Physics from B Decays: Lifetimes, Mixing,
CP-Violating Asymmetriesand Rare Hadronic Decays
Patricia BurchatStanford University
Some of the Highlights …
DPF, May 27, 2002 Patricia Burchat, Stanford 2
Outline
• The B Factory Experiments
• B lifetimes and mixing• Time-dependent CP-
violating asymmetries• CP charge asymmetries• B hadronic decay rates
Motivation for measurements.
How well have we measured these properties?
What have we learned?
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The B Factory ExperimentsBABAR/PEP-II• peak luminosity:
– 4.6 x 1033cm-2s-1 (~5 BB/s)
• max lumi/24h: 303 pb-1
• total recorded lumi to date: ~90 fb-1 recorded (~10% off-peak)
• 4.5-month shutdown starts July 1, 2002
Belle/KEK-B• peak luminosity:
– 7.2 x 1033cm-2s-1 (~8 BB/s)• max lumi/24h: 388 pb-1
• total recorded lumi to date: ~80 fb-1 recorded (~10% off-peak)
• 2-month shutdown starts July 1, 2002
c.f. integrated luminosity for
•Argus (1983-1987): ~100 pb-
1
•CLEO (1981-2000): ~16 fb-1
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The Unitarity Triangles
u
c
t
d s b
apply unitarity constraint to pairs of columns
d•s* = 0
s•b* = 0
d•b* = 0
(K system)
(Bs system)
(Bd system)
These three triangles (and the three triangles corresponding to the rows) all have the same area. A nonzero area is a measure of CP violation and is an invariant of the CKM matrix.
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The Unitarity Triangle
u
c
t
d s b
apply unitarity constraint to these two columns
Vub*Vud Vtb
*Vtd
Orientation of triangle has no physical significance. Only relative angle between sides is significant.
Vcb*Vcd
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The Unitarity Triangle
u
c
t
d s b
apply unitarity constraint to these two columns
(1,0)
(,)
(0,0)
Vub*Vud
Vcb*Vcd
Vtb*Vtd
Vcb*Vcd
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We are sensitive to CP-violating CKM phases through interference between two decays with known (or unknown) CP-conserving relative phases.
Meson mixing provides a source of error-free non-CKM phase shift by 90o ( i ): |B0 (t) cos(m t/2) |B0 – i sin(m t/2) |B0 exp(2i, where the CKM angle is associated with the mixing box diagram.
Interference between two decay diagrams (e.g., tree and penguin amplitudes with different CKM phases) can lead to CP-violating asymmetries but interpretation depends on relative strong phase.
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The Asymmetric-Energy B Factories
z
(4S)
e -
B0 / B0
B0 / B0
e +
z ~ 255 m for PEP-II: 9.0 GeV on 3.1 GeV
~ 200 m for KEKB: 8.0 GeV on 3.5 GeV
e ±, ±, K± tag
+
—
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t distributions with NO experimental effects
dN exp(–|t|/B) ( 1 ± cos(mt) )B Mixing
B0 B0 or B0 B0
B0 B0 or B0 B0
Flavor states sorted by mixing status
dN exp(–|t|/B) ( 1 ± sin2 sin(mt) )CP violation
CP states sorted by B tag flavor
Btag= B0Btag= B0
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Decay Time Difference (reco-tag) (ps)
UnMixedMixed
0
10
20
30
40
50
60
-8 -6 -4 -2 0 2 4 6 8Decay Time Difference (reco-tag) (ps)
UnMixedMixed
0
10
20
30
40
50
60
-8 -6 -4 -2 0 2 4 6 8
perfect flavor tagging and time resolution
realistic mistag and finite time resolution
Unmixed – Mixed
Unmixed + Mixed ~ (1 – 2)
~ mdAsymmetry (1 – 2) cos(md t)
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Increase in precision of B lifetimes and mixing
frequency
PDG2000
PDG2002
B0 Mixing Frequency ( x 1012 ps-1)
0.472 0.017
0.489 0.009
18 measurements
+3 B Factory +1 LEP
CKM/CP III and FP VIII
B0 Lifetime ( x 10-12 ps)
1.548 0.032
1.542 0.016
+3 B Factory +2 LEP
12 measurements
Ratio of B+ to B0 Lifetime
1.060 0.029
1.083 0.017
10 measurements
+2 B Factory +1 LEP
Flavor Session V: U. Nierste (theory)
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Prospects for future lifetime and mixing measurements
•many preliminary lifetime and mixing results.•systematic uncertainties dominated by t resolution function and, for mixing, knowledge of the lifetime.•measure mixing and lifetime simultaneously
•expect <1% uncertainty on Bd mixing in a few years.•measure .•test assumptions of CP/T/CPT symmetries.
Flavor Session VIII, T. Meyer
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sin2
Vtb*Vtd
Vcb*Vcd
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Charmonium modes used for measuring sin2
Both BABAR and Belle use six charmonium modes:
• B J/ Ks0, Ks
0 +-, 00
• B J/ KL0
• B (2S) Ks0
• B c1 Ks0
• B J/ K*0, K*0 Ks0
• B c Ks0
b
d d
c
s
c
B0
, c, c
KS,L
One dominant decay
amplitude theoretically clean!
CKM/CP Session V, S. Olsen
Belle has observed a 6 signal that is most likely the not-well-established c(2S) charmonium state in B0 c(2S) Ks
0 and B+ c(2S) K+
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sin2 data samples in BABAR
J/ Ks (Ks +-)
J/ Ks (Ks 00)
J/ K*0 (K*0 Ks0)
c1 Ks
(2s) Ks
J/ KL
Bflav
Mixing sample
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42 fb-1 (44 M BB) 1772 events (78% purity) 1550 evts with t meas’t
effective tagging efficiency: =(27.0 1.2)%
sin2 = 0.82 0.12 0.05 || = 1.06 0.09 (stat)
Belle
CKM/CP Session I, Wang, Vahnsen
hep-ex/0205020hep-ex/0205020
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56 fb-1 (62 M BB) 1850 tagged events with t (79% purity; 68% tagging
)
effective tagging efficiency:
=(25.1 0.8)%
sin2 = 0.75 0.09 0.04 || = 0.92 0.06 0.02
BABAR
hep-ex/0203007hep-ex/0203007
471 events
524 events
CKM/CP Session I, Rahatlou, Lange
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Constraints on upper vertex of Unitarity Triangle from all measurements EXCEPT
sin2
Regions of >5% CL
A. Hööcker, H. Lacker, S. Laplace, F. Le Diberder, Eur. Phys. Jour. C21 (2001) 225, [hep-ph/0104062]
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World Average sin2 = 0.78 0.08
The Standard Model (and the CKM paradigm, in particular) wins again … at least at the current level of experimental precision, in this decay mode.
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CKM/CP Session I, J. Albert
Measurement of “sin2” in bccd decays: D*D*+ and D*D+
D*D*
Ntag = 76Purity = 80%
• Weak phase for tree decay is same as for bccs but watch out for penguins!
• D*D* is vector-vector decay (L=0,1,2) so mix of CP=+1 and –1.
• Fit for Sf and Cf (no penguin assumptions).
D*D*
S = -0.05 0.45 0.05C = 0.12 0.30 0.05
CP asymmetries in D* D+
have also been studied in BABAR.
b
d d
cd
c
D(*)-b
d d
d
c
c
t
B0
D(*)+B0
D(*)-
D(*)+
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Future sin2 studies:B0 Ks
Pure penguin!
• time-dependent asymmetries in B0 Ks measures sin2.
• direct charge asymmetries in B+ K+ sensitive to new physics.
b
d d
s
s
s
B0
K0
t
b
d d
s
s
s
B0
K0
t
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B K
BABAR K+
111±12 evts
BABAR K0
40±8 evts
~60M BB pairs
Flavor Session VI: A. Telnov
Branching Fractions (10-6) (stat. and syst. errors added in quadrature and symmetrized)
CLEO, Belle, BABAR
K+ 5.5±2.0, 11.2±2.4, 9.2±1.3
K0 <12, 8.9±3.2, 8.7±1.8
K*+ <23, <36, 9.7±4.2
K*0 11.5±4.4, 13.0±6.1, 9.2±1.3
+ < 5, 0.56
B(K) slightly favors pQCD over QCDf.
CP asymmetries also measured: consistent with 0.
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“sin2”
Vub*Vud Vtb
*Vtd
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CP Violation in B0 +-
b
d d
ud
u
+
-b
d d
d
u
u -
+
t
B0
B0
|P/T| and relative phase are unknown but can, in principle, be determined from an isospin analysis that requires measuring BF for B0+-, B0+-, B±±0, B000, and B000
CKM/CP Session II, N. Sinha (theory)
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Expectations/Prejudices…• Measure coefficients for
both sinmt and cosmt terms (S and C).
• S and Care determined by , , |P/T|, and . Assume
22
3021
28.0/
26
)97(
TP
cf. Gronau and Rosner, Phys. Rev. D65, 093012 (2002) CKM/CP Session I, Wang,
Vahnsen
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Sππ= -0.01 ± 0.37 ± 0.07Cππ= -0.02 ± 0.29 ± 0.07
~60M BB pairs
BABAR
qq and K background
CKM/CP Session II: Olsen, Sumisawa
B0 tags
B0 tags Belle
Sππ= -1.21 +0.38 -0.27
+0.16-0.13
Cππ= -Aππ=-0.94 +0.25 -0.31 ± 0.07
B0 tags
bkgdsubtracted
~44M BB pairs
B0 tags
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Interpretation
BABAR
Belle
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Other studies of “sin2”Belle B0 ’ KS
• Penguin mediated.• Sensitive to new physics.• sin2 = 0.29 ± 0.54 ± 0.07
Many other studies of B (’)K (*) are being aggressively pursued.
Challenge to theoretical models to explain relative rates.
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sin2
Vub*Vud
Vcb*Vcd
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Charmless Two-Body Decays
In decays such as B K , interference between the Tree and Penguin amplitudes can lead to CP asymmetries that depend on AND the strong phase difference. Also, ratios of BF for various and K decay modes are sensitive to the angle .
Goal: Measure CP asymmetries AND branching fractions for all charmless two-body final states.
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World average two-body results from CLEO, Belle, BABAR
CKM/CP Sessions I, M. Bona, II: B. Casey
+- 5.2±0.6 C, S
+0 4.9±1.1 (Belle 3.5/BABAR 5.2)
00 < 5.2, 5.6, 3.4
K+- 18.6±1.1
K+0 11.5±1.3
K0- 17.9±1.7
K00 8.9±2.3
K+ K- < 1.9, 0.5, 1.1
K0 K0 < 13, 13, 7.3
Branching Fraction (10-6) CP Asymmetry
+ 0.46 ± 0.15 ± 0.02 - 0.17 ± 0.10 ± 0.02
incompatible at 3.3 level
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Charmless Three-Body B Decays: why are they interesting?
Sensitive to same weak phases as charmless 2-body decays.
Dalitz plot analyses of 3-body decays can (eventually) be used to help disentangle relative strong phases.
Already being done in charm decays.
A long way to go in B physics, but we’re starting…
Charm Session I, D. Asner
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All B+K+h+h-, B0Ksh+h- and BKsKsh modes being studied by Belle
Flavor Session I, N. Gabyshev
>4 signals in six of eleven 3-body modes being studied.
Studying resonance substructure.
Belle B+K++-
237±23 events
K*(892)0 + and f0(980) K+ observed.
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3-body branching fractions
Branching Fractions (10-6)
Belle BABAR
+ +- <15
K++ - 55.6 ± 5.8 ± 7.7 59.2 ± 4.7 ± 4.9
K+ K+ K- 35.3 ± 3.7 ± 4.5 34.7 ± 2.0 ± 1.7
K+ K± ± no signal no signal
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B D(CP)K decays: why are they interesting?
)(21000 DDD
)()()(2000
KDBAKDBAKDBA
1||)(0 ieAKDBA
ii eeAKDBA 2||)( 0 Potential for measuring CKM angle :
Determine through amplitude relationships (up to discrete ambiguities): Gronau & Wiler; Dunietz (1991).
b
u u
cs
u
B-D0
K-b
u u
c
s
u
B-
D0
K-
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B-D
Dfl
DCP
+
DCP-
B-D KCP charge asymmetries in B D(CP)K from Belle and BABAR:
ACP+ = + 0.29 ± 0.26
ACP+ = + 0.16 ± 0.27
Afl = - 0.044 ± 0.059 (stat)
Afl = + 0.003 ± 0.096
ACP- = - 0.22 ± 0.24
E (GeV) Flavor Session V, G. Mancinelli
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Many highlights in hadronic B decays not covered here . . .
B D(*)+ -: potential for measuring sin(2+); See CLEO analysis of strong phase between I = 1/2 and 3/2.
Analysis of partially-reconstructed hadronic decays.
B Ds(*)+ - (Vub suppressed); help in interpretation of B D(*)+
Color-suppressed B decays (e.g., B D(*)0X0)
B D(*)D(*) (BF, ang analysis)
B baryons
Flavor Session V, T. Pedlar
Flavor Session V, T. Orimoto
FP Session I: Fang Fang (Belle); Cheng (theory)
Flavor Session V, M. Krishnamurthy, VI: C.S.Kim; CKM/CP Sesion III: Y. Zheng
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Summary With the rapidly increasing data samples from the B
Factories, many new decay modes are becoming available for
1. time-dependent CP asymmetry measurements (sensitive to and );
2. direct CP asymmetry measurements (sensitive to and );
3. branching fraction and resonant substructure measurements that are crucial for the interpretation of many of the CP asymmetries.
is in agreement with SM predictions; too early to interpret results on .
The summer conferences and the Fall papers will continue to bring many interesting new results to interpret as the B Factory experiments “catch up” on their analyses.