Rare decays at LHCb Siim Tolk (NIKHEF, Amsterdam) on behalf of the LHCb Collaboration Bormio 2014
Rare decays at LHCb Siim Tolk (NIKHEF, Amsterdam) on behalf of the LHCb Collaboration Other talks from LHCb: Monday (11:00) LHCb overview (Ulrich Uwer) Thursday (18:40) CP violation at LHCb (Antonio Romero Vidal) Bormio 2014
Standard Model Rare Decays Flavour Changing Neutral Currents in meson decays: All studied @ LHCb! c! u s! d b! d b! s Covered today 3
Standard Model Rare Decays Tree level diagrams forbidden in SM (GIM suppression) Main contributors: W box and electroweak penguin :, Z 0 Sensitive to new particles with masses ~O(100 TeV!) 4
Standard Model LHCb An event recorded by LHCb 5
Standard Model LHCb An event recorded by LHCb Excellent precision: momentum resolution (Δ p / p ~ 0.4 % at 5 GeV/c to 0.6 % at 100 GeV/c) impact parameter resolution (20 μm for high-pt tracks) invariant mass resolution particle identification (~ 97 % for 1-3 % π μ mis-id probability)! Very efficient trigger: ~ 90 % for dimuon channels ~ 30 % for multi-body hadronic final states 6
Rare decays: 3 groups Electroweak penguin, Z 0 Radiative Semi-leptonic Leptonic B ± u! (K ± res) B 0 d! K µ + µ B 0 s,d! µ+ µ μ + μ + μ - μ -, Z 0, Z0 u d s,d 7
Rare decays: 3 groups Radiative Semi-leptonic Leptonic B ± u! (K ± res) B 0 d! K µ + µ B 0 s,d! µ+ µ Many observables: A CP,A UD,d(BR)/dE A CP,F L,d(BR)/dq 2 BR(B 0 s,d! µ+ µ ) Constraining many NP sensitive Wilson coefficients: C (0) 7,C(0) 8 C (0) 7,C(0) 9,C(0) C (0) 10 10,C(0) S,C(0) P 8
Rare decays: 3 groups Electroweak penguin, Z 0 Radiative Semi-leptonic Leptonic B ± u! (K ± res) B 0 d! K µ + µ B 0 s,d! µ+ µ μ + μ + μ - μ -, Z 0, Z0 u d s,d 9
The decay B 0 s,d! µ+ µ ~10.000x! LHCb: First evidence for Bs to mumu! [PRL 110, 021801 (2013)] >25 years! 10
The decay B 0 s,d! µ+ µ FCNC and helicity suppressed Purely leptonic final state The SM prediction (Buras et al. [arxiv:1303.3820]) BR(B d! µ + µ )=(1.07 ± 0.10) 10 10 BR(B s! µ + µ )=(3.25 ± 0.17) 10 9 11
The decay B 0 s,d! µ+ µ FCNC and helicity suppressed Purely leptonic final state Theory error budget The SM prediction (Buras et al. [arxiv:1303.3820]) BR(B d! µ + µ )=(1.07 ± 0.10) 10 10 BR(B s! µ + µ )=(3.25 ± 0.17) 10 9 1+Aµµ s/2 s 1 ( s/2 s ) 2 =(3.56 ± 0.18) 10 9 Correction due to Γs (De Bruyn et al. [PRD 86, 014027 (2012)]) 12
Analysis +!µ µ Data sample 3fb-1 integrated luminosity Reconstruction improved Dimuon mass signal region blinded [doi:10.1103/physrevlett.111.101805] [arxiv:1307.5024] mµ+µ [MeV/c2] The decay 0 Bs,d 6000 5800 LHCb 1 1.1 fb (8TeV) Bs 5600 5400 5200 Bd 5000 0 0.2 0.4 0.6 0.8 1 BDT 1) Identify signal like events A loose muon pair selection Separate combinatorial background with an (re-optimised) BDT Based on the geometry and kinematics Shape calibrated on the data 13 Signal like
The decay B 0 s,d! µ+ µ Analysis 2) Extract the signal yield [doi:10.1103/physrevlett.111.101805] [arxiv:1307.5024] Mass PDF Signal resolution taken from data Partial reconstruction and mis-id Simultaneous mass fit in 8 BDT bins 14
The decay B 0 s,d! µ+ µ Analysis 3) Normalize to channels with known BR s [doi:10.1103/physrevlett.111.101805] [arxiv:1307.5024] 15 [LHCB-CONF-2013-011] (fs/fd uncertainty reduced from 7.8% to 5.8%)
The decay B 0 s,d! µ+ µ Results LHCb results (3fb -1 ): [doi:10.1103/physrevlett.111.101805] [arxiv:1307.5024] BR(B s! µ + µ )=(2.9 +1.1 1.0 (stat.)+0.3 9 (syst)) 10 BR(B d! µ + µ )=(3.7 +2.4 2.1 (stat.)+0.6 10 0.4 (syst)) 10 0.1 4.0σ! 2.0σ! CMS results (25fb -1 ): BR(Bs 0! µ + µ )=3.0 +1.0 0.9 10 9 BR(Bd 0! µ+ µ )=3.5 +2.1 10 1.8 10 4.3σ! 2.0σ! [doi: 10.1103/PhysRevLett.111.101804] [arxiv:1307.5025] 16
The decay B 0 s,d! µ+ µ Results 6) Combination: B s! µ + µ First observation! B d! µ + µ PRELIMINARY COMB: [LHCb-CONF-2013-012] [CMS-PAS-BPH-13-007] 1 D0 10.4fb 1 CDF 10fb ATLAS 4.9fb preliminary 1 1 CDF 10fb 1 LHCb 3fb SM 1 LHCb 3fb 1 CMS 25fb CMS+LHCb preliminary 0 SM 0 2 4 6 8 10 12 14 16 18 20 22 B(Bs µ + µ ) [10 9 ] 1 CMS 25fb CMS+LHCb preliminary 0 1 2 3 4 5 6 7 0 B(B µ + µ ) [10 BR(B s µ + µ )=(2.9 ± 0.7) 10 9 BR(B d µ + µ )=(3.6± 1.6 1.4) 10 10 >5σ <3σ 10 ] Measured branching ratios are compatible with the SM expectations. 17
The decay B 0 s,d! µ+ µ Implications Before the LHC results [D.Straub arxiv:1205.6094] After the LHC results Cartoon of plot from [D.Straub arxiv:1205.6094] 18
Rare decays: 3 groups Electroweak penguin, Z 0 Radiative Semi-leptonic Leptonic B ± u! (K ± res) B 0 d! K µ + µ B 0 s,d! µ+ µ μ + μ + μ - μ -, Z 0, Z0 u d s,d 19
The decay B ± u! (K ± Motivation res)! K ± ± Measured inclusive BR(B ±! K ± ± ) agrees well with the SM K1(1270) + [LHCb-CONF-2013-009] K1(1400) + K1(1430) + Background subtracted K1(1580) + K1(1770) + K1(1780) + 20
The decay B ± u! (K ± Motivation New Physics models can affect the angular variables: In SM, photon is dominantly left-handed: res)! K ± ± Right-handed component contributes little: m s /m b 0.02 NP models (LRSM, MSSM) can have a significant righ-handed component! 21
The decay Observables B ± u! (K ± res) Measure the up-down asymmetry [Gronau et al, PRL88 (2002) 051802]! K ± ± + K [LHCb-CONF-2013-009] The plane of K + 22
The decay Observables B ± u! (K ± res) Measure the up-down asymmetry [Gronau et al, PRL88 (2002) 051802]! K ± ± + K [LHCb-CONF-2013-009] The plane of K + Directly proportional to photon polarisation for a single resonance: c R 2 c L 2 c R 2 + c L 2 B! K res L,R amplitudes Not possible to translate from AUD to photon polarisation (for inclusive measurement) 23
The decay Analysis strategy B ± u! (K ± res)! K ± ± Data sample: 2fb-1 of 2012 data Mixture of cuts and multivariate techniques 2 Bins of K res mass K1(1270) + K1(1400) + K1(1430) + K1(1580) + K1(1770) + K1(1780) + Background subtracted 24 [LHCb-CONF-2013-009]
The decay Analysis strategy B ± u! (K ± res)! K ± ± Data sample: 2fb-1 of 2012 data Mixture of cuts and multivariate techniques 2 Bins of K res mass signal combinatorial bkg missing pion partially reco. K1(1270) + K1(1400) + K1(1430) + B+, UP B-, UP K1(1580) + K1(1770) + K1(1780) + B+, DOWN B-, DOWN Background subtracted 25 [LHCb-CONF-2013-009]
The decay B ± u! (K ± Results res)! K ± ± The up-down asymmetry: A± UD = U ± D ± U ± +D ± Photons are polarised (strong evidence!) Parity violated. 4.6σ! [LHCb-CONF-2013-009] 26
The decay Results B ± u! (K ± res)! K ± ± The CP asymmetry: 27
The decay Results B ± u! (K ± res)! K ± ± The CP asymmetry: [LHCb-CONF-2013-009] 28
Summary Radiative Semi-leptonic Leptonic B ± u! (K ± res) B 0 d! K µ + µ B 0 s,d! µ+ µ 2fb -1 analysed 1fb -1 analysed 3fb -1 analysed Non-zero A UD, with 4.6σ! No A CP seen. P 5 discrepancy of 3.7σ! Other observables agree to SM Observaion in B s channel (>5σ!) Bd channel (<3σ) Looking forward for the upgrade! 29
Summary Only a few B decays covered here, but many recent results: 30
Extras 31
Rare decays: 3 groups Electroweak penguin, Z 0 Radiative Semi-leptonic Leptonic B ± u! (K ± res) B 0 d! K µ + µ B 0 s,d! µ+ µ μ + μ + μ - μ -, Z 0, Z0 u d s,d 32
The decay B 0 d! K 0 µ + µ Motivation New Physics can alter a) Branching ratio BR(Bd 0! K 0 µ + µ ) O(10 6 ) from B factories, CDF. In agreement with SM.! b) Differential branching ratio: c) Angular distributions: 3 helicity angles ( L,, K ) d(br)/dq 2 (q - dimuon mass) 33
The decay B 0 d! K 0 µ + µ Differential branching ratio [JHEP 1308 (2013) 131] [10.1103/PhysRevLett.111.191801] LHCb Good agreement with SM! 34
The decay B 0 d! K 0 µ + µ Motivation Angular distributions ( L,, K ) o) Differential angular distribution can be written in terms of FL and Si: 35
The decay B 0 d! K 0 µ + µ Motivation Angular distributions ( L,, K ) o) Differential angular distribution can be written in terms of FL and Si: Message: [S. Descotes-Genon, T. Hurth, J. Matias, J. Virto, JHEP 05 (2013) 137] [arxiv:1303.5794] Yield and angular distributions in q2, give us FL and Si F L and Si are functions of Wilson coefficients and form factors 36
The decay B 0 d! K 0 µ + µ Angular observables Message: Yield and angular distributions, give us F L and Si F L and Si are functions of Wilson coefficients and form factors There are combinations of F L and Si with reduced form factor uncertainties: First measurement ever! Complementary to the existing measurements [S. Descotes-Genon, T. Hurth, J. Matias, J. Virto, JHEP 05 (2013) 137] [arxiv:1303.5794] 37
The decay B 0 d! K 0 µ + µ Angular observables IMPROVED FOLDING! P 4,6,8 in agreement with SM BUT: P 5 shows 3.7σ local discrepancy! [JHEP 1308 (2013) 131] [10.1103/PhysRevLett.111.191801] P 4 P 5 Integrated over the region 1.0 < q2 < 6.0 GeV 2 /c 4, the observed discrepancy is 2.5σ 38 Acceptable theory errors
The decay B 0 d! K 0 µ + µ Angular observables P 5! Theory explains? d(br)/dq 2 P 5 [S. Descotes-Genon, J. Matias, J.Virto, arxiv:1311.3876] Wilson coefficient: C 9 NP <0! (Z gauge boson?) 39
40 Mathieu Perrin-Terrin s talk on 16 th of August, 2013 in Meeting of the American Physical Society Division of Particles and Fields Santa Cruz, California!
Implications of the very rare decay results 41
Rare decays in the theory The effective Hamiltonian ( for b! s ) H eff = 4G F p 2 V tb V ts e2 16 Pi (C io 2 i + Ci 0O0 i )+h.c. Wilson coefficients (SHORT-scale effects) Operators (LONG-scale effects) 42
The decay B 0 d! K 0 µ + µ Analysis strategy Dataset: 2011 (1fb -1 ) Select candidates in K*( Kπ) invariant mass range! Reject dimuon resonances: BDT against combinatorial bkg. Topological info and PID Trained with B 0 K*J\Ѱ data for signal Trained with sideband data for bkg. Designed to be flat in angular acceptance Veryify the analysis on B 0 K*J\Ѱ [JHEP 1308 (2013) 131] [10.1103/PhysRevLett.111.191801] 43
The decay B 0 d! K 0 µ + µ Analysis strategy [JHEP 1308 (2013) 131] [10.1103/PhysRevLett.111.191801] Analysis done in 6 bins in q 2 from 0.1 < q 2 < 19 GeV 2 /c 4 With 883 signal candidates (1fb -1 ) Peaking backgrounds reduced to negligible level! 44
The decay B 0 d! K 0 µ + µ Angular observables [JHEP 1308 (2013) 131] [10.1103/PhysRevLett.111.191801] FL : Longitudinally polarised K* fraction Lepton forward-backward asymmetry LHCb A FB =4/3 S 6 Good agreement with SM! 45