New Physics search in penguin B-decays

Transcription

1 New Physics search in penguin B-decays Sanjay Swain, SLAC on behalf of BABAR Collaboration 13 th -18 th Dec 2007 Miami 2007 Outline What is New Physics (NP)? b > (d, s) penguin decays Exclusive Semi-inclusive SM (& BSM) comparison Conclusion

2 How to look for NP? NP Search Indirect Direct Increase the experimental precision Raise the energy scale at on certain process and confront the collider to produce new SM (which h makes accurate prediction particle(s) and study due to renormalizability of the theory) their properties Process that are forbidden, very rare or precisely calculable Most powerful: Flavor Changing Neutral Current (FCNC) and CP violating process because in SM they can not arise at tree level, and even at the loop level they are strongly suppresses by GIM mechanism Talk covers penguin rare B-decays: b >X d,s γ, sl + l exclusive (theoretically difficult) inclusive (experimentally difficult)

3 B-factory techniques channel ϒ(4S) uu dd ss cc Hadronic total σ(nb) 1.05 (bb) BABAR operates here ~ 76% is qq 2 jet-type type ( continuum events ) Spherical Jet-like The continuum is monitored by taking data just below the ϒ(4S) resonance (60 MeV) 1 off ϒ(4S) x on ϒ(4S) (BABAR) Rare decay background is usually dominated by continuum

4 Analysis techniques B f 1.. f n Energy and absolute value of momentum is known: E B = E beam = 5.29 GeV P B = 2 2 E M = 0.34 GeV/c beam Requires that the candidates satisfy n B E B = E P B = i= 1 i n P i i= 1 Instead of E B and P B, we historically use (in CM frame) Energy difference ΔE = E B E beam 2 2 Beam energry substituted mass M ES= Ebeam PB σ M ES ~ MeV ~ Χ 10 better σ inv mass Signals usually peak at zero in ΔE and 5.29GeV in M ES distribution (This will most often be used during the talk)

5 NP search in radiative penguin decay B > (ρ/ω)γ The leading order contribution o is via loop diagram a The non-sm particles in the loop can change the observables, such as branching fraction (SM prediction for B > (ρ/ω) γ 1.5 x 10-6 ) + Isospin asymmetry ( A Γ ( B ρ γ ) I = 1 1% in SM) 0 2 Γ ( B ρ γ ) Compare value of quark-mixing matrix elements V td /V ts wi\th other independent measurements B(B ργ ) * B(B K γ V td α ) Vts 2 compare with Δmm d V Δm V s td ts 2 V td () s b t ds () 0 0 B ds () W W B ds () ds () Vtd () s t b

6 Results from B > (ρ/ω)γ decay Simultaneous fit to: ΔE, M ES, NN output, Data used: 316fb -1, Cos(θ hel ), Dalitz angle (for ωγ) PRL 98, (2007) B > ρ 0 γ B > ρ + γ B > ω γ

7 BF and Isospin asymmetry B + >ρ + γ is the first observation B 0 > ρ 0 γ is the confirmation of Belle result The isospin asymmetry (consistent with SM prediction) Γ( ( B ρ + γ ) AΔ I = 1 = 0.35 ± Γ( B ρ γ ) SM prediction: (1.1±3.9)% Ali, Lunghi & Parkhomenko, PLB 595 (2004) The B-factory measurements are consistent with SM prediction > No NP

8 Comparison with independent measurements Using the world ave B(B > K γ) ) V td / V ts = (exp) ± 0.015(theor) Combined B-factory result: Using ΔM d, and ΔM s from CDF (PRL 97, (2006)): No discrepancy seen > both results consistent with each other

9 Measuring other independent parameters At 1ab 1 data the theory error would be really important > same par as experimental error (rel. error = error w.r.t. central value) The dominant theory error comes from ratio of decay constants t of ρ and dk Experimental error Theory error using Belle+BABAR Input parameter Theory error Isospin asymmetry as function of CKM angle γ (completely Independent measurement) Ball, Jones, Zwicky PRD75, (2007)

10 b >dγ semi inclusive decay Reconstructed B > X d γ in seven exclusive modes: (first step towards inclusive b > dγ measurement) 4 charged B decay modes: π + π 0 γ, π + π π + γ, π + π π + π 0 γ, π + ηγ 3 neutral B decay modes : π + π γ, π + π π 0 γ, π + π π + π γ in the hadronic mass range of 1.0GeV < M(X d ) < 1.8 GeV which covers about 50% of the decay in this mass range -0.1GeV< ΔE< 0.05GeV signal (M ES, ΔE) distribution for 0.6 GeV < M(X d ) < 1.0 GeV used as control sample to validate the analysis > Dominated by resonances: ρ ±, ω 5.275GeV< Μ ES < 5.286GeV #events obtained from fit 73± 25 compared to #events ents expected using the Belle +BABAR combined B(B >ρ/ωγ), is 66±26 Data used: 349fb -1, arxiv:hep-ex/

11 Results from b >dγ semi inclusive decay -0.1GeV< ΔE< 0.05GeV 5.275GeV< Μ ES < 5.286GeV Background subtracted t M ES And ΔE distribution for M(X d ) in the range of 10GeV< 1.0GeV< M(X d )<1.8GeV Branching fraction for these seven decay modes in this mass range: Extraction of V td /V ts > Compare b >dγ and b >sγ in experimentally accessible final states and mass range e.g. extend current mass range to the region 0.6 GeV < M(X d ) < 1.0 GeV because this full range would comprise about 60% of the spectrum

12 Exclusive decay of B -> K (*) l + l - decay B > K ( ) l + l decay via three penguin diagrams: γ, Z and W WW box NP Most interesting parameters to look for NP: Forward-Backward asymmetry (A FB ) K* angular distribution ( F L ), Direct CP asymmetry y (A CP) ) etc e.g. θ lepton- angle w.r.t. B-flight direction in dilepton rest frame is a function of Wilson coefficients l - θ B l + New Physics changes the Wilson Coefficients Change in sign and magnitude of A FB (sensitive to heavy particle: SUSY, non-sm Higgs)

13 Forward-backward asymmetry in B ->K (*) l + l - decay K ( ) ll SM C eff 7 = -C 7 (SM) C 9 C eff 10 = -C 9 C 10 (SM) C eff 7 = -C 7 (SM) C 9 C eff 10 = -C 9 C 10 (SM) ( ) The zero point crossing of A FB is particularly interesting Important t check: A FB (Kl + l ) = 0 for SM and many non-sm scenarios Using result from 208 fb 1 with K + ll, K 0 + S ll, K ll, K ll, weget A FB (B + > K + l + l ) = ± (q 2 > 0.1 GeV 2 /c 4 ) > consistent with SM prediction of zero A FB PRD 73 (2006)

14 A FB (bkg-sub) Belle result K l + l Excluded K * l + l - negative A J/Ψ Ψ 7 A FB of B >K ( ) l + l - decay SM Low q 2 lower limit excludes SM at 95% CL (2.05σ) A FB SM A FB (SM) = C9C10 = -C9C10(SM) q 2 GeV 2 /c 2 At high q 2, wrong-sign C 9 C 10 is excluded at >3σ A FB = A FB (SM) = 0.38 Large lepton forwardbackward asymmetry observed. C 9 C 10 = -C 9 C 10 (SM) is excluded at some level However, errors are still large > Need Super B-factory?

15 PBF measurement of B >K ( ) l + l - decay Kl + l K l + l SM+form factor Non-SM scenario Partial branching fractions vs. dilepton mass consistent with SM + form factors SM K* polarization F L non-sm SM c 7 = c 7 (SM)

16 Direct CP asymmetry (A CP ): A CP and LFV in B >K ( ) l + l - decay A CP (B + > K + l + l ) = 0.07 ± 0.22 ± 0.02 A CP (B > K l + l )= ± 023± The measured values in both channels are consistent with SM prediction of negligible g CP asymmetry y Lepton flavor violation search (doesn t exist in SM framework) > Look for mode where two lepton are different (eμ) B(B > Keμ) < 3.8 x 10 8 B(B > K eμ) < 51 x 10 C.L. No lepton flavor violation observed. All the observables are consistent with SM prediction

17 Inclusive decay B >X s γ Next-to-next-to-leading-order to e t to ead o de (NNLO) calculationcu at BF(B X s γ) ) = ( ) X 10 4 with E γ > 1.6 GeV with uncertainties that vary from 7% to 14% (energy cut off > to avoid the non-perturbative effects at low energy) Photon energy spectrum are sensitive to HQE parameters m b2 (mass of b quark) and μ π2 (momentum of b-quark within B-meson) New approach: Ignore X s system Measure high-energy γ recoiling against a fully reconstructed t hadronic B decay Photon energy spectrum is extracted t from fits to M ES in bins of Eγ e - B signal B tag Xs e + π D * γ

18 Results of semi inclusive decay B >X s γ Data used : 210fb 1,Submitted to PRD arxiv:hep-ex/ For E γ > 1.9 GeV, we observe #X s γ signal events = 119 ± 22 #BB background events = 145 ± 9 X s γ excluded from MC Signal region The measured BF BF(B X s γ) [E γ > 1.9 GeV] = (3.66 ± 0.85 ± 0.59) x 10-4 The extrapolated BF (using method in hep-ph/ ) BF(B X s γ) [E γ > 1.6 GeV] = (3.91 ± 0.91 ± 0.63) x 10-4 The branching fraction measurements are consistent with NNLO

19 New Physics constraint using B(B >X s γ) 650 GeV THDM-II prediction Misiak et al, PRL98, (2007) [ middle lines are central values] Type-II THDM estimation BF(B X s γ) [Eγ > 1.6 GeV] = (3.15 ± 0.23) x 10-4 Experimental measurement SM prediction In the Two Higgs Doublet Model (THDM) the charged Higgs mass (M H+ ) is >295 GeV at 95% C.L or 650GeV (best fit) for HFAG 2006 Need to decrease the experimental error

20 PBF and photon energy moments in B >X s γ Partial Branching fraction inner error-bar: Statistical outer error-bar: Systematic The result is dominated by statistical error which will be reduced with data size. Important parameter to look for NP is to compare the direct CP asymmetry or isospin asymmetry with the SM prediction A CP (E γ >2.2 GeV) = 0.1 ± 0.18 stat ±0.05 syst A I (E γ >2.2 GeV) = ± 0.15 stat ±0.07 syst SM expectation is small > Consistent with SM HQE parameters using the photon energy moments: m b = GeV, μ π2 = GeV

21 Summary There are lots of effort going on in Electroweak and Radiative penguins > an interesting place to look for NP All the measurements ( branching fraction, A FB, F L, Isospin and CP asymmetries) are in good agreement with SM prediction Controlling theory and experimental error would be very important, as we accumulate more and more data Expect about 50% more data before the end of the BABAR program

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23 PBF and photon energy moments in B >X s γ Partial a Branching fraction inner error-bar: Statistical outer error-bar: Systematic The result is dominated by statistical error which will be reduced with data size. A CP (E γ >2.2 GeV) = 0.1 ± 0.18 stat ±0.05 syst (SM ~10-9 ) 1 st E γ Moment lepton tag this analysis 2 nd E γ Moment Sum of exclusive modes

24 Asymmetric energy B-factory 9GeV (e ) 3.1GeV (e + ) Peak luminosity: cm 2 2s 1 1 Instrumented Flux Return 19 layers of RPC/LSTs μ ± and K L ID Electromagnetic Calorimeter 6580 CsI crystals e ± ID, π 0, K L and γ reco Cherenkov Detector (DIRC) 144 fused silica bars K,π separation e - [9 GeV] e + [3.1 GeV] Drift Chamber 40 layers Tracking + de/dx Silicon Vertex Tracker 5 layers of doublesided silicon strips Tracking + de/dx

25 PEP-II and BABAR performance Integrated luminosity > 500 fb -1 σ ΒΒ Cross Section 1.1 nb July 2006 ~ 0.5 billion ΒΒ pairs