Probing Beyond the Standard Model with Flavor Physics

Transcription

1 Probing Beyond the Standard Model with Flavor Physics Matthias Neubert Laboratory for Elementary-Particle Physics Cornell University & Institute for Physics Johannes Gutenberg University October 23-31, 2006 PASI Puerto Vallarta, Mexico 1

2 Outline Lecture 1: Flavor questions Flavor aspects of physics beyond the SM CKM matrix Meson mixing and CP violation Precison measurements in the quark sector Lecture 2: Amplitude interference without mixing Overconstraining the unitarity triangle New Physics analyses in B-B mixing Hints of New Physics! 2

3 Amplitude Interference Without Mixing A tale of trees and penguins 3

4 Flavor topologies Trees: Penguins: Elektroweak b W gz d d u u! - B 0! + b W t,c,u d u u! - B 0! + d 4

5 The penguin trap 5

6 Amplitude interference Rates for rare, charmless B decays are characterized by significant interference of tree and penguin topologies: Amplitudes: Α = iδ iγ Te e + Pe + P 1 iδ 2 iδ 3 EW e Rates: Γ( B f ) + Γ( B f ) ~ cosγ cos( δ i δ j) Asymmetries: Γ( B f ) Γ( B f ) ~ sinγ sin( δ i δ j) 6

7 Reality is far more complicated Until late 90s, nonleptonic weak decays were believed to be theoretically intractable First rigorous theoretical basis: QCD factorization approach Soft-collinear effective theory b W B 0! + Systematic separation of long- and short-distance contributions to these processes d u d u! - Beneke, Buchalla, MN, Sachrajda ( ) Bauer, Pirjol, Stewart (2000, 2001) 7

8 QCD factorization for exclusive decays (BBNS) Beneke, Buchalla, MN, Sachrajda [hep-ph/ , , ] 8

9 QCD factorization for exclusive decays (BBNS) Allows calculation of decay rates and CP asymmetries for energetic two-body decays B_M 1 M 2 Model-independent predictions in heavyquark limit (m b ) Λ QCD /m b corrections can be estimated Good global agreement with experiment 9

10 Determination of _ in B_!_ decay Rare decays B ππ, B ρπ are dominated by tree topologies, but also receive penguin contributions In limit where penguin amplitudes are neglected, decay amplitudes have phase ϕ A = -γ, and hence the time-dependent CP asymmetries measure sin2(β+γ)=sin2α Use QCD factorization approach to estimate the penguin pollution 10

11 Determination of _ in B_!_ decay B_PV modes receive smaller penguin contributions than B_PP modes Allows extraction of _ with small theoretical uncertainties from timedependent rates in B_!_ Result: B_!_ B_!! Old data New data Beneke, MN [hep-ph/ ] _ = (62±8) o Old data New data 11

12 Other decays sensitive to γ Many other (and in principle cleaner ) ways to extract γ exist, which are based on amplitude relations in pure tree processes (such as B DK) or Dalitz-plot analyses (e.g. B ρπ, ρρ) Results agree with our value but have larger uncertainties Many ways to improve this at LHC-b! 12

13 Overconstraining the Unitarity Triangle Many different ways of measuring the CKM matrix 13

14 Tree vs. loop processes 14

15 CP-conserving vs. CP-violating processes 15

16 Sides vs. angles 16

17 Tree plus B mixing vs. K mixing 17

18 Tree plus B d vs. B s mixing 18

19 Summary The CKM model of flavor and CP violation works marvelously! Definitely the main source of these effects We now know that New Physics can only give corrections to the CKM picture Yet, there is some parameter space left to be explored! 19

20 New Physics Analyses in B-B Mixing Model-independent analyses 20

21 General strategy Since mixing is a second-order weak process, it is perhaps plausible that mixing amplitudes are most susceptible to New Physics Many extensions of the Standard Model can give sizable effects Q: Given the quality of the CKM fit, how much space for new Physics is left in B-B mixing? A: Perform model-independent analysis 21

22 New Physics in B d mixing? General parameterization: Δm d = Δm d SM * r d 2 e i 2θ d SM in good shape New Physics contributions of order 50% still allowed 22

23 New Physics in B s mixing? Many analyses after CDF/D0 measurement General parameterization (different!): Δm s = Δm s SM (1+ h s e i 2σ ) s Ligeti, Papucci, Perez hep-ph/

24 New Physics in B s mixing? Many analyses after CDF/D0 measurement General parameterization (different!): Δm s = Δm SM s (1+ h s e i 2σ ) s After 1 year of LHC-b: 24

25 Hints of New Physics! Facts or fiction? 25

26 Searching for the unknown So far, all measurements in the flavor sector are in agreement with the SM However, there are tantalizing hints of New Physics effects in some rare, penguin-dominated decays Not in contradiction with anything we know from other processes (e.g., B_X s _) Experimental situation stabilizes, and theory is under good control 26

27 New Physics in ΔS=1 Penguin Loop Processes? 27

28 CP asymmetry in B K S, η K S Interference of mixing and decay: B 0 B 0 _K S Phase structure identical B 0 to the decay B J/_ K S Model-independent result: S(_K S ) - S(J/_ K S ) = 0.02±0.01 Penguin graph real to very good approximation b W t,c,u g,z d s s s [Beneke, MN] 28 _ K S Grossman, Worah [hep-ph/ ]

29 It s been a rollercoaster! 29

30 Experimental situation: (prior to LP 03) S(_K S ) = -0.18±0.51±0.07 BaBar S(_K S ) = -0.73±0.64±0.22 Belle -0.38±0.41 S(_K S ) - S(J/_ K S ) = -1.11±0.41 (2.8_) 30

31 Experimental situation: (after LP 03) S(_K S ) =+0.45±0.43±0.07 BaBar S(_K S ) = -0.96±0.50±0.10 Belle -0.15±0.33 S(_K S ) - S(J/_ K S ) = -0.88±0.33 (2.7_) Belle data Standard Model [press release] 31

32 Experimental situation: (after ICHEP 04) S(_K S ) =+0.50±0.25±0.06 BaBar S(_K S ) =+0.06±0.33±0.09 Belle 0.27±0.25 S(_K S ) - S(J/_ K S ) = -0.46±0.25 (1.8_) But, trends for deviations are also seen in other b s penguin modes, e.g. a 3_ effect for B _ K S from BaBar! 32

33 New Physics? s-penguin average at 2.7σ different from sin2β[cc] (BABAR) Similar difference at 2.4 σ seen by Belle [A. Hoecker, ICHEP 2004] B φk 0 0 B K K K B η K 0 0 B f K B π K

34 A year later (March 2005) 34

35 7 reasons for excitement! Theory Beneke, MN [hep-ph/ ] Avg.: 0.42±

36 Measurements now consistent Deviation is 3.8_! 36

37 A few months later (July 2005) 37

38 Several small changes Scale shrinked by factor 3.5 Average for standard candle lowered by 1_ to 0.69±0.03 Average of penguin modes raised by 1_: Avg.: 0.50±0.06 Avg.: 0.50±0.06 Discrepancy reduced to 2.8_ 38

39 Present situation Average for standard candle lowered further to 0.68±0.03 Average of penguin modes raised to: Avg.: 0.52±0.05 Avg.: 0.52±

40 Present situation Deviation is reduced to 2.75_ However... Combined average sin2_=0.638± is lower than value preferred by V ub measurements! 40

41 New Physics in B d Mixing? 41

42 Present situation: All sin2β measurements 42

43 Present situation: Only penguin measurements of sin2β 43

44 New Physics in B d mixing? Discrepancy has been sharpened by: Increased precision in V ub determination (error reduction from 15% to 7% in 2 years) Measurement of B s mixing Easiest explanation of effect would invoke extra contribution to B d mixing, since V ub is extracted from tree-level processes 44

45 Precision determination of V ub from inclusive B_X u lν decay Analysis is based on rigorous factorization theorems (valid to all orders in 1/m b ) of the form: Hard corrections (~m b ) Jet functions (~ m b Λ) Shape functions (~Λ) Presence of light energetic final-state particles requires a generalization of the OPE: expansion in non-local string operators (SCET) 45

46 Precision determination of V ub from inclusive B_X u lν decay Model independent relations exist connecting the B_X s _ photon energy spectrum with differential distributions in B_X u l_ decay Most recent analyses include up to NNLO radiative corrections and power corrections up to order (_ QCD /m b ) 2 Theoretical errors 5% for several cuts Bosch, Lange, MN, Paz (2004, 2005) 46

47 What about New Physics in B X s γ? Used to be that B X s γ imposed tight constraints on new contributions in ΔS=1 FCNC processes, since there was excellent agreement between theoretical and experimental values of the rate E.g., bounds on charged Higgs mass in type-ii 2- Higgs-doublet model was: m H + > 500 GeV (95% CL) Similarly constraints (though not as strong in many SUSY models) Gambino, Misiak (2001) 47

48 What about New Physics in B X s γ? Good news: Situation has changed! Recent theoretical calculations at NNLO predict branching ratio to be 1.4σ lower than world-average experimental value: Reduction from large NNLO corrections and low-scale effects Misiak + 14 co-authors; Becher, MN (2006) 48

49 What about New Physics in B X s γ? While this does not point to presence of New Physics effects in this decay, it opens up the parameter space significantly! E.g., interpreting the difference between theory and experiment in the context of the type-ii 2-Higgs-doublet model now gives the preferred value: m H GeV Becher, MN (2006) 49

50 The End Thank you! 50