Transcript CP Violation and David Hitlin Caltech Let’s Celebrate Jonathan July 24, 2008 Babar ™ and © L.

CP Violation
and
David Hitlin
Caltech
Let’s Celebrate Jonathan
July 24, 2008
Babar ™ and © L. De Brunhoff
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Babar ™ and © L. De Brunhoff
David Hitlin
"Let's Celebrate Jonathan"
July 24, 2008
22

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BABAR was a great adventure for two decades, now nearly concluded
This day, devoted to highlighting Jonathan Dorfan’s many contributions, is, of
course, a most appropriate one to look back on BABAR and its accomplishments
Jonathan served as head of the PEP-II project and as BABAR ‘s Technical
Coordinator, succeeding Vera Lüth
 His leadership in these endeavors, as in many others, was characterized by
his skill, drive, understanding of people, deal-making ability and his ability
to keep his eye on the ball
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The latter is perhaps best characterized by the BABAR/PEP-II mantra:
“What is the effect of ……….. on the measurement of sin2b ?”,
where ………….. could be
degree of mode suppression in the RF cavities
gauge of magnet power supply cables
length of the CsI(Tl) crystals
thickness of the drift chamber end plates
or any of a thousand other decisions we had to make
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CP violation and baryogenesis

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The experimental study of CP violation dates back to 1964, when Christensen,
Cronin, Fitch and Turlay discovered that the decays of KL mesons violate CP
invariance by ~2 parts per thousand
In 1967 Andrei Sakharov showed the connection between CP violation and the
dominance of matter over antimatter in the universe
 In the Big Bang there was, by assumption, an equal amount of matter and
antimatter in the universe (i.e., the net baryon number of the universe was
zero), but we now live in a matter universe
 The Sakharov conditions for the disappearance of the antimatter:
 Violation of C and CP symmetry – observed, allowed in the Standard Model


Baryon number-violating interactions - beyond the Standard Model
Departure from thermal equilibrium (an “arrow of time”) - inflation
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Perils of Modern Living
Harold P. Furth
Well up above the tropostrata
There is a region stark and stellar
Where, on a streak of anti-matter
Lived Dr Edward Anti-Teller.
Remote from Fusion's origin,
He lived unguessed and unawares
With all his antikith and kin,
And kept macassars on his chairs.
One morning, idling by the sea,
He spied a tin of monstrous girth
That bore three letters: A. E. C.
Out stepped a visitor from Earth.
ERDA
DOE
Then, shouting gladly o'er the sands,
Met two who in their alien ways
Were like as gentils. Their right hands
Clasped, and the rest was gamma rays.
The New Yorker, 1955
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CP violation and baryogenesis

The annihilation of matter and antimatter in the very early universe was nearly
complete: only a tiny fraction of the baryons escaped annihilation:
 A quantitative measure of the process at early times is provided by the
ratio of baryons to relic photons in the cosmic microwave background
nbaryons/nphotons = (5.1 +0.3-0.2)x10 –10


The baryons that escaped annihilation were those that could not find a an
antiparticle partner, the partner having preferentially decayed due to
CP violation in the weak interaction
However, the expected Standard Model scale of CP violation is far too small
to produce this many baryons. At best, the Standard Model can produce
nbaryons/nphotons ~ 10 –20

Getting a clear handle on the precise strength of CP violation in KL decay
was hard
 because KL mesons are so light, it is difficult to connect the CP asymmetry
measured at the meson level with the underlying strength at the quark
level
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The situation in the mid ’80’s
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In 1981 Bigi and Sanda showed that a measurement of CP violation in B0
meson decay to CP eigenstates could be clearly interpreted, without
theoretical uncertainties.
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 contemplate
measuring 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, at least 107-108 B pairs would be needed, a 2-3 order of magnitude
increase in the existing data sample
Exploiting the quantum correlations of B B 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
0
0
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The Gold Rush

This led to at least 21 e+e- B Factory concepts and proposals (19 ϒ(4S) + 2 Z0)
and several hadronic machine approaches (HERA-B, …….)
ϒ(4S) Storage Rings
ϒ(4S) Recirculating
Linear Collider
Z Factory
Z 0  bb
Symmetric
Asymmetric
ϒ(4S) Linac-Ring
Collider
PSI (2)
APIARY
Grosse-Wiesmann
Amaldi/Coignet
SLC
Novosibirsk
CITAR
JLAB
ARES
LEP
KEK accumulator
PETRA-II
UCLA
CESR Plus
PEP-II
TBA
ISR Tunnel
KEK
accumulator
KEK-B
CESR-B


Oddone’s concept of using an asymmetric e+e- collider to boost the
distance between the two decay vertices o an measurable regime was, in
the end, the most successful approach
Two colliders, PEP-II and KEKB, were ultimately built
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The
resonances in e+e- annihilation: non-relativistic bb atomic systems
The  (4S ) decays to
B0 B0 , B+ B- in a
coherent L=1 state
Mϒ(4s) = 10.5794 + 0.0012 GeV
G
(4s)
= 20.5 + 2.5 MeV
A practical application of EPR
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1010
Motivation for B0 meson CP Violation measurements
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
Since CP violation is a necessary ingredient to produce a baryon asymmetry,
and since the theoretical strength of CP violation in the three generation
Standard Model is numerically insufficient to produce the observed
asymmetry, it was hoped that a measurement of a CP-violating asymmetry
that could be unambiguously related to the Standard Model CP phase would
produce a surprise
The result was that the Standard Model phase produces exactly the needed
amount of CP violation for B meson decays to pass the overconstrained
Unitarity Triangle tests
 Thus at this point, experimentally the Standard Model does not have the
strength of CP violation to produce the observed baryon asymmetry
 How do we measure the strength of CP violation in the Standard Model?
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The B Unitarity Triangle

The CKM matrix describing the transitions among the three quark
generations is unitary
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There are six unitarity relations
The most useful unitarity condition is:
Bd0 ® p + p - b ® uud
VudVub*
*
*
V
V
Vcdub cb
Bs0 ® r KS0


*
*
VudVub
VcdVcb
VtdVtb*  0
VtdVtb*
VcdtdVcb*
V
b ® ddd
b ® ccs Bd0 ® J /y KS0
1V |
|
V
cd are
cb determined by
The sides of the unitarity triangle
measurements of the magnitudes of CKM matrix elements
CP-violating asymmetries in B0 decays to CP eigenstates measure
the angles of the unitarity triangle, thereby providing an
overconstrained situation and thereby a unique test of the
Standard Model in the CKM sector
æ VtdVtb* ö
÷
a º arg ç
÷
ç
* ÷
ç
è VudVub ø
æ VcdVcb* ö
÷
b º arg ç
÷
ç
* ÷
ç
è VtdVtb ø
æ VudVub* ö
÷
g º arg ç
÷
ç
* ÷
ç
è VcdVcb ø
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July 24, 2008
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Interference between B0  J/y KS0 (b  ccs) and B 0  J/y K S0 (b  ccs )
decays allows determination of sin2
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To measure a phase, you need interference of two amplitudes
CP violation can arise due to interference between two amplitudes with
different phases - a weak phase f that changes sign under CP and
a strong phase d that is invariant under CP
A1 = | A1| e
i
i
.
1
e
i
1
CP
f
A2 = | A2| e i 2 e i
A1 = | A1| e i 1 e - i
i
f
A2 = | A2| e i 2 e - i
2
P(i  f )  A1  A2
1
2
2
P(i  f )  P( i  f )  4 A1 A2 sin(1   2 )sin(1  2 )
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The Unitarity Triangle in 1990
Dib, Dunietz, Gilman and Nir, Phys.Rev D41, 1522 (1990)
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Overview of the analysis
Reconstruct exclusive B decays to
CP eigenstates and flavor eigenstates
and tag the flavor of the other B decay


J /y
U (4S )
e-
e+
0
Brec
K

0
S

0
Btag
Select BCP candidates
 z
K
( B 0  J / y K S0 , etc.)
Select Btag events using, primarily,
and Bflav candidates
leptons and K's from B hadronic
decays & determine B flavor
(B
0
 D*- p + , etc.)
Measure the mistag fractions wi and determine the
dilutions Di = 1- 2 wi
Measure Dz between BCP and Btag to determine the
signed time difference Dt between the decays
Determine the resolution function for Dz
i= 3
fi
R(t ; aˆ ) = å
exp(- (t -  i ) 2 ) / 2 i2
i= 1 s
2p
i
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USA
[36/253]
California Institute of Technology
UC, Irvine
UC, Los Angeles
UC, San Diego
UC, Santa Barbara
UC, Santa Cruz
U of Cincinnati
U of Colorado
Colorado State
Elon College
Florida A&M
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
Ohio State U
U of Oregon
U of Pennsylvania
Prairie View A&M
Princeton
SLAC
U of South Carolina
Stanford U
U of Texas at Austin
U of Texas at Dallas
Vanderbilt
U of Wisconsin
Yale
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David Hitlin
Italy
The BABAR Collaboration
10 Countries
73 Institutions
521 Physicists
Canada
[4/15]
U of British Columbia
McGill U
U de Montréal
U of Victoria
China
[1/5]
Inst. of High Energy Physics, Beijing
France
[5/51]
LAPP, Annecy
LAL Orsay
LPNHE des Universités Paris 6/7
Ecole Polytechnique
CEA, DAPNIA, CE-Saclay
Germany
[3/23]
U Rostock
Ruhr U Bochum
Technische U Dresden
"Let's Celebrate Jonathan"
[12/89]
INFN, Bari
INFN, Ferrara
Lab. Nazionali di Frascati dell' INFN
INFN, Genova
INFN, Milano
INFN, Napoli
INFN, Padova
INFN, Pavia
INF, Pisa
INFNN, Roma and U "La Sapienza"
INFN, Torino
INFN, Trieste
The Netherlands [1/5]
NIKHEF
Norway
[1/2]
U of Bergen
Russia
[1/7]
Budker Institute, Novosibirsk
United Kingdom [10/71]
U of Birmingham
U of Bristol
Brunel University
U of Edinburgh
U of Liverpool
Imperial College
Queen Mary & Westfield College
Royal Holloway, University of London
U of Manchester
Rutherford Appleton Laboratory
July 24, 2008
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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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July 24, 2008
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The PEP-II Asymmetric B Factory
Final collisions
12:43pm,Monday 7 Apr 2008
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July 24, 2008
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19
The need for speed
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July 24, 2008
2020
A tagged B0  J / y K S0 event
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



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BABAR employed blind analysis and
sophisticated maximum likelihood techniques
to extract maximum information from the data
in an unbiased manner
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David Hitlin
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July 24, 2008
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sin2b in charmonium modes
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July 24, 2008
2323
Measuring the Unitarity Triangle angles
sin 2 
B  J / y K S0 , y (2S ) K S0 , J / y K L0 ,  c1K S0 , c K S0 , J / y K *0
b  ccs
B  J / y  0 , D  D  , D* D , D* D*
b  ccd with penguin :
D (*)0 h0 ( D 0  CP )
cos 2 , sin 2 
B  J / y K *0 with angular analysis
D (*)0 h0 ( D 0  K S0   ) with Dalitz plot analysis
sin (2   )
B  D (*)  , D    , D (*) K 0
sin 2
B     ,  0  0 with isospin analysis,    0 with time-dependent Dalitz plot analysis

B  D (*) K (*) use e.g ., interference between b  cus and b  ucs decays
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July 24, 2008
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sin2a and g
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2525
Unitarity triangle constraints: sin2, sin2 measurements
The CKM matrix passes
the unique, new
overconstrained tests
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David Hitlin
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July 24, 2008
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The Unitarity Triangle deconstructed

Without
All measurements except
sin2bsin2b
Mixing
Loop (mixing)-dominated measurements
Tree level
Tree-dominated measurements
Loop dominated
CP-violating measurements
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July 24, 2008
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It may not be quite so simple……
• There are discrepancies
in CP
_
asymmetries in bsss loop decays
• There are other hints that there could
be additional phases, i.e., that there is
more in the flavor sector than the three
generation Standard Model
• Four generations can amplify the
baryogenesis effect to the needed
level: Hou (arXiv:0803.1234 [hep-ph] )
and can explain the various anomalies
seen:
Soni, Alok, Giri, Mohanta and Nandi
(arXiv:0807.1971 [hep-ph] )
SuperB, with a 100x larger data sample,
will resolve these issues, and allow us to
understand the flavor sector of
New Physics found at LHC
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The bottom line
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BABAR has tested the Standard Model in unique ways by finding and then
deeply exploring CP violation in the B meson system
BABAR has also done lots of physics beyond CP violation:
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Many other B decay studies, including other hadronic, leptonic and semileptonic
decays and rare loop-dominated processes
0 0
Weak decays of charm, including long sought evidence for D D mixing
t decays
New hadronic states, some unexplained in QCD
And just recently, the discovery of the hb, the ground state of the bb system
as of last week, 324 publications in refereed journals: PRL, PRD, NIM
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