1. CP Violation Brazilian Physical Society Particles and Fields Meeting
Caxambu, 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 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

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

5. 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

6. 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

8. 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

9. 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?

10. 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

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

12. 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 = 

13. 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|

14. 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

15. 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.

16. 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

17. 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

18. 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

19. 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)

20. 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

21. 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

22. 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.

23. 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

24. 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-

25. 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.

26. 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

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

28. 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

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

30. 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

31. 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

32. 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
Bs  m+m-  

33. 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.