Measurement of the CKM angle γ at LHCb

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1 Measurement of the CKM angle γ at LHCb A. Bertolin on behalf of the LHCb collaboration Outlook: short introduction a time-integrated γ measurement a time-dependent γ measurement the LHCb γ combination new channel to measure γ summary and future prospects A. Bertolin, INFN (Padova) 1

The CKM angle γ ( ϕ 3 ) the angle γ: is the least well known phase of the CKM matrix it can be determined: from tree-level decay not affected by BSM processes standard candle for BSM-sensitive

2 The CKM angle γ ( ϕ 3 ) the angle γ: is the least well known phase of the CKM matrix it can be determined: from tree-level decay not affected by BSM processes standard candle for BSM-sensitive measurements using indirect measurements: global CKM fit: using direct measurements: BaBar (DK -, D*K - and DK* - ): Belle (DK - and D*K - ): LHCb (more on this talk): not included in the global CKM fit PRD 87 (2013) arxiv: [hep-ex] JHEP 10 (2014) 97 need to fill the gap between the uncertainty of the direct and indirect measurements A. Bertolin, INFN (Padova) 2

3 LHCb at the LHC p beams 3

Time integrated γ measurement with B ± D K ± and D K 0 s h + h - JHEP 10 (2014) 097 method: γ obtained comparing the distribution of the events in the D K 0 s h + h - Dalitz plot for reconstructed B

4 Time integrated γ measurement with B ± D K ± and D K 0 s h + h - JHEP 10 (2014) 097 method: γ obtained comparing the distribution of the events in the D K 0 s h + h - Dalitz plot for reconstructed B + and B - mesons, h = π, K data sample: 3.0 fb -1 ( ) D K 0 s ( π + π ) π + π long long B + B - downstream downstream m ± = m(k 0 s h ± ) total number of evts 2500 A. Bertolin, INFN (Padova) 4

5 Time integrated γ measurement with B ± D K ± and D K 0 s h + h - JHEP 10 (2014) 097 flattish dotted histo in the right plot: expectation with no CPV continuous histo: expectation with best fit values of the CPV parameters i.e. r B δ B and γ histo not identically at 0 because the B + and B measured yields are not identical final outcome: consistent and competitive with other (more mature) experiments A. Bertolin, INFN (Padova) 5

6 Time dependent γ measurement with B s D s K ± JHEP 11 (2014) 060 method: γ obtained from the study of the time-dependent decay rates of the initially produced flavor eigenstates data sample: 1.0 fb -1 (2011) Γ s, Γ s, m s : fixed from other measurements only 5 parameters: fixed from other measurements γ 2 β S week phase difference r Ds K magnitude δ strong phase difference A. Bertolin, INFN (Padova) 6

7 Time dependent γ measurement with B s D s K ± JHEP 11 (2014) 060 D S K K π D S π π π total number of evts 1800 D S K π π red: failing particle id black: passing particle id A. Bertolin, INFN (Padova) 7

Time dependent γ measurement with B s D s K ± JHEP 11 (2014) 060 fit the decay time distribution to extract: C f, A f, A fbar, S f and S fbar extract γ from them: -2 β S under

8 Time dependent γ measurement with B s D s K ± JHEP 11 (2014) 060 fit the decay time distribution to extract: C f, A f, A fbar, S f and S fbar extract γ from them: -2 β S under minimal theoretical assumptions is a small correction consistent with 0 folded time dependent decay rate asymmetry: shows clearly the effect of CPV A. Bertolin, INFN (Padova) 8

9 γ combination LHCb-CONF several decay channels can be used to measure γ some are more sensitive to γ than others (large r helps) mostly due to unfavorable BRs have O(2000) events for the most sensitive ones combine them all to squeeze the uncertainty on γ h + = K + parameters of the combined fit parameters constrained using external inputs: CLEO-c, CLEO, Belle, HFAG, LHCb (for example for 2β S ) 9

10 γ combination LHCb-CONF final outcome: how to improve further: add more luminosity add new channels do both A. Bertolin, INFN (Padova) 10

First observation of B s D * s K ± with D * s D s γ arxiv:1503.

11 First observation of B s D * s K ± with D * s D s γ arxiv: [hep-ex], submitted to JHEP it looks easy to replace the D s with a D s * BUT BR(D s * D s γ) 94 % BR(D s * D s π 0 ) 6 % (experimentally even worse than the former because of the 2 γ) 1 GeV total number of evts 1000 with 3.0 fb -1 and the K K π decay mode 11

12 First observation of B s D * s K ± with D * s D s γ arxiv: [hep-ex] PRL 104 (2010) so far so good next step: add this decay mode to the LHCb γ combination A. Bertolin, INFN (Padova) 12

13 Summary and future prospects competitive γ results have been reached by LHCb: high statistic, manageable backgrounds using decay modes involving also neutrals! in the present γ combination mixture of 1 and 3 fb -1 data sets update all channels to 3 fb -1 add new channels: B s D * s ( D s γ) h ± B D ( h + h - π 0, K π ± π 0 ) h arxiv: [hep-ex] stay tuned for an updated γ combination! have also B 0 s h + h - (h= π, K) data, JHEP 10 (2013) 183, that should be merged in the big picture last but not least, new pp collisions in LHC are coming closer and closer, will boost the γ accuracy LHCb-CONF A. Bertolin, INFN (Padova) 13

14 Backup slides A. Bertolin, INFN (Padova) 14

15 Time integrated γ measurement with B ± D K ± and D K 0 s h + h - A. Bertolin, INFN (Padova) 15

16 A. Bertolin, INFN (Padova) 16

CP Violation Studies at DØ

CP Violation Studies at DØ Bd Bs Bd Bs Rick Van Kooten Indiana University For the DØ Collaboration LHCP 13 Barcelona, Spain 13 18 May 13? CP Violation Three kinds: In mixing: Mass eigenstates in mesonic