24/08/2005lhcb uk meeting, dublin1 first steps toward γ from b + →d 0 (k 0 π + π - )k + with...
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24/08/2005 LHCb UK Meeting, Dublin 1
First steps toward γ from B+→D0(K0π+π-)K+ with
Tom Barber, Val Gibson, Cristina Lazzeroni and Jim Libby
24/08/2005 LHCb UK Meeting, Dublin 2
γ is the weak phase between b→cus ( Vcb) and b→ucs ( Vub)
can be extracted from the interference of these two processes in charged BD0K decays with D0/D0 decaying to a common final state rB is the relative colour suppression between the two modes O(0.1) – dilutes sensitivity to γ δ is the strong phase difference-invariant under CP
Several methods available to extract γ from two-body decays of the D0/D0 (Gronau-London-Wyler and Atwood-Dunietz-Soffer)
Requires 3+charge conjugate modes to extract the parameters some of these modes have very small BFs which are not observed with current B-factory
statistics Will be interesting for LHCb (see reoptimised TDR for GLW): but γ ambiguities and
doubly Cabbibo suppressed decays interfere
cbV
*usV
ubV
*csV
Measuring γ: B+→D0(K0π+π-)K+
BAKDBA )( 0)(0
)( iBB erAKDBA
No need for a time-dependent
analysis
24/08/2005 LHCb UK Meeting, Dublin 3
0D
Measuring γ: B+→D0(K0π+π-)K+ A method proposed by ADS/Giri, Grossman, Soffer and Zupan alleviates
some of the problems by utilising three body Cabbibo allowed decays of the D0/D0
BR(D0→K0π+π-)=(5.97±0.35)% BR(D0→K+K-)=(3.89±0.14)×10-3%
Also, large strong phases between the intermediate resonances allows the the extraction of rB, δ and γ by studying the Dalitz distribution of events
),(),(
),(),(22)(22
22)(22
mmfermmfA
mmfermmfAi
B
iB
amplitudes Dalitz ),(
massinvariant 22
0
mmf
Km S
)),(),((2|),(||),(||| )(22*2222222222
iBB emmfmmfrmmfrmmfA
where
2m
2m
PRD 63, 036005 (2001) and PRD 68, 054018 (2003)
24/08/2005 LHCb UK Meeting, Dublin 4
Not everything in black and white makes sense
0D
ρ(770)
Doubly Cabbibosuppressed K*
22
2
)(
1
d
Ld2nd derivative of likelihood w.r.t. γ
•Regions of the Dalitz plot with the largest interferences are most sensitive to γ•Need good model for Dalitz amplitudes•Belle/Babar have use an isobar model with:
N
j
ij
ij bemmAeammf j
1
2222 ),(),(
Breit-Wigner + non-resonant
24/08/2005 LHCb UK Meeting, Dublin 5
Measuring the Dalitz model
•B-factories use a O(100k) samples of D+*→D0π+,D0→K0π+π- to measure amplitudes and phases-vary model for systematics•LHCb can exploit these and results from CLEO-c
K*(892)
DCS K*(892)
ρ(770)
24/08/2005 LHCb UK Meeting, Dublin 6
Measuring γ: B+→D0(K0π+π-)K+
= 70°±31°±11°±13° D* and D combined
Dalitz Model error
Belle do significantly better:
reason is measured rB= 0.21±0.08
= 68°±14°±13°±11°
γ(de
g)
1σ 2σ
rB vs σ()
Exp. systematic
hep-ex/0504039
PRD 70, 072003 (2004)
202 )( SKmm
B+ B
2m
24/08/2005 LHCb UK Meeting, Dublin 7
Selection studies so far (T. Barber) Selection to maximise signal to background:
1 year signal yield = 6300 No events in 1.6×105 incl. B and 3×104 min. bias
Limited statistic samples Selection in DC04v2 stripping
Currently being revisited but a very promising start
LL K0S DD K0S
24/08/2005 LHCb UK Meeting, Dublin 8
Next steps: selection and backgrounds Understanding Dalitz acceptance key to the
analysis Assessing this from Tom’s selection
Selection optimisation and improvement Understand and cross check current selection, then Optimisation non-standard due to extraction from fit to
Dalitz space and importance of systematic uncertainties Statistical limits in background MC samples
Sideband techniques for data Good understanding of Dalitz distribution of
background
24/08/2005 LHCb UK Meeting, Dublin 9
HLT K0
S complicates this significantly Only long tracks:
30% of selected signal events LL K short εHLT/track ≈93%, therefore 5-track efficiency ≈70% overall reduces yield to 1300/annum
Including DD non-trivial as topology is under constrained for a kinematic fit
No need to panic yet as B-factories are performing measurements with 5 times less statistics-but clearly increased yields desirable
IP
B+ D0
K+
π+
π-
π+
π-
K0S
24/08/2005 LHCb UK Meeting, Dublin 10
Event model Complex Dalitz model required:
Current simulation phase space: OK for Dalitz efficiency then reweight to any model….. unless the correlations amongst the daughters distort Dalitz
acceptance In LHCb isobar model already implemented for B0→D0
K* studies Want event model in LHCb framework and Standalone: acceptance studies and fitting K-matrix
Transfer BABAR/Belle/CLEO-C measurements
24/08/2005 LHCb UK Meeting, Dublin 11
B+→D0(K0K+K-)K+
Same method works with π→K in D0 decay Reduced BF:
BF(D0→K0K+K-) = (1.03±0.10)% BF(D0→K0 π +π-) = (5.97±0.35)%
But using RICH info maybe a big help for background suppression
Dalitz model has less resonances but complex threshold effects (Babar hep-ex/0507026) what is the sensitivity to γ?
Generated samples in Cambridge to study in parallel to the Kππ mode
PDG ‘04
24/08/2005 LHCb UK Meeting, Dublin 12
Outlook Other issues to feedback to the optimization
studies: fitting for γ, and rB and systematics
Understanding acceptance, B+→D0(K0K+K-)K+ and HLT first
Looking forward to a successful Oxbridge collaboration…..
24/08/2005 LHCb UK Meeting, Dublin 13