studies of b- hadron decays to charming final states at lhcb

Studies of b-hadron decays to charming final states at LHCb

Stefania RicciardiSTFC, Rutherford Appleton Laboratoryon behalf of the LHCb Collaboration

DPF, APS Meeting of the Division of Particles and Fields of the American Physical SocietyAugust 9-13, 2011 , Brown University, Providence, Rhode Island

Stefania Ricciardi 2

Which “charming” final states?b-hadron decays to open charm: Hb→HcX

B+→D0K+ and B+→D0p+

ratio of branching fractions [LHCb-CONF-2011-031] R_CP+ , A_CP R_ADS, A_ADS [LHCb-CONF-2011-044]

Bs→Dsp, B0→D+p-, B0→D+K- , arXiv: 1106.4435Rates and fs/fd production fractions

Production fractions from Hb→HcXmn [LHCb-CONF-2011-028]

Lb→D0pK- and Lb→D0pp- [LHCb-CONF-2011-036] Observation of new decay modes and hints of Xb

Bu

Bs

Semileptonic decays

Lb

fs/fd Average [LHCb-CONF-2011-034]

LHCb Summer 2011 results

Bu BsBd Lb


b-hadron decays to open charm for CP violation studies

g = ( 68 +13 -14 )⁰ CKMFitter

g = ( 76±11 )⁰ UTFit

CKM precision tests Super-clean measurement of g

yLeast well-measured CKM UT angle

Measurements of g via interference of b→c and b→u tree-level transitions

Essentially no theoretical uncertainties

Several decays suitable, e.g.,• B+ →DK+

• B0 →DK*0

• Bs →DsK+

• Lb →Dl


g = (68 +13 -14 )⁰ CKMFitter

g = (76 ± 11 )⁰ UTFit

CP Violation Super-clean measurement of g

QCD• Factorisation • Hadronisation models •Fragmentation fractionsBaryons: a largely unexplored land

G.Tonelli@ EPS2011

b-hadron decays to open charm: physics potential

5

Crucial experimental ingredientsLarge b-DATA SAMPLE • High Integrated Luminosity at LHCb• 2010: 37 pb-1 • 2011: 630 pb-1 (11 Aug)

• Large b-production cross-section at s=7TeV~125 mb (in acceptance)

Dedicated TRIGGERL0 (Hardware) “high pT” (>2-3GeV) m and hadrons HLT (Software) output 3 kHzEfficient selection of key B and D decays

Precision @VERTEXLHCB Vertex detector and trackings(p)/p ~ 0.5-0.8% [3-100 GeV/c]s(IP)~ 16mm + 30mm/pT

Excellent invariant mass resolutionExcellent vertex resolution

Mass resolution and displaced vertices for separation from low-mass background and rejection of combinatorial background

Stefania Ricciardi

2010 data

PID : 2 RICH detectors @LHCb kaon-pion separationover 2—100GeV/c

Effectively separate B→DK from10x more abundant B→Dp


CHARGED B DECAYS

On the g heritage trail: ADS and GLW results from B+->D0K+ (and B+->D0p+)

Stefania Ricciardi

g from direct CPV in B± decays

7

Other parameters measured from data:

dB = B-decay strong phase difference

rB = relative magnitude of suppressed B-decay amplitude

Interference if D0 and D0 decay to common final state f

g extraction from measurements of time-integrated decay rates of B+ and B- to DK±

b → c (favoured)

b → u (suppressed)

Several strategies to extract g:GLW : f =CP eigenstateGronau & London, PLB 253, 483 (1991);Gronau & Wyler, PLB 265, 172 (1991)

ADS: f =Flavour state Atwood, Dunietz, & Soni, PRL 78, 3257 (1997),Atwood, Dunietz, & Soni, PRD 63, 036005 (2001)

GGSZ: f =3-body decays Giri, Grossman, Soffer, & Zupan, PRD 68, 054018 (2003)Bondar, PRD 70, 072003 (2004)


GLW: B+ → D(KK)K+ and B+ → D(KK)p+

Time-integrated CP asymmetry:

01.004.001.0

07.018.007.0

=

=

+

+

pDCP

DKCP

A

A

Branching fractions ratioBF(B→DK)/BF(B→Dp)

)%53.089.131.9(/ =+pK

CPR

Nsig=405 Nsig=419

Nsig=44 Nsig=40

2010 data36.5 pb-1

PRELIMINARY

Negative Positive

B+ → D(KK)K+

B+ → D(KK)p+

B- → D(KK)K-

B- → D(KK)p-


GLW analysis: Cabibbo favoured modesB+ → DK+, B+ → Dp+ (D → Kp, D→ Kppp)

Time-integrated CP asymmetry:


2010 data36.5 pb-1 PRELIMINARY

02.006.008.0 -=DKCFA

)%40.038.030.6(/ =pKCFR

Negative B Positive B

Nsig=235 Nsig=272

Nsig=3486 Nsig=3545

B+ → D(Kp)K+ B- → D(Kp)K-

B+ → D(Kp)p+ B- → D(Kp)p-


GLW results

++ = CPDBCP RrA /sinsin2 gdgd

pp

coscos21

/2

//

BBB

KCF

KCPCP

rr

RRR

++=

= ++

PRELIMINARY

12.031.048.1 =+CPR 07.018.007.0 =+CPA

New HFAG averages including LHCb results

2010 data36.5 pb-1


Towards GGSZ analysis: B±→D(KSpp)K±

2010 data36.5 pb-1

B→D(KSpp)K B→D(KSpp)p

Nsig=95


)%0.10.12( 0.60.5

/ = +-

ppp

KKSR

Nsig=12

PRELIMINARY


ADS: B→D(Kp)K D flav decays to K+p- and K-p+

Experimentally we distinguish SS: Same sign kaons (favoured) OS: Opposite side kaons (suppressed, 10-7

branching fractions) CP asymmetry enhanced by interfering

amplitudes with similar size 4 decay rates to be measured : (B+,B-) x (SS,OS) Yields extracted from simultaneous fit to

B±→DK± and B±→Dp ±

ADS Observables:OS/SS rate

CP asymmetry )]([)]([)]([)]([

)]([)]([)]([)]([

++---+

++---+

+-+-+-

++---+

+-

++

KKKKKKKKA

KKKKKKKKR

DD

DDDKADS

DD

DDDKADS

pppp

pppp

DKADSDBDB

DD

DDDKADS

DBDBDBDD

DDDKADS

RrrKKKKKKKKA

rrrrKKKKKKKKR

/)sin(sin2)]([)]([)]([)]([

)cos(cos2)]([)]([)]([)]([ 22

ddgpppp

ddgpppp

+=+-

+++=++

++---+

++---+

+-+-+-

++---+


ADS fit and yields

Boosted Decision Tree reduces combinatorial backgroundPeaking backgrounds:

charmless: suppressed with D0 vertex separation cuts Double MISID: veto candidates which satisfy SS AND OS

selection criteria at the same time

343 pb-1

2011 data sample

OS

B→Dp

SS

B- B+

B→DK

B- B+

Signal in the suppressed modesHint of charged CP asymmetry


ADS Results

Dominant systematic uncertainties:• Low mass background model• PID efficiency

Suppressed ADS signal:4s significance

B- and B+

Hint of direct CPV

PRELIMINARY

Results consistent and competitive with B-factories and CDF results.

Belle: 4.1s


STRANGE BEAUTIFUL MESONS AND BARYONS

Entering the hadron-colliders specific realm: studies with


BS→ Ds-p+

BS→ Ds-p+,

4. Relative abundance to U-spin related B0 modes can be used to measure fs/fd ratio of Bs and Bd production fractions Necessary for absolute B.F. measurements of Bs decays, e.g. important for Bs→ mm [Marc Olivier Bettler for LHCb @DPF]

Interesting for several reasons:1. World-class measurement of oscillation frequency Dms

[Daan van Eijk for LHCb @DPF]

2. B-Tagging calibration

2010 data,35 pb-1

3. First step to reconstruction and time-dependent measurements of BS→ Ds

-K+ which is sensitive to g+fs

Fleischer, Serra, TuningPhys.Rev.D82:034038,2010Phys.Rev D83: 014017,2011


Bs production fraction from fully hadronic decays: BS→ Ds

-p+, B0→ D-K+, B0→ D-p+

B0→ D-K+ dominated by colour-allowed tree diagram

theoretically well-understood

B0→ D-K+,

B0→ D-p+,

B0→ D-p+ larger yield: smaller statistical uncertainty butadditional theoretical uncertainty contribution from W exchange

[arXiv:1106.4435]

From B.F. (BS→ Ds-p+)/B.F. (B0→ D-K+

)

From B.F. (BS→ Ds-p+)/B.F. (B0→ D-p+

)

2010 data,35 pb-1


Semileptonic decays: b-hadron production fractions

D0mnX

D+mnX

DsmnX

LcmnX

[LHCb-CONF-2011-028]

D0mnX + D+mnX dominant for B0 + B+ DsmnX dominant for Bs

LcmnX dominant for Lb

Yields from 2D ML fit to m(Hc)-ln(IP/mm) to separate prompt charm

Cross-feed contributions corrected for• D0,± Kmn (B0,B+,Bs)•DsKmn (B0,B+,Bs)•D0)±)p(n)mn (B0,B+,Lb)

ln(IP/mm) m(Hc) GeV

Main systematic: charm and Bs B.F.

PRELIMINARY


LHCb fs/fd average

More precise than LEP/Tevatron average <fs/fd> =0.271 ± 0.027 (remarkable agreement, despite not a priori a “universal” number)

No dependence on pT nor h Hadronic and semileptonic results consistent


PRELIMINARY


MORE NEWS ON BARYONS


Lb→D0ph- (h=p,K)

Also colour-suppressed transitions

2011 Data set (330 pb-1)

sensitive to gLb→D0pp Lb→Lcp Lb→D0pK

Enhances sensitivity ofLb→D0L • No long-lived V0

• Full 3-body phase space

PRELIMINARY


Lb →D0pK and Xb→D0pK

First observation


Lb →D0pK: 6.3s significance

Xb→D0pK: 2.6s

PRELIMINARY


Conclusions LHCb on a fast track for precise measurement of CKM angle g using b-

hadron decays to open charm, with both traditional modes:

GLW and ADS results competitive with previous measurements 4s observation of the suppressed ADS modes GGSZ analysis also on the way

and innovative ways: Lb →DpK (first observation)

Important by-product: fs/fd world best measurement (average of results with semileptonic and hadronic modes)

Present results obtained with 2010 (~35 pb-1) or early 2011(<350 pb-1) data, i.e., just a fraction of total expected by end of this year (1 fb-1)

A new blossoming season for charming tree level decays has started at LHCb!


ADDITIONAL MATERIAL


Measurements of Hb→Hch+h-h+

[LHCb-CONF-2011-007; LHCb-CONF-2011-018]

Hb: B0, B-,Lb

h= p or K

Sensitive to CKM-angle g. Relatively large B.F. [> B.F. (B-→D0K)]

First observation of B- →D0Kpp

First observation of B0 →D+K-pp:

First measurement of Lb→Lcppp:

In addition


First observation of Bs →D0K*0 [LHCB-CONF-2011-008]

• Previously unobserved decay • Interesting probe of SU(3)F breaking in colour-suppressed modes• BF predicted to be 3-9 10-4

[Colangelo, Ferrandes, PLB 627,1(2005);Chiang, Senaha, PRD75,074021(2007);Chua, Hou, PRD77,116001(2008)]

• Together with Bs →D*0K*0, potentially large background to Bd→D0K*0 modes sensitive to g

Bs →D0K*0Bd →D0K*0

fs/fd

studies of b- hadron decays to charming final states at lhcb

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