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? - 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 even entirely due to new physics. - Since CP violation is due to an “interference”, it is sensitive to a small effect. - Cosmology (baryon genesis) suggests that an additional source of CP violation other than the Standard Model is needed. A promising place to look for new Physics

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

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

3) Current experimental results are h+- = h00 arg h+- = tan-1 Dm/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

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

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?

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 A2 b d W W W t b u d b A2 (r2 + h2 ) A2 [(1 - r)2 + h2] W

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

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

Vtd  e-ib Vub  e-ig DmdBfB2F(mt)|VtdVtb|2 b and g are 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|

Penguin effect is negligible 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 _ HB-B  (Vtb* Vtd )2  e2ib ABJ/yKs  Vcb* Vcs  e0i _ _ _ t b c J/y b d _ W c Bd Bd- Bd W W s KS t d b d d c J/y c t,c,u g Penguin effect is negligible b s Bd W KS d d

a) There will be already a sign of new physics: 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.

HB-B  [{(1 - r)2 + h2}+ r2db] e2i(b + fdb) 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

Vtd  e-ib Measured Gbu the CKM triangle hD h b defined by the Measured Dm(Bd)  (1 - r)2 + h2 + rdb h (1 - r)2 + h2 from 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 = l2hD dg = l2h

CP measurement and triangle measurements agree each other. 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 agree each other.  Look consistent with the Standard Model! _ Bd-Bd  e2i(b + fdb) BdJ/y KS  Vcb* Vcs  e0i

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- b s K- W s Bd u g b u u Bd p+ p+ d d d d GT  (Vus*Vub)2  l8 GP  [P(mt2)Vts*Vtb]2  P2(mt2)  l4 Top penguin dominates in Bd  K p (P (mt2) <1)

Problem: tree and penguin have different phases GT  (Vud*Vub)2  l6 GP  [P(mt2)Vtd*Vtb]2  P2(mt2)  l6 u W p- t,c,u p- b d W d Bd u g b u u Bd p+ p+ 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

Bd  p+ p- can be used only if we know penguin/tree. 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

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.

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 Bs- Bs  e-2i(dg + fsb) b c J/y W c s f Penguin effect is negligible s s

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-

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

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

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

3) Further CP violation studies with Bd which require 3) Further CP violation studies with Bd which require very high statistics (difficult for BaBar and Belle). 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

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

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

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

An example of shopping list: LHCb ATLAS/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 75 38 Bs  m+m-  

V) Conclusions 1) New results on CP violation in the neutral kaon system will 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 CP violation in BJ/yKS (>2000) if CP violation is largely due to the standard model. 4) In order to look for new physics, a dedicated experiment at LHC, i.e. LHCb is needed.