Observation of CP Violation at Belle - Princeton …marlow/talks/bnl/bnl2.pdfNovember 2001 CP...
Transcript of Observation of CP Violation at Belle - Princeton …marlow/talks/bnl/bnl2.pdfNovember 2001 CP...
November 2001 CP Violation at Belle
Observation of CP Violation at Belle
HEP SeminarBrookhaven National Lab
Daniel Marlow Princeton UniversityNovember 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:
))())(
fBfBfBfBACP →(Γ+→Γ
→(Γ−→Γ≡
fBfB →→ and The CP asymmetry is defined as
The decay amplitudes are
and SWSW iiff
iiff eeAAeeAA φφφφ −==
Note that the weak phase changes sign.
November 2001 CP Violation at Belle
Direct CP ViolationNote that
Yielding
22
ffff AA Γ=Γ⇒=
221121
SWSW iiiif eeAeeAA φφφφ
+=
221121
SWSW iiii
f eeAeeAA φφφφ −−+=
We need some sort of interference, two amplitudes, for example
)cos( 2 212
22
1 SWf AAAA φφ ∆+∆++=Γ
)cos( 2 212
22
1 SWf AAAA φφ ∆−∆++=Γ
November 2001 CP Violation at Belle
Direct CP ViolationDespite 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 φ−∆∆)/2Γ−− +×=
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
tmfBfBfBfBtA
φφη +∆∆−=→Γ+→Γ→Γ−→Γ=∆
Mφ DφWhere and are the weak phases for the mixing and decay diagrams, respectively and 1 ±=
=
f
f ffCPη
η
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* λAVV ubtd ≈+
−−−−−
−−≅
=
1)1(21
)(21
23
22
32
ληρλλλλ
ηρλλλ
AiAA
iA
VVVVVVVVV
M
tbtstd
cbcscd
ubusud
November 2001 CP Violation at Belle
CP Phases in the Gold-Plated Mode
0≈DφSKJB /0 Ψ→
)arg( tdM V≈φ
Decay
Mixing
The KM phase comes from the mixing.
November 2001 CP Violation at Belle
The Unitarity Triangle
η
ρ
3λAVtd
( )ηρ,
( )0,1
3λAVub
∗
3
*
λAVV tsus
1φ
2φ
3φ
The gold-plated mode determines the angle which is also called .
1φ
β
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
sin2β results are average prior to July 2001. They are notincluded in the fit.
November 2001 CP Violation at Belle
The Measurement
0B
+µ−µ
0B
+µtag
CP
z∆
0DNeed to:
•Measure momenta
•ID leptons & K’s
•Measure vertices
−e +e
0K
Ψ/J
November 2001 CP Violation at Belle
B0 B0
SKJB Ψ→ /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( )()()()()(
ϕtmfBfBfBfBtACP
∆∆−=→Γ+→Γ→Γ−→Γ=∆
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 ringse+ (LER) : 3.5 GeVe−−−− (HER) : 8.0 GeV
•ECM : 10.58 GeV at ΥΥΥΥ(4S)•Luminosity
•target: 1034 cm-2s-1
•achieved:5.2x1033cm-2s-1
•±11 mrad crossing angle •Small beam sizes:
σσσσy ≈≈≈≈3 µµµµm; σσσσx ≈≈≈≈ 100 µµµµm
asymmetric e+e−−−− collider
November 2001 CP Violation at Belle
Beam Crossing SchemesBy 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
1865 pb-11661 pb-17 day
59.6 fb-137.6 fb-1Integrated
291 pb-1277 pb-124 hour
103.2 pb-192.8 pb-1Shift
Peak
PEP-IIKEKB
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
! σ ~ 55µm for 1GeV/c @ 90o
! Central Drift Chamber ! σp/p ~ 0.35% @ 1GeV/c! σπ (dE/dx) ~ 7%
! K± id up to plab=3.5 GeV/c! TOF (σ ∼ 95 ps)! Aerogel (n = 1.01 ~ 1.03)
! γ, e± with CsI crystals! σE/Eγ ~ 1.5% @ 1GeV
! KL and µ± with KLM (RPCs)! µ± : effic. > 90% ; ~2% fakes
November 2001 CP Violation at Belle
)(GeV/ 2cM −+ππ
2eff MeV/ 6.4 c=σ
−+→ ππ0SK
Mass Reconstruction
Belle
November 2001 CP Violation at Belle
CsI EM Calorimeter Performance
MeV 50>γE
tionReconstruc 0π
tionReconstruc γγη →
November 2001 CP Violation at Belle
Vertex Detector
σ ~ 55µm 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 σ=100 ps, which provides π/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)
++∗ → π0DD+−→ πK
November 2001 CP Violation at Belle
PID Bake Off
BaBar Belle
Looks like BaBar does better.
November 2001 CP Violation at Belle
Muon Identification
µµµ
side- tagplus
/+−+
++
→
Ψ→
KKJB
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
( )( )−+−+→Ψ→ ππµµSKJB /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/Ψ 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 ;/ ππ→Ψ→ SS KKJB
November 2001 CP Violation at Belle
Ψ’ Modes
Both leptons tagged.
November 2001 CP Violation at Belle
Other Charmonium Modes
M(l++++l−−−−γγγγ) −−−− M(l++++l−−−−)
1st observationof inclusiveB→→→→ χχχχc2 X
χχχχc2
χχχχc1
November 2001 CP Violation at Belle
CP Even Mode (B→J/ΨKL) Reconstruction
KL hits
KL
LKJB Ψ→ /0• Assume(2-body) kinematics.
• Look for KL recoiling from J/ψ
• hits in RPCs
• cluster in ECL
• Remove positively tagged background modes: J/ψK+ , J/ψK* , etc.
• Plot
LKJB Ψ→ /0
**/
*LKJB ppp += Ψ
November 2001 CP Violation at Belle
0LK Detection
Θ
LKP
missP
∑± =
−=hi
iS PPP,
4missγ
Inclusive “KL’s”
November 2001 CP Violation at Belle
B→J/ΨKL Reconstruction
**/
*LKJB ppp += Ψ
61% signal purity
November 2001 CP Violation at Belle
CP Mode Summary
November 2001 CP Violation at Belle
Flavor TaggingWe need to know the flavor of the spectator B0.
• Track level tags
• High momentum leptons
• Medium momentum K±
• High-momentum π± (from e.g., )
• Low-momentum π± (from D*’s).
• Need to take into account multiple tags and correlations.
+−→ π(*)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
ν±→ "#*0 DB
November 2001 CP Violation at Belle
Flavor TaggingTwo measures of tagging performance:
• ε = efficiency
• w = wrong-tag fraction
Amplitude of mixing oscillation depends on w
)21( w−01.027.0eff ±=ε
November 2001 CP Violation at Belle
Vertexing
0B
+µ−µ
0B
+µtag
CP
z∆
0D−e +e
0K
Ψ/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/ψ"l+l- tracks– Reject poorly fit events.
• For Tag-side, use tracks with:– |δz|<1.8mm, |σz|<500 µm, |δr|<500 µm– Iterate: discard worst track until fit is acceptable.
• Require |zCP - ztag|<2 mm (≈10τB)
November 2001 CP Violation at Belle
Test of Vertex Resolution0*0 / KJB Ψ→
November 2001 CP Violation at Belle
Fit to Lifetime
ν"*DB →
(ps) t∆
ps 03.064.1
ps 02.055.10
±=
±=
−B
B
ττ
November 2001 CP Violation at Belle
Fitting
)()'( sigsig tRttPLi ∆⊗∆−∆= )1( bgf−×
bgbgbg )()'( ftRttP ×∆⊗∆−∆+
[ ])sin(2sin)21(12
)( 1
/
sig tmwqetP fB
t B
∆∆−−=∆∆−
ϕητ
τSignal
)()1(2
)(/
bkg tfeftPbg
t bg
∆−+=∆∆−
δτ τ
τ
τ 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 ±±=ϕ
PRL 87, 091802 (2001)
November 2001 CP Violation at Belle
Sources of Systematic Error
±±±±0.06Total
±±±±0.01∆∆∆∆md and ττττB0 errors
±±±±0.01Background shapes
±±±±0.02KL background fraction
±±±±0.02Resolution function
±±±±0.03Flavor tagging
±±±±0.04Vertex algorithm
November 2001 CP Violation at Belle
Time-Dependent AsymmetryOne 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 sin2ϕ1Measurements
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 ≈φδ
November 2001 CP Violation at Belle
Conclusions• CP violation in the B system has been observed at the >6σ 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 ±±=ϕ
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 |λ|≠1 ?
If |λ| is allowed to float, (i.e. a cos(Δm t) term)
14.099.02sin 1 ±=φThe CPV asymmetry is unchanged.
09.003.1 ±=λ
In general we have
Note: if |λ|≠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%) whichare both CP=-1 and 5%(ψK, χc1Ks, ψπ0) whichare 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()(
−++−
−+
×=→ µµKBB
CL 90% 101.3)(
6
*
−
−+
×<→ µµKBB
CL 90% 103.1)(
6−
−+
×<→ eeKBB
CL 90% 106.5)(
6
*
−
−+
×<→ eeKBB
November 2001 CP Violation at Belle
Particle ID (dE/dx, ToF, & Aerogel)