V.V. Gligorov, CERN On behalf of the LHCb collaboration 25th February 2013

Transcription

1 Hadronic b decays to open charm and a measurement of the CKM angle γ V.V. Gligorov, CERN On behalf of the LHCb collaboration 25th February 2013

2 Overview Today I will discuss two topics 1) Searches for suppressed modes and measurements of branching fractions in B decays to open charm => Explores the sizes of decay diagrams (tree/penguin/exchange/etc.) contributing to B decays and the importance of rescattering, which are key inputs for understanding CPV measurements. 2) A combined LHCb measurement of the CKM angle γ with 1fb -1 of data => Includes inputs from ADS, GLW, and GGSZ analyses 2

3 b hadron decays to open charm

4 Studies of double charm B decays A rich collection of decay modes and diagrams CP violation in these modes is sensitive to B(s) mixing phases, γ, ΔΓs Suppressed modes mediated by W-exchange diagrams and suppressed penguin diagrams, and their branching fractions can help us to understand these processes better. Common selection : D 0 #Kπ/K3π, D + #Kππ, Ds#KKπ Arbitration between the different D mesons using RICH information. Decision tree for D-from-B signature trained on real data B#Dπ decays. Charmless decays are suppressed by requiring that the D vertex is separated from the B vertex. NEW FOR Moriond EW 2013! LHCb-PAPER

5 B s D s D s B s D s D s B s D s D + NEW FOR Moriond EW 2013! LHCb-PAPER

6 B s D s D + 10σ observation! NEW FOR Moriond EW 2013! LHCb-PAPER

7 B d,s D + D -,D 0 D σ observation! 10.9σ observation! B s,d D + D - B s,d D 0 D 0 NEW FOR Moriond EW 2013! LHCb-PAPER

8 Measured branching fractions First observations of Bs#DsD,D + D -,D 0 D 0 A strong hint for B 0 #D 0 D 0 NEW FOR Moriond EW 2013! BR results for Bs#D + D -,D 0 D 0 and B 0 #D 0 D 0 at the upper end of rescattering predictions (arxiv: ). LHCb-PAPER

9 Search for B s D *- π + Pure weak exchange decay, helps to understand sizes of various diagrams and rescattering effects in DD decays. Rescattering contributions to this decay are predicted to be small. Interplay with other decays : e.g. if BR(Bs#ππ) is driven by rescattering then expect small BR(Bs#D * π). If BR(Bs#ππ) is driven by short-distance effects then BR(Bs#D * π) could be much larger. NEW FOR Moriond EW 2013! LHCb-PAPER

10 Search for B s D *- π + Signal is divided into five bins based on the opening angle between the D* and π momenta in the lab frame Binning chosen to give equal numbers of events in each bin Width of signal peak in highest bin 60% of that in lowest bin, sensitivity increased by 20%. No signal found, Bayesian limit set BR(Bs#D * π) < 6.1(7.8) 10-6 at 90%(95%) CL Suggestive of dominance of rescattering in BR(Bs#ππ) as recently suggested in e.g. Gronau et al. (arxiv: ). NEW FOR Moriond EW 2013! LHCb-PAPER

11 A measurement of the CKM angle γ

12 γ measurement inputs GLW/ADS in B#DK,Dπ with D#hh ADS in B#DK,Dπ with D#hhhh GGSZ in B#DK with D#KShh 12

13 γ measurement inputs GLW/ADS in B#DK,Dπ with D#hh ADS in B#DK,Dπ with D#hhhh GGSZ in B#DK with D#KShh 13

14 Observables physics parameters GLW : D 0 decays to singly Cabbibo-suppressed final states (KK,ππ), higher absolute yields but lower interference due to colour suppression ADS : Combine colour-suppressed B decays with Cabbibo-favoured D decays in order to increase interference and hence sensitivity to γ In both cases measure branching fractions and charge asymmetries Same principle applies to Dπ decays but interference smaller LHCb-PAPER

15 Observables physics parameters rb,δb are the amplitude ratio and relative strong phase of the interfering B decays rd,δd are hadronic parameters describing the D 0 #Kπ(πK) decays rd is the amplitude ratio of the CF to DCS D 0 decays δd is the relative strong phase between the CF and DCS decays Both are taken from CLEO measurements (arxiv: ) LHCb-PAPER

16 Two body GLW signals ) ) GLW, D KK Events / ( 5 MeV/c B [K K - + B [K K LHCb - ] K D LHCb - ] π - D + + B [K K + + B [K K LHCb - ] K D ± m(dh ) (MeV/c 2 ) + LHCb - + ] π D KK and ππ show similar-sized CP asymmetries, in the same direction Branching fraction ratios consistent with CF D 0 decay mode GLW, D ππ Events / ( 5 MeV/c LHCb B [π π - ] K D LHCb - + B [π π - ] π - D B B LHCb + + [π π - ] K D + LHCb [π π - ] π D ± m(dh ) (MeV/c 2 ) LHCb-PAPER

17 ) Two body ADS signals Events / ( 5 MeV/c 2 ) ADS, D Kπ - B [π - K LHCb + - ] K D LHCb B [π K ] K D The Kaon mode shows a large CP asymmetery LHCb LHCb And there is also a hint of something in the pion mode! 20 - B [π - K + ] π - D B [π K ] π D ± m(dh ) (MeV/c 2 ) ADS modes established at >5σ significance Combining all two body modes, direct CPV is observed at 5.8σ significance LHCb-PAPER

18 γ measurement inputs GLW/ADS in B#DK,Dπ with D#hh ADS in B#DK,Dπ with D#hhhh GGSZ in B#DK with D#KShh 18

19 Observables physics parameters Same formalism as for the two-body case, except for the coherence factor RK3π. This is necessary because the D 0 decay is a sum of amplitudes varying across the Dalitz plot; when we perform an analysis integrating over these amplitudes, we lose some sensitivity because of the way in which the decay interfere. RK3π has been measured at CLEO and is small (~0.33) which indicates that these modes have a smaller sensitivity to γ when treated in this integrated manner than the two-body modes. However, they can still provide a good constraint on rb. NEW FOR Moriond EW 2013! LHCb-PAPER

20 Four body ADS signals ADS, D K3π Once again, indications of CP asymmetries in both the Kaon and the Pion modes, going in the same direction as for the two-body modes. ADS modes established at >5σ significance! NEW FOR Moriond EW 2013! LHCb-PAPER LHCb-CONF

21 Gamma combination inputs 21 GLW/ADS in B#DK,Dπ with D#hh ADS in B#DK,Dπ with D#hhhh GGSZ in B#DK with D#KShh

22 Observables physics parameters Toy simulation Here the decay chain is B#D 0 K, with D 0 #KSππ/KSKK The D 0 decays proceed through many interfering amplitudes, some of which are Cabbibo-favoured, some singly Cabbibosuppressed, and some doubly Cabbibo-suppressed You are effectively doing a simultaneous ADS/GLW analysis, as long as you understand how the amplitudes and their phases vary across the Dalitz plot. Toy simulation 22

23 Observables physics parameters KSππ LHCb LHCb Here the decay chain is B#D 0 K, with D 0 #KSππ/KSKK The D 0 decays proceed through many interfering amplitudes, some of which are Cabbibo-favoured, some singly Cabbibosuppressed, and some doubly Cabbibo-suppressed You are effectively doing a simultaneous ADS/GLW analysis, as long as you understand how the amplitudes and their phases vary across the Dalitz plot. Model-independent : Bin the Dalitz plot and fit for yield of B + and B - in each bin of the Dalitz plot, plugging in the strong phase in each bin from a CLEO measurement. ci,si are the CLEO inputs KSKK Ki are the yields of tagged D 0 decays in each bin LHCb-PAPER

24 K S ππ and K S KK signals Entries / 15 MeV/c LHCb ± 0 B (K + ) ± (b) S D 0 All K S Sum, incld. combinatorics Signal Partially reconstructed K s ππ Entries / 15 MeV/c LHCb ± B (K 0 All K S Sum, incld. combinatorics Signal + K K ) π ± D 0 S Partially reconstructed K s KK (b) Entries / 15 MeV/c m[(k + ) ± ] (MeV/c 2 ) D LHCb S ± B (K 0 All K S 0 S + ± ) K D Sum, incld. combinatorics Signal Mis-ID Partially reconstructed K s ππ (a) Entries / 15 MeV/c m[(k K K ) π ± ] (MeV/c 2 ) D LHCb S ± B (K 0 + ± K K ) K D 0 S All K S Sum, incld. combinatorics Signal Mis-ID Partially reconstructed K s KK (a) m[(k + ) ± K ] (MeV/c 2 ) S D m[(k K K ) ± K ] (MeV/c 2 ) S D LHCb-PAPER

25 x ±,y ± y LHCb γ B B x Largest systematic arises from the assumption of no CPV in the control mode Dπ Little stand-alone sensitivity due to unlucky fluctuation of rb LHCb-PAPER

26 Putting it all together

27 The LHCb γ combination Look at ADS/GLW and GGSZ separately GGSZ has a poor standalone sensitivity because of an unlucky value of rb. LHCb-CONF

28 The LHCb γ combination, DK only Now combine all DK measurements, including D#K3π ADS Rather Gaussian behaviour! LHCb-CONF

29 The LHCb γ combination, DK+Dπ Now combine all DK measurements, including D#K3π ADS, and add Dπ observables as well for the first time (details in the backups). A second solution emerges at 1 sigma but 2 sigma intervals stable. LHCb-CONF

30 Summary The superb performance of the LHCb spectrometer is yielding a rich harvest of results in hadronic B decay modes First observations of more and more suppressed decay modes The combined measurement of the CKM angle gamma with 1 fb -1 of data is as precise as the individual full dataset B factory measurements And we have >3 fb on tape... First measurements with the full data are coming very soon; stay tuned! Many thanks to the organizers for the invitation! 30

31 Backups

32 The LHCb γ combination, DK+Dπ LHCb-CONF

33 CKM triangle history

34 Why γ? It is still probably the theoretically cleanest CKM parameter Zupan, 34

35 Why γ? It is still probably the theoretically cleanest CKM parameter Zupan, 35

36 BABAR γ, CKM BABAR : combination in Cartesian coordinates See D. Derkach, CKM

37 BELLE γ, CKM BELLE : projections in γ, rb See K. Trabelsi, CKM

38 CLEO inputs CLEO Paper 38

39 GGSZ asymmetries per bin -B + N B LHCb 0 π + π K S (b) K + K 0 K S Effective bin number LHCb-PAPER

40 GGSZ only extractions (degrees) δ B 300 LHCb γ (degrees) LHCb-PAPER

41 GLW/ADS full results LHCb-PAPER

42 GLW/ADS 4h full results LHCb Preliminary NEW FOR Moriond EW 2013! LHCb-PAPER

43 GGSZ full results LHCb-PAPER

44 Dalitz distributions for signal /c 4 ) 2 (GeV m /c 4 ) (a) B + 3 (b) B - KSππ KSππ (GeV 2 m LHCb LHCb (GeV /c 4 ) m (GeV /c 4 ) m /c 4 ) 2 (GeV m (GeV 2 /c 4 ) (c) B + (d) 1.8 B - KSKK KSKK 1.6 m LHCb (GeV /c 4 ) m + 1 LHCb m 2 (GeV /c 4 LHCb-PAPER ) 44

45 Multivariate selections from the start Question : How is LHCb achieving clean signals in a much dirtier environment than either the B-factories or CDF? Answer 1 : A state of the art detector with ~0.5% momentum resolution and powerful particle identification. Answer 2 : An aggressive use of multivariate selections from the very first stage of the datataking process, the trigger. 45

46 A topological decision tree trigger missed track PV reconstructed B path HLT2 2-Body Topo measured corrected 5 10 mass (GeV) 46

47 A topological decision tree trigger add momentum PV true B path reconstructed B path m corrected = m 2 + p T missing 2 + p T missing, HLT2 2-Body Topo measured corrected 5 10 mass (GeV) 47

48 A topological decision tree trigger cummulative fraction The corrected mass is a good variable, but not good enough to deal with pileup on its own : deploy a boosted decision tree to discriminate between signal and background displaced vertices See LHCb public notes LHCb-PUB LHCb-PUB LHCb-PUB MB Data cc MC10 bb MC10 MB MC BBDT Response DiMuon Trigger Real Data DiMuon Trigger + Topo Left : J/ψK candidates with a dimuon trigger and no detachment required Right : the subset of these candidates which pass the topological trigger Gligorov&Williams 48

49 The LHCb spectrometer 49

50 The LHCb spectrometer σ eff t = 45 fs 50

51 The LHCb spectrometer 51