November 2001CP Violation at Belle Observation of CP Violation at Belle HEP Seminar Brookhaven...
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Transcript of November 2001CP Violation at Belle Observation of CP Violation at Belle HEP Seminar Brookhaven...
November 2001 CP Violation at Belle
Observation of CP Violation at Belle
HEP Seminar
Brookhaven National Lab
Daniel Marlow
Princeton University
November 8, 2001
November 2001 CP Violation at Belle
Talk Outline
• Introduction/Review (with apologies to the experts)
• The KEK-B Collider• The Belle Detector• Indirect CP Violation Measurement/Analysis• Conclusions
November 2001 CP Violation at Belle
Physics MotivationDirect CP violation is perhaps the simplest case. Consider the CP mirror processes:
))(
))(
fBfB
fBfBACP
fBfB and
The CP asymmetry is defined as
The decay amplitudes are
and SWSW iiff
iiff eeAAeeAA
Note that the weak phase changes sign.
November 2001 CP Violation at Belle
Direct CP Violation
Note that
Yielding
22
ffff AA
221121
SWSW iiii
f eeAeeAA
221121
SWSW iiii
f eeAeeAA
We need some sort of interference, two amplitudes, for example
)cos( 2 21
2
2
2
1 SWf AAAA
)cos( 2 21
2
2
2
1 SWf AAAA
November 2001 CP Violation at Belle
Direct CP Violation
Despite its conceptual and experimental simplicity, there are two problems with direct CP violation:
• Cases where there are two comparable amplitudes that are large are (probably) rare.
• The strong phases are poorly understood, making it difficult to extract the weak (KM) phases that are of greatest interest.
One is thus led in the direction of asymmetric e+e- B factories aimed at the study of indirect CP violation.
November 2001 CP Violation at Belle
Indirect CP Violation
022
02
(0 sincos)( BeiBetB mimtmtimi
In this approach we provide the interference using state mixing, i.e.,
00BB
November 2001 CP Violation at Belle
Indirect CP ViolationThus for a decay where is a CP eigenstate, we have two “indistinguishable” decay paths
fB 0
f0B0B f
Working through the algebra, yields a time-dependent CP asymmetry )(2sin)sin(
)()(
)()()(
00
00
DMf
CP
tm
fBfB
fBfBtA
M DWhere and are the weak phases for the mixing and decay diagrams, respectively and
1
f
f ffCP
November 2001 CP Violation at Belle
The Kobayashi-Maskawa Mixing Scheme
Where the second matrix is the Wolfenstein parameterization.
0* tbubtsustdud VVVVVV
Quark mixing is described via
The “d b” unitarity relation yields 3* AVV ubtd
1)1(
21
)(21
23
22
32
AiA
A
iA
VVV
VVV
VVV
M
tbtstd
cbcscd
ubusud
November 2001 CP Violation at Belle
CP Phases in the Gold-Plated Mode
0DSKJB /0
)arg( tdM V
Decay
Mixing
The KM phase comes from the mixing.
November 2001 CP Violation at Belle
The Unitarity Triangle
3A
Vtd
,
0,1
3A
Vub
3
*
A
VV tsus
1
2
3
The gold-plated mode determines the angle which is also called .
1
1 tbud VV
November 2001 CP Violation at Belle
Constraints
November 2001 CP Violation at Belle
Existing Constraints
Höcker et al. hepex/0104062
Eur.Phys.J. C21 (2001) 225-259
sin2 results are average prior to July 2001. They are not included in the fit.
November 2001 CP Violation at Belle
The Measurement
0B
0B
tag
CP
z
0DNeed to:
•Measure momenta
•ID leptons & K’s
•Measure vertices
e e
0K
/J
November 2001 CP Violation at Belle
B0B0
SKJB /0
The MeasurementThe time-dependent asymmetry appears mainly as a mean shift in the distribution between events tagged
as decays and
events tagged as
decays.
z
0B0B
1
00
00
2sin)sin(
)()(
)()()(
tm
fBfB
fBfBtACP
November 2001 CP Violation at Belle
The KEKB Asymmetric e+e- Collider
KEKB is similar to PEP-II in many ways, although there is an important difference in the way in which the beams are brought into collision.
ee
November 2001 CP Violation at Belle
KEK B Asymmetric Collider
•Two separate rings
e+ (LER) : 3.5 GeV
e (HER) : 8.0 GeV
•ECM : 10.58 GeV at (4S)
•Luminosity
•target: 1034 cm-2s-1
•achieved:5.2x1033cm-2s-1
•±11 mrad crossing angle •Small beam sizes:
y 3 m; x 100 m
asymmetric e+e collider
November 2001 CP Violation at Belle
Beam Crossing Schemes
By colliding the beams at an angle, the KEK-B design achieves a simplified interaction region.
Moreover, every RF bucket (2 ns spacing) can be filled toachieve maximum luminosity. However, this approach risks destabilizing couplings between transverse and longitudinal modes of the machines.
A crab-crossing cavity is under development in case this proves to be a problem.
November 2001 CP Violation at Belle
Machine Performance
Reported here
Summer ’01 shutdown
Integrated/day
Total Integrated
November 2001 CP Violation at Belle Typical~good day.
November 2001 CP Violation at Belle
Another Typical Day
This is probably a bit worse than usual.
November 2001 CP Violation at Belle
KEKB/PEP II Luminosity Bakeoff
KEKB PEP-II
Peak
Shift 92.8 pb-1 103.2 pb-1
24 hour 277 pb-1 291 pb-1
7 day 1661 pb-11865 pb-1
Integrated 37.6 fb-1 59.6 fb-1
1233 scm 102.5 1233 scm 103.4
As of ~November 5, 2001 Comparisons not quite apples to apples.
November 2001 CP Violation at Belle
KEKB Future Prospects• Chief limitation recently has been the photo-electron instability in the LER.
• This has been reduced, although not fully mitigated by installing a solenoidal winding around much of the beam pipe (last ~500 m this summer).
• Past history has shown that the situation slowly improves, in a manner consistent with a reduction in quantum efficiency of the beam-pipe wall brought that is reminiscent of “scrubbing.”
• If that is the case, we can expect additional modest gains in luminosity, but it is hard to know.
November 2001 CP Violation at Belle
November 2001 CP Violation at Belle
An international collaboration involving about 10 Countries, 50 Institutes, & 250 People
The BELLE Collaboration
November 2001 CP Violation at Belle
Detector Performance Silicon Vertex Detector
~55m for 1GeV/c @ 90o
Central Drift Chamber p/p ~ 0.35% @ 1GeV/c (dE/dx) ~7
K id up to plab=3.5 GeV/c TOF (95 ps) Aerogel (n = 1.01 ~ 1.03)
, e with CsI crystals E/E ~ 1.5% @ 1GeV
KL and with KLM (RPCs) : effic. > 90% ; ~2% fakes
November 2001 CP Violation at Belle
)(GeV/ 2cM
2eff MeV/ 6.4 c
0SK
Mass Reconstruction
Belle
November 2001 CP Violation at Belle
CsI EM Calorimeter Performance
MeV 50E
tionReconstruc 0
tionReconstruc
November 2001 CP Violation at Belle
Vertex Detector
~55m for 1GeV/c @ 90o
Occupancy at present luminosity ~4%
Upgraded SVD coming:
• 4 layers
• Radiation hard
• Level 1 trigger
• Summer ’02 installation Excl. mode B lifetime
November 2001 CP Violation at Belle
Belle: ToF & Aerogel
The ToF has a resolution of =100 ps, which provides /K separation up to about 1.2 GeV/c, at which point the ACC array kicks in. The index of refraction of the counters varies as a function of angle, reflecting the boosted CM.
November 2001 CP Violation at Belle
Belle: Aerogel
Barrel Module
November 2001 CP Violation at Belle
Particle ID (dE/dx, ToF, & Aerogel)
0DD K
November 2001 CP Violation at Belle
PID Bake Off
BaBar Belle
Looks like BaBar does better.
November 2001 CP Violation at Belle
Muon Identification
side- tagplus
/
K
KJB
Muons are important for the same reason. They are identified by the way in which they penetrate the iron return yoke of the magnet.
The gaps are instrumented with RPCs.
November 2001 CP Violation at Belle
Putting it all together
SKJB /0
November 2001 CP Violation at Belle
Analysis Flowchart
November 2001 CP Violation at Belle
CP Mode Sample
November 2001 CP Violation at Belle
J/ Reconstruction
• Require one lepton to be positively identified and the other to be consistent with lepton hypothesis.
• For e+e-, add any photon within .05 of electron direction.
November 2001 CP Violation at Belle
B Reconstruction
*beam
*cand EEE
2
cand
2*beam
pEmbc
November 2001 CP Violation at Belle
Other Modes
Mbc
Total events = 76Bkgd 9 evts (12%)
000 ;/ SS KKJB
November 2001 CP Violation at Belle
’ Modes
Both leptons tagged.
November 2001 CP Violation at Belle
Other Charmonium Modes
M(ll) M(ll)
1st observationof inclusiveB c2 X
c2
c1
November 2001 CP Violation at Belle
CP Even Mode (BJ/KL) Reconstruction
KL hits
KL
LKJB /0• Assume (2-body) kinematics.
• Look for KL recoiling from J/
• hits in RPCs
• cluster in ECL
• Remove positively tagged background modes: J/K+ , J/K* , etc.
• Plot
LKJB /0
**/
*
LKJB ppp
November 2001 CP Violation at Belle
0LK Detection
LKP
missP
hi
iS PPP,
4miss
Inclusive “KL’s”
November 2001 CP Violation at Belle
BJ/KL Reconstruction
**/
*
LKJB ppp
61% signal purity
November 2001 CP Violation at Belle
CP Mode Summary
November 2001 CP Violation at Belle
Flavor Tagging
We need to know the flavor of the spectator B0.
• Track level tags
• High momentum leptons
• Medium momentum K
• High-momentum (from e.g., )
• Low-momentum (from D*’s).
• Need to take into account multiple tags and correlations.
(*)0 DB
November 2001 CP Violation at Belle
Flavor Tagging
yreliabilit tag 10 ;1 rq
November 2001 CP Violation at Belle
Flavor Tagging
rq
Data
Monte Carlo
*0 DB
November 2001 CP Violation at Belle
Flavor TaggingTwo measures of tagging performance:
• = efficiency
• w = wrong-tag fraction
Amplitude of mixing oscillation depends on w
)21( w
01.027.0eff
November 2001 CP Violation at Belle
Vertexing
0B
0B
tag
CP
z
0D
e e
0K
/J
Reality
Cartoon
The B lifetime is of the same order as the vertex resolution, so the effect is quite subtle.
November 2001 CP Violation at Belle
Vertexing
• Common track requirements– # of associated SVD hits > 2– Use run-dependent IP
• For CP-side, use J/l+l- tracks– Reject poorly fit events.
• For Tag-side, use tracks with:– |z|<1.8mm, |z|<500 m, |r|<500 m– Iterate: discard worst track until fit is acceptable.
• Require |zCP - ztag|<2 mm (10B)
November 2001 CP Violation at Belle
Test of Vertex Resolution0*0 / KJB
November 2001 CP Violation at Belle
Fit to Lifetime
*DB
(ps) t
ps 03.064.1
ps 02.055.10
B
B
November 2001 CP Violation at Belle
Fitting
)()'( sigsig tRttPLi )1( bgf
bgbgbg )()'( ftRttP
)sin(2sin)21(12
)( 1
/
sig tmwqe
tP fB
t B
Signal
)()1(2
)(/
bkg tfe
ftPbg
t bg
Background
Response function
November 2001 CP Violation at Belle
Fitting
November 2001 CP Violation at Belle
The Data
The first order effect is a mean shift between positively and negatively tagged samples.
November 2001 CP Violation at Belle
The Fitted Result
06.014.099.02sin 1
PRL 87, 091802 (2001)
November 2001 CP Violation at Belle
Sources of Systematic ErrorVertex algorithm 0.04
Flavor tagging 0.03
Resolution function 0.02
KL background fraction 0.02
Background shapes 0.01
md and B0 errors 0.01
Total 0.06
November 2001 CP Violation at Belle
Time-Dependent Asymmetry
One can plot the excess/deficit on a bin-by-bin basis.
First we start with a non-CP sample to look for false asymmetries.
November 2001 CP Violation at Belle
Subsample Dependence
November 2001 CP Violation at Belle
Subsample Dependence
November 2001 CP Violation at Belle
Comparison to other sin21 Measurements
It looks like CDF had it right!
November 2001 CP Violation at Belle
Comparison to Other CKM Results
BaBar
November 2001 CP Violation at Belle
Future Prospects
Oide
2.0)2(sin 2
November 2001 CP Violation at Belle
Conclusions
• CP violation in the B system has been observed at the level.
• Our data are consistent with the SM.
•The KEKB accelerator is working very well and continues to improve.
• There will be lots of good physics to come.
06.014.099.02sin 1
November 2001 CP Violation at Belle
Additional Slides
November 2001 CP Violation at Belle
Two Pseudoscalar Modes
November 2001 CP Violation at Belle
What if ||1 ?
If |λ| is allowed to float, (i.e. a cos(Δm t) term)
14.099.02sin 1 The CPV asymmetry is unchanged.
09.003.1
In general we have
Note: if ||1, then the gold-plated mode isn’t really gold plated.
November 2001 CP Violation at Belle
KL Details
•Two classes: KLM+ECL and ECL only
(397 and 172 entries, respectively)
Fitted yield is 346 events.
• Background composition: 71% non-CP modes.
The remainder is ψKLπ0(13%), ψKs(10%) which
are both CP=-1 and 5%(ψK, χc1Ks, ψπ0) which
are CP=+1.
• pB* background shape is used to find bkg level.
November 2001 CP Violation at Belle
(*)KB613.0 40.0
0.14- 32.0 10)99.0(
)(
KBB
CL 90% 101.3
)(6
*
KBB
CL 90% 103.1
)(6
eeKBB
CL 90% 106.5
)(6
*
eeKBB
November 2001 CP Violation at Belle
Particle ID (dE/dx, ToF, & Aerogel)