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

Which “charming” final states?

2Stefania Ricciardi

b-hadron decays to open charm: Hb→HcX B+→D0K+ and B+→D0

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

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

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

b→D0pK and b→D0p [LHCb-CONF-2011-036] Observation of new decay modes and hints of b

Bu

Bs

Semileptonic decays

b

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

LHCb Summer 2011 results

Bu BsBd b

b-hadron decays to open charm for CP violation studies

3Stefania Ricciardi

= ( 68 +13 -14 )⁰ CKMFitter

= ( 76±11 )⁰ UTFit

CKM precision tests Super-clean measurement of

yLeast well-measured CKM UT angle

Measurements of 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+

•b →D

= (68 +13 -14 )⁰ CKMFitter

= (76 ± 11 )⁰ UTFit

CP Violation Super-clean measurement of

Stefania Ricciardi 4

QCD• Factorisation • Hadronisation models •Fragmentation fractions

Baryons: a largely unexplored land

G.Tonelli@ EPS2011

b-hadron decays to open charm: physics potential

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 b (in acceptance)

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

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

Excellent invariant mass resolutionExcellent vertex resolution

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

5Stefania Ricciardi

2010 data

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

Effectively separate B→DK from10x more abundant B→D

CHARGED B DECAYS

On the heritage trail: ADS and GLW results from B+->D0K+ (and B+->D0


from direct CPV in B± decays


Other parameters measured from data:

B-decay strong phase difference

rB = relative magnitude of suppressed B-decay amplitude

Interference if D0 and D0 decay to common final state f

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

b → c (favoured)

b → u (suppressed)

Several strategies to extract :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)

8Stefania Ricciardi

Time-integrated CP asymmetry:

01.004.001.0

07.018.007.0

DCP

DKCP

A

A

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

)%53.089.131.9(/ K

CPR

Nsig=405 Nsig=419

Nsig=44 Nsig=40

2010 data36.5 pb-1

PRELIMINARY

Negative Positive

B+ → D(KK)K+

B+ → D(KK)+

B- → D(KK)K-

B- → D(KK)-

GLW analysis: Cabibbo favoured modesB+ → DK+, B+ → D+ (D → KD→ K


Time-integrated CP asymmetry:


2010 data36.5 pb-1 PRELIMINARY

02.006.008.0 DKCFA

)%40.038.030.6(/ KCFR

Negative B Positive B

Nsig=235 Nsig=272

Nsig=3486 Nsig=3545

B+ → D(K)K+ B- → D(K)K-

B+ → D(K)+ B- → D(K)-

GLW results


CPDBCP RrA /sinsin2

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(KS)K±

11Stefania Ricciardi

2010 data36.5 pb-1

B→D(KS)K B→D(KS)

Nsig=95


)%0.10.12( 0.60.5

/

KKSR

Nsig=12

PRELIMINARY

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

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±→D±


ADS Observables:OS/SS rate

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

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

KKKKKKKKA

KKKKKKKKR

DD

DDDKADS

DD

DDDKADS

DKADSDBDB

DD

DDDKADS

DBDBDBDD

DDDKADS

RrrKKKKKKKKA

rrrrKKKKKKKKR

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

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

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→D

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:4 significance

B- and B+

Hint of direct CPV

PRELIMINARY

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

Belle: 4.1

STRANGE BEAUTIFUL MESONS AND BARYONS

Entering the hadron-colliders specific realm: studies with


BS→ Ds-+


BS→ Ds-+,

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→ [Marc Olivier Bettler for LHCb @DPF]

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

[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

-+ which is sensitive tos

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

Bs production fraction from fully hadronic decays: BS→ Ds

-+, B0→ D-K+, B0→ D-+


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

theoretically well-understood

B0→ D-K+,

B0→ D-+,

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

[arXiv:1106.4435]

From B.F. (BS→ Ds-+)/B.F. (B0→ D-K+

)

From B.F. (BS→ Ds-+)/B.F. (B0→ D-+

)

2010 data,35 pb-1

Semileptonic decays: b-hadron production fractions


D0X

D+X

DsX

cX

[LHCb-CONF-2011-028]

D0X + D+X dominant for B0 + B+ DsX dominant for Bs

cX dominant for b

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

Cross-feed contributions corrected for• D0,± K•DsK•D0)±)p(n)b

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 Hadronic and semileptonic results consistent


PRELIMINARY

MORE NEWS ON BARYONS


b→D0ph- (h=,K)

Also colour-suppressed transitions


2011 Data set (330 pb-1)

sensitive to b→D0p b→c b→D0pK

Enhances sensitivity ofb→D0• No long-lived V0

• Full 3-body phase space

PRELIMINARY

b →D0pK and b→D0pK


First observation


b →D0pK: 6.3 significance

b→D0pK: 2.6

PRELIMINARY

Conclusions LHCb on a fast track for precise measurement of CKM angleusing b-

hadron decays to open charm, with both traditional modes:

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

and innovative ways: b →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-,b

h=or K

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

First observation of B- →D0K

First observation of B0 →D+K-:

First measurement of b→c:

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

Bs →D0K*0Bd →D0K*0

fs/fd



Documents

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