Transcript Slide 1

Why BaBar Was Built
• PEP-II and BaBar were designed to study CP violation (CPV) in
B-meson decay, especially time-dependent CPV.
• CPV emerges from the quantum mechanical interference of
multiple amplitudes contributing to the same final state; it
requires a complex relative phase between the amplitudes.
• In the Standard Model of particle physics, the KobayashiMaskawa (KM) phase is responsible for all CPV. Prior to
BaBar, CPV had been observed in kaon and hyperon decays.
• CPV naturally probes physics at the electro-weak scale,
including physics Beyond the Standard Model (BSM), also
called New Physics (NP).
• Goals:
(1) test the KM phase as a source of CPV in Bmeson decay.
(2) test the KM phase as the source of CPV in Bmeson decay.
SLUO Annual Meeting
Michael D Sokoloff
1
Weak Charged Current Interactions
neutrino scattering
charm decay
f
g
~
f~
f
As a first approximation, the weak charged current
interaction couples fermions of the same generation.
The Standard Model explains couplings between quark
generations in terms of the Cabibbo-KobayashiMaskawa (CKM) matrix.
SLUO Annual Meeting
Michael D Sokoloff
2
Weak Phases in the Standard Model
b = f1; a = f2; g = f3
SLUO Annual Meeting
Michael D Sokoloff
3
BaBar Detector
All subsystems
crucial for CPV
analysis
SVT:
97% efficiency, 15 mm z hit resolution
(inner layers, transverse tracks)
SVT+DCH: (pT)/pT = 0.13 %  pT + 0.45 %
DIRC:
K- separation 4.2  @ 3.0 GeV/c  2.5  @ 4.0 GeV/c
EMC:
E/E = 2.3 %E-1/4  1.9 %
SLUO Annual Meeting
Michael D Sokoloff
4
Time-Dependent CPV at the (4S) Resonance
e+e-  (4S)  B B
m-
Boost: bg = 0.55
e-
-
K
Btag
(4S)
Flavor tag and
vertex
reconstruction
e+
B0
B
KS
0
Coherent L=1 state
t 
z
bg c
m-
Brec

+
-
z
m
+
Exclusive B meson and vertex
reconstruction
Start the Clock
Stop the Clock
SLUO Annual Meeting
Michael D Sokoloff
5
sin(2b) Fit Results from J/YKS, etc.
Summer 2002
hf =-1
hf =+1
sin2b = 0.755  0.074
sin2b = 0.723  0.158
sin2b = 0.741  0.067 (stat)  0.034 (sys) with
|lf| = 0.948  0.051 (stat)  0.017 (syst)
Sf = 0.759  0.074 (stat)  0.032 (syst)
SLUO Annual Meeting
Michael D Sokoloff
|l f | = 1
}h
f
=-1
6
The CKM Matrix Today
SLUO Annual Meeting
Michael D Sokoloff
7
The 2008 Nobel Prize in Physics
•
“The broken symmetries described by Makoto
Kobayashi and Toshihide Maskawa … seem to
have existed in nature since the very beginning
of the universe and came as a complete surprise
when they first appeared in particle experiments
in 1964. It is only in recent years that
scientists have come to fully confirm the
explanations that Kobayashi and Maskawa made
in 1972. It is for this work that they are now
awarded the Nobel Prize in Physics. They
explained broken symmetry within the framework
of the Standard Model, but required that the
Model be extended to three families of quarks.
These predicted, hypothetical new quarks have
recently appeared in physics experiments. As
late as 2001, the two particle detectors BaBar
at Stanford, USA and Belle at Tsukuba, Japan,
both detected broken symmetries independently
of each other. The results were exactly as
Kobayashi and Maskawa had predicted almost
three decades earlier.”
SLUO Annual Meeting
Michael D Sokoloff
8
2010 Dirac Medal
The 2010 Dirac Medal and Prize are awarded to
Nicola Cabibbo (University La Sapienza, Rome,
Italy) and Ennackal Chandy George Sudarshan
(University of Texas, Austin, Texas, USA) in
recognition of their fundamental contributions to
the understanding of weak interactions and other
aspects of theoretical physics.
Cabibbo’s important contributions to theoretical
physics include the recognition of the
significance of mixing in weak interactions, which
has established the existence of a new class of
physical constants, whose first example is the
Cabibbo angle. This angle determines the mixing
of strange quarks with non-strange quarks and
has been measured experimentally. With the
discovery of a third family of quarks and leptons,
quark mixing led to the understanding of the
phenomenon of CP violation.
SLUO Annual Meeting
Michael D Sokoloff
9
Discovery of Narrow DSJ States (2003)
[primary decay modes do not conserve isospin]
SLUO Annual Meeting
Michael D Sokoloff
10
The Y(4260): Not Anticipated, Still Not Understood
SLUO Annual Meeting
Michael D Sokoloff
11
Charm Mixing
Time-Evolution of D0K Decays
RS = CF
WS = DCS
DCS and mixing amplitudes
interfere to give a “quadratic”
WS decay rate (x, y << 1):
DCS
K+
D0
-
D0
where
and is the phase difference between DCS and CF
decays.
SLUO Annual Meeting
Michael D Sokoloff
12
Simplified Fit Strategy & Validation (2007)
Rate of WS events clearly increases with time:
WS/RS (%)
(stat. only)
SLUO Annual Meeting
Michael D Sokoloff
13
Simplified Fit Strategy & Validation (2007)
Rate of WS events clearly increases with time:
WS/RS (%)
(stat. only)
Inconsistent
with no-mixing
hypothesis:
2=24
SLUO Annual Meeting
Michael D Sokoloff
14
Simplified Fit Strategy & Validation (2007)
Rate of WS events clearly increases with time:
WS/RS (%)
(stat. only)
SLUO Annual Meeting
Consistent with
prediction from
full likelihood fit
2
Inconsistent
with no-mixing
hypothesis:
2=24
Michael D Sokoloff
15
=
Time-Dependence in D0 → KSπ+π-
box size is “capped” linear
box size is logarithmic
These plots illustrate the average decay time as a function of
position in the Dalitz plot for (x,y) = (0.8%, 0.3%). The sizes
of the boxes reflect the number of entries, and the colors
reflect the average decay time.
SLUO Annual Meeting
Michael D Sokoloff
16
Charm Mixing Today
SLUO Annual Meeting
Michael D Sokoloff
17
Discovery of the hb [2008]
SLUO Annual Meeting
Michael D Sokoloff
18
Hard scattering amplitude
for ggqq transition
which is calculable
in pQCD
Nonperturbative meson
distribution amplitude
describing the transition
P  qq
x: fraction of the meson momentum carried by one quark in the infinite momentum frame
SLUO Annual Meeting
Michael D Sokoloff
19
BaBar for Bean-Counters
SLUO Annual Meeting
Michael D Sokoloff
20
The Beauty of SuperB
SLUO Annual Meeting
Michael D Sokoloff
21
The Charm of SuperB
480 fb-1
SLUO Annual Meeting
75 ab-1
Michael D Sokoloff
22
The Charm of SuperB
480 fb-1
SLUO Annual Meeting
75 ab-1
Michael D Sokoloff
Based on material found
in the SuperB Progress
Report: Physics
arXiv:1008.1541v1
(August 2010)
23
Possible LFV in the MSSM at SuperB
Material extracted from the
SuperB Progress Report: Physics
arXiv:1008.1541v1 (August 2010)
SLUO Annual Meeting
Michael D Sokoloff
24