Measurement of 2 / using B Decays at Belle and BaBar Alexander Somov CKM 06, Nagoya 2006...
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Transcript of Measurement of 2 / using B Decays at Belle and BaBar Alexander Somov CKM 06, Nagoya 2006...
Measurement of 2/ using B Decays at Belle and BaBar
Alexander Somov
CKM 06, Nagoya 2006
Introduction (CP violation in B0 + decays) Measurements in B0 + B 0 B0 0 0
2 constraint from an Isospin analysis
CP Violation in BCP Violation in B00 + + decaysdecays
d
W +
b u
d
u
d
B0
+ (+)
- (-)B0
b
d
d
du
u+ (+)
- (-)
W +
u,c,t
)2sin(
0
2
S
A
Tree Penguin
)2sin(1
)sin(~2
effAS
A
)sin()cos()()()()(
00
00
tmStmABNBNBNBN
direct CP violation
determine 2 using isospin analysis
Tree only Tree + Penguin
Direct CPV Mixing induced CPV
B0 + relatively clean signal, large penguin contribution
B0 not a CP eigenstate, time-dependent Dalitz analysis
B0 +
Advantages of + : small penguin contribution due to relatively small [Babar, hep-ex/0607097] relatively large measured branching fraction for b b u u process
637.036.0
000 10)27.016.1()( BBr
Three main decays used for the extraction of 2 ( )
4.4~)ππBr(B)ρρBr(B
0
0
22// measurement
+ is a VV state 3 helicity states (three helicity amplitudes should be considered) +
H0
H+
H odd) CP 1(
even) CP 1(
even) CP 1
| |
2
2
(00
HHA
HHA
HA
longitudinal polarization
Fortunately, longitudinal polarization dominates
Complications:
015.0013.0024.0977.0
Lf
022.0027.0967.0
Lf
030.0941.0 034.0040.0
Lf
BaBar: hep-ex/0607098
PDG
Belle: PRL96, 171801 2006
CP analysis in B + decays
Complications (cont’d):
‘Dirty’ final state + + 0 0 ; () = 150 MeV large backgrounds
I = 1 contribution due to finite width of [A.F.Falk, Z.Ligeti, Y. Nir, H.Quinn PRD69, 011502, 2004]
Contribution from EW penguin
CP analysis in B + decays (cont’d)
Constraint on 2 /
Extract 2 using an Isospin analysis (similar to + analysis) - ‘model independent’ approach
The penguin contribution can also be bound using flavor SU(3) relations [M.Beneke, M.Gronau, J.Rohrer, M.Spranger hep-ph/0604005] [M.Gronau, O.F.Hernandez,D.London,J.L.Rosner, Phys.Rev.D50,4529 ,1994]
)2sin(1 2effAS 22
eff
200~A
2
~ A
0~ A
00A2
A
0A
Measure A and S:
Use isospin relations [M.Gronau and D.London, Phys.Rev.Letter. 65, 1990]
,2
000
AAATwo amplitude triangles:
000
2AAA
Calculate confidence level applying R-fit method (see next talks) [J.Charles et. Al. Eur.Phys.J.C41:1-131, 2005 ]
Isospin analysis in B ()
)(~)(
)(~)(
)(~)(
00
00
00000
00000
0
0
BAA
BAA
BAA
BAA
BAA
BAA
6 unknowns, and 5 observables: Br’s, A, S ( + 2, not yet measured CP asymmetries in 00)
Common features of B measurements
small branching fractions: 10-6 – 10-5
Large background S/B ~ O(1%)
All types of background contribute: continuum, b c and b u continuum is a dominant background. Use Fisher or neural nets (BaBar) to discriminate Multiple B candidates in the same event. Best candidates selection based on best 0 mass and best 2 of the vertex fit. Events with misreconstructed pions, SCF. Use separate PDFs.
Several variables used to separate signal from backgrounds: mbc, E , m, cos , event topology, flavor, t
Analysis strategy
BaBar Determine signal yield, polarization, CP parameters simultaneously using a multidimensional fit. Loose cuts on kinematical variables more signal events in the fit. Use PDFs for ‘all’ variables to discriminate against background - PDF shapes, correlations among variables (sometimes fits exhibit small bias)
Belle Relatively stringent cuts on kinematical variables. Separate fits for event yields, polarization, and CP parameters. - larger statistical errors
Mbc - E - LR fit results
567N
LR fit projection
high quality taghigh quality
tag
Fit results:
Nevt in the fit = 176843
535 Million BB pairs
NEW Belle results (preliminary)
%20f % 35
f
High quality tag
Low quality tag
)()(19.0
)(07.0)(21.016.007.006.0
29.030.0 syststatS
syststatA
535 Million BB pairs
Preliminary t)}msin( S t)mcos( q(A
4τeP ρρρρ
/τ|Δt|long
B
1q
1
Signal true PDF
fit for two parameters A, S
CP fit results
57615N
high-purity events347 Million BB pairs
Updated this summer hep-ex/0607092
6104.1)2.2(23.5Br
0.0150.013L .024 0 0.977f
mES E
cos
m(0)
Simultaneous fit for the yield, polarization, and CP parameters C and S
Previous BaBar:
Previous Belle:(PRL 96,171801, 2006)
3.26.28.38.22
Br
021.0029.0014.0978.0
Lf
030.0941.0 034.0040.0
Lf
(PRL 95,041805, 2005)
540.30 Br(PRL 95,041805, 2005)
B0 + fit results
hep-ex/0607092
)(21.0)(19.0
)(06.0)(15.007.005.007.0 syststatS
syststatC
Signal true PDF
t)}mcos( C
t)msin( S q( 4τ
eP
ρρ
ρρ
/τ|Δt|long
B
1q
1
B0 tags
B0 tags
background
CP Asymmetries
NEW measurements last summer, hep-ex/0607092 232 Million BB pairs
Extract signal yield, polarization and charge asymmetry using an extended unbinned (7-dimensional) ML fit to mES, E, m()+0, cos+0, xN
493900 N
Ntotal = 74293
Simultaneous fit for the yield, polarization, and charge asymmetry
Measurements in B 0 decays
Determine signal yield from a fit to E distribution Obtain polarization from a simultaneous fit to background subtracted cos + cos 0 distributions Determine charge asymmetry from separate fits to E distributions of B+ +0 and B 0 candidates
Background subtracted m(+) and m(0)
Belle results (old), PRL 91, 221801 (2003)
Background subtracted cos + cos 0
2.137.580 N
Measurements in B 0 decays (cont’d)
85 Million BB pairs
0.030.220.000.100.130.12A0.0210.1060.9480.0420.905 f
7.131.7 2.32.216.8)(10Br
CP
0.0230.027L
3.86.7
-6
0.130.080.912
3.018.20.0440.045
67.54.5 10)8.55.22(
Br
HFAG
Previous BaBar measurement: 04.097.0 03.007.0
Lf
03.023.019.0 CPA
Phys. Rev. Lett. 91, 171802 (2003)
B 0 results85 Million BB pairs232 Million BB pairs
Use an unbinned extended ML fit to extract signal yield and polarization 8 dimensional fit: mES, E, m()1,2, cos 1,2, event topology, flavor tags total number of events in the fit 65180, N(00) =
Main components in the fit signal, = 24.2% continuum background (use neural network and tagging information) float parameter values b c background b u background - similar topology: B0 a1 (dominant peaking background), 0f 0, f0f0
- other modes: 0K*0, +0, , +, remaining float normalization
348 Million BB pairs hep-ex/0607097
Evidence for B 00
323198
Evidence for B 00 (cont’d)
637.036.0
000 10))(27.016.1()( systBBr
)(2298 323100 systN
)(05.086.0 11.013.0 systfL
mES E
hep-ex/0607097
background00
Results statistically consistent with previous BaBar measurements, PRL 94, 131801 (2005) Br < 1.1 10-6 at 90% CL
Sourses of dominant systematic errors: PDF shapes, interference with B0 a1 , fit bias
B 00 - last minute results!
6000 10))(19.0)(33.007.1()( syststatBBr )(04.0)(1387.0 syststatfL
mESE
hep-ex/0612021 (12/11/2006)submitted to PRL
background
00
m cos
384 Million BB pairs
)(173210000 systN
Constraint on Constraint on 22//
N.A.)ρA(ρ0.86
100.46)(1.16 )ρ(ρf)ρB(ρ
0.0230.96810)(23.1
)ρ(ρf)ρB(ρ
0.912 103.0)(18.2
)ρ(ρf)ρB(ρ
00
0.120.14
6
00L
00
63.23.3
L
0.0440.045
6
0L
0
Caveats ignore interference with , +00, a1
ignore possible I = 1 contribution neglect EW penguin (all believed to be small)
Branching fractions and polarization fractions used in the calculations(HFAG, Aug. 2006)
(26 ± 6) 10-6
(25 ± 4) 10-6
>1.1 10-6
The isospin triangle is ‘closed’ with new measurements of Br(+), Br(+0), Br(00),
OLD
is not measured. We have6 unknowns and 5 measurements. leads to plateau on 1-CL plot the plateau width depends on Br(00)
Constraint on Constraint on 2 2 // (cont’d)(cont’d)
113/71 2
at 68% CL
1-C
L
B (WA)
B (BABAR)
B (Belle) & B00 (BABAR)
(92 21)
Squashed Isospin triangles at Belledue to large Br(B 0) = 31.7 no ‘plateau’, 2-fold ambiguity
Generally, Isospin analysis allows toextract 2 / with 8-fold ambiguity
)(S A 0000 ρρρρ
If Br(0 0) 0, Isospin triangles squashes
00
Several new results during this year:Several new results during this year: Measurement of CP asymmetries in B + at Belle
Measurement of branching fractions, polarization fractions, and CP asymmetries in B + and B +0 decays at BaBar
First evidence for B 00 decays at BaBar
From an Isospin analysis From an Isospin analysis 22// is constrained asis constrained as
SummarySummary
at 68% CL
New measurements are awaited to improve our knowledge on New measurements are awaited to improve our knowledge on 22//
(Belle first results on Br(B 00) will appear soon)
113/71 2
Backup slides
B0 00
B0 +
B 0
Summary of systematic errors
BB pairs 106 Value BB pairs 106 Value
Br 347 4.1 274 +2.3-2.6
fL 347 +0.015-0.013 274 0.03
A(C) 347 0.06 535 0.07
S 347 +0.05-0.07 535 +0.07- 0.06
BB pairs 106 Value BB pairs 106 Value
Br 232 0.23 85 +3.8-6.7
fL 232 +0.023-0.027 85 0.021
ACP 232 0.10 85 0.03
BB pairs 106 Value
Br 348 0.27
Mixing induced CP violation (sin 2Mixing induced CP violation (sin 222//))
B0 B0
Mixing
b
d
d
b
t
t
*tdVtbV
WW
d
W +
b u
d
u
d
B0
+ (+)
- (-)
Tree
*ubV
udV
*cbcdVV
*ubudVV
1()3()
2() *tbtdVV
*
*
2 argubud
tbtd
VVVV ACP = S sin(mt)
S = sin 22B0
B0
fCP
A
A
pq