Musy

LHCb Physics reach : LHCb Physics reach Marco Musy Università di Milano Bicocca and INFN Milano LHC2003 International Symposium Fermilab, 3th May 2003


Ambitious physics goals of LHCb : Ambitious physics goals of LHCb Precision CPV measurements, using also pure hadronic and multi-body final states (Bd pp, Bd D*p, . . .) Exploit CPV in new decay channels as in Bs (BsKK, BsDsK, BsJ/yf , . . .) Rare b-decays (BdK* g, BdK*mm, Bsmm . . .) New particles may show up in loop diagrams, overconstrain will allow to disentangle SM components from the new-physics ones Overconstrain the unitarity triangles Search for New Physics beyond SM NP? b d d b t t High statistics is a requirement


CPV from LHCb in one year : CPV from LHCb in one year r h sin 2b |Vtd/Vts| |Vub/lVcs| now 2007 2008 LHCb g and dg not well known 2007 BdJ/yKS Bdpp BsJ/yf Bs DsK


Experimental challenge : Experimental challenge LHCb has to deal with a large variety of final states with different topologies Hot pp environment needs a robust trigger sbb / sinel.~ 0.01 (sbb~ 500 mb), many particles are not associated to b-hadrons b-hadrons do not evolve coherently High bb yield, 1012/year of Bd, Bs , baryons, Bc with bgct ~ 7mm HIGH STATISTICS Bd K*g BdJ/y r 0


LHCb detector : Detector has undergone a reduction of material in front of RICH2 (60%  40% for X0, 20%  12% for lI) Less interactions in detector, Level-1 Trigger includes momentum measurement Technologies have not changed  September 2003: 'Detector Reoptimization TDR' and 'Trigger TDR' Construction phase is in good shape ( T. Nakada talk) LHCb detector


Fully simulated bb event in Geant3 : MC Pythia 6.2 tuned on CDF and UA5 data Multiple pp interactions and spill-over effects included Complete description of material from TDRs Individual detector responses tuned on test beam results Complete pattern recognition in reconstruction: MC true information is never used 1M inclusive bb events produced in Summer 2002 New 'Spring' production ready: 10M events for September TDRs Sensitivities quoted here are obtained by rescaling earlier studies to the new yields Fully simulated bb event in Geant3


Main performances : VELO Bs mixing Measure Dms at 5s up to 48 ps-1 VELO PV: s ~ 47 mm SV: s ~170 mm Main performances  see dedicated talks!


Event yielduntagged : Efficiency includes: Geometrical acceptance, eacc including detection efficiency, material Trigger efficiency: Level-0 andamp;andamp; Level-1, eL0,1 including expected Pile-up rate veto Reconstruction efficiency (tracking, calorimeters, PID), etrack Selection cuts efficiency to reconstruct the final state and reject background, ecut Event yield untagged 1 year = 2 fb -1 L = 2x1032 cm–2s-1 norm. to 4p


Flavour tagging : Flavour tagging Knowledge of flavour at birth is essential for the majority of CPV measurements Opposite side lepton tag ( b  l ) Opposite side kaon tag ( b  c  s ) - unique to LHCb, BTeV - correlated to hadron trigger Same side pion and kaon tag (with p coming either from B** or fragm. successfully used by CDF already) Vertex charge tagging Only single particle tagging (e, m, K) from opposite side B decay used in this presentation e = 0.40, D = 0.40  e D2 = 6.4% The new MC data give similar results


Flavour tagging : Flavour tagging Work is in progress to update and improve the efficiencies Typical tagging efficiencies: in Bs  K p, KK, Dsp channels (after L0*L1 trigger, any nr of collisions) Bs Same Side IP/s Bs Opposite Side eeff K-tag K-tag


B(s)  p p, K p, K K : B(s)  p p, K p, K K Selection cuts on Signal charged tracks, PID Reconstructed B max pT min IP/s pT(B) L/sL incl. bb signal Proper time s = 41 fs s=18 MeV/c2 92% purity Combinatorial bb bckgr, can be fully rejected even relaxing mass cut S/B ~ 1


g from B(s) p p, K K (proposed by R. Fleischer ) : g from B(s) p p, K K (proposed by R. Fleischer ) Relies on 'U-spin' symmetry assumption (ds) which is the only source of theoretical uncertainty Clean measurement of g assuming dg from Bs  J/y f and b from B  J/y Ks Sensitive to New Physics contribution which can be pointed out by comparing with g obtained from DsK


Slide13 : g from B(s) p p, K K Evaluation of and sensitivity from time-dependent measured asymmetry input values


Slide14 : B0  + - BS  K+ K- g from B(s) p p, K K In one year:


a from B0  p p : Decay is polluted by penguin diagrams Penguin/Tree might be as high as 0.2 RICH PID and hadron trigger are fundamental If |P/T| will be known to ±0.1 then 5°andlt; s(a) andlt; 10° (depending on parameter value) a from B0  p p


Bs  Dsp, DsK : Bs  Dsp, DsK When selecting Bs  Ds K BR(Ds K)/BR(Ds ) = 1/15 while (Ds K)/ (Ds ) = 70 thanks to the RICH PID Ds mass (GeV) ~ 6.5 MeV/c2 s = 168 mm s = 418 mm 72k Ds  8k Ds K Bs vtx resolution (mm) Ds vtx resolution (mm)


g from Bs  D-s K+ , D+s K- : Needed: Hadronic trigger K/p separation Good proper time resolution Sensitivity depends upon relative amplitudes strong phase difference values of g, Dms , DGs /Gs For Dms=20 ps–1: s(g) ~ 10o For Dms=30 ps–1: s(g) ~ 12o In one year: 8k BsDsK reconstructed events g from Bs  D-s K+ , D+s K- From the measurement of 4 time-dependent asymmetries one gets g-2dg (with 2dg from BsJ/yf) 2 same order tree level amplitudes (3) : large asymmetries, NP contributes unlikely Same principle holds for B0  D*p, (study at the time of TP gives similar precision on g, a new evaluation is under way)


dg from Bs  J/y f : dg from Bs  J/y f In SM fS = -2dg = -2l2h ~10-2 Sensitive to New Physics effects in the Bs-Bs system In one year: 109 k events Bs J/y (m+m-) f 19 k events Bs J/y (e+e-) f Determination of DGs s( DGs/ Gs) ~ 0.03 for DGs/Gs = 0.15 J/y f is not CP eigenstate: needs fit to angular distributions of decay final states as a function of proper time Assuming Dms=20 ps–1: s (2dg) ~ 2o s =36±1 fs will be updated for TDR


b from B0  J/y Ks : b from B0  J/y Ks The ‘gold plated’ channel at B-factories Precision measurement of this parameter is very important: =0 in SM =sin 2b LHCb will bring a lot of statistics to this channel, which can be used to look into higher order effects, and fit Adir In one year with 119k events: s (sin 2b ) ~ 0.02 Comparing with other channels may indicate NP in penguin diagrams will be updated for TDR


Rare decays: B0  K0* g : BR( B0  K0* g ) = (4.30.4) 10-5 Direct CP violation in SM andlt;2%  Sensitive to New Physics effects Rare decays: B0  K0* g In one year: 20k events B0  K0* (K+p-) g triggered and reconstructed Mass resolution ~ 72 MeV Background from B0K*p0 can be rejected using K* helicity g W b u,c,t s


Bc mesons : LHCb preliminary study s(ppBc) ~300 nb  109 Bc/ year Bc  J/y p (BR ~10-2) e ~ 2% 12k events/year Background from B  J/y X and prompt J/y reduced cutting on the distance between primary vertex and Bc vertex Bc mesons CDF: mBc= 6.4  0.4 GeV, tBc ~ 0.5 ps LHCb acceptance ~30% M( J/y(mm) p) GeV/c2 Possible CPV with Bc J/y D, Bc  DsD, DD, ... Precision measurement of mass, life-time p (GeV)


Current status of LHCb Physics Reach in 1 year (2fb–1) : Current status of LHCb Physics Reach in 1 year (2fb–1) *Precisions obtained by scaling old results with the new yields All numbers will be updated together with more channels in the re-optimization TDR (September 2003)


Systematics in CPV measurements : Possible sources of systematic uncertainty: Asymmetry of b vs b production Detector efficiencies which depend on charge can bias tagging efficiencies can fake CP asymmetries CP asymmetry also in background processes Systematics in CPV measurements Alternate runs, swapping the orientation of magnetic field Use control samples available with high statistics: Bs  Dsp 72k events/year B0  J/y K* 600k events/year B  J/y K 600k events/year Study CP asymmetries in the B mass side bands (from Technical Proposal)


Conclusion : Conclusion LHCb is a dedicated detector for B physics measurements in many channels from the beginning of LHC A very precise determination of CKM unitarity triangle will be possible Detector performances are being evaluated with a realistic and complete Monte Carlo simulation LHCb offers an excellent opportunity to spot New Physics signals beyond Standard Model very soon at LHC


back-up slides : back-up slides


p0 reconstruction : p0 reconstruction PreShower (scintillator+Pb+scintillator) 2X0 ECAL (Pb+ 'shashlik' scintillator) 25X0 s(E)/E=10% /E 1.5% HCAL (Fe+scintillator) 5.6 lI s(E)/E=80% /E 10% Purity ~20% in range 0.1andlt;m andlt;0.17 GeV/c2 pTandgt;200 MeV