6 th international conference on hyperons, charm and beauty hadrons july 2, 2004 rare b decays at...

6th International Conference on Hyperons, Charm and Beauty Hadrons July 2, 2004

Rare B Decays at LHC

Sébastien VIRETLaboratoire de Physique Subatomique et de Cosmologie, Grenoble

ATLAS

1. Presentation

2. Not so rare: BX

3. Rare: BX

4. Very rare: B+-

5. Conclusions

Outline

ATLAS

1. Presentation

2. Not so rare: BX

3. Rare: BX

4. Very rare: B+-

5. Conclusions

1 6th International Conference on Hyperons, Charm and Beauty Hadrons S. Viret


ATLAS

Rare B-Decays

From ‘not so rare’ to ‘very rare’

10-5

10-6

10-7

10-8

10-9

10-10

Branching ratio Radiative penguins: BdK, BsBd

Electroweak penguins: BdKBd

BsBd

Many interesting observables inaccessible to classic B-factories

Not accessible to B-factories

(No Bs at B-factories)

(No precision measurements at B-factories)

Need a rare B-factory

LHC first results in 2008

Super-BaBar? Super-BELLE?


ATLAS

The Detector

LHCb

Since 2003: reoptimized detector (VELO, RICH, TT, tracking stations)

Main characteristics:

4.6x1011

Acceptance1.9<<4.9

pTb>2GeV

230 barnbbAcceptance

Lumi.(in cm-2s-1) 2x1032

bb pairs/year


ATLAS

The Detector

ATLAS & CMS

ATLAS

CMS

Acceptance|<2.5

pTb>10GeV

100 barnbbAcceptance

Lumi.(in cm-2s-1) 2x1033 & 1034

2x1012 & 1013

bb pairs/year


ATLAS

B production at LHC

Rare B Factory ?

LHC = Rare B factory

LHCb ATLAS/CMS

Luminosity (in cm-2s-1) 2x1032 2x1033 & 1034

bb pairs/year 4.6x1011 2x1012 & 1013

But trigger challenging

inelastic= 80 mbarn

rare B~ picobarnfemtobarn


ATLAS

LHCb Trigger Strategy

For Rare B decays

Electromagnetic trigger Muon & Di-Muon

Rate (in Hz)

107

106

105

104

103

102

L0

L1

HLT

1 MHz

40 kHz

200 Hz

Radiative decays Other decays

Vertex reconstruction, topological cuts (IP, displaced vertex,…)

Full B reconstruction

Trigger entirely dedicated to B decays Low Pt thresholds


ATLAS

ATLAS & CMS Trigger Strategy

For Rare B decays

Single Muon+

Electromagnetic trigger

Di-Muon

Rate (in Hz)

107

106

105

104

103

102

L1

L2

EF

75 kHz

3 kHz

100 Hz

Radiative decays Other decays

ID reco.+

Photon identification

ID reco.+

Di-Muon confirmation

Full B reconstruction

Bandwith constraints: 200 Hz at L2, 20 Hz at EF (ATLAS)

High Pt thresholds

ATLAS

1. Presentation

2. Not so rare: BX

3. Rare: BX

4. Very rare: B+-

5. Conclusions



ATLAS

Radiative penguinsPhysics interest & observables

Isospin Violation

b s

u

b s

d

CP Violation

b s

b s

b s

?

Branching ratio enhancement by new

contributions

Interesting Channels (only exclusive at LHC):

BdK*, Bd, Bd, Bs,…

Interesting measurements:

Bs radiative penguins accessible at LHC


ATLAS

Radiative penguinsLHCb

Estimations for one year @ 2x1032cm–2s-1 (2fb-1):

9300 Bs35000 BdK*0

Study done with reoptimized detector & realistic trigger simulation:

Specific background

under control

Balso studied, lots of accessible channels

=65 MeV/c2=64 MeV/c2


ATLAS

Radiative penguinsATLAS

BdK* Bs

Preliminary results

Non-optimized offline cuts, resolution (>100 MeV/c2)

could be improved.


[2500,3200] Bs[4200,8500] BdK*0

Trigger strategy dependent


ATLAS

Radiative penguinsATLAS/LHCb comparison after 1 year

ATLAS

LHCb

ATLAS

LHCb

BdK*

Bs

S/B

>1.3

>0.4

>0.04

>0.01

Int. lumi.

20 fb-1

20 fb-1

2 fb-1

2 fb-1

S/√B

>5

>7

>210

>60

Results limited by background statistics, S/B might be much better (particularly for Bs)

Significant amount of statistics after just one year of LHCb

Parallel measurements possible with ATLAS if radiative penguin trigger accepted

ATLAS

1. Presentation

2. Not so rare: BX

3. Rare: BX

4. Very rare: B+-

5. Conclusions



ATLAS

BK*

Experimentally speaking…

Branching ratio enhancement by new

contributions

b s

?

CP Violation

b s

b s

Forward-Backward Asymmetry (Dimuon-cms system)

K*0

Bd

Many interesting observables:

… and also the di-muon mass spectrum,etc…


ATLAS

BK*

Hunting New Physics

Phys.Rev. D61 (2000) 074024 Differences between SM and models predicting C7

eff>0 (SM predicts C7eff<0)

FB AsymmetryLarge differences for small s

if C7eff>0

SUSY 1, 2, and SM with C7

eff<0

SUSY 1 & 2 with C7

eff>0

Di-muon mass spectrumLarge theoretical uncertainties

SUSY 1 & 2

SM w/uncert.


ATLAS

BK*

LHCb

Estimation with reoptimized detector & trigger simulation:

Bd mass resolution √S resolutionIntegrated on whole di-muon mass spectrum

BA resolutionFor Forward-Backward asymmetry measurement


4400 BdK*0

Precise measurements possible if enough statistics


ATLAS

BK*

ATLAS

ATLAS

ATLAS

Interesting area for New Physics reach

1999 TDR results: 1.5 year @ low lum, ancient detector layout….

… but small modifications expected with initial layout (~15% worse)

Expected mass spectra for 30 fb-1


1400 BdK*0

=50 MeV/c2


ATLAS

BK*

Comparison

ATLAS

CMS

LHCb

BdK*

S/B

~9

>0.4

~7

Int. lumi.

20 fb-1

2 fb-1

100 fb-1

S/√B

~97

>42

~194

High Lum.estimation

only

Expected results after one year of running:

…New Physics evidence only if C7eff>0

Precise AFB measurements possible but…


ATLAS

BX

Only for LHCb

Partial semi-inclusive branching ratios could give theoretically clean constraint on CKM matrix parameters (Eur.Phys.J. C8 (1999) 619-629):

√R ~

Experimentally accessible to LHCb a good accuracy could be

obtained after 5 years of running

Old LHCb geometry

ſB(BXdll

ſB(BXsll

=Vtd

Vts

2

1+o(1)R =

s

s

ATLAS

1. Presentation

2. Not so rare: BX

3. Rare: BX

4. Very rare: B+-

5. Conclusions



ATLAS

B

Physics & experimental interest

•Very-rare decay (10-9, 10-10):

large New Physics effects possible

•Very clean signature even at high-luminosity observable with a sufficient amount of bb pairs

•Current experimental limits:

Br(Bs) < 9.5x10-7 (CDF)

Br(Bd) < 1.6x10-7 (Belle)


ATLAS

Bs

LHCb


17 Bs120 background events

Analysis using reoptimized detector:


ATLAS

Bs

ATLAS/CMS

CMS background rejection significantly better

Estimations for one year @ 1034cm–2s-1 (100fb-1) (1999 TDR results):

92 Bs14 Bd660 background events

26 Bs 4 Bd

6 background events

ATLAS


ATLAS

B

Comparison

ATLAS

CMS

LHCb

Bs

S/B

>4

>0.2

~0.14

Int. lumi.

100 fb-1

2 fb-1

100 fb-1

S/√B

~3.6

>1.7

>10

Results after one year of running at high luminosity:

Difference between ATLAS & CMS due to:

•Better resolution on muon impulsion•Calo isolation not yet implemented in ATLAS

ATLAS

1. Presentation

2. Not so rare: BX

3. Rare: BX

4. Very rare: B+-

5. Conclusions



ATLAS

After one year of LHC (2008):

Œ Significant statistics in BX and BX (ATLAS/CMS & LHCb) First precision measurements (AFB & ACP for BX, ACP for BX,…) (ATLAS/CMS & LHCb)Ž First evidence of B ? (ATLAS?/CMS)

Conclusion

What could we expect?

At LHC high luminosity era (2008…):

Œ & to be continued in LHCb & ATLAS/CMS (except BX in ATLAS/CMS) Ž Precise observation of B (CMS, ATLAS & LHCb)

Thanks to S.Amato, G.Pakhlova, P.Koppenburg, N.Nikitin, L.Silvestris & S.Sivoklokov

Backup Material

B2 6th International Conference on Hyperons, Charm and Beauty Hadrons S. Viret

ATLAS

BK*

BK*FB asymmetry measurement will give C7

eff sign in any case.

Difference is not model dependent

6 th international conference on hyperons, charm and beauty hadrons july 2, 2004 rare b decays at...

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