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Harvard B A B AR Group

Harvard B A B AR Group. Masahiro Morii Harvard University Laboratory for Particle Physics and Cosmology. Upcoming Presentations. B A B AR overview Masahiro Morii Status of B A B AR /PEP-II Harvard group in B A B AR Measurement of CP violation Jinwei Wu Angle  from B → ppp decays

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Harvard B A B AR Group

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  1. Harvard BABAR Group Masahiro Morii Harvard University Laboratory for Particle Physics and Cosmology

  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→ ppp decays • Angle  from B→ KSpp decays • Measurement of |Vub| Masahiro Morii • Exclusive B(B→ pℓn) with semileptonic tags 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 University Stephen Bailey  LBNL • Students: Kris Chaisanguanthum Corry Lee • Undergrad: Ben Smith  Harvard (ATLAS) Kevin Chan  BerkeleyKevin Weil  Stanford 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 = 12.11033 cm-2s-1quadrupled the design • Vast statistics opens a new era ofprecision flavor physics M. Morii, Harvard

  5. History of CP Violation (1) • 1964: Cronin & Fitch discover CPV • KL(thought to be CP = −1) decayed into p+p−(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 M. Morii, Harvard

  6. History of CP Violation (2) • 1970s–90s: 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? 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=–1 CP=+1 M. Morii, Harvard

  8. 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 Current Status of CPV Does everything fit together? M. Morii, Harvard

  9. CPV Precision Tests • We’ve 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 M. Morii, Harvard

  10. 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? M. Morii, Harvard

  11. Taming Penguins • With B→ rp, one can use interference between different (2+1)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 M. Morii, Harvard

  12. 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 M. Morii, Harvard

  13. State of Penguins • BABAR/Belle pursue penguin in many channels • sin2penguin < 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 M. Morii, Harvard

  14. 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? M. Morii, Harvard

  15. Detecting b → uℓn • 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 → 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) M. Morii, Harvard

  16. 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 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 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 a using the Dalitz plot of B→ ppp • Angle  using the Dalitz plot of B→ KSpp • |Vub| using B→ pℓndecays • Major contribution to detector operation • The new trigger system in stable operation • Contribution to the data-validation effort Next 2 talks M. Morii, Harvard

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