Harvard BABAR Group

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Harvard BABAR Group

• Masahiro Morii
• Harvard University
• Laboratory for Particle Physics and Cosmology

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Upcoming Presentations

• BABAR overview Masahiro Morii
• Status of BABAR/PEP-II
• Harvard group in BABAR
• Measurement of CP violation Jinwei Wu
• Angle ? from B ? ppp decays
• Angle ? from B ? KSpp decays
• Measurement of Vub Masahiro Morii
• Exclusive B(B ? pln) with semileptonic tags

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Harvard BABAR Group

• Current and past membership
• Faculty Masahiro Morii (PI) (also in
  ATLAS) George Brandenburg ? ATLAS
• Postdocs Jinwei Wu ? ATLAS Eunil Won ? Korea
  University Stephen Bailey ? LBNL
• Students Kris Chaisanguanthum Corry Lee
• Undergrad Ben Smith ? Harvard (ATLAS) Kevin
  Chan ? Berkeley Kevin Weil ? Stanford

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BABAR Experiment

• Operates at PEP-II storage ring at SLAC
• Collides e and e- at ECM 10.58 GeV (?4S)
• Luminosity L 12.1?1033 cm-2s-1quadrupled the
  design
• Vast statistics opens a new era ofprecision
  flavor physics

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History of CP Violation (1)

• 1964 Cronin Fitch discover CPV
• KL (thought to be CP -1) decayed into pp- (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 t lepton, 1977 bottom
  quark

The only source of CPV in the Minimal SM
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History of CP Violation (2)

• 1970s90s CPV in K0-K0 mixing (e) studied in
  great details
• 1999 Direct CPV in K0 decays (e') confirmed
• KM mechanism most likely explanation
• 1999 BABAR and Belle start taking data
• 2001 CPV in B0 decays (sin2b) 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?
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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

CP1
CP1
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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?
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CPV Precision Tests

• Weve measured one angle (b) very well
• Next step Add more constraints to make precision
  tests of the SM in the CP sector
• Harvard group is involved in a, ?penguin, and
  Vub

• Measure the other angles a and g
• Measure b with alternative methods
• Different sensitivity to New Physics ? Penguin
  decays
• Measure the opposite side
• i.e., Determine Vub

a
g
b
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Measuring Angle a

• At the tree level, the CP violation in
  measures sin2a
• B ? pp, rp, rr, etc.
• Problem penguin contamination
• How large is the penguin amplitudecompared with
  the tree amplitude?
• What is the relative strong phase?
• Measured BFs suggest that penguins are
  significant in B ? pp? rr
• Dominant error (20) on ?
• What else can we do?

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Taming Penguins

• With B ? rp, one can use interference between
  different (21)p 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

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Angle b from Penguin Decays

• The Golden mode is
• Consider a different decaye.g.,
• The phase from the CKM matrix is identical to the
  Golden Mode
• We can measure angle b in e.g.B0 ? f ? KS
• New Physics may enter the loop in the penguin
  diagram
• Difference between ?tree and ?penguin would be a
  tell-tale sign

Tree
Penguin
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State of Penguins

• BABAR/Belle pursue ?penguin in many channels
• sin2?penguin lt sin2? at 2.6?
• All statistics limited
• Jinwei Wu leads an analysis of B ? KSpp
• Combines B ? ?0KS, f 0KS,K? into a single
  Dalitz-plot analysis
• Presented at ICHEP 2006, hep-ex/0607105

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Measuring Vub

• Vub determines the length of the sideof the
  Unitarity Triangle opposite to b
• Measured by charmless B semileptonicdecays
• Problem b ? cln background

b
at tree level
How can we suppress50x larger background?
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Detecting b ? uln

• Inclusive Use mu ltlt 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 ? pln, B ? rln, B ? wln, B ? hln,
• Example the rate for B ? pln is
• How accurately do we know the FFs?

Form Factor(3 FFs for vector mesons)
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Harvard Group in Vub

• Harvard group has established strong presence in
  the study of the b ? uln ?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()ln
• More efficient than B ? hadron recoil, but more
  difficult to control the background due to the
  missing n
• Inclusive Kris Chaisanguanthum
• Exclusive Masahiro Morii, Kevin Chan
• Submitted to PRL, hep-ex/0607089
• Share the data samples, know-how, and software
  tools

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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

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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 a using the Dalitz plot of B ? ppp
• Angle ? using the Dalitz plot of B ? KSpp
• Vub using B ? pln decays
• Major contribution to detector operation
• The new trigger system in stable operation
• Contribution to the data-validation effort

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