Studies of b-hadron decays to charming final states at LHCb
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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
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Which “charming” final states?
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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
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b-hadron decays to open charm for CP violation studies
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= ( 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
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= (68 +13 -14 )⁰ CKMFitter
= (76 ± 11 )⁰ UTFit
CP Violation Super-clean measurement of
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QCD• Factorisation • Hadronisation models •Fragmentation fractions
Baryons: a largely unexplored land
G.Tonelli@ EPS2011
b-hadron decays to open charm: physics potential
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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
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2010 data
PID : 2 RICH detectors @LHCb kaon-pion separationover 2—100GeV/c
Effectively separate B→DK from10x more abundant B→D
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CHARGED B DECAYS
On the heritage trail: ADS and GLW results from B+->D0K+ (and B+->D0
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from direct CPV in B± decays
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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)
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GLW: B+ → D(KK)K+ and B+ → D(KK)
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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)-
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GLW analysis: Cabibbo favoured modesB+ → DK+, B+ → D+ (D → KD→ K
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Time-integrated CP asymmetry:
Branching fractions ratioBF(B→DK)/BF(B→D)
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)-
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GLW results
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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
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Towards GGSZ analysis: B±→D(KS)K±
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2010 data36.5 pb-1
B→D(KS)K B→D(KS)
Nsig=95
Branching fractions ratioBF(B→DK)/BF(B→D)
)%0.10.12( 0.60.5
/
KKSR
Nsig=12
PRELIMINARY
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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±
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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
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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
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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
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ADS Results
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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
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STRANGE BEAUTIFUL MESONS AND BARYONS
Entering the hadron-colliders specific realm: studies with
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BS→ Ds-+
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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
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Bs production fraction from fully hadronic decays: BS→ Ds
-+, B0→ D-K+, B0→ D-+
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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
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Semileptonic decays: b-hadron production fractions
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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
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LHCb fs/fd average
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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
[LHCb-CONF-2011-034]
PRELIMINARY
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MORE NEWS ON BARYONS
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b→D0ph- (h=,K)
Also colour-suppressed transitions
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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
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b →D0pK and b→D0pK
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First observation
[LHCb-CONF-2011-036]
b →D0pK: 6.3 significance
b→D0pK: 2.6
PRELIMINARY
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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)
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A new blossoming season for charming tree level decays has started at LHCb!
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ADDITIONAL MATERIAL
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Measurements of Hb→Hch+h-h+
[LHCb-CONF-2011-007; LHCb-CONF-2011-018]
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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
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First observation of Bs →D0K*0 [LHCB-CONF-2011-008]
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• 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
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