cp asymmetry in b 0 ->π + π – at belle kay kinoshita university of cincinnati belle...
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CP AsymmetryCP Asymmetryin Bin B00->π->π++ππ–– at Belle at Belle
Kay KinoshitaUniversity of Cincinnati
Belle Collaboration
•BB00->π->π++ππ–– and CP asymmetry in CKM and CP asymmetry in CKM• ee++ee–– -> -> (4S) at KEKB and Belle(4S) at KEKB and Belle• • Belle dataBelle data Measurement of CP asymmetry in BMeasurement of CP asymmetry in B00->π->π++ππ––
Interpretation vis-a-vis CKMInterpretation vis-a-vis CKM••FutureFuture
2DPF, April 5, 2003
Represented in complex plane as
"unitarity triangle"
BB00->π->π++ππ–– involves involves 22 ( () of CKM:) of CKM:
Vub*Vud
Vcb*Vcd
Vtb*Vtd
Vcb*Vcd
+ 1 + = 0
CKM: matrix of W-quark couplings - 3x3, unitary
One condition of unitarity:
V V *V V *cd cbtd tb
1.00.0
1.0(,)φ2
3φ φ *V V *V V cd cb ud ub
3DPF, April 5, 2003
VVtbtb*2*2VVtdtd
22VVububVVudud**
VVubub**VVudud
bdWuuπ+dπ–
uu}π–π+
bdWuuπ+dπ– V V *V V *cd cbtd tb
1.00.0
1.0(,)φ2
3φ φ *V V *V V cd cb ud ub
BB00->π->π++ππ––
2 =arg2 paths, each w/wo mixing:2 paths, each w/wo mixing:TreeTree PenguinPenguin
VVtbtb**VVtdtd
VVtbtb*2*2VVtdtd
22VVtbtbVVtdtd**
"direct" asym"direct" asym
VVtdtdVVtbtb**
––VVududVVubub**
mixing+ "mixing+ "
Bottom line: CP-asymmetric time-dependent rate from x-termsBottom line: CP-asymmetric time-dependent rate from x-terms
4DPF, April 5, 2003
Uncertainty: relative amplitudes of Tree, PenguinUncertainty: relative amplitudes of Tree, Penguin
• • if T dominates, if T dominates, AAππππ=0, S=0, Sππππ=sin2=sin222
• • if P, T comparable, if P, T comparable, AAππππ≠0, S≠0, Sππππ~sin(2~sin(222+2+2)•2/(|)•2/(|||22+1)+1)Direct CP violationDirect CP violation
Now:Now:• • more data - 78 fbmore data - 78 fb–1–1
• • improved analysis - tracking, improved analysis - tracking, t resolution, event selectiont resolution, event selection• • statistical analysisstatistical analysis(total 126 fb(total 126 fb–1–1, ~1.3x10, ~1.3x1088 B events) B events)Each 2.9 from
zero;note physical region is
difference ofdifference ofstrong phasestrong phase
≠≠1 if direct CP1 if direct CPviolationviolation
+0.38+0.16+0.38+0.16––0.27–0.130.27–0.13
+0.25+0.09+0.25+0.09––0.31 –0.090.31 –0.09
SSππππ= –1.21= –1.21
AAππππ= +0.94= +0.94
Previous Belle resultPrevious Belle result {PRL 89, 071801 (2002)} (42 fb {PRL 89, 071801 (2002)} (42 fb–1–1 ~45M B pairs) ~45M B pairs)
5DPF, April 5, 2003
B production:B production:
} B} B(4S)
BB thresholdBB threshold
ee-- ee++
CP=–1, CP=–1,
conservedconserved
++ee-- -> -> (4S(4S) {) { = 0.425} = 0.425}
z≈z≈ttcc~200 µm~200 µm CP modeCP mode
@ t=@ t=tt
flavor tag flavor tag @t=@t=: e, µ, K: e, µ, K±±, ..., ...
As with sin2As with sin21 1 via J/via J/K:K:• • reconstruct CP modereconstruct CP mode• • tag flavortag flavor• • reconstruct verticesreconstruct vertices• • unbinned max. unbinned max. likelihood fit to likelihood fit to tt
BB
22
t=0t=0
BB11
first B decay first B decay (t=0), break CP(t=0), break CP
6DPF, April 5, 2003
Belle detectorBelle detector
Charged tracking/vertexingCharged tracking/vertexing- SVD: 3-layer DSSD Si µstrip- SVD: 3-layer DSSD Si µstrip– – CDC: 50 layers (He-ethane)CDC: 50 layers (He-ethane)Hadron identificationHadron identification– – CDC: dE/dxCDC: dE/dx– – TOF: time-of-flightTOF: time-of-flight– – ACC: Threshold Cerenkov (aerogel)ACC: Threshold Cerenkov (aerogel)Electron/photonElectron/photon– – ECL: CsI calorimeterECL: CsI calorimeterMuon/KLMuon/KL– – KLM: Resistive plate counter/ironKLM: Resistive plate counter/iron
7DPF, April 5, 2003
……the peoplethe people
274 authors, 45 institutions274 authors, 45 institutions many nationsmany nations
8DPF, April 5, 2003
BB00->π->π++ππ–– reconstructionreconstruction
final selection: E E*E E*candcand–E*–E*beambeam: : 0±0.057 GeV(E*0±0.057 GeV(E*beambeams s 1/21/2/2) {Kπ shift –45 MeV}/2) {Kπ shift –45 MeV}
MMbc bc (E*(E*beambeam22-p*-p*candcand
2 2 ))1/21/2: : 5.271 –5.287 GeV/c5.271 –5.287 GeV/c22(Beam-constrained) (Beam-constrained)
… … but less clean than Bbut less clean than B00->J/->J/KKss::• • "physics bg" "physics bg" BB00->K->K++ππ–– => hadron ID, kinematics dE/dx, TOF, Aerogel – “positive ID” π=91%, K=10%• • continuumcontinuum => event shape {qq “jet-like” vs BB “spherical”)=> event shape {qq “jet-like” vs BB “spherical”) Fisher discriminant from modified Fox-Wolfram momentsFisher discriminant from modified Fox-Wolfram moments B candidate direction relative to beam axisB candidate direction relative to beam axis
Construct Likelihood ratio LR=LConstruct Likelihood ratio LR=LBBBB/[L/[LBBBB+L+Lqqqq], 2 selections:], 2 selections:LR > 0.825 {LR > 0.825 {BB=53%, qq=5%}}0.825 > LR > LR0.825 > LR > LRminmin (cut depends on flavor tag classification)(cut depends on flavor tag classification)
9DPF, April 5, 2003
BB00->π->π++ππ–– Candidates Candidates
LR>0.825LR>0.825
0.825>LR>LR0.825>LR>LRminmin
ππππ ππππ
ππ:106±16ππ:106±16Kπ:41±10Kπ:41±10qq:128±6qq:128±6
ππ:57±8ππ:57±8Kπ:22±6Kπ:22±6qq:406±17qq:406±17
Total signal 163±24Total signal 163±24
760 in signal box - 391 B760 in signal box - 391 B00, 369 B, 369 B00
10DPF, April 5, 2003
Flavor tagging: same as for sin2Flavor tagging: same as for sin211
bb cc ssll-- ll++
KK––D0
π+D*+
high-p lepton (p*>1.1 GeV): b->l-net K charge b->K–
medium-p lepton, b->c-> l+soft π b->c{D*+->D0π+}hard π b->{c}π–X
* multidimensional likelihood, >99%
oror π π––
• wrong-tag fraction w classify events based on expected w (MC) - 6 bins. (B0 mixing amplitude in data) =>• effective efficiency = (1-2w): net (28.8±0.5)%
mixing amplitude <-> mixing amplitude <-> ww
11DPF, April 5, 2003
K-
K-
z vertex reconstruction: same as for sin2sin211
t~1.43 ps (rms)
z
BB00DD, , DD**, , DD**, , JJ//KKSS, , JJ//KK**00
Resolution function:Resolution function:validate via lifetimevalidate via lifetime<=<= B0B0 = 1.551±0.018 ps = 1.551±0.018 ps(PDG02: 1.542±0.016)(PDG02: 1.542±0.016)
zz
12DPF, April 5, 2003
More checks of t resolution+flavor tag
B0B0 = 1.42±0.14 ps = 1.42±0.14 ps(PDG02: 1.542±0.016)(PDG02: 1.542±0.016)
B0B0 = 1.46±0.08 ps = 1.46±0.08 ps
BB00->K->K++ππ–– mixing mixingmmdd = 0.55±0.07 ps = 0.55±0.07 ps–1–1
(PDG02: 0.489±0.008)(PDG02: 0.489±0.008)
Fitted bg agrees w sidebandFitted bg agrees w sideband
13DPF, April 5, 2003
Check for flavor biasCheck for flavor bias
Look where zero asymmetry expected:Look where zero asymmetry expected:
"S"Sππππ"= –0.045±0.033"= –0.045±0.033"A"Aππππ"= -0.015±0.022"= -0.015±0.022
SSKπKπ= –0.03±0.11= –0.03±0.11AAKπKπ= +0.08±0.16= +0.08±0.16
14DPF, April 5, 2003
Fitting for CP asymmetryFitting for CP asymmetry
Same technique as with sin2Same technique as with sin211 • • unbinned maximum likelihood fitunbinned maximum likelihood fit• • resolution function event-by-event: resolution function event-by-event: tracking, misreconstruction,tracking, misreconstruction, physics, approximation of physics, approximation of t=t=z/z/c c
• • wrong tag fraction w, backgroundswrong tag fraction w, backgrounds
Fit for Fit for AAππππ, , SSππππ : :
rootroot
DilutedDiluted
+Kπ (set A+Kπ (set AKπKπ = 0) = 0)
+resolution + bg+resolution + bg
15DPF, April 5, 2003
5-5 0 5-5 0
Background Background subtractedsubtracted
rawrawasymmetryasymmetry
LR>0.825LR>0.825
Fit ResultsFit Results display display t projection (78 fbt projection (78 fb–1–1 ~85M B pairs) ~85M B pairs)
Likelihood not parabolicLikelihood not parabolic-> statistical errors-> statistical errors
estimated numericallyestimated numericallyvia MC ensemblevia MC ensemble
SSππππ= –1.23±0.41= –1.23±0.41
AAππππ= +0.77±0.27±0.08= +0.77±0.27±0.08 (stat) (sys)(stat) (sys)
+0.08+0.08––0.070.07
still outside physical region => still outside physical region => investigate …investigate …
16DPF, April 5, 2003
Fit Results: statistical analysisFit Results: statistical analysis
• • MC ensemble - 30k expts, 760 events ea, AMC ensemble - 30k expts, 760 events ea, Aππππ=0.569, S=0.569, Sππππ=–0.822=–0.822 probability of being outside physical boundary =60.1%probability of being outside physical boundary =60.1% " further (in " further (in ) from (0,0)=16.6%) from (0,0)=16.6%
SSππππ
AAππππ xx
datadata
physical boundaryphysical boundary
check linearity:check linearity:generatedgeneratedvs fitted Avs fitted Aππππ, S, Sππππ
17DPF, April 5, 2003
• Feldman-Cousins frequentist approach.• Acceptance regions from MC ensembles.• Systematic errors included.• Confidence Level (CL) calculated at each point.
Confidence regionsConfidence regions
(2.2(2.2)) hint of directhint of directCP non-conservationCP non-conservation}}
interpret as evidence for interpret as evidence for CP non-conservation in BCP non-conservation in B00->π->π++ππ––(3.4(3.4))}}
18DPF, April 5, 2003
Constraints on the CKM angle Constraints on the CKM angle 22
• • SSππππ, A, Aππππ depend on 4 parameters: depend on 4 parameters: 22, , 11[21.3°-25.9°][21.3°-25.9°], |P/T|, |P/T|[0.15-0.45][0.15-0.45], , -> plot confidence contours in (-> plot confidence contours in (22, , )for various |P/T|)for various |P/T| e.g.e.g. |P/T|=0.3|P/T|=0.3
11 =23.5° =23.5°
22
From other CKM (CKM fitter group, 2002):78.378.3°≤ °≤ 22 ≤ 121.6° ≤ 121.6° (95% C.L.)=> consistent
Find:Find:7878°≤ °≤ 22 ≤ 152° ≤ 152° (95% C.L.)insensitive to
19DPF, April 5, 2003
SummarySummary
Belle, 2000-2:Belle, 2000-2:• • peak peak LL= 9.5x10= 9.5x103333cmcm–2–2ss–1–1 - nearly at design - nearly at design (1x10(1x103434cmcm–2–2ss–1–1) ) • • passed 100 fbpassed 100 fb-1-1 in Oct. 2002 in Oct. 2002• • with 78 fbwith 78 fb–1 –1 on on (4S), sensitive to large values of (4S), sensitive to large values of sin2sin222
• • measure CP asym in Bmeasure CP asym in B00->->ππ++ππ–– constraints on constraints on 22, , consistent with other CKM consistent with other CKM
constraintsconstraints..hint of direct CP non-conservationhint of direct CP non-conservationresult submitted to PRD.result submitted to PRD.
NextNext• • ->150 fb->150 fb–1–1 by summer, 500 fb by summer, 500 fb–1–1 by 2005 by 2005• • Luminosity >@ designLuminosity >@ design• • the CP challenge: stay tuned on the CP challenge: stay tuned on 22
20DPF, April 5, 2003
additional slidesadditional slides
21DPF, April 5, 2003
Systematic uncertainties*
sourceAππ Sππ
+error error +error error
Background fractions +0.058 0.048 +0.044
0.055
Vertexing +0.044 0.054 +0.038
0.012
Fit bias +0.016 0.021 +0.052
0.020
Wrong tag fraction +0.026 0.021 +0.015
0.016
B, md, AKπ +0.021 0.014 +0.022
0.022
Resolution function +0.019 0.020 +0.010
0.013
Background shape +0.003 0.015 +0.007
0.002
Total +0.08 0.08 +0.08 0.07
* blind analysis: actual estimations done before seeing fit result.
22DPF, April 5, 2003
221
21
12
212
|/|cos)cos(|/|21
,/]sin)sin(|/|2[
,/]2sin|/|
cos)sin(|/|22[sin
TPTPR
RTPA
RTP
TPS
++−=
+−=−
−+=
φφ
φφφ
φφφ
TP −≡
convention taken fromM.Gronau & J.L.RosnerPhys Rev D65, 093012 (2002)
Constraints on the CKM angle 2
4 parameters
|P/T| 0.15-0.45 (representative) Theory ~0.31 21.3 - 25.9deg (Belle & BaBar combined)
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