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ATLAS preparations for precise measurements in B-physics channels

potentially sensitive to NP

SUSY 2005, M.Smizanska, Lancaster University, UKSUSY 2005, M.Smizanska, Lancaster University, UK

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The ATLAS DetectorThe ATLAS Detector

• Inner Detector (ID)Semiconductor pixel and

strip detectorTransition radiation tracker:

straw-tubes interspersed with a radiator (e/ separation)Inside solenoid of 2T

magnetic field

•CalorimeterHighly granular LAr EM

calorimeter: < 3.2Hadron calorimeter: < 4.9 (scintilator-tile in barrel and LAr in end-caps and forward)

•Muon spectrometerAir-core toroid system on

average ~ 0.5 TMDTs & CSCs; RPCs &

TGCs

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ATLAS is Getting ReadyATLAS is Getting Ready

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ATLAS Detector in 2007ATLAS Detector in 2007According to the present schedule the ATLAS detector will have full geometrical coverage for muons, electrons and hadrons for first collisions in 2007

However, it will have some differences compared to the design that was presented in the early layout - TDR, some of which affect the B-physics programme

•In the Inner Detector The innermost pixel layer will be at a radius of 5 cm (4.3 cm in TDR) from the

beam line As a consequence, the secondary vertex resolution degrades by ~40% with respect to the originally foreseen

Some parts of the TRT wheels will not be installedReduced number of hits per track in forward region

•High Level Trigger System Computing resources at startup will be reduced

•Nominal early luminosity is now foreseen to be 1-2.1033 cm-2s-1

All values in this presentation are for Final (2007) Detector layout and for 3y@1033cm-2s-1

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ATLAS B-physics trigger strategiesATLAS B-physics trigger strategies

• Flexible B trigger strategies, according to luminosity conditions.• All ATLAS LVL1-trigger objects: , e/jet to be

combined• At luminosity few times 1033 cm-2s-1

(pT>6GeV) + (5GeV) Bs→J/Bd→B→

(pT>6GeV) + e/(ET>6GeV) Bd→KBs→B→

(pT>6GeV) + Jet (ET>10GeV) Bs→Ds

• At nominal luminosity 1034 cm-2s-1 2 ( pT > 6 GeV) B→

• At low luminosity (end of spill) < ~1033 cm-2s-1 single ( pT > 6-8 GeV) leaving further selections for High Level triggers.

• Objects identified at LVL1 are futher analysed at High-level triggers using full detector granularity. Inner detector is involved.

• B-events written to permanent storage → 108/year all passed criteria for specific exclusive B-decays modes.

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Number of events after trigger + offline reconstruction 3y@1033cm-2s-1

Models used in MC or to confront experimental sensitivities.

Signal Backgr

Bs→J/

Bs→J/

s s, 300k

9000

30%

<100%

SM: Fleisher CERN-TH-2000-101

NP: Ball,Khalil, Phys.Rev.D69:115011,2004

Bs→Ds

Bs→Dsa1 Ms

6750

3620

<100%

<100%

NP: Ball,Khalil, Phys.Rev.D69:115011,2004

ATLAS sensitivity in BATLAS sensitivity in Bss tree-level dominated decay tree-level dominated decay channels with possible signatures of NPchannels with possible signatures of NP

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LHC sensitivity to CPV BLHC sensitivity to CPV Bss mixing phase in B mixing phase in Bs s J/ J/

Expected LHC sensitivity

after 3 years SUSY model

Ball,Khalil,2004

ATLAS(2005) final detectorATLAS(2005) final detector

LHCb (2003) performance still to be updatedLHCb (2003) performance still to be updated

SUSY example for R = MSUSY example for R = M1212SUSYSUSY/ M/ M1212

SMSM = 0.5 = 0.5

•Not full experimental potential exploited since far – work continues

•SM – is already OUT of experimental sensitivity (would need 30 years …)

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Sensitivity to CPV BSensitivity to CPV Bss mixing phase 2005-2000 comparison mixing phase 2005-2000 comparison

Expected LHC sensitivity

after 3 years

Update 2005Situation in 2000

ATLAS final detector (Roma-2005) , early detector (before 2000)

LHCb final detector (TDR-2003), early detector (before 2000)

SM combined fit tighter in 2004 than in 2000

SUSY model Ball, Khalil,2004 replacing old NP- LR model Ball,Fleischer, 2000 - excluded by data at 2003

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Another parameters of Another parameters of BBs s J/ J/Extraction of weak phase s from BBs s J/ J/ requires simultaneous

determination of other weak Γs, ΔΓs, xs and parameters of strong

amplitudes : : A┴,A║, δ1,δ2.Despite enormous LHC statistics (ATLAS 270.000/3years) and well controlled background (ATLAS 15%) – several parameters get highly correlated in maximum likelihood fit.

To avoid failing a fit due to high xs – s correlation xs- was fixed – will be determined independently in Bs Ds

ΔΓs 13%

Γs 1%

A║0.9%

A┴3%

s (Xs = 20) 0.034

s (Xs = 40) 0.131

Гs ΔΓs δ1 δ2

Гs70%

ΔΓs

δ198%

δ2

σ(Bs)=96fsΔГs=0.1

Errors: Correlations:

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BR used in the MC

Signature after trigger +offline reconstruction 3y@1033cm-2s-1

Models used in MC or to confront experimental sensitivities.

Signal Backgr

2.0 10-6

Bd→

Bd →

Bs →

Br.fraction

-mass

AFB

3000

300

900

<3000

1000

<3000

Melikhov, Nikitin, Simula, PRD57,98;

Melikhov, Stech, PRD62, 2000

WC: SM Buras, Munz, PRD52, 95;

MSSM Cho, Misiak,Wyller, PRD54,96.

b→ 1500 NP: Chen, Geng, PRD64,2001

Aliev NPB649,2003

Semi-muonic exclusive rare B-decays Semi-muonic exclusive rare B-decays in ATLASin ATLAS

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Variables to be measured in semi-muonic exclusive rare decaysVariables to be measured in semi-muonic exclusive rare decays

Most th authors - suggest to measure variables describing di-muon system, namely: shapes of s = mass()2 and Forward-backward asymmetry AFB as a function of s. The calculations show differences between SM and SUSY in some parts of phase space.

Shapes of this distributions are sensitive to trigger and offline selections cuts – especially for small opening di-muons angles and for pT near threshold. The acceptance control is one of the main subjects in these studies.

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Semi-muonic rare decays, sensitivity to triggerSemi-muonic rare decays, sensitivity to trigger

All events produced in pp collisions

LVL1 trigger selections (x 100)

All trigger cuts (x 100)

Example of a preliminary study for b→ to investigate sensitivity to trigger.

Comparison of q2/MB2 (left) and of ‘AFB versus q2/MB

2’ (right) before and after trigger

AFB - q2/MB2 shape is less sensitive to trigger cuts than q2/MB

2 distribution.Results are preliminary. Study continues to include a control of fake and real di-muon background sources, which may have impact especially on small opening angles.

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Examples of offline reconstruction performance Examples of offline reconstruction performance for semi-muonic decaysfor semi-muonic decays

Inv. Mass Res. 47 MeV

Reconstruction of Bs (K+K-)+

Inv. Mass Res. 51 MeV

Reconstruction of 0

b+- 0(p-) Proper Time Resolution

102 fs

Reconstruction of BdK*0(K+-) +-

Resolution for cos θ angle between +and 0

b

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Sensitivity to New Physics in Sensitivity to New Physics in BBdd →→KK0*0*

In low values of di-muon masses

ATLAS can after 3 years @1033cm-2s-1 = 30 fb-1

distinguish

MSSM C7geff>0 from SM

ATLAS statistical errors2% in this

area

→ 3000 events with 30 fb-1

SM

MSSM C7geff>0

MSSM C7geff<0

AFB (muon asymmetry) plotted versus mass2/MB

2

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Sensitivity to New Physics in Sensitivity to New Physics in bb →→

ATLAS can already after 3 years @1033cm-2s-1 = 30 fb-

1 distinguish MSSM C7geff>0 from SM in low values of di-muon mass

b→ events with30fb-1

ATLAS MC events generated with SM

after trigger and reconstruction analysis

ATLAS MC events generated with MSSM C7geff>0

after trigger and reconstruction analysis

ATLAS statistics errors corresponding to 1500 events –

expected after 3 years

ATLAS statistical errors 5% in this

area

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Signature after trigger + offline reconstruction 3y@1033cm-2s-1

Models used in MC or to confront experimental sensitivities.

Signal Backgr

Bd→K

Bs→

10700

3400

S/√B >5

S/√B >7

Ali, Braun, Simma, Z.Phys.C63,1994; Melikhov, Stech, PRD62,2000

WC SM : Buras, Munz, PRD52, 1995.

Radiative rare B-decays in ATLASRadiative rare B-decays in ATLAS

•A complete trigger strategy to select these channels has been studied showing that at a luminosity of 1-2.1033 cm-2s-1 the output rate is controllable

LVL1: pT > 6GeV + secondary EM RoI ET > 5GeV

trigger not required by signal, however reduce rate while enrich B yield 25 times. in CP violation studies all events will be tagged

LVL2: identification and reconstruction of K*0 and EF: Inv. Mass cuts and vertex reconstruction

•An important ingredient is the rejection of BK0*0 Good 0/ separation

Data were collected at the test-beam in 2004 for a dedicated study of this

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BR used in the MC

Signature after trigger +offline reconstruction 3y@1033cm-2s-1

Models used in MC or to confront experimental sensitivities.Signal Backgr

3.5 10-9 Bs → 21 <60

Ali, Greub, Mannel, DESY-93-016.0.9 10-10 Bd →

3. 10-10 at

1y@1034cm-2s-1

95%CL

1.0 10-10

1.9 10-8

1.9 10-8

Bd→

Bs →

Bd→

particle level since far

Melikhov, Nikitin, PRD70, 2004

WC: SM Buras, Munz, PRD52, 1995.

ATLAS performance for B ATLAS performance for B decays decays

Full trigger and detector TDR study was made also for luminosity 1034cm-2s-1 It proved that

• the B → program can be continued at nominal LHC luminosity.

• already after 1 year a signal of 92 Bs → events can be extracted over background of 900 events and a limit 3. 10-10 can be posed on Bd →

The study continues for Final detector layout. Values in table given for 1033cm-2s-1 are already for Final detector.

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BB00d,sd,s →µ →µ++µµ--γγ as BG to Bas BG to B00

dd →µ →µ++µµ--

Interesting study (since far limited to “particle-level” = fiducial and trigger cuts) checks B0

d,s →µ+ µ- γ as a possible background to B0d →µ+ µ-. Study concluded

the background is small in comparison with signal and negligible comparing to combinatorial background.

Plan is to study a feasibility of extraction of B0d,s →µ+ µ- γ as a signal. Preliminary

results show potential background from channel B0d,s →µ+ µ- 0

Number of events

pT(γ) < 2 GeV

← φ – resonant

contribution

B0s →µ+ µ- γ

B0d →µ+ µ- γ

Mµµ GeV

B0d →µ+ µ-

pT(γ) < 4 GeV

B0d →µ+ µ-

← φ – resonant

contribution

B0s →µ+ µ- γ

B0d →µ+ µ- γ

Number of events

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Conclusions -1Conclusions -1

• ATLAS preparations for B channels potentially sensitive to New Physics are in progress both at trigger and off line.

• In Bs J/there is clearly a potential to achieve NP values of weak phase

s, precision will depend on value of xs. Rate s will be measured in the

same analysis with precision of 13%. Strong phases cannot be decoupled.

• Semi-muonic rare decays of all B-mesons species Bd, Bs b are under

preparation and will allow to distinguish between SM and certain classes of MSSM.

• ATLAS can collect 10000 BK0* and 3400 Bs events in 3 years.

• In 3 years of 1033cm-2s-1 ATLAS can observe Bs with st significance of 3.

• After 1 year of nominal LHC luminosity 1034cm-2s-1 ATLAS can pose a limit of 3. 10-10 on branching fraction of Bd → with 95%CL.

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Conclusions-2Conclusions-2

ATLAS B-group physicists are excited about the work on New physics signatures and would welcome

more theory works predicting B exclusive channels we can measure in LHC

more types of measurable variables sensitive to NP contributions

models allowing to study synergy of Beauty and high-pT SUSY measurements:

You are warmly invited to

FLAVOUR IN THE ERA OF THE LHCa Workshop on the interplay of

flavour and collider physics

First meeting: CERN, November 7-10 2005

http://mlm.home.cern.ch/mlm/FlavLHC.html

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… … and in 2006 we warmly invite you toand in 2006 we warmly invite you to

 

The 7th International Conference on Hyperons, Charm And Beauty Hadrons- BEACH

2006

will be held from 2nd to 8th July , 2006

at the University of Lancaster , England. 

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BackupsBackups

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ATLAS Final detector layout with 1st pixel layer radius 5cm( 4.3 cm in Early layout ‘98)

Proper-time resolution for representative B-decays

Detector layout Final

‘2005

Early

‘1998

Bs Ds 99 fs 66 fs

B 101 fs 69 fs

BsJ/ 96 fs 63 fs

Final Layout

pT- range B

Early Layout

pT- range

Bs Ds

Impact parameter resolution (d0)and pT-range of secondary tracks for two example B-decays channels

Impact Parameter and Proper Time ReconstructionImpact Parameter and Proper Time Reconstruction

Proper Time Resolution

102 fs

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ATLAS measurement of ATLAS measurement of mmss withwith BBssDDss

BBssDDss

Already after 1 year ATLAS reach 25.6 ps-1 @ 95%CL