Transcript BaBar - Physics

The BaBarians are coming
Neil Geddes
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•
•
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Standard Model CP violation
BaBar
Sin2b
The future
The Aims
CP violation in B mesons:
Standard Model CP Asymmetry:
c
b
d


c
d
s
J/YK0s
B0

 ηsin2β  sin ΔmB 0 Δt
B0
B0
 CP
J/YK0s
B0
uct
w
d
w
uct
b



 = CP of final state
= -1 for J/YK0s, +1 for J/YK0L
b = arg[-VcdVcb * /VtdVtb*]
b
d
 
 
N B 0  J/Ψ KS0  N B 0  J/Ψ KS0
A
N B 0  J/Ψ KS0  N B 0  J/Ψ KS0
Complex phase in CKM matrix
produces different phases for
B0anti-B0 and anti-B0B0
Unitarity Triangle
Quark mixing described by complex
Cabibbo-Kobayashi-Maskawa matrix
 d   Vud
  
 s    Vcd
 b   V
   td
Vus Vub  d 
 
Vcs Vcb  s 
Vts Vtb  b 
B  pl , rl ,... (r,
V*i1V1j+V*i2V2j+V*i3V3j = 0/1
a
B  pp , r p,...
Bd  Bd
V*tbVtd
V*ubVud
VCKM unitary
 V†V = 1
Bdpp,r±p ,...
g
b
(0,0
B
D±K
V*cbVcd
(1,0
BdJ/y Ks,D*±D,..
B  Dl , D*l ,...
B  Dp ,...
(rescale sides by 1/|V*cbVcd| and choose V*cbVcd real )
Constraining The Triangle
sin2b = (0.5, 0.8)
Asymmetric B-factories
e+e-  (4s)
 B0B0 (50%)
B+B- (50%)
B0
9GeV
e-
+ 3.1GeV
measure
e+
A(t ) 
  boosted in lab

N B

 N B
Y(4s)
N B 0  f CP  N B 0  f CP 
0
 f CP
Small branching ratio for fCP
0
 f CP 
e+
e-
J/y
K0
_
B0
p+
pe, m K tag
Dz~Dt
PEP-II design luminosity 3x1033 cm-2sec-1
+ Continuous high precision running
PEP-II and BaBar
Canada
China
France
Germany
Italy
Norway
Russia
UK
USA
~600 Collaborators
9 Countries
~ 70 Institutions
The BaBar Detector
(5) 1.5 T Solenoid
(4) Electromagnetic
Calorimeter
(3)
CerenkovDetector
(6) Instrumented
Iron Yoke
(1) Silicon Vertex Detector
(2) Drift Chamber
Chronology
1995 - Approval
1998 - Construction completed
1999 - Started taking data - events !!
2000 - Taking data
first measurements
2001 - Taking data
first results
2,000,000 events per day, 20,000 Bs per day
20,000,000 events per day 100,000 Bs per day
2002 - “Results”
120,000,000 Bs
2002-2005 - Detailed results
1,000,000 Bs per day
The Method




N B 0  J/Ψ KS0  NB0  J/Ψ KS0 
A(t) 
N B 0  J/Ψ KS0  NB0  J/Ψ KS0 
1)
2)
3)
4)
Reconstruct CP eigenstates, J/YK0
“tag” other B flavour
Measure Dz  Dt
Fit A(t) for sin(2b)
Complicated by:
•Mistags
•Finite time (vertex) resolution
Also need
•B mass difference DM(B0)
•B0 lifetime

f
|Dt|
B
( Dt )  e  1  sin 2 b sin D mB Dt 

4 B
B0  fCP (f+ )
B0  fCP (f- )
K0, p0 and J/Y Reconstruction
K0sp+p-
K0sp0p0-
B Reconstruction
Completely reconstruct many (anti-)B0’s
B0  J/yK*0(K+p),D(*)-p,D(*)- r,D(*)- a1 & c.c.
Total sample ~6000
Flavour
Sample
From this sample determine.
A) Tagging efficiency
B) Mistag fraction
B Mixing
Semi-leptonic decays
Mistags
di-lepton events
Dilution D = 1-2w
A = (Nu-Nm)/(Nu+Nm)
Ameasured = Datrue
DMB
CP B Reconstruction
B0 
y(2s)K0s
B0  J/yK0s
All K0s modes
EMC
For KL:
We do not know KL
momentum.
We know direction
•Impose MB constraint
•Imply momentum
•Measure DE
IFR
all
B0  J/yK0L
Tagging
Non CP vertex “tagged” as B or anti-B by:
•Presence of charged lepton
• Electron Pcm >1.0 GeV/c; Muon Pcm >1.1 GeV/c
•Presence of charged Kaons
 Kaon Charge  0
•Overall event properties (l,K,slow-p...)
Neural Network
e,m

b
c
s
Time Resolution
Dominated by vertex resolution for Tagging B
Common parameterisation for CP and flavour samples
• Sum of three Gaussians: Core (88%), Tail (11%), and Outliers (1%)
• Parameters determined from likelihood fit and other consistency checks
B flavor eigenstates
B charmonium
Dz = 180 mm for tagging vertex, Dz = 70 mm for fully reconstructed vertex
Mistags and s(t)
Dm(B0) = (0.519 ± 0.020 ± 0.016)  ps-1
Flavour Sample
Determines
Mistag and Dt
Resolution
parameters
preliminary
Parameter
S core
S tail
f tail
f outlier
 core,lepton ( ps )
 core,Kaon ( ps )
 core,NT1 ( ps )
 core,NT2 ( ps )
 Tail ( ps )
Value
1.1  0.1
3.8  0.9
(11  5) %
(0.8  0.5) %
0.08  0.10
-0.21  0.05
0.010.10
-0.18  0.09
-0.46  0.38
Tag Type
Lepton
Kaon
NT 1
NT 2
Total
eff’cy (%)
10.9  0.4
35.6  0.7
7.7  0.4
13.7  0.5
68.9  1.0
W (%)
11.6  2.0
17.1  1.3
21.2  2.9
31.7  2.6
Q(%)
6.4  0.7
15.8  1.3
2.6  0.5
1.8  0.5
26.7  1.6
Quality factor Q = e (1-2w)2 . s(sin2b) a 1 / QNrec
if no background
Fit for sin2b
sin2b is measured with a 35 parameter simultaneous fit to data flavour and CP samples:
unmixed :
pdf1 
mixed :
pdf 2 
N flav
4
N flav
4
e
e
  Dt
1  Di cos DmDt   Ri Dt 
  Dt
1  Di cos DmDt   Ri Dt 
DmB and B are
fixed at the PDG
world average
values:
DmB = 0.472 ps-1
B = 1.548 ps
B 0 tag :
B 0 tag :
N CP    Dt
1  Di sin 2 b  sin DmDt   Ri Dt 
e
4
N    Dt
1  Di sin 2 b  sin DmDt   Ri Dt 
pdf 4  CP e
4
pdf 3 
Fit Parameters
•Sin2b
•4 signal dilutions (D=1-2w)
•4 values of DD for the 4 signal categories
•9 parameters for the signal Dt resolution function
•8 background dilutions
•3 parameters describing the background resolution function
•1 parameter for the fraction of CP background
•5 parameters for the fractions and lifetime of the Bflav background
Measured Asymmetries
f-
f+
f+
f-
sin 22b
b ==0.25 ± 0.22 (stat)
sin 2
b ==0.87 ± 0.51 (stat)
2b
CP +1
• sin2b = 0.34  0.20  0.05
CP -1
Cross Checks
Systematic Errors
Systematic
Dt resolution function
((J/Y & Y(2s))Ks bgrd
J/Y KL bgrd compostion
J/Y KL bgrd fraction
B lifetime
DM
Other
Total
(J/Y&Y(2s))Ks
0.04
0.02
0.01
0.01
0.01
0.05
J/Y KL
0.04
0.09
0.10
0.01
< 0.01
0.01
0.14
Full Sample
0.04
0.02
0.01
0.01
< 0.01
0.01
0.01
0.05
BaBar, Belle and the Rest
Feb 2001
Belle
(~10 fb-1)
BaBar
sin(2b) = 0.58 ±0.33±0.1
(~22fb-1)
sin(2b) = 0.34 ±0.20±0.05
Allowed region (blue) is determined using
theoretical inputs and fitting many
experimental measurements
What if sin(2b) is < 0.5 ?
Standard model bound ~ 0.59  sin2b  0.82
SM constraints are wrong because:
SM valid but:
•|Vub| smaller than theoretically favoured range
•SU(3) breaking in Bd0 /Bs0 mixing larger than favoured range
•BK larger than theoretically favoured range
SM incomplete; new flavour violating and/or CP violating physics:
•New contributions to Bd0 mixing and Bs0 mixing
•New CP violating contribution to B0 mixing
•New CP violating contribution to K0 mixing (and Kpp)
Eyal, Nir and Perez
hep-ph/008009
Covering the Angles
 r , 
a
B0dpp
-6
B.R. ~ few 10
Theoretically uncertain
B0dDK
 0, 0
g
BABAR can
measure the
phase angles
Eff B.R ~10- 7; tough!!
B0dJ/yK0S
b
 1, 0
Very clean,
Eff B.R. ~ 10
-4
Prospects
(fb-1)
18
CESR/CLEO (from CESR
Web page)
12
PEPII/BABAR
30 fb-1
6
‘80
‘90
‘00
‘80
‘90
‘00
‘05
Conclusions
•PEP-II and BaBar collected/analysed ~25 fb-1 in 2000
•More than double our data by the end of the run in August
•By 2005, we should accumulate ~ 500 fb-1
• Measure sin 2a, compare sin 2b in individual modes
•Measurements of direct CP violation and rare decays.
•sin 2b = 0.34  0.20  0.05
The BaBarians have already arrived !