Study of the LFV channel

3

19/05/06 LNF – Spring school 2006

Silvia VenturaLaboratori Nazionali di Frascati

3 decay 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 10-10 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!

h0,H0,A

L and R are dimensionless functions of the MSSM mass parameters and takeinto account one-loop diagrams, which involve the exchange of sleptons, gauginos and Higgsinos

Minimal Supersymmetric Standard Model

In the MSSM the Lepton Flavour Violating couplings of the Higgs bosons can induce the decays (h0, H0, A) with non-negligible rates.

Experimental resultsCLEO: 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 has already collected 520fb-1 can reach now (3-5)x10-8 al 90% C.L.2ab-1 are foreseen for 2010

Belle expectation:Tau04 International workshop on lepton physics

At LHC the will be produced in several ways:(mesons D,B decays + Z + W)

The most powerfull and clean signal source will be from the W decay, produced ’s are: isolated high Pt high missing energy

With (W)*BR(W) = 19 nb and assuming the present limit of BR ( 3 ) = 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

LHC SIGNAL FEATURES

3 10fb-1 from W decay

SIGNAL + BACKGROUNDafter 1 year of LHC withthe hypothesis ofBR=1.9E-6

In case of NO signal events: BR<8.4E-8 @ 90% C.L.

CMS

3 reconstructed muons withpt>3GeV in the barrel total charge +/-1 common secondary vertex isolation missingEt > 20GeV-mass veto

0.6 background eventsand 17 signal eventsexpected at the endof the analysis in 10fb-1

with the hypothesis of BR(3)=1.9x10-6

Analysis of 2002:

THE ATLAS DETECTORTHE ATLAS DETECTOR

Hadroniccalorimeter

Muonspectrometer

Inner detectorBarrel toroid

solenoid

Elettromagneticcalorimeter Forward

calorimeter Endcaptoroid

Shielding

SIGNAL: PRESELECTION and di-muon TRIGGER (Fast Simulation)

Efficiency of tracks in low PT region (3-6 GeV) assumed = 100%

PRESELECTION = 3 muons with pt > 3GeV and |η|< 2.5 = 30%

The decay has been inserted in PYTHIA 6.152 forcing the two neutrinos of 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).

Signal: Atlfast M3

At preselection level:

Mean 1777 ± 0.2 MeVSigma 16.75 ± 0.16 MeV

MeV

TRIGGER: L1/L2 26 (200 Hz @ L=2x1033 cm-2s-1, DAQ limited 10 Hz )

HLT specific requirements under study ex: 26 + Etmiss

3 muons invarinat mass distribution

BACKGROUNDSMain background source from ccbar and bbbar production,with cascade decays producing light mesons as , η, ,η’

The preselection requirement of 3 with pt>3GeV in the same branchis 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

(ccbar) = 8 mb pt(quark)>10GeV (ccbar) = 3.76 x 10-2 mb

(bbbar) = 470 b pt(quark)>10GeV (bbbar) = 2.99 x 10-2 mb

Real backgroundonly from processes of type B,same branch forthe 3 muons

Processes of type A are no to be considered:topologicallydifferent from signal (large R)

PRODUCED BACKGROUNDS

1) Ds (3%) with (BR=2.5 x10 -4) 434x103 events in 10 fb-1

2) Ds η (2%) with η (BR=3.1 x10 -4) 316x103 events in 10 fb-1

3) Bs Ds (2%) Ds* (5.5%) with Ds* Ds with Ds K 0.5% Ds 2.8% Ds 5.2% (BR=2.5x10-4)

4) Bs Ds (2%) Ds* (5.5%) with Ds* Ds with Ds Kη 0.5% Ds K*η 0.5% Ds η 1.5% Ds η 7.9% η (BR=3.1x10-4)

Other channels give smaller contribute:D+η (0.1%) con η (3.1x10-4) D+ (0.1%) con (4.6x10-5)D+η’ (0.1%) con η’ (1.0x10-4)

From PDG table we select the most dangerous sources of background.Four channels were considered:

75x103 events in 10 fb-1

113x103 events in 10 fb-1

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 BACKGROUNDMeV

MeV

MeV

MeV

Spatial separation between the muons cut: Rij < 0.2

-veto

mclosest < (m- 30MeV)mclosest > (m+30MeV)

For bcgk involving a decay.

Invariant mass distribution of di-muon combination closest to the mass.

Signal-background comparison

(*) 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 mass window.

Preselection

pt > 3GeV |eta|<2.5

Trigger MissingEt R -veto -window

SIGNAL

3075

(12)

2693 2550 2431 1997 1852

(7)

DSPHI 8846

(7600)

2412 270 227 24 0

DSETA 1663

(1225)

381 77 71 68 0

BSPHI 3758

(826)

872 147 40 2 0

BSETA 1047

(280)

185 44 17 16 2

(0.53)

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

tg=50=-/2Mh=MH=MA=100GeVL = 0.0006 R = 0.0006

No effect on global efficiency!

Signal selection efficiency as a function of muon pt

MeV

(MeV) (GeV)

SIGNAL: “first” comparison Fast /Full simulation

Start Presel Trigger MissingEt R -veto -window eff tot

FASTSIM

9959

(38)

3075 (30.8%) 2693(87.6%) 2550(94.6%) 2431(95.3%) 1997 (82%) 1852 (93%)

(7)

18.6%

FULLSIM

7450

(38)

2525(34%) 2207(87.4%) 1998(90.4%) 1910(95.5%) 1568(82%) 1061(68%)

(5.4)

14.2%

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…

CONCLUSIONS and OUTLOOK

BABAR: Analysis of 91fb-1 BELLE: Analysis of 87fb-1

B-factory results on 3l analysis