Harvard BABAR Group

Masahiro Morii

Harvard University

Laboratory for Particle Physics and Cosmology

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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