Редкие B- распады на установке ATLAS

1. Редкие B-распады на установке ATLAS Н.В.Никитин (к Лекциям по B-физике) http://nuclphys.npi.msu.su/b/index.html 18.04.2005 1

2. LHC – Large Hadron Collider – Большой адронный коллайдер строится в настоящее время в CERNе: pp-столкновения (14 ТэВ). Планируемое начало работы: весна 2007 г. Четыре детектора: ATLAS, CMS – для поиска бозона Хиггса, суперсимметрии и других задач, в том числе исследовании свойств b-адронов; LHCb – оптимизирован под B-физику; ALICE – для исследования свойств КГП. Эксперимент LHC

5. Мы сконцентрируемся на поиске редких В-распадов на установке ATLAS только потому, что группа МГУ активно принимает участие в данной работе. Следует иметь ввиду, что коллаборации CMS и, особенно, LHCb имеют не менее обширную программу по поиску редких распадов

6. Introduction - I Physics: b → d, stransitions (FCNC) are forbidden at the tree levelin SMand occur at the lowest order throughone-loop-diagrams “penguin” and “box”. Main points forstudy: a) The good test of SM and its possible extensions -SUSY, Two Higgs-doublet, LR, Extra Dimensions; b) Information of the long-distance QCD effects; c) Determination of the │Vtd│and│Vts│; d) Some of rare decays as BG to other rare decays (for example: B0d → π0 µ+ µ- as BG to B0s →µ+ µ- γ). 2

7. Introduction - II Branching Ratios Hierarchi in SM: Br(B0d→µ+ µ-) ~“a few” *10-10 Br(B0d→µ+ µ- γ) ~“a few”*10-10 Br(B0s →µ+ µ-) ~“a few”*10-9 Br(B0s →µ+ µ- γ) ~“a few” *10-8 Br(B0d → π0 µ+ µ- ) ~“a few”* 10-8 Br(B0d → ρ0 µ+ µ- ) ~“a few”* 10-7 Br(B0d → K µ+ µ-) = (4.8 ± 1.2) *10-7 (BaBar, Belle, ‘02) Br(B0s → φ µ+ µ-) ~“a few”*10-6 Br(B0d → K* µ+ µ-) = (1.17 ± 0.33) *10-6 (BaBar, Belle, ‘03) Br(B0d → K*γ) = (4.3 ± 0.4) * 10-5(CLEO, ‘93) 3

8. Which new measurements can LHC make comparing with B-factories? a) The rare decays ofB0s – meson (B0s→φγ, B0s→φ µ+ µ- , B0s →µ+ µ- γ and B0s →µ+ µ-) and Λb - baryon; b) Differencial distributions for rare semileptonic B-meson decays (dimuon-mass spectra, forward-backward asymmetries) – very sensitive to the SM extensions; c) Branching fractions of rare muonic and rareradiative muonic B-meson decays – good sensitivity to the SM extensions. 4

9. The basic theoretical description -I Effective Hamiltonian for b → d,s transition: Heff (b → q)~ GFV*tqVtb∑ Ci(µ) Oi (µ), includes the lowest EW-contributions and perturbative QCD corrections for Wilson coefficients Ci(µ) . µ - scale parameter ~ 5 GeV : separates SD (perturba- tive) and LD (nonperturbative) contributions of the strong interactions. SM NLO:A.Buras, M.Munz, PRD52, p.182, 1995 SM NNLO: C.Bobeth et al., JHEP 0404, 071, 2004 MSSM NNLO: C.Bobeth et al., hep-ph/0409293. 5

10. The basic theoretical description -II Oi (µ) – set of the basic operators (specific for each model: SM, MSSM, LR and others); LD (nonperturbative) contribution of the strong inte- ractions are contained in the hadronic matrix elements: and are described in the terms of relativistic invariant function - transition formfactors. Need the nonperturbative methods (SR, QM, Lat). 6

11. The accuracy of calculations Stability of the Wilson coefficients to the choice of mt and μ [mb/2, 2mb]: SM NLO: approximately 15%; SM NNLO: approximately 6% - 7%; MSSM NNLO: ≈30% depends from the parameters set. Accuracy of the nonperturbative calculations: depends on a method, but it’s not less, than 15%. For SM calculations – NLO, for MSSM – NNLO. 7

12. Simulations of rare B-decays for ATLAS detector 8

13. B0d,s →µ+µ- decays in ATLAS Points for study in ATLAS: Branching ratio - sensitive to the SUSY. Simulations: Full Inner detector simulation and reconstruction at low and nominal LHC luminosity 1) for TDR layout signal + background (ATLAS TDR 15, Vol.II, 1999) 2) for Initial layoutonly signal (ATL-COM-PHYS-2003-003 ). 3)signal + background in DC2. Results: Using SM teoretical predictions: Br(B0d,→µ+µ-) ≈ 1.5*10-10 and Br(B0d,→µ+µ-) ≈3.5*10-9 we obtaned the following sensitivities for ATLAS After3 year LHC work at L=1033 cm-2s-1 (30 fb-1) will be expected B0d :4 signal ev., B0s :27 signalev., 93 BG ev. common to both After1 year LHC work at L=1034 cm-2s-1 (100 fb-1) will be expected B0d :14 signalev., B0s :92 signal ev., 660 BG ev. common to both We expect the 3*1010 sensitivities at CL 95% for rare leptonic decays. 9

14. B0d→K*(892)µ+µ- decay at ATLAS Points for study in ATLAS: Branching ratio - sensitive to the SUSY; Differencial distributions (dimuon-mass spectra, AFB) – very good sensitivity to the SUSY. Simulations: Full ATLAS Inner detector simulation and reconstruction at low luminosity (ATLAS TDR 15, Vol.II, 1999) using theoretical matrix element from paper D.Melikhov, N.Nikitin, S.Simula, PRD57, 6814, 1998. Results of simulation: After3 year LHC work at L=1033 cm-2s-1 (30 fb-1) will be expected ~2000 signal events at 290 BG events 10

15. Bd®K*g Bs®fg Radiative penguins inATLAS Points for study in ATLAS: Branching for Bs®f g, polarization measurements and CP-violation effects. Preliminary results Non-optimized offline cuts, resolution (>100MeV/c2) could be improved. Using DC1 simulation tools: estimations including trigger and off-line selection cuts for 1year LHC work at L=2*1033cm–2s-1 (20fb-1) : Bs®f g: 3200 signal ev., S/√BG > 7; Bd®K*0 g:8500 signal ev., S/√BG > 5. B→K*0p0BG rejection under investigation combiningπ0/ γrejection cuts, kinematics and angle between B0 and K+ at K*rest frame cuts. 11

16. Baryonic rare decay of Λb→ Λ µ+ µ- Points for study in ATLAS: Branching ratio - sensitive to the SUSY; FB asymmetry - very sensitive to the SUSY. Generation procedure: EvtGen used to generate events using amplitudes from works (C-H.Chen, C.Q.Geng, PRD64, 074001, 2001 ) and (T.M.Aliev et.al. , NPB649, p. 168-188 , 2003). Results of DC1-simulation: At Br(Λb→ Λ (p π-) µ+ µ-)~2·10-6 after1 year LHC work at L=2*1033 cm-2s-1 (20 fb-1) will be expected~1800eventsof the decay Λb→ Λ (p π-) µ+ µ-. 12

17. Number of events Number of events B0s →µ+ µ- γ B0d →µ+ µ- γ B0s →µ+ µ- B0d →µ+ µ- B0d → π0 µ+ µ- B0d → π0 µ+ µ- Mµµ Mµµ B0d → π0 µ+ µ- as BG to B0d,s →µ+µ-γand B0d,s →µ+µ- decays |η(μ)| < 2.5, pT(μ) > 6 GeV, π0 → γ γ, pT(π0)< 4GeV The decayB0d →π0 µ+ µ-are essential background for the decay B0d,s →µ+ µ- (γ)at the particle level simulation. 16

18. SUSY in rare B-decays at ATLAS detector

19. SUSY: main motivations for study in rare B-decays I) Many kinds of heavy (m > 1 TeV) SUSY particles. II) Only lightestof these particles can be detected on LHC. III) Other SUSY-particles give the tiny contributions as virtual particles in SM processes.To find the information on such particles it is necessary to choose the decays : a) where SM contributions are suppressed as much as possible; b) QCD nonperturbative corrections well known; c) branchings can be measured in ATLAS. Rare B0d,s and Λbdecays are IDEAL CHOICE for that! 18

20. tan β = 50 tan β = 60 Br(B0q→ µ+ µ-) x 108 Br(B0q→ µ+ µ-) x 108 SM SM 95% CL for ATLAS sensitivity MSSM for B0d,s→µ+µ- decays and ATLAS sensitivity C.Bobeth et al., PRD66, 074021, (2002) The B0d,s→µ+µ-barnchings as functions of charge Higgs boson mass MH for two choice the tan β. 19

21. MSSM in B →K*(892) µ+µ- decay and ATLAS precision Sensitivity of AFB to the choice of the Wilson coefficients in one MSSM scenario: P.Cho, M.Misiak, D.Wyller, PRD54, p.3329, 1996. Three intervals for variable q2 /M2B. If in the first interval the negative average asymmetry will be measured, it will be convincing demonstration of a SM exten- sions reality. 20