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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