1 babar & belle: results and prospects claudio campagnari university of california santa barbara
TRANSCRIPT
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BaBar & Belle: Results and Prospects
Claudio CampagnariUniversity of California
Santa Barbara
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Physics Program at the B-Factories
• Comprehensive investigation of CKM structure of SM– CP-Violation (CPV) a key ingredient
• CPV from just one phase in SM
– Other measurements very important too
• Rare B-meson decay (but also D, )– Sensitive to new particles in loops– Indirect signature of new physics?
• B (and D and ) decay dynamics
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Today:
Concentrate (mostly) on measurements related to
the unitarity triangle
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B-factories and the unitarity triangle
B0 J/ Ks, D*D*,…
B0 , ,..
B,DK,D*,…
B-mixingB(,)
BulB(,,)l
BclBD(*)l
Both angles and sides of U.T. are accessible through measurements at the B-factories
Both angles and sides of U.T. are accessible through measurements at the B-factories
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Outline• BaBar and Belle
– Luminosity, present and future
• Lifetimes and mixing• Sin2 results• Working towards sin2• Comments on • Vub
• Conclusions
Note: averages from Heavy Flavor Averaging Group(unless otherwise specified)
Note: averages from Heavy Flavor Averaging Group(unless otherwise specified)
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B-factories performance
Belle: 132 fb-1
Record lumi: 9.5 1033
BaBar: 117 fb-1
Record lumi: 5.2 1033Note: 100 fb-1
~ 108 106 BB pairs
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B-factories prospects
• Luminosities are improving– PEPII up to ~ 2 to 4 1034 cm-2 sec-1
– KEKB perhaps as high as 1035
• Detectors need modest upgrades to cope
• Should have ~500 fb-1 by 2005-2006, 1000-2000 fb-1 by end of decade– Now have ~ 100 fb-1 per expt
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Mixing and lifetimesResults based on large samples of
– Fully or partially reco. hadronic decays– Fully or partially reco. D* l – Dileptons
8K events
12K events29 fb-1
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t Distributions Lifetimes
t = proper time differencebetween the decay times of the two B-mesons
t = proper time differencebetween the decay times of the two B-mesons
t resolution of ~ same order of magnitude as lifetime
t resolution of ~ same order of magnitude as lifetime
0 = 1.554 0.030 0.019 psec- = 1.695 0.026 0.015 psec
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Adding Tagging Information
md = 0.516 0.016 0.010 ps -130 fb-1
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Lifetimes results summary
• Belle and BaBar now dominate world averages• Improvement by x2 over pre B-factory era• Order 1% uncertainty on lifetimes and ratio
• Belle and BaBar now dominate world averages• Improvement by x2 over pre B-factory era• Order 1% uncertainty on lifetimes and ratio
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} LEP+CDF0.497§0.014 ps-1
} BaBar + Belle0.502§0.006 ps-1
World Average0.502§0.006 ps-1
Dominated by BaBar & Belle
Partial averagesfrom F. RongaCKM Workshop03
Mixing results summary
3% precision!
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Mixing and Lifetimes - Prospects
• Hard, precision measurements• Many are based on only a fraction of
the available dataset– Statistical uncertainties still significantroom for improvement
Theoretical uncertainties limiting factor in ability to extract clean CKM information
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The measurements of mixing and lifetimesprovide the foundations for the
time dependent CPV measurements that follow
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General time-dependent formalism
Interfering amplitudes with different CP-violating (weak) phases can give a non-zero CP asymmetry. For B0 ! fCP:
Then, when one of the interfering amplitudes is B-mixing
with
S C
Only one decay amplitude (or all decay amp. same CKM phase):C=0 and S gives clean CKM phase information
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Sin2 in b ! c c s
• Golden modes:– clean theory– “relatively easy” experiment
• Tree and leading penguin have same phase • sinmt coeff. measures sin2 cleanly• Not just J/ KS:
– Also ’ KS, c1 KS, c KS (CP=-1)
– J/ KL (CP=+1)
– J/ K*0 (Mixed CP)
b
d
d
W cc
s
0B /J
0K
0K0Bb
dW
s
d
c
cg
u,c,t
/J
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1.6K events
~500 signal ev.
Event Samples
Clean ~2K KS sample
+~ 500 KL events
with ~ 60% purity
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t distributions and asymmetries
CP=-1 CP=+1
Events with KS Events with KL
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Summary of sin2 in b ccs
7.5% precision
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Fit for cosmt coefficient, extract ||
5% precisionconsistent with ||=1(as expected in SM)
5% precisionconsistent with ||=1(as expected in SM)
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Sin2 from other modes
• b ! ccd– D(*) D(*) and J/ 0
• penguins with different phases can be important
• b ! s (penguin)– KS, ’ KS etc
• sensitive to new physics in the b!s penguin
Results from these modes are very much statistics limited
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J/ 0
~ 40 evD*D*
~ 130 ev
KS
~ 36 ev ‘ KS
~ 150 ev
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B0 ! J/ 0b
d
d
W cc
d
0B /J
0 0Bb
dW
d
d
c
cg
u,c,t
/J
0
S = - sin2 if no penguin C = 0 if no penguin
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B0 ! D*D*
• Vector-Vector final state: could have CP even and odd components
• Both BaBar and Belle measure mostly CP even
• BaBar fits S and CS = -0.32 § 0.43 § 0.13C = +0.02 § 0.25 § 0.09
b
d d
Wccd )(D
)(D0B
0Bt,c,ub
dd
W
d
)(D
c
cg
)(D
S = sin2 if no penguin
C = 0 if no penguin
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b ! s modes
Bb
d,u
W
ss
sg
Kd,u
bW
s
s
sg
u,c,t
Kd,u d,u
B
B ! KS B ! KS
B ! ‘ KS B ! ‘ KS
• Same CKM structure as J/ KS
• u-penguin down by ~1/50• Expect S=sin2 to 5%
• Same CKM structure as J/ KS
• u-penguin down by ~1/50• Expect S=sin2 to 5%
• Like KS but also u-tree• Still, S~sin2
• Like KS but also u-tree• Still, S~sin2
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bs penguin: S coefficient (sin2)
bs penguin average
0.18 0.20
~ 2.5 from ccs modes
bs penguin average
0.18 0.20
~ 2.5 from ccs modes
Expectation from J/KS
‘
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Sin2 prospects
• Sin2 in b ccs is already a precision measurement– But still statistically limited– Will be improved
• Measurements in other modes will improve as luminosity– Maybe faster, as techniques improve
• Improved results in the b s modes will be particularly interesting!
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Sin2• In the absence of penguins, sin2 from
B0 ! + - asymmetry• BR of B0 ! K+ - and B+ ! + 0 tell us that
interference between P and T is large• In principle isospin analysis of +-, +0,
and 00 allows for clean extraction of • In practice 00 very hard
b
d d
ud
u
+
-
B0
b
d d
d
u
u -
+
t
B0
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B ! hh Branching Ratios (x 10-6)
Averages from J. Olsen, CKM Workshop 2003
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Time dependent fits to +-
78 fb-1
~ 106 events 84 fb-1
~ 160 events
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+ - Fit Results
Belle rules out CP conservation (C=S=0) at 99.93% C.L.BaBar is still consistent with C=S=0The discrepancy is at ~ 2-2.5 level
Belle rules out CP conservation (C=S=0) at 99.93% C.L.BaBar is still consistent with C=S=0The discrepancy is at ~ 2-2.5 level
S C
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Sin2 from • from full, time dependent, tagged,
Dalitz plot analysis of +-0
• Hard analysis• For starters, BaBar
– Quasi two body analysis, only +- and - + – Also +K- and -K+
– BF(B0K)= (7.31.31.3) 10-6
– BF(B0)= (22.61.82.2) 10-6
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~ 430 events
ACP = -0.18 § 0.08 § 0.03 Ã time integrated termC = 0.36 § 0.18 § 0.04S = 0.19 § 0.24 § 0.03
• 2 CPV effect• first step towards full Dalitz analysis
B
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Sin2- Prospects
• Clean extraction without theoretical assumptions will be hard
• If B0 0 0 very small, bounds on sin2 could become quite useful
• We will most likely see CPV (maybe we are already seeing it)– but we will have a hard time
disentangling the weak phases
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What can we say about ?
• B ! vs K– From tree-penguin interference– Needs some theo assumptions
• B ! DK– Theoretically clean– Interference between bu(cd) and bc(ud)
• B D(*) D(*)D(*)a1 – Theoretically clean– Sin(2+)
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B DK
B - b
u
u
u
sc
D 0
B - b
s
D0
u c
Information on through interference in final states common to D0 and D0 (e.g. , KK..)
Several variants on the market• prospects look a little brighter, as color suppression not as large as previously thought
Measurements of various BR done or in progress
First asymmetry measurements
u u
Vub ~ ei
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from B DK, an example
D is CP-odd or CP-even neutral D combination
with strong phase
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DK D
D K+K-, +-
D KS0, Ks, KS , KS , KS ‘
no usefulconstraints yet
no usefulconstraints yet
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- Prospects• Many methods, many theoretically clean• Problems:
– Need a lot of luminosity!– Often methods have ambiguities
• , + 45o, + 90o, etc.
• Will need to combine many channels• It will be a long and arduous journey
• We are taking the first steps– Many more B D(*)K(*) modes have been/are being
measured
• Not sure where we will end up– But it should be fun
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Vub from b u l
Two complementary approaches• Reconstructed exclusive states
– B l B l B l B l – Theoretical uncertainties– Lattice could eventually come to the
rescue• Inclusive b u l
– Theoretically cleaner– Experimenters make cuts into phase
spaceintroduce theoretical uncertainties
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Vub: Exclusive Decays
• Branching ratios: BaBar, Belle, Cleo
• General agreement
• Working to combine into single Vub
• Typical individual measurement
|Vub| ~ 20%
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Exclusive Branching Ratios
Compilation from Gibbons, CKM Workshop 2003Compilation from Gibbons, CKM Workshop 2003
x 10-4
x 10-4
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E(lepton)
M2(X) E(X)
q2(l)
From Muheim, CKM Workshop 2003:Blue lines indicate bc l regionsFrom Muheim, CKM Workshop 2003:Blue lines indicate bc l regions
Inclusive decays: b u l
X=hadronic systin bX l
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b u l : new expt. technique
• Fully reconstruct one B• Then look only at what’s left
– Reduce combinatorics– Know momentum vector of recoil
• Important for kinematic reconstruction
– Reduce continuum
Brecoil
BrecoD* Y(4S) l
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S/B~0.3
MES [GeV]
Leptonpl>1.0 GeV/cS/B ~ 2.5
• B D(*) n• Efficiency only 0.4%• But statistics are OK• M(X) reconstruction• Belle, similar technique with B D(*) l
• B D(*) n• Efficiency only 0.4%• But statistics are OK• M(X) reconstruction• Belle, similar technique with B D(*) l
MX < 1.55 GeV
Signal167 ± 21events
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b u l inclusive: summary
•Individual measurements in agreement• ~ 15-20% uncertainty each• improvement on LEP
•Individual measurements in agreement• ~ 15-20% uncertainty each• improvement on LEP
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Vub Summary
• Much progress is being made• Very active area, both theory and
experiment• Lattice improvements soon• Want to go well below 10%
uncertainty for Unitarity Triangle constraints
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Conclusions• The B-factories have gone
through a very successful first three years
• Today I showed you only a small fraction of their physics program, there is much more
• We are looking forward to increases in luminosity, eventually x10-20 more data
• The SM is still alive and well, but we’ll continue poking at it
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THE END