D fits:

• mmiss2 for m 2

miss< 0:85 GeV/c 2

• Neural network output for mmiss2 > 0:85 GeV/c 2 , trained to distinguish B → D(∗)_fi− fi from backgrounds R(D) = 0:375 ± 0:064 (stat) ± 0:029 (syst) R(D∗) = 0:293 ± 0:038 (stat) ± 0:015 (syst)

• Combination 1:8ff from SM, 1:4ff from BaBar result

[PRD 92, 072014 (2015)]

Belle: R(D)–R(D∗ ) hadronic tag PRD 94, 072007 (2016)

Belle R(D∗_{) with semileptonic tag}

• Reconstruct B0tag→ D∗+‘−‘ along with B0sig→ D∗+‘−‘ or D∗+fi−fi

• Yields determined 2D fit:

• EECL≡ energy in ECAL not associated with

reconstructed B

• Neural network output, trained to distinguish

D∗fi  from D∗‘

R(D∗) = 0:302 ± 0:030 (stat) ± 0:011 (syst)

• 1:6ff above SM

[PRD 94, 072007 (2016)]

Belle: R(D)–R(D∗ ) hadronic tag PRD 94, 072007 (2016) Introduction to LHCb measurements LHCb measurements: R(Xc) = B(Xb→ Xcfi+fi) B(Xb→ Xc—+—)

• Same visible final state Xc—+

+ µ 0 D 0 B p PV p τ ν τ+ − → * 0 D B + K − * D µ ν 0 D 0 B p PV p µ ν µ+ − → * 0 _D B + K + µ µ ν − * D

Belle: R(D)–R(D∗ ) hadronic tag PRL 115, 112001 (2015) LHCb R(D∗_{) muonic: introduction} R(D∗) = B(B 0_{→ D}∗−_fi+_ fi) B(B0_{→ D}∗−_—+_ —)

• Both modes havesame visible final state: D∗−—+.

• Neither fully reconstructable, due to neutrinos.

• B0_{momentum approximated using B}0_{decay vertex and scaling visible}

longitudinal momentum by m(B0)=m(D∗−—+)

• Resolution on kinematic variables enough to distinguish between fi /— modes.

• 3D binned template fit to extract yields:

• q2_{≡ |P}

B0− PD∗|2,

• m2miss≡ |PB0− PD∗− P_—+|2,

• E_—∗+≡ muon energy in B0rest frame.

Belle: R(D)–R(D∗ ) hadronic tag PRL 115, 112001 (2015)

LHCb R(D∗_{) muonic: fit and result}

R(D∗) = 0:336 ± 0:027 (stat) ± 0:030 (syst)

• 1:9 ff above SM

• Largest systematics: simulated sample size and mis-ID — template

) 4 /c 2 (GeV miss 2 m -2 0 2 4 6 8 10 Pulls -2 2 4) /c 2 (GeV miss 2 m -2 0 2 4 6 8 10 5000 10000 15000 20000 −0.40 < q2 < 2.85 GeV2/c4 LHCb ) 4 /c 2 Candidates / (0.3 GeV ) 4 /c 2 (GeV miss 2 m -2 0 2 4 6 8 10 Pulls -2 2 4) /c 2 (GeV miss 2 m -2 0 2 4 6 8 10 10000 20000 30000 2.85 < q2 < 6.10 GeV2/c4 LHCb ) 4 /c 2 Candidates / (0.3 GeV ) 4 /c 2 (GeV miss 2 m -2 0 2 4 6 8 10

Pulls -2 2 miss (GeV2/c4) 2 m -2 0 2 4 6 8 10 5000 10000 15000 20000 25000 LHCb 4 /c 2 < 9.35 GeV 2 6.10 < q ) 4 /c 2 Candidates / (0.3 GeV ) 4 /c 2 (GeV miss 2 m -2 0 2 4 6 8 10 Pulls -2 2 ) 4 /c 2 (GeV miss 2 m -2 0 2 4 6 8 10 1000 2000 3000 4000 LHCb 4 /c 2 < 12.60 GeV 2 9.35 < q ) 4 /c 2 Candidates / (0.3 GeV * (MeV) µ E 500 1000 1500 2000 2500 Pulls -2 2 500 1000 1500 2000Eµ* (MeV)2500 1000 2000 3000 4000 −0.40 < q2 < 2.85 GeV2/c4 LHCb Candidates / (75 MeV) * (MeV) µ E 500 1000 1500 2000 2500 Pulls -2 2 500 1000 1500 2000Eµ* (MeV)2500 2000 4000 6000 8000 10000 12000 2.85 < q2 < 6.10 GeV2/c4 LHCb Candidates / (75 MeV) * (MeV) µ E 500 1000 1500 2000 2500 Pulls -2 2 500 1000 1500 2000Eµ* (MeV)2500 5000 10000 15000 6.10 < q2 < 9.35 GeV2/c4 LHCb Candidates / (75 MeV) * (MeV) µ E 500 1000 1500 2000 2500 Pulls -2 2 * (MeV) µ E 500 1000 1500 2000 2500 1000 2000 3000 4000 9.35 < q2 < 12.60 GeV2/c4 LHCb Candidates / (75 MeV) Data ν τ D* → B X')X ν l → ( c D*H → B ν D**l → B ν µ D* → B Combinatorial µ Misidentified [PRL 115, 112001 (2015)]

Belle: R(D)–R(D∗ ) hadronic tag PRL 120, 121801 (2018) LHCb R(J= ) muonic: introduction R(J= ) = B(B + c → J= fi+fi) B(Bc+→ J= —+—)

• Both modes havesame visible final state: J= —+.

• 3D binned template fit to extract yields:

• B+

c decay time,

• m2miss,

• Z(E_—∗+; q2) ≡ flattened 4 × 2 histogram of E_—∗+, q2.

• B+

c decay form factors not precisely determined;

constrained experimentally from this analysis.

• Low rate of B_c+production, but no long-lived D-meson background. + µ + c B p PV p µ ν τ ν ψτ+ +_{→ /J} Bc ψ / J − µ + µ + µ + c B p PV p µ ν µ ν ψµ+ +_{→ /J} Bc ψ / J − µ + µ

Belle: R(D)–R(D∗ ) hadronic tag PRL 120, 121801 (2018)

LHCb R(J= ) muonic: fit and result

• First evidenceof the decay B+

c → J= fi+fi (3 ff

significance).

R(J= ) = 0:71 ± 0:17 (stat) ± 0:18 (syst)

• 2 ff above the SM.

• Largest systematics: B+

c → J= form factors and

MC statistics 5 − 0 5 10 ) 4 /c 2 Candidates / ( 0.6 GeV 1000 2000 3000 4000 5000 ) 4 /c 2 (GeV miss 2 m 5 − 0 5 10 Pulls−05 5 LHCb 0.5 1 1.5 2 Candidates / ( 0.376 ps ) 2000 4000 6000 8000 10000 12000 14000 16000 (ps) τ 0.5 1 1.5 2 Pulls−50 5 0 2 4 6 8 Candidates / ( 1 ) 1000 2000 3000 4000 5000 6000 7000 8000 ) * µ ,E 2 Z(q 0 2 4 6 8 Pulls−50 5 [PRL 120, 121801 (2018)]

Hadronic fi modes

Hadronic fi modes

Hadronic fi modes PRL 118, 211801 (2017) and PRD 97, 012004 (2018)

Belle R(D∗_{) 1-prong hardonic and fi}−_polarisation

• Using fi−→ ı−_

fi and fi−→ −fi

• Reconstruct hadronic mode of other B (Btag) +

D∗+ fi /‘

• B → D∗_fi−_

fi yield from simultaneous fit to EECLin different signs of cos „h, B species and fi− decay

• B → D∗‘‘ yield from fitting mmiss2

R(D∗) = 0:270 ± 0:035 (stat)+0:028_−0:025(syst) Pfi(D∗) = −0:38 ± 0:51 (stat)+0:21−0:16(syst)

[PRD 97, 012004 (2018)]

Hadronic fi modes PRL 120, 171802 (2018) and PRD 97, 072013 (2018)

LHCb R(D∗_{) 3-prong hadronic: introduction}

K(D∗) =B(B 0_{→ D}∗−_fi+_ fi) B(B0_{→ D}∗−_3ı±₎ = Nsig Nnorm "norm "sig 1 B(fi+_{→ 3ı}±_(ı0_) fi)

• Signal and normalisationsame visible final state:

D∗−3ı±.

• Nsig from 3D binned template fit:

• q2≡ |PB0− PD∗|2_,

• fi+ decay time,

• Output of BDT trained to discriminate signal from D∗D+s.

• Nnormfrom unbinned max likelihood fit to

m(D∗3ı±).

• Make use ofthree-prong tau vertexin selection.

• Convert K(D∗) to R(D∗): R(D∗) = K(D∗) B(B 0_{→ D}∗−_3ı±₎ B(B0_{→ D}∗−_—+_ —) B0_{→ D}*−_τ+_ν τ π− π+ π+ ντ D0 B0 π− p PV p B0 → D*− τ+_ν τ π− K+ τ+ Δz > 4σΔz ντ B0_{→ D}*−_τ+_ν τ π−_K+ π− ππ− + π+ D0 B0 π0_... PV p p B0_{→ D}*−_π+_π−_π+_X

Hadronic fi modes PRL 120, 171802 (2018) and PRD 97, 072013 (2018)

LHCb R(D∗_{) 3-prong hadronic: fit and result}

[ps] τ t 0 0.5 1 1.5 2 Candidates / ( 0.25 ps ) 0 500 1000 1500 2000 2500 3000 3500 LHCb Data Total model τ ν + τ − * D → 0 B τ ν + τ ** D → B (X) + s D − * D → B (X) + D − * D → B X π 3 − * D → B (X) 0 D − * D → B Comb. bkg. (a) ] 4 c / 2 [GeV 2 q 0 5 10 ) 4 c/ 2 Candidates / ( 1.375 GeV 0 500 1000 1500 2000 2500 (b) BDT 0 0.1 0.2 0.3 Candidates / 0.1 0 1000 2000 3000 4000 5000 6000 _(c) [PRL 120, 171802 (2018), PRD 97, 072013 (2018)] K(D∗) = 1:97 ± 0:13 (stat) ± 0:18 (syst)

R(D∗) = 0:291 ± 0:019 (stat) ± 0:026 (syst) ± 0:013 (ext):

• 0:9 ff above SM, compatible with experimental average.

Averages

Averages

Averages World averages R(J/ψ) LHCb R(J/ψ) PRL 120, 121801 (2018) 0.71± 0.17± 0.18 -0.5 0 0.5 1 SM predictions PLB 452 (1999) 129 arXiv:hep-ph/0211021 PRD 73 (2006) 054024 PRD 74 (2006) 074008 Range 0.25 - 0.28 • 6 × R(D∗), 2 × R(D), 1 × R(J= ).

• All lie above the SM expectation.

0.2 0.3

R(D*)

BaBar had. tag

0.018

±

0.024

±

0.332

Belle had. tag

0.015 ± 0.038 ± 0.293 Belle sl.tag 0.011 ± 0.030 ± 0.302

Belle hadronic tau

0.027 ± 0.035 ± 0.270 LHCb muonic tau 0.030 ± 0.027 ± 0.336 LHCb hadronic tau 0.029 ± 0.019 ± 0.291 Average 0.007 ± 0.013 ± 0.306 SM Pred. average 0.005 ± 0.258 PRD 95 (2017) 115008 0.003 ± 0.257 JHEP 1711 (2017) 061 0.008 ± 0.260 JHEP 1712 (2017) 060 0.005 ± 0.257 HFLAV Summer 2018 /dof = 0.4/ 1 (CL = 52.00 %) 2 χ [HFLAV Summer 2018] 0.2 0.4 0.6 R(D) BaBar had. tag

0.042

±

0.058

±

0.440 Belle had. tag

0.026 ± 0.064 ± 0.375 Average 0.024 ± 0.039 ± 0.407 PRD94,094008(2016) 0.003 ± 0.299 FNAL/MILC (2015) 0.011 ± 0.299 HPQCD (2015) 0.008 ± 0.300 HFLAV Summer 2018 /dof = 0.4/ 1 (CL = 52.00 %) 2 χ

Averages

World averages

• HFLAV summer 2018 R(D)–R(D∗) average is

3:8 fffrom the SM.

• Reduction from 4:1 ff due to increase in theory uncertainties. 0.2 0.3 0.4 0.5 0.6 R(D) 0.2 0.25 0.3 0.35 0.4 0.45 0.5 R(D*) BaBar, PRL109,101802(2012) Belle, PRD92,072014(2015) LHCb, PRL115,111803(2015) Belle, PRD94,072007(2016) Belle, PRL118,211801(2017) LHCb, PRL120,171802(2018) Average Average of SM predictions = 1.0 contours 2 χ ∆ 0.003 ± R(D) = 0.299 0.005 ± R(D*) = 0.258 HFLAV Summer 2018 ) = 74% 2 χ P( σ 4 σ 2 HFLAV Summer 2018 [HFLAV Summer 2018]

Averages

Conclusions and prospects

• Hints of LFU violationin semitauonic B decays.

• R(D)–R(D∗): 3:8 ff away from SM.

• R(J= ): 2 ff above SM.

• BaBar and Belle results statistics dominated

• Improved precision from Belle II

• LHCb results only use Run 1 data: Runs 2,3,4... will bring much larger statistics.

• LHCb results systematics-dominated

• Many systematics will reduce with more data and more MC

• Others will reduce with improved external measurements (BESIII, Belle II)

• LHCb plans: analyses of more modes

• b → cfi−fi: R(D+), R(D0), R(Ds+ (∗) ), R(˜+c (∗) ) ... • b → ufi−fi: ˜0b→ pfi − fi, B+→ ppfi+fi ...

• New observables beyond ratios of branching fractions, e.g. angular analyses to discriminate between NP models.

Backup slides

Backup slides

Backup slides

Tau branching fractions

Mode BF (%) fi−→ ı−_ı0_ fi 25:49 ± 0:09 fi−→ e−_ efi 17:82 ± 0:04 fi−→ —−_ —fi 17:39 ± 0:04 fi−→ ı−_ fi 10:82 ± 0:05 fi−_{→ 3ı}∓_ fi 9:31 ± 0:05 fi−_{→ 3ı}∓_ı0_ fi 4:62 ± 0:05 [PDG]

Backup slides

LHCb R(D∗_{) muonic systematics}

• MC statisticslargest

systematic.

• Mis-ID — template: reduce

withimproved rejectionand

more sophisticated technique.

Source ‹R(D∗)[×10−2]

Simulated sample size (model) 2.0

Misidentified — template shape 1.6

B0_{→ D}∗+_(fi−_=—−_{) form factors 0.6}

B → D∗+Xc(→ —X0)X shape corrections 0.5 B(B → D∗∗_fi−_

fi)=B(B → D∗∗—−—) 0.5

B → D∗∗(→ D∗ıı)— shape corrections 0.4

Corrections to simulation 0.4

Combinatorial background shape 0.3

B → D∗∗_{(→ D}∗+_ı)—−_

—form factors 0.3

B → D∗+(D+

s → fi )X fraction 0.1

Simulated sample size (normalisation) 0.6

Hardware trigger efficiency 0.6

Particle identification efficiencies 0.3

Form-factors 0.2

B(fi−_{→ —}−_

—fi) < 0:1

Total systematic uncertainty 3.0

[PRL 115, 112001 (2015)]

Backup slides

LHCb R(J= ) systematics

• B_c+form factors: recent

improvements should enter into updated measurement.

• MC statisticssecond-largest

systematic.

Source ‹R(J= )[×10−2_]

Simulation sample size 8.0

B_c+→ J= form factors 12.1 B+ c→ (2S) form factors 3.2 Bias correction 5.4 B_c+→ J= XcX cocktail composition 3.6 Z binning strategy 5.6

Misidentification background strategy 5.4

Combinatorial background cocktail 4.5

Combinatorial J= sideband scaling 0.9

Empirical reweighting 1.6

Semitauonic (2S) and fflcfeed-down 0.9

Fixing A2(q2) slope to zero 0.3

Efficiency ratio 0.6

B(fi+_{→ —}+_

—fi) 0.2

Total systematic uncertainty 17.7

[PRL 120, 121801 (2018)]

Backup slides

LHCb R(D∗_{) hadronic systematics}

• Largest systematic

uncertainty isMC statistics.

• Uncertainties on double charm backgrounds should improve withmore dataand

improved external

measurements.

• Uncertainty on efficiency ratio should improve with more statistics.

Source ‹R(D∗ )_{R(D∗ )}[%]

Simulated sample size 4.7

Empty bins in templates 1.3

Signal decay model 1.8

D∗∗fi fiand D∗∗s fi fifeed-down 2.7 D+_s→ 3ı±_{X decay model 2.5} B → D∗D_s+X; D∗D+X; D∗D0X backgrounds 3.9 Combinatorial background 0.7 B → D∗−3ı±X background 2.8 Efficiency ratio 3.9

Normalisation channel efficiency 2.0

(modelling of B0→ D∗−_3ı±₎

Total systematic uncertainty 9.1

[PRL 120, 171802 (2018), PRD 97, 072013 (2018)]

Backup slides

LHCb R(D∗_{) hadronic backgrounds}

• Most abundant background: Xb→ D∗−3ı±X.

• ∼ 100× more abundant than signal.

• Suppressed by requiring fi+_vertex

to be 4ff∆z downstream from B

vertex.

• Improves S=B by factor 160.

• Remaining backgrounds: double charm modes with non-negligible

lifetimes: • Xb→ D∗D+sX ∼ 10× signal, • Xb→ D∗D+X ∼ 1× signal, • Xb→ D∗D0X ∼ 0:2× signal. z ∆ σ z/ ∆ -8 -4 0 4 8 12 16 20 Candidates / 0.1 1 10 2 10 3 10 4 10 → LHCb simulation ) X π π π * D Prompt ( ) DX * D Double-charm ( ) ν τ * D Signal ( [PRD 97, 072013 (2018)]

Backup slides

LHCb R(D∗_{) hadronic backgrounds}

Discriminate between signal and double charm backgrounds using a BDT that exploits the resonant structures in the 3ı± systems from fi+ _{and D}+

s decays. Control samples of D∗D+ sX, D∗D+X and D∗D0X used to correct simulation. BDT response -0.4 -0.2 0 0.2 Candidates 0 0.02 0.04 0.06 0.08 0.1 _→ Signal Background LHCb simulation [PRD 97, 072013 (2018)] ] 2 c ) [MeV/ + π − π + π − * D ( m 4000 4500 5000 5500 ) 2 c Candidates / ( 24 MeV/ 0 20 40 60 80 100 120 140 160 180 200 (a) Data Total model + s D − * D → 0 B + * s D − * D → 0 B (2317) + * 0 s D − * D → 0 B (2460) + 1 s D − * D → 0 B X + s D ,0 − ** D → 0,+ B X + s D − * D → 0 s B Comb. bkg. [PRL 120, 171802 (2018), PRD 97, 072013 (2018)]