ATLAS B-Physics Reach

ATLAS B-Physics ReachM.Smizanska, Lancaster University, UK

[email protected]

25.4.2003 M.Smizanska: ATLAS B-physics reach 2

ATLAS: b-events from central pp LHC collisions

230b100b

LHC total = 100 mb inelastic = 80 mb bb = 500 bATLAS Central detector

LHCb Forward detector

||<2.5 pT>10GeV one b in = 100 b

1.9<<4.9 pT>2GeV one b in = 230b

L = 1-2 x 1033 cm-2 s-1

Rare decays 1034 cm-2 s-1 L = 2 x 1032 cm-2 s-1

Exclusive channels 1 y@1033 cm-2 s-1 2.6 x 106 dominated by bb J/hadronic <5 (all -tag)

Exclusive channels 1 y@2x1032 cm-2 s-1 3.4 x 106

1.7 x 106 bb J/x 106 hadronic


B-physics strategy with tight funding constraints

• Recent work has addressed the issue of maximizing B-physics capabilities in context of reduced initial Trigger/DAQ system (funding limitations)

– Extend Region-of-Interest mechanism of level-2 trigger to reconstruction of B decays:

• Level-1 muon was always used to provide region of interest• Now, level-1 jet to guide reconstruction of hadronic modes, e.g. Bs Ds , and electrons,

e.g. J e+e-

– Use result of level-2 trigger to seed reconstruction in the Event Filter• Only reconstruct limited region of Inner Detector containing B candidate

– Strong reduction in processing requirements compared to previous strategy that involved full scan of Inner Detector at level-2

• Nevertheless, with presently assured funding, the initial Trigger/DAQ system will be almost saturated by the priority “discovery physics” programme when the luminosity is at the target of L = 2 1033 cm-2s-1

– At this luminosity, B-physics would be based on dimuon trigger only which has very low rate but nevertheless covers many interesting channels

– At lower luminosities, e.g. towards end of LHC coast, spare Trigger/DAQ capacity can be used to extend the B physics potential


B – physics trigger strategies, cont. Level-1: single-muon or di-muon

Efficient down to pT 5GeV ( lower still in endcap). Different scenarios according to luminosity conditions & rates

single-muon

di-muon

all

all

h

h

b

b

c

c

J/

@1033cm-2s-1

1. Di-muon trigger:L1 2 + L2 precision tracking in muon spectrometer and Inner detector.Bd J/Ks

0 , Bs J/,etc b J/ , rare decays B Bd K0* Bd etc

2. Muon-electron() trigger: L1 + L1 e/cluster (ET>2GeV)+ L2 tracking in regionBd J/ (ee) + Ks

0 + B b J/ (ee) + B Bd K0* + B etc

3. Muon-hadron trigger:L1 + L1 Jet (ET>5GeV) + L2 tracking in regionB + BBs DsBetc


ATLAS performance parameters principal for B-physics Low pT electron identification

Combined EM calorimeter-TRT electron identification

Rejection of bb 6X events without electron vs efficiency of events bb 6e5X. Eff=70%,R=570, level-2 rate of signal is 40Hz, fake rate 10Hz due to hadrons misidentified as electrons.

TRT electron identification

Invariant mass for all track pairs in bb J/ (ee)K0 events before and after TRT selection cuts. Electrons have pT>1GeV.


ATLAS performance parameters principal for B-physics, cont.

Low and medium-pT muon performanceLowest pT muon identification & reconstruction efficiency

Inner detector + Muon spectrometer

Inner detector + Muon spectrometer+ Hadron calorimeter

J/) reconstruction in the environment of b-jet with pT~(50-80) GeV (for QCD b-production studies)

the same in log scale

Even in high pT jet, a mass reconstruction is negligibly affected by fake pairs when a muon identified in Muon spectrometer match to the wrong track in the Inner Detector.

muons

pions


Precise measurements of Bd J/Ks0 decay

3years@1033cm-2 s-1 J/63)

J/65)

J/(ee) +B->6

All reconstructed evts S/B

490k 28

250k 32

15k 16

sin2statistical Lepton tag Jet/charge tag Total

0.023 0.015 0.0126

0.030 0.019 0.016

0.018 - 0.018

Total J/63) + J/(ee)B->6)

0.010

Total J/65) + J/(ee)B->6

0.012

sin2systematics 0.005 prod. asymmetry, tagging, background

Method: maximum likelihood fit, using experimental inputs: proper time resolution, tag probability,

wrong tag fraction, background composition. Direct CP violation term neglected here.


sensitivity in dB

%0|| TP

%30|| TP

Signal yields 3y @1033cm2s-1

Atlas LHCb 5y

Offline 2-body select. 2.3k 4.9k Mass resol [MeV] 70 17 Signal/2-body bck 0.19 15 Signal/other bck 1.6 >1 Adir 0.16 0.09 Amix 0.21 0.07 correlation 0.25 0.47

Max.likelihood computedfrom: *Proper time *Invariant mass *Flavour at production *Specific ionisation:

Simulateous fit of 6 contributingdecays parametrized by 9coefficients, constrained bycurrent experimental limits.

Signal decay parametrized in terms of Adir , Amix:

Adir cos( m t) + Amix sin( m t) Adir , Amix in SM depend on or eff

PT

were used to derive sensitivity to

The current theoretical uncertainty |P/T|~30% dominates other systematical and statistical errors of full LHC potential.

-sensitivity as a function of and theoretical uncertainty of |P/T| using full LHC potential


Physics of Bs meson

ms from Bs Dsand Bs Ds a1 already after 1 year sensitivity up ms - 36 ps-1 fully explore SM

allowed range ms (14.3 - 26) ps-1

Program for precise measurements of Bs-anti-Bs system parameters : s, ms and probing Bs mixing phase s allowing to investigate new physics.

s and s= - from Bs J/ or Bs J/ both sensitive, but precision

sufficient only in Bs J/

Angular analyses of cascade decay Bs J/determine s, s and s simultaneously with parameters of helicity amplitudes A||(t=0), AT(t=0),

A0(t=0), 1, 2. Parameter ms will be measured by decays to flavor specific final states Bs Dsand Bs Ds

a1 .

Bs


CP - violation weak phase in Bs J/

Standard Model region-updated 2003

New physics Left-right symmetric model (NP-LR) - version used here last updated in 2000.

ATLAS (3years): 1st level trigger 1 only. Extension by 2 trigger under investiga- tion, not included. TDR Detector.

ATLAS - same – as above with Final Detector Layout– Preliminary

LHCb(5years): full 1st Level trigger, performance parameters as given in 2000

Experimental potential of both experiments not yet fully exploited: more studies on additional triggers, tagging.


Potential for Rare decays

Before LHC

BK*will be measured however mass and angular distributions detailed enough to show New Physics only at LHC.

B can be seen before LHC only if drastically enhanced.

Signal Bs->

Signal Bd->

BG

ATLAS 92 14 660

A study proved good performance at nominal LHC luminosity. After 1 year 1034cm-2 s-1

Signal Bs->

BG

ATLAS 27 93

3 years at luminosity 1033cm-2 s-1

BWill measure branching ration of Bs

which is in SM of order Br<(10-9) Perform high sensitivity search on Bd


Exclusive Rare decays of B mesonsATLAS statistics will allow angular analyses that can carry evidence for new physics. E.g. forward-backward asymmetry: *0

d KB

SM

MSSM C7 >0

MSSM C7 <0

Lowest mass region: sufficient accuracy to separate SM and MSSM if Wilson coefficient C7 <0

)cos(

0

1 )cos()cos(

1

0 )cos(

1)(

22

ddsd

dd

dsd

ddsdsAFB

Three points: mean values of AFB in three q2/MB

2 experimental regions with error bars


Studies not mentioned here:

1. Double heavy flavor mesons.

2. QCD tests of beauty production at LHC central region. Correlations bb.

3. Physics of Beauty baryons, production polarizations, decays.

other studies of ATLAS b-physics group


B-physics prospects with ATLAS - conclusions1. ATLAS is preparing a multi thematic B-physics program - including B-decays

and B-production.

2. ATLAS B-physics trigger strategy revised to maximize physics potential within tight funding constraints - rely on dimuon trigger for initial luminosity 2 1033 cm-2s-1 - extend selection at lower luminosities when there is spare processing capacity.

3. In CP violation the main emphasis will be on underlying mechanisms and evidence of New physics. ATLAS is especially precise in measurement of In Bs J/ large CP violation would indicate new physics.

4. Bs mixing studies make clear that there is sensitivity to ms beyond SM expectations. The width difference s can be measured best in Bs J/with relative precision

5. Rare decays B have favorable experimental signature allowing to measure also at nominal LHC luminosity 1034cm-2 s-1. Will measure branching ration of Bs which is in SM of order Br<(10-9) Precision measurements will be done for B K*.

6. Beauty production and bb correlations in central LHC collisions will be measured for QCD tests.

Documents

ATLAS B-Physics Reach