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Laboratory for Particle Physics and Cosmology

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1 Laboratory for Particle Physics and Cosmology
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 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 University Stephen Bailey  LBNL Students: Kris Chaisanguanthum Corry Lee Undergrad: Ben Smith  Harvard (ATLAS) Kevin Chan  Berkeley Kevin Weil  Stanford August 2006 M. Morii, Harvard

4 BABAR Experiment Operates at PEP-II storage ring at SLAC
Collides e+ and e- at ECM = GeV (4S) Luminosity L = 12.11033 cm-2s-1 quadrupled the design Vast statistics opens a new era of precision flavor physics August 2006 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 August 2006 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? 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/ CP=–1 CP=+1 August 2006 M. Morii, Harvard

8 Does everything fit together?
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? August 2006 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 August 2006 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 amplitude compared 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? August 2006 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/ August 2006 M. Morii, Harvard

12 Angle b 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 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 August 2006 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/ August 2006 M. Morii, Harvard

14 How can we suppress 50x larger background?
Measuring |Vub| |Vub| determines the length of the side of the Unitarity Triangle opposite to b Measured by charmless B semileptonic decays Problem: b → cℓn background b at tree level How can we suppress 50x larger background? August 2006 M. Morii, Harvard

15 Form Factor (3 FFs for vector mesons)
Detecting b → uℓn Inclusive: Use mu << mc  difference in kinematics Maximum lepton energy 2.64 vs 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) August 2006 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/ 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 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 Next 2 talks August 2006 M. Morii, Harvard

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