Study of the LFV channel t  3m Silvia Ventura Laboratori Nazionali di Frascati studio di fattibilta’ 19/05/06 LNF – Spring school 2006

t  3m decay This decay is very sensitive to non-SM physics! forbidden in the classical SM, allowed but very small BR (BR<10-21) considering neutrinos oscillations, foreseen in several models beyond the SM (BR~10-10-10-7) mSUGRA+seesaw 10-9 Phys. Rev. D 66,115013 (2002) SUSY+SO(10) 10-10 Phys. Rev. D 68,033012 (2003) SM+seesaw Phys. Rev. D 66,034008 (2002) Non-Universal Z’ 10-8 Phys. Lett. B 547,252 (2002) MSSM 10-7 Phys. Lett. B 566,159 (2002) This decay is very sensitive to non-SM physics!

Minimal Supersymmetric Standard Model In the MSSM the Lepton Flavour Violating couplings of the Higgs bosons can induce the decays (h0, H0, A)  mt with non-negligible rates. DL and DR are dimensionless functions of the MSSM mass parameters and take into account one-loop diagrams, which involve the exchange of sleptons, gauginos and Higgsinos m t h0,H0,A

Experimental results CLEO: current upper limit in the PDG BR<1.9 x 10-6 90% C. L. Big improvement from B-factory: BABAR: BR< 1.9 x 10-7 90% C.L. on 91.5 fb-1 hep-ex/0511045 BELLE: BR< 2.0 x 10-7 90% C.L. on 87.1 fb-1 Phys.Lett.B589:103-110,2004 Belle expectation: Tau04 International workshop on t lepton physics Belle has already collected 520fb-1 can reach now (3-5)x10-8 al 90% C.L. 2ab-1 are foreseen for 2010

LHC SIGNAL FEATURES At LHC the t will be produced in several ways: (mesons D,B decays + Ztt + Wtn) The most powerfull and clean signal source will be from the W decay, produced t’s are:  isolated  high Pt  high missing energy With s(W)*BR(Wtn) = 19 nb and assuming the present limit of BR (t  3m ) = 2 x 10-7 we expect: 38 events in 10 fb-1 corresponding to 1 year of LHC running at low luminosity 2x1033 cm-2s-1

CMS t3m 10fb-1 t from W decay 3 reconstructed muons with pt>3GeV in the barrel total charge +/-1 common secondary vertex isolation missingEt > 20GeV F-mass veto SIGNAL + BACKGROUND after 1 year of LHC with the hypothesis of BR=1.9E-6 Analysis of 2002: 0.6 background events and 17 signal events expected at the end of the analysis in 10fb-1 with the hypothesis of BR(t3m)=1.9x10-6 In case of NO signal events: BR<8.4E-8 @ 90% C.L.

THE ATLAS DETECTOR Muon spectrometer Elettromagnetic calorimeter Forward calorimeter solenoid Endcap toroid Inner detector Barrel toroid Hadronic calorimeter Shielding

SIGNAL: PRESELECTION and di-muon TRIGGER (Fast Simulation) The t  3m decay has been inserted in PYTHIA 6.152 forcing the two neutrinos of tm n n to be muons with a uniform PHASE SPACE. A modelling of the decay tried at the end to study systematics on reconstruction efficiency Reconstruction with fast simulation programs of ATLAS Transverse momentum (MeV) distributions of the 3 muons (pt-ordered). PRESELECTION = 3 muons with pt > 3GeV and |η|< 2.5 = 30% Efficiency of tracks in low PT region (3-6 GeV) assumed = 100%

Signal: Atlfast M3m At preselection level: Mean 1777 ± 0.2 MeV TRIGGER: L1/L2  2m6 (200 Hz @ L=2x1033 cm-2s-1, DAQ limited 10 Hz ) HLT  specific requirements under study ex: 2m6 + Etmiss 3 muons invarinat mass distribution At preselection level: Mean 1777 ± 0.2 MeV Sigma 16.75 ± 0.16 MeV MeV

BACKGROUNDS Main background source from ccbar and bbbar production, with cascade decays producing light mesons as f, η,  ,η’ Real background only from processes of type B, same branch for the 3 muons Processes of type A are no to be considered: topologically different from signal (large DR) The preselection requirement of 3m with pt>3GeV in the same branch is very hard on backgroud events. Out of 106 ccbar produced events not one survives this preselection. We produce ccbar and bbbar events imposing the c,b quark to be generated by PYTHIA with pt>10GeV s(ccbar) = 8 mb  pt(quark)>10GeV s(ccbar) = 3.76 x 10-2 mb s(bbbar) = 470 mb  pt(quark)>10GeV s(bbbar) = 2.99 x 10-2 mb

PRODUCED BACKGROUNDS From PDG table we select the most dangerous sources of background. Four channels were considered: 1) Ds  mnf (3%) with fmm (BR=2.5 x10 -4) 434x103 events in 10 fb-1 2) Ds  mnη (2%) with η mmg (BR=3.1 x10 -4) 316x103 events in 10 fb-1 3) Bs  Ds mn (2%) Ds* mn (5.5%) with Ds*  Ds g with Ds Kf 0.5% Ds pf 2.8% Ds rf 5.2% fmm (BR=2.5x10-4) 4) Bs  Ds mn (2%) with Ds Kη 0.5% Ds K*η 0.5% Ds pη 1.5% Ds rη 7.9% ηmmg (BR=3.1x10-4) 75x103 events in 10 fb-1 113x103 events in 10 fb-1 Other channels give smaller contribute: D+mnη (0.1%) con η mmg (3.1x10-4) D+mnr (0.1%) con rmm (4.6x10-5) D+mnη’ (0.1%) con η’ mmg (1.0x10-4)

Background PRESELECTION Transverse momentum distributions of the 3 muons (pt-ordered) for one of the four backgrounds. PRESELECTION = 3 muons with pt > 3GeV and |η|< 2.5 = 2%

Missing Et cut MEt > 15 GeV SIGNAL BACKGROUND MeV MeV MeV MeV

Spatial separation between the muons cut: DRij < 0.2

F-veto mclosest < (mf- 30MeV) mclosest > (mf+30MeV) For bcgk involving a fmm decay. Invariant mass distribution of di-muon combination closest to the f mass. mclosest < (mf- 30MeV) mclosest > (mf+30MeV)

Signal-background comparison Preselection pt > 3GeV |eta|<2.5 Trigger MissingEt DR F-veto t-window SIGNAL 3075 (12) 2693 2550 2431 1997 1852 (7) DSPHI 8846 (7600) 2412 270 227 24 DSETA 1663 (1225) 381 77 71 68 BSPHI 3758 (826) 872 147 40 2 BSETA 1047 (280) 185 44 17 16 (0.53) (*) values in red are events normalized to 10fb-1 (**) for the normalization of the signal a BR of 2 x 10-7 is assumed 7 signal events and 0.53 bckg events are counted in the t mass window. REMINDER 1: modelling of global efficiency (next slide) REMINDER 2: the efficiency for low pt muons assumed to be 100% both for signal and backgrounds!! -----> go to full simulation

Modelling of acceptance Dalitz plot for PHASE SPACE decay Dalitz plot for MSSM matrix element tgb=50 a=b-p/2 Mh=MH=MA=100GeV DL = 0.0006 DR = 0.0006 (MeV) (GeV) Signal selection efficiency as a function of muon pt No effect on global efficiency! MeV

SIGNAL: “first” comparison Fast /Full simulation Start Presel Trigger MissingEt DR F-veto t-window eff tot FAST SIM 9959 (38) 3075 (30.8%) 2693(87.6%) 2550(94.6%) 2431(95.3%) 1997 (82%) 1852 (93%) (7) 18.6% FULL 7450 2525(34%) 2207(87.4%) 1998(90.4%) 1910(95.5%) 1568(82%) 1061(68%) (5.4) 14.2% CONCLUSIONS and OUTLOOK Good efficiency for the signal expected… small dependence from models. Study of the backgrounds is crucial full simulation needed to add fake muons (mostly from pions) Estimate of reach for upper limits on BR in progress .. Results seem to be promising with the fast simulation. … FULL SIMULATION IN PROGRESS…

B-factory results on t3l analysis BABAR: Analysis of 91fb-1 BELLE: Analysis of 87fb-1