A study of B meson decays involving a J/[psi] meson

165 Pages·2006·3.391 MB·English

by  George Sganos, Pekka Sinervo (supervisor)

SLAC-R-810

Study of B Meson Decays to ppbarh Final States

Tetiana B. Hryn’ova

Stanford Linear Accelerator Center
Stanford University
Stanford, CA 94309

SLAC-Report-810

Prepared for the Department of Energy
under contract number DE-AC02-76SF00515
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STUDY OF B MESON DECAYS TO pp(cid:22)h FINAL STATES
A DISSERTATION
SUBMITTED TO THE DEPARTMENT OF PHYSICS
AND THE COMMITTEE ON GRADUATE STUDIES
OF STANFORD UNIVERSITY
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
Tetiana B. Hryn’ova
March 2006
c Copyright by Tetiana B. Hryn’ova 2006
(cid:13)
All Rights Reserved
ii
I certify that I have read this dissertation and that, in my opinion, it
is fully adequate in scope and quality as a dissertation for the degree
of Doctor of Philosophy.
Rafe H. Schindler Principal Co-Advisor
I certify that I have read this dissertation and that, in my opinion, it
is fully adequate in scope and quality as a dissertation for the degree
of Doctor of Philosophy.
Peter C. Kim Principal Co-Advisor
I certify that I have read this dissertation and that, in my opinion, it
is fully adequate in scope and quality as a dissertation for the degree
of Doctor of Philosophy.
Stanley J. Brodsky
I certify that I have read this dissertation and that, in my opinion, it
is fully adequate in scope and quality as a dissertation for the degree
of Doctor of Philosophy.
Patricia Burchat
iii
I certify that I have read this dissertation and that, in my opinion, it
is fully adequate in scope and quality as a dissertation for the degree
of Doctor of Philosophy.
Charles Prescott
Approved for the University Committee on Graduate Studies.
iv
Acknowledgments
There is no way I could possibly thank all those who have contributed to my graduate
experience. IwishonlytohighlightthosetowhomIoweaparticulardebtofgratitude.
Foremost, I would like to thank my advisors, Rafe Schindler and Peter Kim. Rafe,
for supporting me all these years and allowing me to work on so many interesting
projects, and Peter, without whom this work would not have been possible, for his
contagious enthusiasm, unfaltering attention, and guidance both as a mentor and a
friend. I would also particularly like to thank Bill Wisniewski, for his support and
sage advice, Bob Cahn for many useful discussions and constant encouragement, and
Bill Dunwoodie for reminding me that physics is more than just data analysis.
Iwould like tothank themembers ofGroupE, fortheir support andhelp through-
out my endeavors: Judy Meo and Melodi Masaniai, for creating a homey group envi-
ronment so far away from home, Martin Perl, for being a wonderful group co-leader,
Steven Robertson, for getting me started, Martin Kocian, Hojeong Kim, Johannes
Bauer, Howard Rogers, Eric Lee and Valerie Halyo for being there for me. I would
like to thank the members of my dissertation committee, Stanley Brodsky, Patricia
Burchat, and Charles Prescott, for their time and many useful discussions through-
out my graduate career. Many thanks to Jerome Friedman, for agreeing to chair the
committee. I also thank Jim Allen, Ron Seefred, Justino Escalera, Mark Freitag,
Lupe Salgado and Santa Chatterji for their help with my hardware project.
Finally, I would like to thank my best friends, Jo(cid:127)rg Stelzer and Erkcan O(cid:127)zcan,
for providing their companionship and advice, without them the past four years in
Stanford would have been much less enjoyable experience. Ogromnoe spasibo to my
family, for their patience, support and understanding. But most of all I am indebted
to my husband, Nicolas, for his support and encouragement through all these years.
v
Abstract
B mesons are unique among well-established non-quarkonium mesons in their ability
to decay into baryons. Baryonic B decays o(cid:11)er a wide range of interesting areas of
study: they can be used to test our theoretical understanding of rare decay processes
involving baryons, search for direct CP violation and study low-energy QCD.
This thesis presents measurements of branching fractions and a study of the decay
dynamics of the charmless three-body decays of B meson into pp(cid:22)h (cid:12)nal states, where
h = (cid:25)+; K+; K0; K(cid:3)0 or K(cid:3)+. With a sample of 232 million (cid:7)(4S) BB(cid:22) events
S !
collected with the BaBar detector, we report the (cid:12)rst observation of the B pp(cid:22)K(cid:3)0
!
decay, and provide improved measurements ofbranching fractions oftheother modes.
The distribution of the three (cid:12)nal-state particles is of particular interest since
it provides dynamical information on the possible presence of exotic intermediate
states such as the hypothetical pentaquark states (cid:2)(cid:3)++ and (cid:2)+ in the m and
pK+
m spectra, respectively, or glueball states (such as the tensor glueball f (2220))
pK0 J
S
in the m spectrum. No evidence for exotic states is found and upper limits on the
pp(cid:22)
branching fractions are set.
An enhancement at low pp(cid:22) mass is observed in all the B pp(cid:22)h modes, and
!
its shape is compared between the decay modes and with the shape of the time-like
protonformfactor. ADalitzplotasymmetryinB pp(cid:22)K+ modesuggestsdominance
!
of the penguin amplitude in this decay and disfavors the possibility that the low mass
pp(cid:22)enhancement originates from the presence of a resonance below threshold (such as
the recently seen baryonium candidate at 1835MeV=c2).
We also identify decays of the type B X h pp(cid:22)h, where h = K+; K0; K(cid:3)0 or
! cc(cid:22) ! S
K(cid:3)+, andX = (cid:17) orJ= . Inparticular, wereportontheevidence oftheB (cid:17) K(cid:3)+
cc(cid:22) c c
!
decay and provide a measurement of the width of (cid:17) .
c
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Contents
Acknowledgments v
Abstract vi
1 Introduction and Motivation 1
1.1 QCD and Exotics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Glueballs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Baryonium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4 New charmonium resonances . . . . . . . . . . . . . . . . . . . . . . . 8
1.5 Pentaquarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.6 B decays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2 The BABAR Detector and Data 23
2.1 The PEP-II Collider . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.2 The BABAR Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.3 The Silicon Vertex Tracker . . . . . . . . . . . . . . . . . . . . . . . . 26
2.3.1 Layout and Electronics . . . . . . . . . . . . . . . . . . . . . . 26
2.3.2 Reconstruction and Performance . . . . . . . . . . . . . . . . 28
2.4 The Drift Chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.4.1 Design and Geometry . . . . . . . . . . . . . . . . . . . . . . . 29
2.4.2 Electronics and Readout . . . . . . . . . . . . . . . . . . . . . 30
2.4.3 Calibration and Single-Cell Performance . . . . . . . . . . . . 32
2.4.4 Tracking and Performance . . . . . . . . . . . . . . . . . . . . 33
2.5 The Ring-Imaging Cerenkov Detector (DIRC) . . . . . . . . . . . . . 34
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2.5.1 Design and Geometry . . . . . . . . . . . . . . . . . . . . . . . 35
2.5.2 Electronics and Reconstruction . . . . . . . . . . . . . . . . . 35
2.6 Trigger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
2.6.1 The Level 1 Trigger . . . . . . . . . . . . . . . . . . . . . . . 38
2.6.2 The Level 3 Trigger . . . . . . . . . . . . . . . . . . . . . . . 39
2.7 The Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3 B+ pp(cid:22)K+ Branching Fraction Measurement 42
!
3.1 Track reconstruction requirements . . . . . . . . . . . . . . . . . . . . 42
3.2 Particle Identi(cid:12)cation (PID) . . . . . . . . . . . . . . . . . . . . . . . 43
3.3 B+ pp(cid:22)K+ Selection . . . . . . . . . . . . . . . . . . . . . . . . . . 44
!
3.4 Background Characterization . . . . . . . . . . . . . . . . . . . . . . 46
3.4.1 Continuum (qq(cid:22)) Background . . . . . . . . . . . . . . . . . . . 46
3.4.2 B Background . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.5 Event Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
3.6 Branching fraction measurement . . . . . . . . . . . . . . . . . . . . . 50
3.6.1 (B+ pp(cid:22)K+; m < 2:85GeV=c2) measurement . . . . . . . 53
pp(cid:22)
B !
3.6.2 (B+ (cid:17) K+) ((cid:17) pp(cid:22)) and (cid:0)((cid:17) ) measurements . . . . 55
c c c
B ! (cid:2)B !
3.6.3 Total (B+ pp(cid:22)K+) measurement . . . . . . . . . . . . . . . 57
B !
3.6.4 Measurement of the charge asymmetry in B+ pp(cid:22)K+ . . . . 60
!
3.6.5 Search for B+ p(cid:3)(cid:22)(1520) . . . . . . . . . . . . . . . . . . . 61
!
3.6.6 (cid:2)(cid:3)++ pentaquark search . . . . . . . . . . . . . . . . . . . . . 62
3.7 Systematic Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
3.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
4 The B pp(cid:22)h Maximum Likelihood Analysis 69
!
4.1 Event Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.1.1 Track reconstruction . . . . . . . . . . . . . . . . . . . . . . . 69
4.1.2 Particle Identi(cid:12)cation . . . . . . . . . . . . . . . . . . . . . . . 70
4.1.3 K0 Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
S
4.1.4 K(cid:3)+ Selection . . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.1.5 K(cid:3)0 Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
viii