Rare decays, radiative decays and b sll transitions at LHCb

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1 Rare decays, radiative decays and b sll transitions at Andrew Crocombe, on behalf of the collaboration University of Warwick 19/3/18-3 rd Rencontres de Moriond - QCD and High Energy Interactions

2 Rare decays - Searching for new physics Rare decays are rare in the context of the Standard Model (SM) Flavour-changing neutral current (FCNC) processes are of particular interest They are heavily suppressed and so new physics (NP) can appear at a similar or larger level as SM contributions New particles can appear at loop or tree level Search both for small deviations in precisely predicted SM processes and for forbidden processes that can only occur through NP A rich field with many interesting current anomalies and prospects For results on lepton flavour universality see talk by J. Albrecht b R(L) W s L(R) V tb V ts b t s b s t γ L(R) W W + ν µ + µ t W γ,z µ + µ A. Crocombe Rare decays, radiative decays and b sll transitions Moriond QCD 18

3 B (s)! µ+ µ A golden channel rare decay mode, loop and helicity suppressed in the SM Both theoretically and experimentally clean Search carried out with 3 fb 1 Run 1 and 1.4 fb -1 Run data Results in the first single experiment observation of Bs! µ + µ (with a significance of 7.8σ), first measurement of the B effective lifetime and sets a limit on B! µ + s! µ + µ µ B(B s! µ + µ )=(3. ± ) 1 9 (B s! µ + µ )=.4 ±.44 ±. ps B(B! µ + µ ) < [9% C.L] All of these are consistent with SM predictions, setting stringent limits on possible NP models [Phys. Rev. Lett. 118, (17)] A. Crocombe Rare decays, radiative decays and b sll transitions Moriond QCD 18 3

4 Photon polarisation in B s! Candidates / ( MeV/c ) Candidates / ps Data B s φγ 6 m(φγ ) [MeV/c ] Data Fit SM Model Signal Peaking Missing kaon Combinatorial B s φγ [Phys. Rev. Lett. 118, 181 (17)] t [ps] First study of photon polarisation in a radiative decay B s Study carried out with 3 fb 1 Run 1 data Extract the polarisation parameter A the decay time distribution of events A = Agrees with the SM expectation within standard deviations A SM = from Muheim et al. [Phys. Le1. B664 (8) ] A. Crocombe Rare decays, radiative decays and b sll transitions Moriond QCD 18 4

5 ] [c 4 /GeV db/dq Branching fractions in b sll decays B! K µ + µ 1 1 q [GeV /c 4 ] [JHEP 11 (16) 47] [JHEP 4 (17) 14] c 4 ] - GeV -8 [1 φµµ)/dq db(bs B s! µ + µ 1 1 q SM pred. Data [JHEP 9 (1) 179] [GeV /c 4 ] [JHEP 6 (14) 133] A. Crocombe Rare decays, radiative decays and b sll transitions Moriond QCD 18

6 ] [c 4 /GeV db/dq Branching fractions in b sll decays B! K µ + µ The differential branching fractions of a variety of b sll processes all tend q [GeV to /cbe 4 ] systematically lower then SM predictions q c 4 ] - GeV -8 [1 φµµ)/dq db(bs B s! µ + µ [JHEP While 11 there (16) is 47] no individually large tension, perhaps this is [JHEP 4 (17) 14] pointing towards some consistent deviation from the SM? SM pred. Data [JHEP 9 (1) 179] [GeV /c 4 ] [JHEP 6 (14) 133] A. Crocombe Rare decays, radiative decays and b sll transitions Moriond QCD 18 6

7 B! K µ + µ Four body final state, with the system described by 3 angles and the invariant mass squared of the dimuon system (q ) The angular distribution provides access to observables that are sensitive to new physics These observables depend on Wilson coefficients and hadronic form factors Try to construct ratios of observables with less form factor dependence (e.g. ) P P P' measurement of from run 1 data (3 fb -1 ) shows local tensions with the SM at a combined significance of 3.4σ angular analysis 1.. J/ψ(1S) data SM from DHMV SM from ASZB ψ(s) [JHEP (16) 14] q Descotes-Genon et al. [JHEP 1 (14) 1] Altmannshofer and Straub [Eur. Phys. J. C7 (1) 38] [GeV /c 4 ] A. Crocombe Rare decays, radiative decays and b sll transitions Moriond QCD 18 7

8 B! K µ + µ Four body final state, with the system described by 3 angles and the invariant mass squared of the dimuon system (q ) The angular distribution provides access to observables that are sensitive to new physics These observables depend on Wilson coefficients and hadronic form factors Try to construct ratios of observables with less form factor dependence (e.g. ) P P P' measurement of from run 1 data (3 fb -1 ) shows local tensions with the SM at a combined significance of 3.4σ angular analysis 1.. data Belle data J/ψ(1S) ATLAS data CMS data SM from DHMV SM from ASZB ψ(s) [JHEP (16) 14] [CMS-BPH-1-8] q [ATLAS-CONF-17-3] [GeV /c 4 ] [Phys. Rev. Lett. 118, (17)] A. Crocombe Rare decays, radiative decays and b sll transitions Moriond QCD 18 8

9 Global fits Global fits can be carried out to take into account multiple measurements SM Re C NP 9 Altmannshofer et al. [Eur.Phys.J. C77 (17) 377] Global fits favour a modified SM vector-current up to 4.9σ C9 NP Whether this is new physics or the effect of underestimated QCD uncertainties remains to be seen A. Crocombe Rare decays, radiative decays and b sll transitions Moriond QCD 18 9

10 b dll transitions Further suppressed in SM by CKM factor V td /V ts Provide similar but complementary information compared to b sll Some of the rarest decays that we have the potential to observe at the moment, will require more data for angular analyses Will be important to see if similar anomalies are seen in these decay as are seen in their b sll counterparts B s s b t s d K W Z/γ µ + µ A. Crocombe Rare decays, radiative decays and b sll transitions Moriond QCD 18 1

11 b dll transitions So far the decay B +! + µ + µ has been observed by and can be used in combination with B +! K + µ + µ and lattice results to measure V td /V ts Also have observed and seen evidence for a B! + µ + b! p µ + µ µ at B(B ±! ± µ + µ )=(1.83 ±.4 ±.) 1 8 B( b! p µ + µ )=(6.9 ± 1.9 ± ) 1 8 B(B! + µ + µ )=(.11 ±.1 ±.1 ±.16) 1 8 V td V ts =.1 ±. Du et al [Phys. Rev. D93 (16) 34] Candidates per 63 MeV/c 3 1 Data Signal and bkg Λ b pπµµ Combinatorial Part reco ) Events/( MeV/c Bs π + π µ + µ - - B π + π µ + µ B - K*(89) µ + µ s B η' µ + - µ Combinatorial Total fit [JHEP 1 (1) 34] m pπµµ / (MeV/c ) [JHEP 4 (17) 9] M(π + π µ + µ ) [GeV/c [Phys. Lett. B743 (1) 46] ] A. Crocombe Rare decays, radiative decays and b sll transitions Moriond QCD 18 11

12 B s! K µ + µ Further CKM suppressed version of B! K µ + µ Could be used to measure V td /V ts in a similar way as done between B -> + K! mu + mu µ + µ and B +! K + µ + µ Perform a search using 3 fb 1 Run 1 and 1.6 fb -1 Run data Normalise the decay to B! J/ [! µ + µ ]K Candidates / 1. MeV/c Data Fit * Bs K µ + µ * B K µ + µ Λb pk µ + µ Comb. bkg. Preliminary Candidates /. MeV/c Preliminary Data Fit Bs J/ψ K * B J/ψ K * B K * µ + µ Λb J/ψ pk + + B J/ψ K Comb. bkg [-PAPER-18-4] m(k π + µ + µ ) [MeV/c ] m(j/ψ K π + ) [MeV/c ] A. Crocombe Rare decays, radiative decays and b sll transitions Moriond QCD 18 1

13 First evidence for B s! K µ + µ Provides first evidence for this decay with significance of 3.4σ First measurement of the branching fraction: NEW! B(B s! K µ + µ )=(3. ± 1.(stat) ±.(sys) ±.3(norm)) 1 8 Candidates / / MeV/c Data Data Fit Fit * Bs K * µ s + µ + * B K µ + µ * B K µ + µ Λb pk µ + µ Comb. Λb pk bkg. µ + µ Comb. bkg. Preliminary [-PAPER-18-4] m(k π m(k π + µ + µ + µ ) [MeV/c + µ ) [MeV/c ] ] 11 1 Preliminary ΔlogL1 N[B s K * µ + µ ] A. Crocombe Rare decays, radiative decays and b sll transitions Moriond QCD 18 13

14 Search for + c! pµ + µ Rare baryonic c ull FCNC process Search for non-resonant component carried out on 3 fb 1 Run 1 data Normalise to the resonant mode No significant non-resonant component is found, as such a limit is set: B( + c + c! p! pµ + µ ) < [9% C.L.] This is the best set limit on this mode In addition, the resonant + c! p! mode is observed for the first time at σ with branching fraction: B( + c! p!) =(9.4 ± 3. ± 1. ±.) 1 4 Candidates / (7 MeV/c ) Candidates / (7 MeV/c ) Candidates / (7 MeV/c ) a) nonresonant b) c) φ region 3 4 ω region m(p µ + µ ) [MeV/c ] 3 4 m(pµ + µ ) [MeV/c ] [arxiv: , Submitted to Phys. Rev. Lett.] A. Crocombe Rare decays, radiative decays and b sll transitions Moriond QCD 18 14

15 Evidence for Rare baryonic s dll FCNC process +! pµ + µ Previous evidence for this decay reported by the HyperCP collaboration, with the observed events all having very similar dimuon invariant mass search carried out on 3 fb 1 Run 1 data Evidence for the decay at the level of 4σ, no significant structure in m µ+ µ B( +! pµ + µ )=( ) 1 8 [Phys. Rev. Lett. 94, 181 ()] [arxiv: , Submitted to Phys. Rev. Lett.] A. Crocombe Rare decays, radiative decays and b sll transitions Moriond QCD 18 1

16 Summary Rare decays provide powerful probes of the SM and potential NP scenarios has the ability to make a wide variety of rare decay measurements Rare decay observables can provide stringent limits on NP models Measurements in b sll transitions seem to be pointing towards a modification of the SM The range of b dll measurements that are possible are opening up with more data, will tensions be seen here as well? Baryonic charm and strange FCNC decays are probing largely unexplored CKM transitions More and more analyses are being carried out with the larger LHC Run datasets, keep watching for more results from! A. Crocombe Rare decays, radiative decays and b sll transitions Moriond QCD 18 16

17 Backup

18 Angular observables Complex angular distribution Observables with reduced form factor dependence A. Crocombe Rare decays, radiative decays and b sll transitions Moriond QCD 18 18

19 Wilson coefficients Can parameterise an effective field theory for b s transitions with the Hamiltonian: X H e / V tb Vts (C i O i + CiO i) i C i Wilson coefficient (short distance physics) O i Local operators CiO i Right handed counterparts (suppressed in SM) New physics can either modify the existing Wilson coefficients or add new operators C 9 and C 1 quantify contributions through the vector and axial-vector couplings A. Crocombe Rare decays, radiative decays and b sll transitions Moriond QCD 18 19