Hadronic B→DX Decays at LHCb and CDF

Laurence Carson, Imperial Collegeon behalf of the LHCb Collaboration

CIPANP 2012, St. Petersburg,FL

Outline• Physics motivation: why study hadronic B→DX

decays?• Selection of recent measurements:– Observation of new Bs→DD’ decays (LHCb)

– Improved measurements of Bs→DsDs (LHCb and CDF)

– Improved measurements of Bs→DsK and Bs→Dsπ (LHCb)– Observation of B→DKππ decays (LHCb)

• Many other interesting results not covered here

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Physics Motivation• A variety of interesting physics is accessible using B→DX decays:• Different methods to measure γ with B+/-→D0K+/- decays [talk of K.Akiba].• The decays Bd→D+D- and Bs→Ds

+Ds- can be used to measure γ, using

U-spin symmetry [e.g. hep-ph/0310252].• In addition, Bd→D+D- can be used to measure sin(2β). Belle reported

unexpectedly large direct CPV in this mode [hep-ex/0702031].• The decay Bs→Ds

+/-K-/+ allows a theoretically clean γ measurement, uniquely possible at LHCb, via a flavour-tagged and time-dependent analysis [hep-ph/0304027, see also talk of K.Akiba].

• The same methods used to measure γ using B+/-→D0K+/- can also be applied to B+/-→D0K+/-π+π- decays [hep-ph/0211282].

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( )

The LHCb Experiment• Situated on LHC ring; pp collisions at ECM = 7 TeV. (8 TeV in 2012)• Forward arm spectrometer, optimised for study of B and D decays.

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Hardware trigger reduces event rate to 1MHz, followed by software trigger reducing to several kHz. This allows high trigger efficiency, even on purely hadronic final states.

The CDF Experiment• Situated on TeVatron ring; pp collisions at ECM = 1.96 TeV• Central detector, tracks reconstructed by Si vertex detector and drift

chamber (COT).

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• Charged hadron PID using– dE/dx in COT– TOF system between COT and solenoid

• Hadronic trigger searches for two oppositely-charged tracks with vertex displaced from primary interaction

Bs→DD’ at LHCb• D mesons are reconstructed as D0→Kπ , D+→Kππ or Ds→KKπ.• Final selection based on BDT for each D type, trained on data using

relevant B(s)→Dπ decay (signal) and D mass sidebands (background).

• Cross-feeds (and Λc) suppressed using combined mass/PID vetoes.

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LHCb-CONF- 2012-009

1.0/fb

Bs→DsDs Bd→D+Ds

(loose selection)

Syst dominated by fs/fd

(true for all modes)Preliminary

• Around five times more precise than previous world average.

Bs→DD’ at LHCb• First observations of Bs→D+Ds (10.1σ) and Bs→D+D- (10.7σ):

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Bd,s→D+Ds

(tight selection)

Bd,s→D+D-

• Both are in agreement with expectations of ≈|Vcd/Vcs|2 = 0.05 and ≈1.

Preliminary

LHCb-CONF- 2012-009

Bs→DD’ at LHCb• First observation of Bs→D0D0 (5.4σ), and hint of Bd→D0D0 (2.1σ):

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Bd,s→D0D0 B-→D0Ds

• Again, this is in agreement with expectations.

• Future plans include measurements of β and γ with Bd→D+D- and Bs→Ds

+Ds-, once more data has been collected.

Preliminary

LHCb-CONF- 2012-009

• Reconstruct Ds→KKπ, with KK in φ window or Kπ in K* window.

• Soft π0 or γ from Ds*→Ds not reconstructed.

• Normalisation is made to Bd→DsD-.

Bs→Ds(*)Ds

(*) at CDF

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6.8/fb

CDF Note 10721

which is smaller than ΔΓs measured in Bs→J/ψφ [e.g. LHCb-CONF-2012-002], suggesting that the three-body contribution is sizeable.

and can be used to measure ΔΓs, ignoring possible contributions from three-body modes [PLB 316, 567]:

• This yields: ,

Bs→Ds(*)Ds

(*) at CDF

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• The result for Bs→DsDs is in agreement with the LHCb value.

Third error is from fs/fd and B(Bd→DsD- )

• The inclusive B is:,

Bs→Dsh at LHCb• An accurate measurement of B(Bs→DsK) is an important stepping

stone on the path to a γ measurement with this mode [talk of K.Akiba].• High Bs→Dsπ yield allows benchmark B measurement for Bs modes.

• Final selection uses a BDT, trained on Bs→Dsπ data and optimised for significance of the Bs→DsK signal.

• Backgrounds from Λc are vetoed, similarly to the B→DD’ analysis.

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0.37/fb hep-ex/ 12041237

Bs→Dsπ Bd→D-π (normalisation)

Bs→Dsh at LHCb: DsK• Tight PID criterion applied to bachelor K, to suppress Bs→Dsπ.• Performance of PID criteria measured on data using D*+→D0(Kπ)π+.• Shape of misidentified Bs→Dsπ component determined from data,

accounting for effect of PID requirements. • Dsπ yield is left free, and cross-checked against expectation from PID.

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• Background from Bd→D-K constrained using misID probability of PID criteria.

• Cross-check: fitted yield of Bd→DsK agrees with expectation from PDG.

Bs→Dsh at LHCb• Experimental systematics include fit model, and translation of PID

performance from D* calibration sample to signal B decays.

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• For absolute B measurements, additional external systematics include B(Bd→D-π) and LHCb value of fs/fd (from semileptonic decays).– However the D branching fraction uncertainties are subtracted from the fs/fd

uncertainty, since fs/fd extraction also depends on these branching fractions.

Experimental, plus B(Bd→D-π) fs/fd only

• Total errors are 10% (Dsπ) and 12% (DsK) respectively.• Both measurements significantly improve on the previous world

average values of (3.2±0.5)x10-3 (Dsπ) and (3.0±0.7)x10-4 (DsK).

Observation of B→DKππ• B measured relative to the Cabibbo-favoured B→Dπππ modes.• Tight PID criterion is applied to bachelor K, to suppress B→Dπππ.

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35/pb (2010) PRL 108,

161801

First observations of (c) Bd→D-Kππ (7.2σ) and (d) B+→D0Kππ (9.0σ).

LHCb trigger in 2011/ 2012 contains improvements leading to higher B→Dhhh yields per pb-1 than in 2010 data

Observation of B→DKππ

• In the future, the B- mode will be used to add sensitivity to the γ measurement with B+/-→D0K+/- decays.

• Also, method to measure γ with Bs→DsK can be extended to Bs→DsKππ - search for this mode is underway. 15

• Systematics arise from fit model, PID efficiency and Kππ invariant mass distribution.

• Kππ system consistent with decays of excited strange states, such as K1(1270).

Summary • Many interesting physics measurements can be

made with hadronic B→DX decays.• Observations made of many new modes: Bs→D+Ds,

Bs→D+D-, Bs→D0D0, Bd→D-Kππ and B+→D0Kππ.

• Greatly improved measurements of Bs→DsDs and Bs→Dsh.

• These measurements open the road to new ways to measure physics parameters such as γ.

• Stay tuned for more results in the future!– LHCb expects to collect ≈1.5/fb at 8 TeV in 2012 16

Backup

Semileptonic fs/fd at LHCb

• Can measure fs/(fu+fd) using D0Xμν, D+Xμν, DsXμν, after correcting for cross-feeds.

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fs/(fu + fd) = 0.134 ± 0.004 (stat) – 0.010 (syst) + 0.011

• No dependence on pT or η is seen.

• Assuming fu=fd, simply doubling this value gives fs/fd.

PRD 85, 032008

B→DD’

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from hep-ph/07054421

aeiθ is the ratio of penguin to tree amplitudes

Measuring γ with Bs→DsK

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• The final state Ds-K+ is accessible by both Bs and Bs:

• Both diagrams have similar magnitudes, hence large interference between them is possible.

• Using a flavour-tagged, time-dependent analysis, we can measure four decay rates - Bs or Bs to Ds

+K- or Ds-K+

• From these rates, γ can be extracted in an unambiguous and theoretically clean way.

Measuring γ with Bs→DsK

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Strong phase difference