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August 2006 M. Morii, Harvard 2
Upcoming Presentations BABAR overview Masahiro Morii
Status of BABAR/PEP-II Harvard group in BABAR
Measurement of CP violation Jinwei Wu Angle from B → decays Angle from B → KS decays
Measurement of |Vub| Masahiro Morii Exclusive B(B → ℓ) with semileptonic tags
August 2006 M. Morii, Harvard 3
Harvard BABAR Group
Current and past membership Faculty: Masahiro Morii (PI) (also in ATLAS)
George Brandenburg ATLAS Postdocs: Jinwei Wu ATLAS
Eunil Won Korea UniversityStephen Bailey LBNL
Students: Kris ChaisanguanthumCorry Lee
Undergrad: Ben Smith Harvard (ATLAS)Kevin Chan BerkeleyKevin Weil Stanford
August 2006 M. Morii, Harvard 4
BABAR Experiment Operates at PEP-II storage ring at SLAC
Collides e and e at ECM = 10.58 GeV (4S)
Luminosity L = 12.11033 cm-2s-1
quadrupled the design
Vast statistics opens a new era ofprecision flavor physics
4( ) 1nbSe e BBσ + −→ → ≈
Ldt∫ =400 fb−1
4×108 BB events
August 2006 M. Morii, Harvard 5
History of CP Violation (1) 1964: Cronin & Fitch discover CPV
KL (thought to be CP = −1) decayed into +− (CP = +1)
1973: Kobayashi-Maskawa mechanism proposed
Unitary matrix VCKM translates mass and weak basis
3 real parameters + 1 complex phase
1974: charm quark, 1975: lepton, 1977: bottom quark
( ) . .2
ud us ub
cd cs cb
td ts tb
L
L L L L
L
V V V
V V V
V V V
dg
u c t s W h c
b
μμγ +
⎛ ⎞⎜ ⎟= − +⎜ ⎟⎜ ⎟⎝ ⎠
⎛ ⎞⎜ ⎟⎜ ⎟⎜ ⎟⎝ ⎠
L ( ) . .2
ud us ub
cd cs cb
td ts tb
L
L L L L
L
V V V
V V V
V V V
dg
u c t s W h c
b
μμγ +
⎛ ⎞⎜ ⎟= − +⎜ ⎟⎜ ⎟⎝ ⎠
⎛ ⎞⎜ ⎟⎜ ⎟⎜ ⎟⎝ ⎠
L
The only source of CPV in the Minimal SM
August 2006 M. Morii, Harvard 6
History of CP Violation (2) 1970s–90s: CPV in K0-K0 mixing () studied in great details ~1999: Direct CPV in K0 decays (′) confirmed
KM mechanism most likely explanation 1999: BABAR and Belle start taking data 2001: CPV in B0 decays (sin2) measured
Agrees with expectation from the KM mechanism
Kobayashi-Maskawa mechanism is likely the dominant source of the CP violation observed in the lab
Is it the sole source?Is it the sole source?
August 2006 M. Morii, Harvard 7
CPV in the Golden Channel BABAR measured CPV in B0 charmonium + KS/L
Latest preliminary result based on 348 million BB pairs
Presented at ICHEP 2006 hep-ex/0607107
CP=–1CP=–1
CP=+1CP=+1
sin 2 =0.710 ±0.034(stat.) ±0.019(syst.) sin 2 =0.710 ±0.034(stat.) ±0.019(syst.)
0.674 ±0.026 0.674 ±0.026
August 2006 M. Morii, Harvard 8
Current Status of CPV CPV in the B0 system established by BABAR and Belle
Remarkable agreement with the CKM prediction
Standard Model passes the first test in the CP sector
Does everything fit together?Does everything fit together?
August 2006 M. Morii, Harvard 9
CPV Precision Tests We’ve measured one angle () very well Next step: Add more constraints to make precision tests of the
SM in the CP sector
Harvard group is involved in , penguin, and |Vub|
Measure the other angles and Measure with alternative methods
Different sensitivity to New Physics Penguin decays
Measure the opposite side i.e., Determine |Vub|
Measure the other angles and Measure with alternative methods
Different sensitivity to New Physics Penguin decays
Measure the opposite side i.e., Determine |Vub|
*
*td tb
cd cb
V V
V V*
*ubud
cd cb
V
V V
V
August 2006 M. Morii, Harvard 10
Measuring Angle At the tree level, the CP violation in
measures sin2 B → etc.
Problem: penguin contamination How large is the penguin amplitude
compared with the tree amplitude? What is the relative strong phase?
Measured BFs suggest that penguins are significant in B → Dominant error (~20°) on
What else can we do?
b uud→
August 2006 M. Morii, Harvard 11
Taming Penguins With B → , one can use interference between different
(2+1) combinations to determine the size and the strong phase of the penguin amplitude Quinn and Snyder, PRD 48, 2139 (1993) Measure time-dependent CP asymmetry simultaneously in
different parts of the Dalitz plot One of the most advanced fitting techniques used in BABAR
Need precise description of the resonant structures
Jinwei Wu leads this analysis Presented at ICHEP 2006, hep-ex/0608002
August 2006 M. Morii, Harvard 12
Angle from Penguin Decays The Golden mode is Consider a different decay
e.g., The phase from the CKM matrix is
identical to the Golden Mode We can measure angle in e.g.
B0 KS
New Physics may enter the loop in the penguin diagram Difference between tree and penguin
would be a tell-tale sign
b ccs→
b sss→
Tree
0Kb
c
sc
d
0B
/J ψ
d
Penguin
0Kb
s
ss
d
0B
φ
d
g
August 2006 M. Morii, Harvard 13
State of Penguins BABAR/Belle pursue penguin in
many channels sin2penguin < sin2 at 2.6σ All statistics limited
Jinwei Wu leads an analysis of B → KS Combines B → 0KS, f 0KS,
K* into a single Dalitz-plot analysis
Presented at ICHEP 2006, hep-ex/0607105
August 2006 M. Morii, Harvard 14
Measuring |Vub|
|Vub| determines the length of the sideof the Unitarity Triangle opposite to
Measured by charmless B semileptonicdecays
Problem: b → cℓ background2
2
( ) 1
( ) 50ub
cb
Vb u
b c V
Γ →≈ ≈
Γ →ll
2
2
( ) 1
( ) 50ub
cb
Vb u
b c V
Γ →≈ ≈
Γ →ll
How can we suppress50x larger background?
*
*ubud
cd cb
V
V V
V
b
u
−l
ubV
22 5
2( )
192F
ub b
Gb u V m
−Γ → =l
22 5
2( )
192F
ub b
Gb u V m
−Γ → =l at tree level
August 2006 M. Morii, Harvard 15
Detecting b → uℓ Inclusive: Use mu << mc difference in kinematics
Maximum lepton energy 2.64 vs. 2.31 GeV First observations (CLEO, ARGUS, 1990)
used this technique Only 6% of signal accessible
How accurately do we know this fraction?
Exclusive: Reconstruct final-state hadrons B → ℓ, B → ℓ, B → ℓ, B → ℓ, … Example: the rate for B → ℓ is
How accurately do we know the FFs?
El
b c→
b u→
222 3 2
2 3
( )( )
24F
ub
Gd BV p f q
dq
+Γ →
=l 2
22 3 22 3
( )( )
24F
ub
Gd BV p f q
dq
+Γ →
=l
Form Factor(3 FFs for vector mesons)
August 2006 M. Morii, Harvard 16
Harvard Group in |Vub|
Harvard group has established strong presence in the study of the b → uℓ decays Two active analyses that measure |Vub|
Morii is a convener of the semileptonic-decay working group Coordinates 11 ongoing analyses related to |Vub|
We specialize in analyses using recoil of B D(*)ℓ More efficient than B → hadron recoil, but more difficult to
control the background due to the missing Inclusive: Kris Chaisanguanthum Exclusive: Masahiro Morii, Kevin Chan
Submitted to PRL, hep-ex/0607089 Share the data samples, know-how, and software tools
August 2006 M. Morii, Harvard 17
Detector Upgrade & Operations Harvard group played a key role in upgrading the L1 trigger
Higher luminosity higher trigger rate bottleneck Designed and built the central component of the improved track-
trigger system: “Z-Pt Discriminator” (ZPD) Performs real-time, 3-d tracking in hardware S.J. Bailey et al., Nucl. Instrum. Meth. A 518, 544 (2004)
Project has completed successfully ZPD has been triggering BABAR since June 2004 Kris Chaisanguanthum served as the Trigger Data-Quality expert
to ensure smooth operation through 2005
Validation Review effort to ensure physics data quality Corry Lee contributed since sprint 2006
August 2006 M. Morii, Harvard 18
Summary BABAR is producing exciting physics results thanks to the
exceptional performance of PEP-II CPV in the B sector firmly established Entering the era of precision CPV measurements
Harvard BABAR group actively pursue tests of unitarity of the CKM triangle Angle using the Dalitz plot of B → Angle using the Dalitz plot of B → KS |Vub| using B → ℓ decays
Major contribution to detector operation The new trigger system in stable operation Contribution to the data-validation effort
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