Measurements of the CKM angle γ at LHCb

Transcription

1 Measurements of the CM angle γ at onal Hill on behalf of the collaboration 6 July 217 EPS Conference on High Energy Physics Venice Italy

2 What is γ? Least well measured CM angle [ No top quark coupling in its definition, γ = arg V udv ub V cd V cb New physics expected to enter in loops Measure γ at tree and loop level and compare them! Theoretically clean irect: γ = ( ) Indirect: γ = ( ) ] η excluded area has CL >.95 γ CM f i t t e r ICHEP 16 η excluded area has CL >.95 sin 2β m d m d & m s ε CM f i t t e r ICHEP 16 sol. w/ cos 2β < (excl. at CL >.95).3.3 α α.2.2 V ub.1 SL,excl β γ ρ.1 β γ ρ CMfitter group - 1

3 ) ) B ± ± AS/GLW Well established tree-level modes for γ measurement GLW: Interference between B and B, with CP eigenstate decay e.g., ππ ( = / ) AS: Additional γ sensitivity with non-cp eigenstate decay e.g. π GLW: B ± [π ± π ] h ± AS: B ± [π ± ] h ± 15 Events / ( 1 MeV/c B [π + π ] + B [π + π ] + Events / ( 1 MeV/c B [π ] B [π + ] B [π + π ] π B [π + π ] π B [π ] π 2 + B [π + ] π ± m(h ) 55 [MeV/c 2 ] ± m(h ) 55 [MeV/c 2 ] 3. fb 1 Run 1 results [Phys. Lett. B 76 (216) ] 2

4 GLW update including 215 & 216 data [-PAPER ] uring 215 and 216 (Run 2), an additional 2 fb 1 was taken at s = 13 TeV ataset roughly doubled GLW modes (, ππ) measured again in Run 1 + Run 2 data B ± h ± 2-body GLW update () A π =.19 ±.5 (stat.) ±.2 (syst.) A π =.8 ±.3 (stat.) ±.2 (syst.) A A ππ π A ππ = ±.14 (stat.) ±.1 (syst.) =.8 ±.6 (stat.) ±.2 (syst.) = ±.25 (stat.) ±.8 (syst.) R =.988 ±.15 (stat.) ±.13 (syst.) R ππ =.992 ±.27 (stat.) ±.32 (syst.) Tension between A Run 2 compatible at 2.6σ and Aππ in Run 1 analysis has eased - A in Run 1 and 3

5 γ γ What else can we do? Alternative approach to B ± ± - add a star! B ± ( ± s π ± ) with hh AS/GLW Analysis close to finalisation: 4 fb 1 shown at CM Candidates / (1. MeV/c 2 ) B L dt = 4. fb 1 * ( + ) m(*) [MeV/c 2 ] L dt = 4. fb 1 B + ( + ) * m(*) [MeV/c 2 ] [ ] 18 [ ] σ 2σ 3σ σ σ r B δ B [ ] [-CONF ] 4

6 B ± ± with π / γ Theoretically similar to B ± h ±, with an interesting extra feature π and γ variants of the decay have an exact strong phase difference of π [Phys. Rev. 7, 9153(R)] Measure both B ± ( π ) ± and B ± ( γ) ± decays to determine r B, δ B, γ Experimental challenge: π /γ reconstruction is difficult and has limited efficiency at [Int. J. Mod. Phys. A 3, (215)] 5

7 Partially reconstructed B ± h ± [-PAPER ] Solution: completely ignore the π and γ from the! No penalty from π /γ reconstruction efficiency Select signal candidates identically to B ± h ± Fit variable is m( h) uniquely related to angular properties of decay daughters ifferent mass and spin of π and γ lets you tell their m( h) distributions apart - central idea of the analysis ) 2 Events / (4 MeV/c 1 simulation 8 6 ) 2 Events / (4 MeV/c simulation ± 2 m(h ) [MeV/c ] ± 2 m(h ) [MeV/c ] Figure 1: Analytical PF fits to B ± ( π ) ± (left) and B ± ( γ) ± (right) simulated decays. Analytical PF fits to B ± ( π ) ± (left) and B ± ( γ) ± (right) simulated decays 6

8 Sources of background [-PAPER ] B ( π )h + B ± h ± π B s π B h ± X X = π, π ±, γ 7

9 ) B ± ( ) h ± with π [-PAPER ] NEW Events / ( 1 MeV/c B [ π + ] B [ π ] B [ π + ] π B [ π ] π ± m(h ) [MeV/c 56 2 ] B ±! (! )h ± B! (! )h ± B ±! (! )h ± B ±! h ± B! h ± Bs! ± b! ch ± Part. reco. mis-i B ±! ± B ±! ± Charmless Combinatorial 8

10 ) B ± ( ) h ± with [-PAPER ] NEW Events / ( 1 MeV/c B [ ] B [ ] B [ ] π 5 + B [ + ] π ± m(h ) [MeV/c 56 2 ] B ±! (! )h ± B! (! )h ± B ±! (! )h ± B ±! h ± B! h ± Bs! ± b! ch ± Part. reco. mis-i B ±! ± B ±! ± Charmless Combinatorial 9

11 ) B ± ( ) h ± with ππ [-PAPER ] NEW Events / ( 1 MeV/c B [π + π ] + + B [π + π ] B [π + π ] π B [π + π ] π ± m(h ) [MeV/c 56 2 ] B ±! (! )h ± B! (! )h ± B ±! (! )h ± B ±! h ± B! h ± Bs! ± b! ch ± Part. reco. mis-i B ±! ± B ±! ± Charmless Combinatorial 1

12 Results [-PAPER ] NEW B ± h ± modes measured for the first time at with a brand new technique! Currently GLW modes are included - AS under investigation Fully reconstructed B ± h ± results (Slide 3) are measured with the same fit B ± ± results () A π,γ A π,π A CP,γ A CP,π = +.1 ±.22 (stat.) ±.7 (syst.) = +.6 ±.12 (stat.) ±.4 (syst.) = ±.93 (stat.) ±.4 (syst.) =.151 ±.33 (stat.) ±.13 (syst.) R CP,γ =.99 ±.87 (stat.) ±.99 (syst.) R CP,π = ±.29 (stat.) ±.82 (syst.) 11

13 Measuring r B, δ B, γ [-PAPER ] NEW 6 partially reconstructed GLW CP observables used to constrain the fundamentals etermine profile likelihood contours for r B, δ B and γ Measurements included in new γ combination (along with B ± ± GLW) r B and δ B align with GGSZ averages [arxiv: ] γ within 1σ of current combination [JHEP 12 (216) 87] Hope to further improve precision with addition of AS modes * r B [ ] * δ B

14 Latest γ combination [-CONF-217-4] NEW Includes the following updates since last combination: B ± ± AS/GLW [-CONF ] NEW B ± ± GLW [-PAPER ] NEW Bs s ± T [-CONF ] 1 fb 1 3 fb 1 B ± ± GLW [-PAPER ] γ = ( ) () 3 fb 1 5 fb 1 1 CL 1.8 Preliminary % 95.5%

15 Summary continues to drive forward γ precision through studying tree-level B ± decays In addition to B ± ±, great progress has been made on B ± ± and B ± ± These brand new modes at contribute important information in the latest γ combination Addition of more Run 2 data (217 & 218) promises further excitement ahead - stay tuned! 14

16 Backup

17 GGSZ Run 1 γ combination B [JHEP γ s decays [ ] 12 (216) 87] B decays + B decays Combination GLW/AS Single most precise γ measurement from a single experiment Figure 6: 1 CL plots, γ = ( using 7.3 ) the profile likelihood method, for combinations split by the initial B meson flavour (left) and split by analysis method (right). Left: (orange) Bs initial state, (yellow) B Includes initial states, (blue) Run 1 B ± B + initial states ± and (green) the full combination. Right: (yellow) GGSZ methods, (orange) GLW/AS methods, AS/GLW (blue) other methods and GGSZ and (green) the full combination. Now being updated with B ± ± AS/GLW, B ± ( ) ± GLW and Bs s ± Others Combination [ ] δ B 15 r B B, h3π/hh' π + B + B + All B +, S hh +, /π/ modes ππ Full Combination 15

18 Time-dependent B s s ± [-CONF ] γ = ( ) δ s = ( ) r s = CL 1.8 Preliminary r s.8.6 Preliminary [ ] δ s 45 4 Preliminary % % contours hold 68%, 95% CL contours hold 68%, 95% CL Input: φ s =.1 ±.39 rad [Phys. Rev. Lett. 114, 4181 (215)] 3.6σ evidence of CP violation in B s s ± 2.2σ compatibility with time-integrated γ combination 16

19 GGSZ modes Candidates / [18 MeV] has a suite of completed 3 fb 1 GGSZ analyses: B ± ± 1 with s π + π, s + [JHEP 1 (214) 97].8 M B with s π + π [JHEP 8 (216) 137] MI B.4 with s π + π, s % [JHEP 6 (216) 131] B ± ± Figure 8. Confidence level curve on δ update is active B, obtained using the plugin method [58]. Only the δ B solution corresponding to < γ < 18 Run 1 + Run 2 data is highlighted; the other maximum is due to the 1 B * * B s Combinatorial B ** ** B s B ρ m(*) (MeV) JHEP8(216)137 Figure 2. Invariant mass distribution for B long and downstream candidates. Figure 9. Two-dimensional The fit confidence level curves in the (γ,r B ) plane, obtained Figureusing 1. the Two-dimensional profilelikelihood The points method. are confidence level curves in the (γ,δ B ) plane, obtained using the result, including signal and background components, is superimposed (solid blue). profile-likelihood method. data, and the different fit components are given in the legend. The two vertical lines represent the signal region in which the CP fit is performed. giving the values functions, with the fraction of the longitudinal polarisation in the B s decays unknown and accounted for with a free parameter in the fit. Each of the two functions describing the different helicity states is a weighted sum of non-parametric functions obtained from simulated B s ( γ) and B s ( π ) decays, taking into account the known π and γ branching fractions [48] and the appropriate efficiencies. The PF for B decays is obtained from that for Bs decays, 1 CL % (δ B,γ) (δ B + π, γ + π) ambiguity. r B contours hold 68%, 95% CL δ [ ] B [ ] B δ JHEP8(216)137 contours hold 68%, 95% CL M B with s π + π [JHEP 8 (216) 137] γ = ( 8 +21, 22) r B =.39 ±.13, δ B = ( ) 17 Here, r B and δ B are defined for a π mass region of ±5 MeV around the (892) mass and for an absolute value of the cosine of the decay angle greater than.4.

20 Summer 217 averages - B ± CP ± BaBar PR 82 (21) 724 Belle PR 73 (26) 5116 CF PR 81 (21) 3115(R) -PAPER ππ -PAPER Average CP A CP+ Summer 217 Summer 217 PRELIMINARY.25 ±.6 ±.2.6 ±.14 ±.5.39 ±.17 ±.4.13 ±.1 ±..12 ±.3 ±.1.13 ± BaBar PR 82 (21) 724 Belle PR 73 (26) 5116 CF PR 81 (21) 3115(R) -PAPER ππ -PAPER Average CP R CP+ Summer 217 Summer 217 PRELIMINARY 1.18 ±.9 ± ±.16 ± ±.24 ± ±.1 ±.1.99 ±.3 ±.3 1. ±

21 Summer 217 averages - B ± CP ± BaBar PR 78, 922 (28) * CP A CP+ Summer 217 PRELIMINARY -.11 ±.9 ±.1 BaBar PR 78, 922 (28) * CP A CP- Summer 217 PRELIMINARY.6 ±.1 ±.2 Belle PR 73 (26) PAPER Summer ±.22 ± ±.3 ±.1 Belle PR 73 (26) PAPER Summer ±.3 ±.8.27 ±.9 ±.4 Average -.14 ±.3 Average.15 ±.7 correlated average correlated average BaBar PR 78, 922 (28) * CP R CP+ Summer 217 PRELIMINARY 1.31 ±.13 ±.3 BaBar PR 78, 922 (28) * CP R CP- Summer 217 PRELIMINARY 1.9 ±.12 ±.4 Belle PR 73 (26) PAPER Summer ±.25 ± ±.3 ±.8 Belle PR 73 (26) PAPER Summer ±.31 ± ±.9 ±.1 Average 1.21 ±.7 Average 1.4 ±.9 correlated average correlated average