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 + D 0 (K 0 π + π - )K + with Tom Barber, Val Gibson, Cristina Lazzeroni and Jim Libby
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Transcript of 24/08/2005LHCb UK Meeting, Dublin1 First steps toward γ from B + →D 0 (K 0 π + π - )K + with...

Page 1: 24/08/2005LHCb UK Meeting, Dublin1 First steps toward γ from B + →D 0 (K 0 π + π - )K + with Tom Barber, Val Gibson, Cristina Lazzeroni and Jim Libby.

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

Page 2: 24/08/2005LHCb UK Meeting, Dublin1 First steps toward γ from B + →D 0 (K 0 π + 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

Page 3: 24/08/2005LHCb UK Meeting, Dublin1 First steps toward γ from B + →D 0 (K 0 π + π - )K + with Tom Barber, Val Gibson, Cristina Lazzeroni and Jim Libby.

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)

Page 4: 24/08/2005LHCb UK Meeting, Dublin1 First steps toward γ from B + →D 0 (K 0 π + π - )K + with Tom Barber, Val Gibson, Cristina Lazzeroni and Jim Libby.

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

Page 5: 24/08/2005LHCb UK Meeting, Dublin1 First steps toward γ from B + →D 0 (K 0 π + π - )K + with Tom Barber, Val Gibson, Cristina Lazzeroni and Jim Libby.

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)

Page 6: 24/08/2005LHCb UK Meeting, Dublin1 First steps toward γ from B + →D 0 (K 0 π + π - )K + with Tom Barber, Val Gibson, Cristina Lazzeroni and Jim Libby.

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

Page 7: 24/08/2005LHCb UK Meeting, Dublin1 First steps toward γ from B + →D 0 (K 0 π + π - )K + with Tom Barber, Val Gibson, Cristina Lazzeroni and Jim Libby.

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

Page 8: 24/08/2005LHCb UK Meeting, Dublin1 First steps toward γ from B + →D 0 (K 0 π + π - )K + with Tom Barber, Val Gibson, Cristina Lazzeroni and Jim Libby.

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

Page 9: 24/08/2005LHCb UK Meeting, Dublin1 First steps toward γ from B + →D 0 (K 0 π + π - )K + with Tom Barber, Val Gibson, Cristina Lazzeroni and Jim Libby.

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

Page 10: 24/08/2005LHCb UK Meeting, Dublin1 First steps toward γ from B + →D 0 (K 0 π + π - )K + with Tom Barber, Val Gibson, Cristina Lazzeroni and Jim Libby.

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

Page 11: 24/08/2005LHCb UK Meeting, Dublin1 First steps toward γ from B + →D 0 (K 0 π + π - )K + with Tom Barber, Val Gibson, Cristina Lazzeroni and Jim Libby.

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

Page 12: 24/08/2005LHCb UK Meeting, Dublin1 First steps toward γ from B + →D 0 (K 0 π + π - )K + with Tom Barber, Val Gibson, Cristina Lazzeroni and Jim Libby.

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…..

Page 13: 24/08/2005LHCb UK Meeting, Dublin1 First steps toward γ from B + →D 0 (K 0 π + π - )K + with Tom Barber, Val Gibson, Cristina Lazzeroni and Jim Libby.

24/08/2005 LHCb UK Meeting, Dublin 13