Ivan Belyaev LAPP/Annecy & ITEP/Moscow Rare decays at LHCb Ivan Belyaev LAPP/Annecy & ITEP/Moscow

Loop induced rare decays Outline Loop-induced rare decays Event Simulation Event selection at LHCb Annual Event yields Background estimates Summary Loop induced rare decays Radiative penguins B → K*0g, Bs → fg, B → wg EW-penguins B → K*0m+m- Gluonic penguins Bs → ff , B → f KS “Very rare” B → m+m- LHCb detector and its status is presented in detail in plenary talk by T.Nakada I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

Rare (=“loop-induced”) decays Loop-induced decays are the perfect place to search for New Physics hints SM model loops are suppressed GIM cancellation “rare decays” Penguins b →s(d) g,Z0,g Boxes Heavy particles are suppressed in trees could appear in the loops New particles in loops: Enhancement in decay rates New phases New asymmetries … ? Ideal laboratory for New Physics search But also some QCD tests I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

Radiative penguin decays No so rare decays PDG Br(B→K*0g ) = (4.3±0.4)x10-5 Br(B-→K*-g ) =(3.8±0.5)x10-5 Isotopic asymmetries ~C6+C5/NC ~O(1%) Suppressed by : as , 1/mb or |VCKM| I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

b→s(d)g : CP-asymmetries 1-amplitude dominance strong phase appears at order of as or 1/mb →“Direct” asymmetries are small (≤1%) Bs → fg : not CP-eigenstate! V-A: g is circular polarized “Wrong polarization”: ~ms(md)/mb Both Amix and Adir are small I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

g Event Simulation p(K) K B(Bs) PYTHIA as pp-event generator as √s= 14 TeV QQ for weak-decays GEANT 3.21 Realistic geometry & material description The pile-up is included “Realistic” digitization, reconstruction algorithms & L0/L1 trigger simulation Background: “forward” bb̄-production in 400mrad cone 107 available events g p(K) K B(Bs) [PV] PV z I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

Background suppression Beauty particles: mb ~ 5 GeV/c2 bgct ~O(1cm) Particles from B-decays: Large pT L0 (hardware) trigger: leptons (e±,m±,mm), photons hadrons Large impact parameters L1 (software) trigger Background: bb̄-production with at least one B within 400mrad cone High Level Trigger and Off-line background suppression continues to utilize these properties B-decay products do not point to reconstructed primary vertices Exclusively reconstructed B-candidate does point to primary vertex B-candidate is associated with primary vertex with minimal impact parameter (significance) I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

Selection of Bd→ K*0g and Bs →fg p±,K± : charged tracks consistent with PID Inconsistent with any PV c2IP > 16(4) Two prong vertex c2VX < 49 K*0 : |DM| < 60 MeV/c2 f : |DM| < 10 MeV/c2 g : clusters in Ecal not associated with any reconstructed track ET > 2.8 GeV 2.2(2.0) < ET* < 2.7 GeV Bs →fg bb̄ K*0 f I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

Selection of Bd→ K*0g and Bs →fg (II) |qB| < 6 (15) mrad Correlated feeddown with merged p0, wrongly reconstructed as single photon B →K*0 p0 , Bs →fp0 opposite K*0(f) polarization |cos q| < 0.75 I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

Bd→ K*0g Bs →fg (III) B-mass window is defined as ±200 MeV/c2 s(MB) = 65 MeV/c2 The correlated feeddown is well under the control Annual yield ( using 1012 bb̄ events/107 second) Bd→ K*0g Bs →fg eREC [%] 4.5 4.3 eTRIG/REC [%] 19 eSEL/TRIG [%] 18 27 eTOT [%] 0.16 0.22 Bd→ K*0g Bs →fg N/year 35k 9.3k I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

Background Background estimation is limited by the size of available sample of 107 forward bb̄ events and 3x107 minimum bias events No background events are found in “wide” mass interval 4.5-6.0 GeV/c2 only 90%CL upper limits can be set now from bb̄-background We consider now forward bb̄ production as a major source of background large pT, large impact parameters, secondary verticies, … (This assumption need to be properly validated and proved) Bd→ K*0g Bs →fg B/S <0.7 <2.4 I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

First look at Bd→ wg 40 b→dg transition |Vtd| can be extracted without large theoretical uncertanty also for large Dms Br (B  K*g) /Br (B  wg ) ~ 65 reconstruction efficiency is low: p0 need to be reconstructed Background condition is difficult 3 neutral particles in final state s = (63 ± 9) MeV/c2 eTOT [%] N/year 0.012 40 B / S < 3.5 @ 90 % CL Br ( B0  w g ) = 0.5 × 10-6 I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

EW penguins: Bd →K*0m+m- Combination of b→sZ, b→sg penguins with the box diagram Both G and dG/ds is very sensitive to New Physics as well as the forward-Backward AFB(s) asymmetry q is angle between m+ and K*0 in dimuon restframe dG/ds AFB(s) I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

Selection of Bd→ K*0mm m±: charged tracks consistent with PID pT > 500 MeV/c2 Two prong mm-vertex c2VX < 8 J/y,y(2S) veto: 2.9-3.2, 3.65-3.75 GeV/c2 K,p pT(p) > 200 MeV/c2 K*0 pT > 900 MeV/c2 |DM|<100 MeV/c2 I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

Efficiencies, Event yields and B/S eTOT = 0.7%, eTRIG = 74% Annual yield : 4400 events B/S for forward bb̄ events [0.2-2.0] at 90% CL Various b→mX, mmX, J/yX channels were studied as sources of potential feeddown B/S at90%CL forward bb̄ [0.2, 2.0] b→m(c→mX)X <1.1 b→mX + c.c 0.5±0.2 B→J/yK* <0.04 B→J/yKS Bs→J/yf <0.05 I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

Gluonic penguins: Bd→ fKS Bs→ ff SM: Channels with domination of 1-gluonic penguin amplitude The contributions from EW-penguin amplitudes O(10%) CP-violation for Bd→ fKS ACP(Bd→ fKS ) = ACP(Bd→ J/yKS ) The accuracy: O(5%) →30% Last summer Belle reports the value ACP(Bd→ fKS ) inconsistent with ACP(Bd→ J/yKS ) = - sin(2b) Hints for New Physics in b→sg transitions ? or The probe for FSI ? I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

Selection of Bd→ fKS and Bs →ff charged tracks consistent with PID Inconsistent with any PV c2IP > 4 Two prong vertex c2VX < 10(100) f : |DM| < 17(12) MeV/c2 Bs →ff c2VX < 100 qB < 10 mrad Decay angle: |cos q| < 0.75 |DM| < 24 MeV/c2 f →KK Bs →ff I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

Selection of KS for Bd→ fKS Secondary vertex from p+p- pair consistent with PID c2VX < 20 Different track categories: With and without track fragments measured in precise silicon vertex detector |DM| < 15(25) MeV/c2 no ‘long’ tracks KS →p+p- 2 ‘long’ tracks 1 ‘long’ track 1 ‘long’ track I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

Selection of Bd→ fKS B : Impact parameter to the primary vertex IP < (250,200,100)mm pT(KS) > 1100(500) MeV/c2 pT(f) > 1350 MeV/c2 qB < 10 mrad |DM| < 55 MeV/c2 s(MB) = 16 MeV/c2 KS →p+p- I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

Efficiencies, Event Yields and B/S Enlarged mass window Bs →ff 4-7 GeV/c2 Bd→ fKS 4-6.6 GeV/c2 No background events from 107 forward bb̄ events 1 event from 106 b→fX sample (for Bd→ fKS) effectively x3.5 statistics as forward bb̄ Bd→ fKS Bs →ff eTRIG[%] 19 23 eTOT[%] 0.074 0.45 N/year 800 1200 B/S <1.1 (bb̄) <0.3 (b→fX) <0.2 I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

Real rear decay: Bs →m+m- SM: Br ~ 3x10-9 Many New Physics models predict enhancement 101-103 m± Compatible with m PID pT > 1.3 GeV/c mm c2VX < 4 DZ/sZ > 29 pT > 3 GeV/c |DM| < 600 MeV/c2 I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

Efficiencies, Event Yield and B/S eTOT = 2.5%, eTRIG = 80% N/year = 17 events No background events neither from 107 forward bb̄ sample no from 107 b→mX,b̄→mX sample 5 years at LHCb B/S at 90% Forward bb̄ <440 b→mX,b̄→mX <6 I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna

Summary LHCb has a good physics potential for study of rare decays N/year B/S @90%CL Bd → K*0g 35k <0.7 Bs → fg 9.3k <2.4 Bd → K*0m+m- 4.4k [0.2, 2.0] Bs → fKS 800 <1.1 (bb̄) <0.3 (b→fX) Bs → ff 1.2k <0.2 Bs → mm 17 <440 (bb̄) <6 (b→mX) I.Belyaev "Rare decays at LHCb" 15.07.2k+4 “Physics at LHC”, Vienna