no slide title · i will interpret my assigned title: ... infn, superiore di sanita', roma...
TRANSCRIPT
David Hitlin
Caltech
Leith SymposiumDecember 12, 2014
and Science
David Hitlin BABAR and Science Leith Symposium Dec.12, 2014
Une brève histoire de BABAR
I will interpret my assigned title:
“BABAR and Science” to mean that
I can (briefly) tell you about the
formation and early days of the
collaboration: how it came together,
especially David Leith’s role, and a bit
about the physics, in particular, the
measurement of CP violation, and then
tabulate the extraordinary amount of
interesting physics that BABAR has
produced
There is no time to go into any detail on
the prehistory, the history, the design and
construction of the detector, ……
2
David Hitlin BABAR and Science Leith Symposium Dec.12, 2014
Une brève histoire de BABAR
I will interpret my assigned title:
“BABAR and Science” to mean that
I can (briefly) tell you about the
formation and early days of the
collaboration: how it came together,
especially David Leith’s role, and a bit
about the physics, in particular, the
measurement of CP violation, and then
tabulate the extraordinary amount of
interesting physics that BABAR has
produced
There is no time to go into any detail on
the prehistory, the history, the design and
construction of the detector, ……
2
The flavor physics situation in the mid ’80’s
In 1981 Carter and Sanda and then Bigi and Sanda showed that a
measurement of CP violation in B0 meson decay to CP eigenstates could
be clearly interpreted in terms of CKM matrix elements, without
theoretical uncertainties due to hadronic structure.
The prospect of a clean measurement in B0 decays was exciting; perhaps
the Standard Model prediction of the strength of CP violation would fail
With the observation in ’83 of a long B meson lifetime by Mark II and
MAC and in ’87 of substantial Bd mixing by ARGUS and UA1, one could
envision measurable CP-violating asymmetries in B0 meson decays
Doing so would require flavor-tagging a B meson and then untangling
mixed from unmixed decays, which could be done using B’s produced in
e+e- annihilation or in hadronic collisions
However, ~107-108 pairs would be needed, a 2 to 3 order-of-
magnitude increase in the then-existing data sample
Exploiting the quantum correlations of pairs produced in ϒ(4S)
decays in e+e- seemed like a particularly elegant approach, but separating
the decays was difficult as the B0 lifetime in the laboratory corresponds
to 19μm
David Hitlin BABAR and Science Leith Symposium Dec.12, 2014
0 0B B
0 0B B
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The flavor physics situation in the mid ’80’s
In 1981 Carter and Sanda and then Bigi and Sanda showed that a
measurement of CP violation in B0 meson decay to CP eigenstates could
be clearly interpreted in terms of CKM matrix elements, without
theoretical uncertainties due to hadronic structure.
The prospect of a clean measurement in B0 decays was exciting; perhaps
the Standard Model prediction of the strength of CP violation would fail
With the observation in ’83 of a long B meson lifetime by Mark II and
MAC and in ’87 of substantial Bd mixing by ARGUS and UA1, one could
envision measurable CP-violating asymmetries in B0 meson decays
Doing so would require flavor-tagging a B meson and then untangling
mixed from unmixed decays, which could be done using B’s produced in
e+e- annihilation or in hadronic collisions
However, ~107-108 pairs would be needed, a 2 to 3 order-of-
magnitude increase in the then-existing data sample
Exploiting the quantum correlations of pairs produced in ϒ(4S)
decays in e+e- seemed like a particularly elegant approach, but separating
the decays was difficult as the B0 lifetime in the laboratory corresponds
to 19μm
David Hitlin BABAR and Science Leith Symposium Dec.12, 2014
0 0B B
0 0B B
3
The flavor physics situation in the mid ’80’s
In 1981 Carter and Sanda and then Bigi and Sanda showed that a
measurement of CP violation in B0 meson decay to CP eigenstates could
be clearly interpreted in terms of CKM matrix elements, without
theoretical uncertainties due to hadronic structure.
The prospect of a clean measurement in B0 decays was exciting; perhaps
the Standard Model prediction of the strength of CP violation would fail
With the observation in ’83 of a long B meson lifetime by Mark II and
MAC and in ’87 of substantial Bd mixing by ARGUS and UA1, one could
envision measurable CP-violating asymmetries in B0 meson decays
Doing so would require flavor-tagging a B meson and then untangling
mixed from unmixed decays, which could be done using B’s produced in
e+e- annihilation or in hadronic collisions
However, ~107-108 pairs would be needed, a 2 to 3 order-of-
magnitude increase in the then-existing data sample
Exploiting the quantum correlations of pairs produced in ϒ(4S)
decays in e+e- seemed like a particularly elegant approach, but separating
the decays was difficult as the B0 lifetime in the laboratory corresponds
to 19μm
David Hitlin BABAR and Science Leith Symposium Dec.12, 2014
0 0B B
0 0B B
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The Gold Rush
There were at least 21 e+e- B Factory concepts and proposals (19 ϒ(4S) + 2 Z0)
and several hadronic machine approaches (HERA-B, …….)
Oddone’s concept of using an asymmetric e+e- collider to boost the distance
between the two decay vertices to a measurable regime, implemented in a
multibunch machine stabilized by feedback, was, in the end, the successful approach
Two asymmetric colliders, PEP-II and KEKB, were ultimately built
David Hitlin BABAR and Science Leith Symposium Dec.12, 2014
ϒ(4S)Storage Rings ϒ(4S) Linac-Ring
Collider
ϒ(4S) Recirculating
Linear Collider
Z Factory
Symmetric Asymmetric
PSI (2) APIARY Grosse-Wiesmann Amaldi/Coignet SLC
BINP CITAR JLAB ARES LEP
KEK accumulator PEP-II UCLA
CESR Plus PETRA-II TBA
ISR Tunnel
KEK accumulator
KEK-B
CESR-B
0Z bb
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The SLAC program in the mid ’80’s looking forward
In the late ’80’s, SLAC’s main project was the SLC (with the Mark II and
SLD detectors)
Laboratories are always searching for their next big project
What was next?
Burt Richter: “We at SLAC believe that “next” for us is a larger scale
[0.5-1.5] linear collider” (ICHEP XXIII Berkeley, July 1986)
[est. 5 years to a proposal]
There was, however, interest in a smaller near term project
SBF (Bloom, Fridman, …) – symmetric, two rings in the PEP tunnel
Apiary (Oddone, Feldman, ….) – asymmetric, small ring on PEP ring
These schemes did not provide sufficient sensitivity to measure
CPV in the B system
Neither went forward
New ideas – SLAC/SLUO Workshops
PEP-II – asymmetric, two rings in the PEP tunnel – CPV capable
t/charm factory (Kirkby, Perl,…)
Charm photoproduction in End Station A (Brau, …)
David Hitlin BABAR and Science Leith Symposium Dec.12, 2014
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The SLAC program in the mid ’80’s looking forward
In the late ’80’s, SLAC’s main project was the SLC (with the Mark II and
SLD detectors)
Laboratories are always searching for their next big project
What was next?
Burt Richter: “We at SLAC believe that “next” for us is a larger scale
[0.5-1.5] linear collider” (ICHEP XXIII Berkeley, July 1986)
[est. 5 years to a proposal]
There was, however, interest in a smaller near term project
SBF (Bloom, Fridman, …) – symmetric, two rings in the PEP tunnel
Apiary (Oddone, Feldman, ….) – asymmetric, small ring on PEP ring
These schemes did not provide sufficient sensitivity to measure
CPV in the B system
Neither went forward
New ideas – SLAC/SLUO Workshops
PEP-II – asymmetric, two rings in the PEP tunnel – CPV capable
t/charm factory (Kirkby, Perl,…)
Charm photoproduction in End Station A (Brau, …)
David Hitlin BABAR and Science Leith Symposium Dec.12, 2014
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Embedding PEP-II/BABAR at SLAC
The approach to the new accelerator and detector project within SLAC was, of
necessity, different from past practice
PEP-II was to be built by a SLAC/LBNL/LLNL collaboration
The detector was to follow a “CERN model”
David laid the groundwork for this new approach to the detector with a number
of visits to Europe in which he studied in some detail the CERN model, in
particular that employed for the LEP collaborations, and was able to interest the
funding agencies of France, Italy, Germany, the UK and Canada in participating
An important mechanism was the International Finance Committee (c.f. Ian
Corbett’s talk) that managed both the initial investment shares and the ongoing
commissioning and operating costs
The “Common Fund” was a crucial concept
David managed the IFC meetings in his typical skillful manner:
A day of meetings with an “exchange of views”, followed by a good
dinner with adequate liquid refreshment, and a resolution of issues the
next day
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USA [33/244]California Institute of Technology
UC, Davis
UC, Irvine
UC, Los Angeles
UC, San Diego
UC, Santa Barbara
UC, Santa Cruz
U of Cincinnati
U of Colorado
Colorado State
U of Iowa
Iowa State U
LBNL
LLNL
U of Louisville
U of Maryland
U of Massachusetts, Amherst
MIT
U of Mississippi
Mount Holyoke College
Northern Kentucky U
U of Notre Dame
ORNL/Y-12
U of Pennsylvania
Prairie View A&M
Princeton
Rutgers
SLAC
U of South Carolina
Stanford U
U of Texas at Dallas
Vanderbilt
U of Wisconsin
Canada [7/25]U of British Columbia
Carleton U and CRPP
McGill U
U de Montréal
TRIUMF
U of Victoria
York U
China [4/19]Beijing Glass Research Inst.
Inst. of High Energy Physics, Beijing
Shanghai Inst. of Ceramics (SICCAS)
Tsinghua U, Beijing
France [5/44]LAPP, Annecy
LAL Orsay
LPNHE des Universités Paris 6/7
Ecole Polytechnique
CEA, DAPNIA, CE-Saclay
Germany [1/7]Technische U Dresden
Italy [13/72]INFN, Bari and U di Bari
INFN, Ferrara
Lab. Nazionali di Frascati dell' INFN
INFN, Genova and U di Genova
INFN, Milano and U di Milano
INFN, Napoli and U di Napoli
INFN, Padova
U di Pavia
INFN, Pisa, U di Pisa & Scuola Normale
INFN, Roma and U "La Sapienza"
INFN, Superiore di Sanita', Roma
INFN, Torino and U di Torino
INFN, Trieste and U di Trieste
Norway [1/1]U of Bergen
Russia [2/28]Budker Institute, Novosibirsk
JINR, Dubna
United Kingdom [10/42]U of Bristol
Brunel University
U of Edinburgh
U of Lancaster
U of Liverpool
Imperial College
Queen Mary & Westfield College
Royal Holloway & Bedford New College
U of Manchester
Rutherford Appleton Laboratory
Taiwan [1/3]Academia Sinica
The BABAR Collaboration
10 Countries
77 Institutions
485 CollaboratorsOctober 1995
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How BABAR got its name
The first use of the name was in 1990, spelled as (not an acronym)
In 1992 the question of copyright was raised and we asked the SLAC™
Business Office to make inquiries
In the Fall of 1993 I wrote to Laurent de Brunhoff extolling the virtues of
CP violation measurements in the meson system and the importance of
investigating the origin of the matter-antimatter asymmetry
He did not answer directly, but in December, 1993 I received a call from Nelvana,
which held the licensing rights to Babar, offering a five year, renewable, royalty-
free license for use of the Babar name and images
The SLAC™ Business Office then concluded a formal agreement
With the new initiative to form a detector collaboration for a detector for
PEP-II it seemed wise to have the new group choose its own name
An email vote was organized, with John Fry as Election Commissioner, and the
name chosen by the proto-Collaboration Council, on May 12, 1994, was BABAR,
with capitalization and relative letter size subsequently decided upon by the
Interim Steering Committee:
\def\babar{\mbox{\slshape B\kern-0.1em{\smaller A}\kern-0.1em B\kern-0.1em{\smaller
A\kern-0.2em R}}}
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BaBar
BB
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Preparing to do physics – four more workshops
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Distribution of BABAR physics topics
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Topic Papers
CP Violation a 20
CP Violation b 52
CP Violation g 29
B→ charmonium 32
B → open charm 58
B → charmless hadronic 107
B → semileptonic 28
Radiative penguin decays 36
Leptonic decays 11
B mixing and lifetimes 12
D mixing and CP Violation 11
production and decay 10
Charmonium production and decay 14
Charm production and decay 35
Light quark production and decay 19
Tau decays 16
New Physics searches 49
Distribution of BABAR physics topics
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Topic Papers
CP Violation a 20
CP Violation b 52
CP Violation g 29
B→ charmonium 32
B → open charm 58
B → charmless hadronic 107
B → semileptonic 28
Radiative penguin decays 36
Leptonic decays 11
B mixing and lifetimes 12
D mixing and CP Violation 11
production and decay 10
Charmonium production and decay 14
Charm production and decay 35
Light quark production and decay 19
Tau decays 16
New Physics searches 49
• After a plenary discussion
at the Padova Collaboration
Meeting in 1997, BABAR
committed to employing
blind analysis techniques,
becoming one of the first
major experiments to do so
• We also pioneered the use
of sophisticated maximum
likelihood and multivariate
techniques that enabled us
to extract maximum
information from the data
in an unbiased manner
CPV-related physics goals
Our initial goal was to measure sin2b, i.e., to find evidence for
CP violation in the interference of mixing and decay in the B meson
system
We then added a series of measurements that allowed us to
overconstrain the Unitarity Triangle
This required measurements of Vub, Vcb, Dmd, and tB,
as well as sin2a and g
We were also able to resolve intrinsic trigonometric ambiguities
We were able to exploit other features of the entangled state
to observe T violation in particle decay
As the data sample increased, it became possible to investigate rare
inclusive and exclusive penguin-dominated decays and to search for
CPV in these decays, in which physics beyond the Standard Model is
most likely to be observable
B0B0
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The CKM Matrix
d s b
u
c
t
ud us ub
cd cs cb
td ts tb
V V V
V V V
V V V
VCKM = V
udV
ub
* +Vcd
Vcb
* +VtdV
tb
* = 0
There are six unitarity conditions:
only one has elements of comparable size:
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Wolfenstein: 4 parameters
2 3
2 2
3 2
1 / 2 ( )
1 / 2
(1 ) 1
A i
A
A i A
2 2
1 ... 1 ...2 2
( , ) * *
* *
* *
* *
arg arg
arg arg
td tb cd cb
ud ub td tb
ud ub ts tbs
cd cb cs cb
V V V V
V V V V
V V V V
V V V V
a b
g b
The Unitarity Triangle * * * 0ud ub cd cb td tbV V V V V V
CKMV 4( ) O
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The unitarity triangle is fully specified by any combination of three
sides and/or angles. If we can measure more than three overconstrained test
The unitarity triangle construction clearly illustrated the overconstrained
Standard Model tests that would be made possible with a measurement
of CP-violating quantities in the B meson system, but which triangle?
The top quark mass was not known.
Dib, Dunietz, Gilman and Nir 1989
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The unitarity triangle construction clearly illustrated the overconstrained
Standard Model tests that would be made possible with a measurement
of CP-violating quantities in the B meson system, but which triangle?
The top quark mass was not known.
Dib, Dunietz, Gilman and Nir 1989
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Measuring CP violation at the
The CP asymmetry is
, 0
, 0
:tag
tag
f B B t
B B t
0
( ) ( )
( ) ( )
sin 2 sin( )
CP
f B
f t f tA
f t f t
m t
are produced at the ϒ(4S) in pairs in a coherent L=1 state0 0B B
Decay + mixing
There are four time distributions : , 0
, 0
tag
tag
f B B t
B B t
sin ( ) cos( )d dB BS m t C m t D D D D
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eigenstateCP
f CP0 / , ,....S
J K
i
i
i
Measure the and determine the
dilut
mistag fractions
ions
= 1- 2 w
w
D
Determine the resolution function for D z
e+ e-0
tagB
0
recB(4 )S
0
SK
K
Measure D z between BCP and Btag to determine the
signed time difference D t between the decays
zD
Reconstruct exclusive B decays to
CP eigenstates and flavor eigenstates
and tag the flavor of the other B decay
Select events using, primarily,
leptons and 's from hadronic
decays & determine flavor
tagB
K B
B
Overview of the analysis
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The BABAR Detector
1m
Si Vertex-Tracker, Drift Chamber,
DIRC (Cherenkov), CsI-Calorimeter,
Superconducting Coil, Iron Yoke + RPCs/LSTs
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Measuring CP violation at the (4 )S
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Measuring CP violation at the (4 )S
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An early global CKM Fit
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Lepton/Photon 2001 Rome
(BABAR)
sin2b
Chronology of
sin2b measurements
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A current global CKM Fit Consistency of angles
Consistency of angles and
sides from global fit
o4.4
4.2
o
o10
11
89.0
21.1 0.9
68
a
b
g
o
11
12178
a b g
0.026
0.013
0.013
0.014
CKMFitter: 0.131
0.345
UTFit: 0.132 0.023
0.351 0.014
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Further unitarity triangle tests
CP-violating measurements
Tree-dominated measurements
Loop (mixing)-dominated measurements
All measurements
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BABAR has been a great adventure for
two decades
We produced results on CP violation
that resulted in the 2008 Nobel Prize
for Kobayashi and Maskawa, as well as
more than 540 papers in refereed
journals
Athough data-taking ended in 2008,
significant results are still emerging
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The BABAR adventure
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David Hitlin BABAR and Science Leith Symposium Dec.12, 2014