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CP Violation Brazilian Physical Society Particles and Fields Meeting Caxambu, 10-14 August 1998

CP Violation Brazilian Physical Society Particles and Fields Meeting Caxambu, 10-14 August 1998 Tatsuya Nakada CERN * Geneva, Switzerland * On leave from Paul Scherrer Institute. I) Why CP violation is highly interesting?

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CP Violation Brazilian Physical Society Particles and Fields Meeting Caxambu, 10-14 August 1998

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  1. CP Violation Brazilian Physical Society Particles and Fields Meeting Caxambu, 10-14 August 1998 Tatsuya Nakada CERN* Geneva, Switzerland * On leave from Paul Scherrer Institute

  2. I) Why CP violation is highly interesting? - Currently observed CP violation in the kaon decays can be accommodated within the Standard Model. BUT, it cannot exclude that CP violation is partly or evenentirely due to new physics. - Since CP violation is due to an “interference”, it issensitive to a small effect. - Cosmology (baryon genesis) suggests that an additional sourceof CP violation other than the Standard Model is needed. A promising place to look for new Physics

  3. II) CP violation in the Kaon system Observed CP violation in the kaon system: CP  -1 CP = +1 1) Re h2p CP  -1 CP and T so called CP violation in K0- K0 oscillations

  4. 2) Im h2p K0 K0 2pt=t1 2pt=t1 K0t=0 K0t=0 K0 K0 So called CP violation in the interplay between oscillations and decays

  5. 3) Current experimental results are h+- = h00 arg h+- = tan-1Dm/2DG 43.5 (Dm = mL-mS, DG = GS-GL ) NA31,CPLEAR (CERN) E731, E773 (FNAL) This is compatible with Standard Model but also with Superweak Model

  6. 4) Experimental attempt to exclude the Superweak model 1) To show |h+-|  |h00| so called Re(e/e)  0 or CP violation in decay: due to penguins NA48 (CERN), KTeV(FNAL) 2) To show Br(KL p0nn)  10-11 Being discussed at FNAL and BNL

  7. Standard model predictions are uncertain for h+- and h00 hadronic effects: long range interactions penguins etc. Br(KL p0nn) is experimentally really hard. Another place to look for CP violation?

  8. III) CP Violation and B-meson System If there is nothing else but the standard model, |Vcb|, |Vub| B-meson decays Dmd Bd-Bd oscillations will fix all the Wolfenstein’s parameters, A, r and h (l is well known). _ _ _ b c t b d A2 W W W t d b b u A2(r2 + h2 ) A2[(1 - r)2 + h2] W

  9. i i    i  VCKM =  i   i i  CKM matrix relevant for B Physics (CP violation is all due to ≠ )

  10. CKM Unitarity Triangles VtdVud + VtsVus + VtbVub = 0 VtdVtb + VcdVcb + VudVub = 0  Vub  Vtd Vtd Vub      Vcb Vts arg Vcb = 0, arg Vub = , arg Vtd = , arg Vts = 

  11. From the neutral kaon system h > 0 DmdBfB2F(mt)|VtdVtb|2 b and g are defined by the sides Unitarity triangle h Gbu g b 1 r Vtd e-ib Vub e-ig NB: Br(K±p ± nn) measures also |Vtd|

  12. CP violation in Bd J/y KS v.s. Bd J/y KS measures the phase of Vtd, i.e. b compare two b measurements = consistency test Bd Bd J/yKS Bd _ HB-B(Vtb*Vtd )2e2ib ABJ/yKsVcb* Vcse0i _ _ _ b c t J/y b d c _ W Bd Bd- Bd W W s KS t d b d d c J/y c Penguin effect is negligible g t,c,u b s W Bd KS d d

  13. By 2005, CLEO, BaBar, BELLE, CDF, D0 and HERA-B will have -accurate |Vub|, |Vcb| and -b from CP violation in Bd J/y KS with s ~ 0.025 (Expected range in the Standard Model: 0.3<sin2b<0.8) Possibilities are a) There will be already a sign of new physics: -precision measurements in different decay modes in order to pin down the details of new physics. b) Measurements look “consistent” with the Standard model. -what could happen? Let’s make the following “interesting” scenario.

  14. A model for new physics _ HB-B[{(1 - r)2 + h2}+ r2db]e2i(b + fdb) _ _ _ _ _ t b d b d new FCNC _ Bd- Bd Bd- Bd W W t d b d b _ HB-B[ l-2 + r2sb]e-2i(dg + fsb) _ _ _ _ _ t b s b s new FCNC _ Bs- Bs W W t s b s b

  15. Measured Dm(Bd)(1 - r)2 + h2+ rdb h (1 - r)2 + h2from SM box Measured Gbu b defined by the CKM triangle Vtd e-ib hD h g r 1 gD b defined by the measured triangle. dgD = l2hDdg = l2h

  16. CP violation in Bd J/y KS v.s. Bd J/y KS measures bJ/yK = b + fdb If the model is such that numerically fdb ≈ bD-b “bJ/yK = bD ” CP measurement and triangle measurements agreeeach other.  Look consistent with the Standard Model! _ Bd-Bd e2i(b+ fdb) BdJ/y KS Vcb* Vcse0i

  17. BABAR and BELLE may have difficulty to access g+b CP violation in Bdp+ p- -experimental problem small branching fraction < 810-6 (CLEO) -theoretical problem large penguin contribution CLEO: Br(p+p-) < Br(K+p-)  1.4 10-5 penguin is large W u t,c,u K- K- b s s W u Bd g b u u p+ p+ Bd d d d d GT(Vus*Vub)2l8 GP [P(mt2)Vts*Vtb]2P2(mt2) l4 Top penguin dominates in Bd Kp (P (mt2) <1)

  18. GT (Vud*Vub)2l6 GP [P(mt2)Vtd*Vtb]2P2(mt2) l6 W u t,c,u p- p- b d d W u Bd g b u u p+ p+ Bd d d d d Br(p+p-)<Br(K+p-)  penguin is large; P (mt) > l (= 0.22) Vud*Vube-ig Vtd*Vtb [P(mt2)-P(mc2)] + Vud*Vub [P(mu2)-P(mc2)]  [P(mt2)-P(mc2)]eib +[P(mu2)-P(mc2)] e-ig Problem: tree and penguin have different phases

  19. CP violation in Bdp+ p- is not really possible for CDF and D0: no particle ID, HERA-B: not enough statistics Bdp+ p- can be used only if we know penguin/tree. A way out: measure Br(p+ p0) and Br(p0 p0)  not enough statistics CP violation in Bdr+p-, r-p+, r0p0 -experimental problem decay time dependent Dalitz plot analysis  not enough statistics -theoretical problem assume p+p-p0 to be always rp

  20. CDF, D0 and HERA-B may be able to measure Dm(Bs) If Dm(Bs)/Gb <20. Does this help? Not really. -It helps to reduce hadronic uncertainties: fB2B (~20% error, lattice calculation) fB2B(Bd)/fB2B(Bs) is much better known (~5% error) -It is interesting if Dm(Bs) is really large; new physics. But it is out of their sensitivities.

  21. How can LHC attack the problem? 1) Improve bJ/yK measurement. ATLAS, CMS: s ~ 0.02/year LHCb: s ~ 0.01/year 2) Measure other angles using Bs CP violation in BsJ/yf measures dgJ/yf = dg+ fsb _ BsJ/y f Vcb* Vcse0i e-2i(dg+ fsb) Bs- Bs b c J/y c W s f Penguin effect is negligible s s

  22. If the model is such that numerically fsb ≈ dgD-dg “dgJ/yf = dgD ” It will still look consistent. J/y f is a easy final state to reconstruct if the decay time resolution is good enough! ATLAS, CMS: s ~ 0.03/year LHCb:s ~ 0.01/year CP = +1 (l = 0, 2) *additional complication: J/y f CP = -1 (l = 1) -angular momentum configuration has to be studied-

  23. We need to do much more! CP violation in Bs Ds+K-, Ds-K+ Bs Ds+K-, Ds-K+ s Ds+ c W eig b u K- Bs Ds+K- Bs Ds-K+ s s Bs s K+ e0i u W b c Ds- e-2i(dg +fsb) s s + c.c.

  24. measures gDsK = g-2dg - 2fsb g - 2dgD There is no more freedom left to make gDsK = gD - 2dgD No hadronic uncertainty Measured gDsKdisagrees with what one expects fromthe triangle relation  New Physics What are experimentally needed? - decay time resolution - K/p separation

  25. Bs DsK Major background: Bs Ds(No CP violation) Importance of particle identification and mass resolution

  26. 3) Further CP violation studies with Bd which requirevery high statistics (difficult for BaBar and Belle). Bd D0K*0, D0K*0,D1,2K*0 Bd D0K*0, D0K*0,D1,2K*0 measure g. Bd D*+p-, D*-p+ Bd D*+p-, D*-p+ measure 2b + fdb + g; 2bD + gD i.e. inconsistent No hadronic uncertainties. Experiment requires: K/p separation hadron trigger

  27. Very small visible branching fractions (10~10 ) Importance of particle identification m = 13 MeV/c2 With signal events

  28. More generally new physics can appear in Db = 1 process through penguin Db = 2 process through box through tree newparticles b b, s b b, s l or l newparticles d,s d b d, s l or l newparticles d,s b

  29. CP violation must be studied in Bd decays via Oscillations  bc+W and bu+W Bs decays via Oscillations  bc+W and bu+W Bd,s,u decays via penguins Bd,s decays via box Experimental conditions are Small branching fractions many Bd,s,u’s Rapid Bs oscillations decay time resolution Including multi-body hadronic final states particle ID mass resolution  LHCb experiment

  30. An example of shopping list: LHCbATLAS/CMS Bd J/yKS  Bs J/yf  Bs DSK  (PID) Bd DK* (PID,Trigger) Bd D*p (PID) Bd pp  (PID) Bd Kp (CP in gluonic penguin) (PID) Bd rp ? ( BaBar 160 events, LHCb 670 events) Bs K*g (CP in radiative penguin)? Bs K*l+l- (CP in radiative penguin)  Bs oscillations, xs up to 7538 Bs m+m- 

  31. V) Conclusions 1) New results on CP violation in the neutral kaon systemwill be available soon (~2000) and may indicate that the Superweak model is not valid. 2) B-meson system will provide a rich field for CP violation studies. 3) BaBar, Belle, CDF, D0 and HERA-B will observe CPviolation in BJ/yKS (>2000) if CP violation is largely due to the standard model. 4) In order to look for new physics, a dedicatedexperiment at LHC, i.e. LHCb is needed.

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