lhcb - Nikhef

Status and future of
measuring the CP angle  at Babar
Jeroen van Hunen
(Babar plots: Max Baak , NIKHEF)
Some decay modes to access 
•
0
B (B )  D
0
(*)
π

 sin(2+)
hep:ex/309017 (fully reconstructed) and 307036 (partially rec.)
• B  DCP K 

Theoretically clean, but the 2 triangles of the 6 decay amplitudes
are squashed since
0
B  D K 
is suppressed with respect to
B  D 0 K 
• B  ππ, πK, K K  
Theoretical uncertainties: FSI, SU(3)-breaking corrections, etc.
• and others……………
Jeroen van Hunen
CERN B-Journal Club
October 3, 2003
2
0
The B (B )  D(*) h decay mode
0
V*
d
ud
c
b
B
0
Vcb
h
d
Vcd

u
u
b
*
B
D
0
c
V*ub
d
d
 
D* 
0
B0 and B both decay into D(*)-h 
h

h = , , a1
 Interference between the mixing and the decay
Large BR, but:
Vub* Vcd
r
 0.02
*
VcbVud
 Interference is tiny
No penguin pollution, theoretically clean
Jeroen van Hunen
CERN B-Journal Club
October 3, 2003
3
The angle 
q Af
f 
p Af
D
(* ) 

 q  AD(* ) 
  
 p  AD(* ) 
  Vtb*Vtd  i VubVcd*
i (   ( 2   ))


e

r
e
  VtbVtd*  Vcb*Vud

 
1
2
  2  (arg   arg  )
mixing term
D
(*) 

 p  AD(*) 
  
 q  AD(*) 
Jeroen van Hunen
  VtbVtd*  i VcbVud* 1 i ( ( 2   ))
   *  e
 e
*
VubVcd r
  VtbVtd 
CERN B-Journal Club
October 3, 2003
4
0
The B (B )  D(*) h decay rates
0
4 decay rates, for example:
B0  D    f (t ) 
S
2( )
1 
2
C
 t 
e 1  S sin md t   C cosmd t 
4
t  trec  ttag
2
1 r
1 r2
Vub* Vcd
r
 0.02
*
VcbVud
Fit the 4 decay rates with the data to obtain  and thus sin(2+) , but the value
of r is unknown (not enough statistics to fit it together with ).
Jeroen van Hunen
CERN B-Journal Club
October 3, 2003
5
The value for r
Temporary solution:
With SU(3) symmetry relation determine r from the branching
fractions for B0  Ds π  and B0  D- π. This gives:
r  0.019  0.004 and r *  0.017 00..005
007
Add additional theoretical uncertainty of 30% on validity of SU(3) symmetry
In future (statistical errors on measurements reduced) improvement is needed:
• theoretical models ~ 20% spread
• other options? (no solution yet)
Jeroen van Hunen
CERN B-Journal Club
October 3, 2003
6
0
The results for B (B )  D(*) π  full reconstruction
0
Jeroen van Hunen
CERN B-Journal Club
October 3, 2003
7
The t distribution
Jeroen van Hunen
CERN B-Journal Club
October 3, 2003
8
The Measurements
The results of the Babar fit :
(*)
 2r sin( 2   ) cos 
(*)
 2 cos(2   )r sin 
a
c
(*)
(*)
(*)
(*)
If become smaller
value of r is problem
Jeroen van Hunen
CERN B-Journal Club
October 3, 2003
9
Interpretation : what is sin(2+)
~
xi  xi 

  (r (*) )
  
i  i

2
*
with : ~
xi  a, a* , clep , clep
xi  eq. for  ,  , 
68% CL : |sin(2+)|>0.69 (43<2+<137)
Probabilistic interpretation:
simulate (many) experiments
with characteristics as data for
many sin(2+) values, and
count number of experiments
where 2(sin(2+)- 2min is
smaller then the data
83% CL : |sin(2+)|>0 (at 98% CL for partial reco)
sin(2+) 1  sine not very dependent on 2+ (Bd : sin(2)  0.7 , but for Bs the phase s
very small (with BsDsK we measure s + )
Jeroen van Hunen
CERN B-Journal Club
October 3, 2003
10
The Measurements
Full and partial reconstruction combined (roughly same precision)
If sin(2+)  0.94  continue setting lower limits
If sin(2+) < 0.75 (but excluded at 60% CL)  not good for SM
Jeroen van Hunen
CERN B-Journal Club
October 3, 2003
11
The future
No error on r included
: 82fb-1
Current
Summer 2007 : 500fb-1
Summer 2009 : 1000fb-1
Thus:
Summer 2007 : err*0.4
Summer 2009 : err*0.3
68% CL |sin(2+)|>0.92
(67 <2+<113)
Jeroen van Hunen
CERN B-Journal Club
October 3, 2003
12
Some conclusions
0
• B0 (B )  D(*) π  now :
• Full reco = at 68% CL |sin(2+)|>0.69
(43<2+<137)
• Partial reco = at 90% CL |sin(2+)|>0.75
• B (B )  D(*) π  in 2009 :
0
0
• full reco = at 68% CL |sin(2+)|>0.92 ? (67 <2+<113)
(but no error on r included!)
• partial reco similar/better
• Other modes will improve the results (how much?)
Jeroen van Hunen
CERN B-Journal Club
October 3, 2003
13

Download Report