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UCSD Physics Activities on BaBar
Progress Report to DOE: 2004
Vivek Sharma
University of California, San Diego
Prize For Best PhD Dissertation At a US University or Laboratory
2004
Mitsuyoshi Tanaka Dissertation Award
to
Shahram Rahatlou
University of California, San Diego
Citation:
"For his role in the development of the tools needed for the analysis of B factory data, including the tFIT program, a
unique and comprehensive fitting framework for time-dependent analyses. The tools he developed played a key
role in the observation of CP violation in the B system by the BaBar collaboration. These tools will be essential to
the ongoing program of work as the B factories continue to probe the origins of CP violation."
PhD Thesis Advisor : Vivek Sharma
2
Outline of This Talk
•
•
•
•
•
•
BaBar highlights from this summer
Physics responsibilities and activities of UCSD physicists
UCSD Physics Objectives
Brief description of analyses pursued
Outlook
Enclosed with this document, for more elaborate reading:
• David MacFarlane’s comprehensive review of ICHEP04 results from
Babar and Belle
• Vivek Sharma’s review talk on Rare B and D Decays at “Physics at Meson
factories”, Frascati 2004.
• Daniele delRe’s talk on Vub at ICHEP04, Beijing
• Daniele delRe’s talk on Recoil-side physics at SuperBfactory workshop
• Shahram Rahatlou’s review talk on sin2+ at DPF 2004
• Shahram Rahatlou’s talk on BaBar Event Reconstruction at DPF2004
3
Reminder Of The Terminology
*
VudVub
a

*
VtdVtb
Vtd Vtb*
a  arg 
Vud Vub*
Vcd Vcb*
  arg 
Vtd Vtb*

*
VcdVcb
Vud Vub*
  arg 
Vcd Vcb*
In a time-dependent CPV measurements:
f  f
A fCP ( t) 
 S fCP sin md t  CfCP cos md t
f  f
With only one amplitude driving the decay,
Direct CP asymmetry C=0
4
Summary Of BaBar Physics Productivity
PEP-II machine
continues to Excel !
3 x design
~245 million BB pairs
BaBar quick to analyze and
provide public results
Journal Publication
(PRL, PR(D) RC ,
PR(D), NIM etc
112
Papers submitted to
ICHEP04 conference
in Beijing
72
Parallel session
speakers at ICHEP04
conference in Beijing
22
5
BaBar Physics Highlights: Discovery of Direct CPV in B Decays
B
A( B  f )
ACP 
f
2
Br  B  f   Br  B  f 
Br  B  f   Br  B  f 


B0K+
Af
Af
B
A( B  f )
2
2
 Af
2
 Af
2
 0  Direct CPV
BABAR
SM amplitude   2e i T  P AK
sin   
BABAR First Observation (4.2
Signal (in 227M BB pairs): 1606  51
B0K+
4.2
f
2
ACP  0.133  0.030  0.009
Belle
CPV
Confirms at ICHEP04 3.9
Signal (in 274M BB pairs): 2140  53
ACP  0.101  0.025  0.005
signal enhanced
Average
ACP  0.114  0.020
6
BaBar Physics Highlights: Precision Measurement of sin2
Just Three years after its discovery CPV in B J/K0 is now a
precision measurement
B (cc) KS (CP odd) modes
B J/ψ KL (CP even) mode
sin2β = 0.722  0.040 (stat)  0.023 (sys)
(2002 measurement:
sin(2β) = 0.741±0.067±0.034)
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CP asymmetries in Penguin Dominated B Decays (sin2eff)
Penguin dominated modes sensitive to New Physics in the loop
Without NP, expect “sin2” from penguin modes to be same as “sin2”
from K0 modulo corrections due to (small) contribution from other
SM amplitudes
u , c ,t
B

0
KS0
B 0  K 0
Difference is 2.7
B 0  K 0

B0
KS0
Adding Belle results, difference between measured sin2
8
from s-penguin and charmonium modes grows to 3.6 ??
BaBar Physics Highlights: No CPV Seen in B0+ B 0     (227M pairs)
3.2
5.2
S  0.30  0.17  0.03
BaBar C  0.09  0.15  0.04

S
 1.00  0.21  0.07
Belle C   0.58  0.15  0.07

> 3 discrepancy
between BABAR & Belle
9
BaBar Physics Highlights: Towards Precise Measurement of Angle a
, 
Tree
, 
•
•
, 
Penguin
, 
In absence of Penguin contributions, can measure CKM angle a from B0+ - or + BaBar measurements show that B0+ - is most suited for measuring a since
– Penguin pollution is more under control (limits on B00 0, B-- 0)
– The decay is dominated by one helicity amplitude  well defined CP state
– Rate is reasonably large; first observation by BaBar (2003)
B0+
-
Clean tags
Run1-3 data (122M BB)
314±34 Signal Events (205 tagged)
Longitudinal polarization frac. fL=1.00±0.02
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BaBar Physics Highlights: Towards Precise Measurement of Angle a
Time-dependent CP Asymmetry
Slong  0.19  0.33  0.11
Clong  0.23  0.24  0.14
Can Measure a more precisely
a  96  10(stat )  4(sys )  11( peng ) 
o
11
Inclusive
studies*
LEP
Exclusive
modes
BaBar Physics Highlights: Measurements of Vub In Semileptonic Decay
Using new Belle photon
spectrum from b  s
*
Vub WA   4.70  0.44(stat sys )  x 103
12
Physics Analysis Focus of The UCSD-BaBar Group
UCSD-Babar group led the measurements of sin2 from B 
charmonium modes between 1998-2003. These measurement has
now become “routine”. UCSD group has moved on more
challenging measurements.
With the large data set BaBar is accumulating our major physics
focus is now on:
– Search for the decay B0 D0 K0 and measurement of CKM
angle  by time-dependent CP asymmetry.
– Developing massive samples of fully reconstructed B mesons
for Recoil side B meson decay studies. The aim is to measure
CKM element Vub from inclusive and exclusive bu l
decays
– Probe CP violation in b  sss Penguin decays such as
B0  KS KS KS
– Measurement of production ratio
(4S )  B 0 B 0
(4S )  B  B 
Brief Description of UCSD analysis follows
13
UCSD Physics Activities On Babar
•
David MacFarlane (PI):
– Main author of BaBar 2002 Phys. Rev. (D) on Measurement of B oscillation and CP
violation.
– Measurement of inclusive bu l spectrum (with Student Ed Hill)
– Search for Time-dependent CP asymmetry in B0 KS KS KS (with student
Haleh Hadavand)
(4S )  B 0 B 0
– Measurement of production ratio
(with student Haleh
 

(4
S
)

B
B
Hadavand)
– BaBar Spokesperson
14
UCSD Physics Activities On Babar
• Vivek Sharma (PI) :
– led, as co-convener, the BaBar physics group on Exclusive B decays to
Open charm ( BRECO group) between 1999 –July 2004. All analyses
involving exclusive hadronic B  Charm reconstruction are developed in
this group. Guided thru publication 9 PRL, 2 PR(D)RC and 2 PR(D) articles
and multiple conference papers including 11 papers at ICHEP04 in Beijing.
• Physics goals of the BRECO group include:
– exploration of decay modes capable of measuring CKM angle  and sin2+
– Decay dynamics in hadronic B decays to charm
– Spectroscopy of new charm mesons from their production in B decays
– Develop large sample of fully reconstructed B mesons for measuring
inclusive properties of the recoiling B meson. This paradigm shifting
enterprise is already contributing to several key measurements in B decays
such as Vub and measurement of photon spectrum in b s  decays .
• Breco group oversees the physics analysis of about 80 BaBar physicists from
US, France, Italy and Germany. It is one of the largest analysis groups in Babar.
– Guiding role in BaBar observation of CP violation (sin2) in BJ/K0 .
Main author of the 2001 and 2002 PRLs on measurement of Sin2
– Member (since 2002) of the Babar Publication Board.
15
UCSD Physics Activities On Babar
•
Shahram Rahatlou (Post-doc):
– Major contributions to BaBar observation of CP violation in B decays to
charmonium (e.g. BJ/K0). Tools and samples he developed (BrecoUser, tFIT
etc) are still used in many CP violation studies. Awarded The 2004 APS Tanaka
prize for the best PhD thesis at a US university or Laboratory.
– BaBar Event Reconstruction Manager since Jan 1, 2004.
• The reco manager is Responsible for development and deployment of the common
aspects of reconstruction, including the reconstruction geometry & alignment calibration
model & code, the overall organization of reconstruction executables, and the reco
infrastructure packages. He is responsible for the system-specific aspects of the
reconstruction code to the level desired by the specific system managers. The reco
manager is responsible for the technical aspects of the reco software within the five
systems and their integration into the whole.
• Shahram brings a unique and comprehensive knowledge of Babar analysis tools,
computing and physics to this job. His leadership has been crucial in ensuring prompt
and high quality event reconstruction and allowed BaBar to analyze the data
collected till the end of Run 4 in mid July and present results based on it at the
Beijing ICHEP04 in mid-August !
– Developing the time-dependent CP asymmetry analysis of B0 D0 K0 for
measurement of sin2+ and . First results presented at ICHEP04 (hepex/0408052 ).
16
UCSD Physics Activities On Babar
•
Daniele delRe (Post-doc):
– Primary physicist in the development of large sample of fully reconstructed
hadronic B decay (Semi-exclusive B sample).
– Co-convener of the “Recoil Side Physics” forum in BaBar in charge of coordinating
and assisting in the development of a variety of inclusive measurements in the
decay of the B meson recoiling against the fully reconstructed B meson (in the semiexclusive sample).
– Led the pioneering measurement of Vub by measuring the hadronic mass spectrum in
b u l from the recoil side B. Results published in PRL (92) 07180, 2004.
Updated Vub results with more data (x 3) and improved observables in preparation.
– Key contributor in the migration of BaBar analysis software to the new computing
model implemented since September 2003. Technical coordinator of the data and
MC “skims” and tagbits for the Breco and Semileptonic Physics groups.
– Appointed co-convener of the Breco Physics group in August 2004.
17
UCSD Physics Activities On Babar
•
Haleh Hadavand (PhD. Student):
– Member of BaBar charge Particle tracking group with important contributions to the
Drift chamber calibration and Ks reconstruction studies. Her tracking efficiency
studies provide the official BaBar “recipes” for all analyses involving branching
fraction measurements.
– Primary author of the measurement of the B+/B0 production ratio from the (4s)
Meson using B+J/ K+ and B0J/  Ks decays to be published in Phys. Rev. (D).
– Primary author of the measurement of time-dependent CP asymmetry in penguin
dominated mode B0 KS KS KS .
•
Edward Hill (Ph.D Student):
– Drift chamber calibration.
– Migration of BaBar analysis software related to Semi-leptonic decay physics to the
new computing model and data-mining for the entire semi-leptonic physics group.
– Developed algorithms for bcl background rejection for Semileptonic physics
group
– Measurement of Vub from inclusive semi-leptonic decay using the photon energy
spectrum from b s  decays.
18
UCSD Physics: Probing CKM Angle 
Look for B decays with 2 amplitudes with relative weak phase 


K K


 
K 0
0


K  
V ei
ub
Direct CP Asymmetry
 Angle 
19
Angle  from B±DK±: Critical Requirement
•
Relative size of the 2 B decay amplitudes Crucial for interference and rate of CPV
Color suppression: Fcs  [0.2,0.5]
Left side U.T.: Ru  0.4
Expected range
•
Want rb to be large to get more interference  Large CP asymmetry
– Diff. between rb=0.1 and rb=0.2 substantial for precision on 
– Theory cannot calculate r reliably must measure experimentally
20
Measuring rb By Reconstructing B±DK± in different D final states

B D K
0
B  D0 K 

K S  
K  
[deg]
BaBar : rB  0.23 (90% CL)
68% 90%
R ADS
D0 K 
rB  0.17 (90% CL)
rB
rB
Belle : rB  0.28 (90% CL)
Bottomline : With low value of rb likely, need to consider multiple
observables sensitive to CKM angle   B0D0K0
21
Measurement of sin(2+) with B0/B0 D(*)0K(*)0
c
b
Vcb*
B
u
s
Vub
B0
B0
VcbVus* A
b
D (*) 0
c
Vcs*
K (*)0
d
u
b
D (*) 0
Vus
0
d
•
•
d
s
K (*)0
d
d
VubVcs* ei  rB A ei ei
Strong phase
difference
Interference between decay and mixing
Advantages:
A B0  D0 K (*)0
VubVcs*

~ 0.4
• Expected large asymmetries rB 
*
0
0 (*)0
VcbVus
A B D K




• Time-dependent measurement with K0 KS
• Probe rB in self-tagging final state K*0K
– Disadvantages:
• Color suppressed decays: Smaller branching fractions than D*
• Possible competing effects from Doubly-Cabibbo-suppressed D0 decays
22
Study of B0/B0 D*0KS Decays
124 million BB
hep-ex/0408052
Cannot distinguish
0
0
B from B
N=64 ± 11
Hidden strangeness
with KS in final state
D0 Sidebands
First Evidence
Shahram Rahatlou
& Vivek Sharma
N=11 ± 4
BF (10-5)
Mode
0
0
0
*0
0
B D K
6.2 ±1.2 ±0.4
0
B D K
4.5 ±1.9 ±0.5
23
r
Self-Tagging B0 D0K*0 and limit on B
Charge correlation to
0
0
separate B from B
B D K
D0  K  X 
K *0  K  
0
0
*0
B 0  D0 K *0
D0  K  X 
K *0  K  
124 million BB
Vcb transition
N=45 ± 9
Vub transition
No Signal in
Vub mediated
Decay
Preliminary
Mode
BF (10-5)
0
0 *
B
D
K
0
6.2 ±1.4 ±0.6
0
0 *
B
D
K
0
< 4.1 @ 90% CL
Results based on more data and refined
analysis technique forthcoming; targeted for
24
publication in early 2005.
Measurement of | Vub | From Inclusive and Exclusive Final States
New Idea: Measurement of |Vub| From Semileptonic B Decays
recoiling against (large samples of) Fully Recostructed B mesons
Capitalizes on UCSD Expertise in B meson Reconstruction
(Breco Samples  SemiExcl Samples)
25
Beginning of an Experimental Paradigm Shift in Vxb Measurements in Semileptonic
Decays at B Factories
•
Hermiticity, so vital for SL measurements is not the best feature of Belle/ Babar
detectors due to intrusion of machine into detector
•
But B-factory detectors recording ever increasing samples of BB pairs (> 250 Million
BB recorded already  1000 Million soon)
– At the price of modest efficiency (4%), can fully reconstruct one B decay into all
hadronic final states (Breco) and examine the other (recoiling) B decay
• This “Recoil side” studies perfectly suited for many Vxb studies
• Much “cleaner” and more powerful than neutrino reconstruction a la CLEO
• This is the most promising way for the future Vub and other Semileptonic
measurements
26
The Perfect (4S) Event: Example of Recoil Side Analysis
In this (rare) case all
particles were
sprayed within fiducial
volume of detector
Replace this with your
Favourite Vxb mode
e.g: b  u l
27
Hadronic B Decay Reconstruction Rate: 4000/ fb-1
80fb-1
World’s largest sample of
Fully reconstructed B mesons
 1,000,000 and growing!
Full B reconstruction on one side
provides kinematic constraints and
Background reduction allowing
Important inclusive B decay
Measurements like Vub.
S/B~0.3
Require Lepton (p*>1.0GeV)
S/B~2.5
Largely the work of UCSD postdoc Daniele delRe
28
Recoil Side B Decay Rate Measurement : Technique
Can measure Neutrino 3-vector
Breco
D*

Y(4S)
Reco side
Xu
Brecoil
l

Recoil side


D*
B
Y(4s)
missing
mass
squared
l
Xu
B
Y(4s)
B Candidate Mass
•MX reconstruction
•Kinematic constraints to
improve MX resolution
29
Resulting MX Spectrum clearly separates b c l  & b  u l
mX  1.7
q2  8
167  21
signal events
Vub   4.92  0.39stat  0.36sys  0.46theo   103
30
Measurements of |Vub| from b u l
Daniele delRe &
Ed Hill (UCSD)
Most Measurements are
systematic limited or
model dependent.
ucsd
The Recoil side method
has the best potential
for precise measurement
of |Vub| with larger data
samples already
available
31
Exclusive Final States: B (,,w) l
Approach similar to the inclusive analysis but
In
resonances are exclusively and fully reconstructed on recoil side.
We measure, very cleanly and over large kinematic range:
B±0l
B±0l
B0l
B0wl
Breco Sample
B0   l 
B(B0   l  )  (1.08  0.28stat  0.16syst ) 104
B(B0   l  )  (2.57  0.52stat  0.59syst ) 104
As Lattice calculations become more
robust, measurement of B l rate over
large kinematic range may lead to one of
the best measure Vub precisely.
Experimental measurement is statistics
limited
32
(4S )  B0 B 0 and B B- Rates : Needed for all Br. Ratio Measurements
From clean samples of
B 0  J /   e  e   K S0
B   J /   e  e   K 
Measure ratio of branching fractions:
B   J / K 

and 0
0
0
B  J / K S

Determine production ratio
assuming isospin:
  (4S )  B  B  
  (4S )  B B
0
0

 1.006  0.036( stat )  0.031( sys)
Haleh Hadavand
David MacFarlane
Accepted in
PR(D) RC
33
Determining KS+ - Tracking Efficiency Correction
Precise data and MC comparison
to determine efficiency correction
in bins of trans. momentum (Pt)
and polar angle  for various
drift chamber high voltage conditions
during data taking periods.
Algorithm and “recipe” is now a
BaBar standard.
Hadavand
&
MacFarlane
34
CPV In Pure s-Penguin Decay B0KS KS KS
-
y
x
KS
+
~4 mm
KS
+
K0s
+
K0 s
KS
-
B
0 ~30 mm
~200 mm
K0
s
Beam
Inflated Beam
90 10 signal
after bkgnd
subtraction
•
•
•
Hadavand
•
•
New probe of CPV in s-penguin decays, clean signal
Perform Ks and B vertexing using 5 layer Silicon tracker
(technique pioneered by BaBar and tested on BKs0
sample). Often one of three Ks decays inside SVT.
Reconstructed B vertex resolution sufficient for timedependent CPV measurement a la B  J/ KS
First analysis of its kind, currently “blind”, expect public
results and publication by early 2005.
CPV precision expected to be statistics limited, will
improve with rapidly accumulating BaBar data
35
UCSD-Babar Physics Outlook
Golden years of Babar physics productivity enabled by excellent
PEP-II running and success of the new Babar computing model
• UCSD-Babar physicists continue to play a key role in BaBar
productivity by contributing to physics and computing leadership,
service tasks and by performing outstanding and topical analyses.
• The UCSD-Babar group’s planned near-term physics focus is on
– Strategies for measurement of , particularly B0/B0 D(*)0K(*)0
– Determination of |Vub| with the novel recoil side method
•
• Inclusive bul measurements
• Exclusive bul final states (exploring new ideas such as that of
Grinstein & Pirjol hep-ph/0404250 )
– Innovative new probe of CPV in s-penguin modes with
B0 KSKSKS
36