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A first look at B s → J/ YF in LHCb. Paul Soler University of Glasgow and Rutherford Appleton Laboratory. LHCb-Babar Meeting 8 April 2005. Contents. Motivation Physics aims Angle c from B s → J/ Yf LHCb Experiment Analysis of B s → J/ Yf Toy Monte Carlo Sensitivity New Physics

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slide1

A first look at Bs→J/YF in LHCb

Paul Soler

University of Glasgow and

Rutherford Appleton Laboratory

LHCb-Babar Meeting

8 April 2005.

contents
Contents
  • Motivation
  • Physics aims
  • Angle c from Bs→J/Yf
  • LHCb Experiment
  • Analysis of Bs→J/Yf
  • Toy Monte Carlo
  • Sensitivity
  • New Physics
  • Conclusions

Work carried out in

collaboration with:

Stuart Paterson (Glasgow)

Andrew Pickford (Glasgow)

Borrowed from:

G. Raven’s analysis in 2003

LHCb-Babar Meeting,

4 April 2005

motivation
Motivation
  • Bs → J/Yf is the “gold plated” decay mode in the Bs system, similar to theBd → J/YKs in the Bd system
  • This mode is theoretically clean (very small penguin contributions).
  • It provides a measurement of the unitarity angle cdg, which is predicted to be very small (~0.02) in the SM.
  • Sensitive to new physics
  • Exploits the production capabilities of Bs mesons at the LHC (not available at B-factories)
  • Exploits UK investment in the RICH and VELO detectors

LHCb-Babar Meeting,

4 April 2005

slide4

Physics aims

  • CKM matrix:

CKM matrix provides link between mass eigenstates and weak eigenstates

Experimentally:

LHCb-Babar Meeting,

4 April 2005

physics aims
Physics aims

CKM matrix in Wolfenstein parametrization ~O(l5):

_

b: Bd-Bd Mixing Phase

g: Weak Decay Phase

_

cdg : Bs-Bs Mixing Phase

(From CKM-fit hep-ph/0406184)

Standard Model: a=p-b-g

LHCb-Babar Meeting,

4 April 2005

physics aims1

(db)

(ut)

Im

Im

a

a







c

Re

1

Re

c

c

Physics aims
  • Two main unitarity triangles:

LHCb-Babar Meeting,

4 April 2005

physics aims2
Physics aims
  • Channels to be used to extract unitarity triangles:

LHCb-Babar Meeting,

4 April 2005

c from b s j yf diagrams
c from Bs→J/Yf (Diagrams)

Decay

Mixing

(This l is not Wolfenstein parameter!)

LHCb-Babar Meeting,

4 April 2005

c from b s j yf asymmetry
c from Bs→J/Yf (Asymmetry)
  • Asymmetry:

(if J/YF is eigenstate)

  • But J/Y F is not pure CP eigenstate:

CP even

CP odd

CP even

LHCb-Babar Meeting,

4 April 2005

c from b s j yf non cp
c from Bs→ J/Yf (Non-CP)
  • Change due to mixed eigenstate:

The effect of the CP admixture is to dilute extraction of c and to add a small coefficient in front of cos(Dms) since:

LHCb-Babar Meeting,

4 April 2005

c from b s j yf transversity
c from Bs→ J/Yf (Transversity)
  • Extraction of CP eigenstates (transversity analysis):

Three polarization states

  • Bs→J/Y(l+l-)F(K+K-) has three angles but can be put into J/Y reference frame with only one angle (the transversity qtrq) that comes out of F(K+K-) decay plane .

J/Y rest frame

LHCb-Babar Meeting,

4 April 2005

c from b s j yf transversity1
c from Bs → J/Yf (Transversity)
  • Angular distribution in transversity:
  • Once CP eigenstates established, the analysis proceeds in the same manner to establish CP asymmetries.
  • References:
    • Durham workshop CERN-TH/2001-034 (hep-ph/0102159)
    • LHCb notes: LHCb 98-067 & G. Raven, LHCb 2003-118 and LHCb 2003-119
    • “B decays at the LHC”: CERN-TH/2000-101

LHCb-Babar Meeting,

4 April 2005

slide13

LHCb Experiment

  • LHCb Detector: forward single arm spectrometer at LHC
  • Acceptance:

10-300 mrad bending

10-250 mrad non-bending

LHCb-Babar Meeting,

4 April 2005

slide14

LHCb Experiment

  • Exploit VELO for Bs proper time measurement (Bs oscillations)
  • Proper time resolution: ~40 fs
  • Dms sensitivity: 68 ps-1(Standard Model ~ 20 ps-1)
  • Exploit RICH for particle identification: F(K+K-)
  • PID: p-K separation 1-100 GeV

RICH1

LHCb-Babar Meeting,

4 April 2005

RICH2

b s j yf da vinci analysis

Select J/ψ

Calculate Transversity

Combine to select Bs

Real MC Data

SelectФ

Write Histos & NTuples

Bs → J/Yf (Da Vinci Analysis)
  • Work flow of Bs → J/Yfanalysis using Da Vinci (LHCb analysis package)
  • First ever LHCb analysis run on the Grid (GLite) by S Paterson

LHCb-Babar Meeting,

4 April 2005

b s j yf da vinci analysis1
Bs → J/Yf (Da Vinci Analysis)
  • Ran with 100,000 Bs → J/Yfsignal events

Efficiency F(K+K-): 9.8%

Energy resolution: 9 MeV

Efficiency J/Y(m+m-):14.4%

Energy resolution: 13 MeV

LHCb-Babar Meeting,

4 April 2005

b s j yf da vinci analysis2
Bs → J/Yf (Da Vinci Analysis)
  • Transversity distribution looks promising
  • Contributions from CP odd (ℓ=1) & CP even (ℓ=0,2) states
  • Bs Efficiency ~ 8.2%
  • Energy resolution: 17 MeV
  • Event selection quite clean

LHCb-Babar Meeting,

4 April 2005

b s j yf da vinci analysis3
Bs → J/Yf (Da Vinci Analysis)
  • LHCb 2003-119 by Gerhard Raven, used a toy MC for re-optimization TDR (20% CP odd; 80% CP even)

Very similar to distribution extracted. Need to fit to CP-odd versus CP-even

LHCb-Babar Meeting,

4 April 2005

b s j yf g raven toy mc
Bs → J/Yf (G. Raven toy MC)
  • Proper time resolution: 38 fs

(G Raven LHCb 2003-118)

  • Annual yield:

Assume Lint=2 fb-1(107 s at 2x1032 cm-2s-1); sbb=500mb;

fB=10% for Bs hadronization; BRvis=3.1x10-5

  • Implies: 113 k events per year (with 8.2% efficiency)

LHCb-Babar Meeting,

4 April 2005

b s j yf g raven toy mc1
Bs → J/Yf (G. Raven toy MC)
  • G. Raven’s toy Monte Carlo varied a number of parameters to extract sensitivities

_

q=+1(-1) for events tagged as Bs (Bs)

w=wrong tag fraction (=0.5 for untagged)

Assumed Q=etag(1-2w)2=4.5% (w=35%, etag =50%).

Untagged sample can be used to extract lifetime difference:

  • One can fit for 5 parameters:

LHCb-Babar Meeting,

4 April 2005

b s j yf g raven toy mc2
Bs → J/Yf (G. Raven toy MC)
  • Results:

LHCb-Babar Meeting,

4 April 2005

slide22

Sensitivity Bs→ J/Yf

  • In one year expect ~ 113 k events (negligible background)
  • s(sin 2c) ~ 0.064 (depending on )
  • In five years:s(sin 2c) ~ 0.03 (Standard Model:sin 2c ~ 0.04)

One year

LHCb-Babar Meeting,

4 April 2005

slide23

New Physics

  • Left-Right symmetric models (eg. SB-LR)

LHCb-Babar Meeting,

4 April 2005

slide24

Conclusions

  • Bs→J/Yf is a very promising channel to study at LHCb
  • Not accessible at B factories or Tevatron
  • Standard Model prediction for cis very small (~ 0.02)
  • New Physics could make c significantly larger than SM
  • Started analysis of Bs→J/Yf and can achieve yields of ~100k events per year
  • Using Toy Monte Carlo (G Raven), LHCb can probe c to values very close to SM predictions, s(sin 2c) ~ 0.064 within 1 year.

LHCb-Babar Meeting,

4 April 2005

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