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Transcript of τ physics at Belle
BESIII workshop 2
001oct13-15
H . Hayashii
Nara , Japan
Contents1 . Tau physics at Belle 2 . KEKB and Belle detector3. Present status4. Future Prospect
PRESENT status and FUTURE prospect
International Workshop on
BESIII Detector
ττ physics at Bphysics at Belleelle
BESIII workshop 2
001oct13-15
τlepton• Heaviest lepton ... Sensitive to NewPhysics• Only lepton that can decay to hadron ..….
• Less known compared to e and μ• No of tau`s
PQCDCPVCVCgs
,,2, α
BESIII workshop 2
001oct13-15
ττ physics physics at Belleat Belle(Presen(Present status)t status)
We present 3 topics a) decay ( ) b) tau EDM moments (CP violation in lepton sector) c) rare(forbidden) decay (Lepton Flavor Violation) c-1) c-2) neutrinoless 3 Charged decays
τνππτ 0
γμτ
μ2)(g
+‘forbidden` decay
Results are preliminary
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IntroductionIntroduction toto KEKBKEKB // BelleBelle
• With the goal of measuring CP - violating asymmetry inB meson decays ,- construction of KEKB asymmetric collider and the Belle detector was started in April 1994, and was co
mpleted in December 1998.- Belle Physics run was started June 1999.• Luminosity Goal: to produce more than 108BB pairs/year(=1
00/fb/year)• Same amount of tau-pairs (108ττ ) are
produced.
-> tau -physics: important target at Belle
113410 scm
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001oct13-15
KEKB acceleratorKEKB acceleratorKEKB : Asymmetric e+e- collider
•CM energy : 10.580 GeV at(4S)•Two separate rings :
•e+ (LER:3.5GeV) •e- (HER:8.5GeV)
•Luminosity•Target : 1034 cm-2s-1
•Achieved : 4.5x1033 cm-
2s-1
•Design Parameters •3016 m circumference•5120 RF buckets (2ns) •2.6 A for e+, 1.1 A for e-
•22 mrad crossing angle at IP• y 3 m, x 100 m
•History•First collision : Jan. 1999•Physics run : since June 1999
Belle detector
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KEKB performanceKEKB performance
225pb-1/dayIntegrated luminosity/day
Total accumulated luminosity 32.8fb-1
2001 / 7/29
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SVD CDCACCTOFCsIKLMSolenoid
Belle DetectorBelle DetectorEvent reconstruction Charged tracks
Silicon Vertex Detector (SVD) Central Drift Chamber (CDC)
Electrons and photons Electromagnetic Calorimeter (CsI)
Vertexing SVD
Particle identification K/separation
CDC : dE/dx Aerogel Cherenkov Counter (ACC) Time of Flight Counter (TOF)
electron identification ECL
KL and muon identification KL and muon detector (KLM)
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001oct13-15
How Belle How Belle data look likedata look like
r- view in SVD y-z view near IP
B0 J/+Ks
+- +
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001oct13-15
τ-→π ー π 0 ντ decay
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001oct13-15
ofprediction ltheoretica the get to
sobservableimportant are dMdN
N1 spectrum
massits and fraction Branching
20ππ0ππ
i
on)conservativector(currentCVCofTest
μ2)(g
)Br( τ0νππτ
accuracy1% measuredbetoneed:Br
μτνππτ 2)-(g and) 0 a
This is a trial to make a precision physics at Belle
τνππτ 0 has largest Branching fraction
)(arg
onpolarizativacuumhadronafromisainerrorestl
th
th
μ
μ
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001oct13-15
observedevent pair -tauof#N samplehπof#N
)correctionacceptance&d(backgroun2N
NB
0hπ
ττ
hπ
hπ
0
0
0
::
ττ
mesurementofmethod
:selection generic
τ0νπhτ2.
: 1.
selectionpairstepstwofromconsistsAnalysis
τ
0hπB
0hπB
→Determine Nττ ,→Determine Nhπ
0
● We first measure
)(: 0 Korhh πνπτ τ
(from ratio)
ratio :
cancel many systematics in Lumi ., tracking eff .
can be used for Br meas . of other decay mode
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Generic Generic tautau -pair-pair selectionselection
triggersEnergyand3)2,(track TriggerPhysics
)nn(n 30)(n)(n
boundaryECLpointingnottrackanycutθandMM
145θ35
N
γtrackpart
partpart
cmmiss
event
track
otherone
usesatisfy
n
GeVptGeVEGeVp
e
cm
,1
5.00.9,0.9||
42
max
If
The other hemi
One hemi
(rad - Bhabha , two - photon rej . )
(conti ., BB reject . )
(bhabha rej .)
(Bhabha , μμγ rej .)
•Signature ofττ event : low multi ., missing mom .
Criteria:
Cuts→As loose as possible
BBcontiqqphotontwoeeee ),(,),(),( γμμγ•B.G. :•Requirement:
●
●
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001oct13-15
MissingMissing massmass vsvs ThetaTheta __ mimissingssing
2γtrackinit
2 )pp(pMM
M
M(G
eV)
Data MC( )
M
M(G
eV)
*missθ *
missθ
ττtwo photon
rad . bhabha
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001oct13-15
MCandDatabetweenComparisonSamplePairTau
CMeventθ
otherone )(n)(naxisevent partpart
Background 6.8% qqeefrommainly
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decayhofSelection 0τνπτ
π0
GeVwithadditional No
condition
conditionπOne
hemisphereaintrackchargedOne0
0.2Eγ sγ`
9.0σ
)m(m-9.0
:π0.08GeVEγ
150γθ20 : γ
γγ
0π
0
γγ
Veto γ γγγγσ PondepMeV .5.98.4
signal0π1417.4
416 0
fbLathK π
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Pi0 momentum &Pi0 momentum & ThetaTheta (τ(τ±±→→ hh ±±ππ 00
ννττ))
P π 0(Lab)
θπ 0(Lab)
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001oct13-15
Charged Particle `sCharged Particle `s MomentumMomentum &Theta &Theta (τ(τ±±→→ hh ±±ππ 00 ννττ))
Ph ± (Lab)
θ h ± (Lab)
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001oct13-15
ππππ 00 massmass
0ππM
Linear scale
)2(..
0 nnhfrommainlyGBτνπτ
samplekN
fbL
h 416
417.4
0
1
π
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Log scaleππππ 00 massmass
GeVsignal 3.1at' ~ρ
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Br ( )Br ( )τνπhτ 0
%04.029.25)1(2
)1(
ππτ
ττπ
ττττ
εε
εττhID
hh
non
bN
bbNBr
τ-pair selection
Observed event with 4.42/fb data
sampleMNeventMN
h )193,416(42.0)695,432,1(4.1
0
π
ττ
%78.6:)(..%99.36:)(%37.33:)(
0
ττ
πτ
ττ
ττεπεττ
bfractionGBhefficiency
efficiencyh
hπ selection
%21.3%,94.9:)(..%24.48:)(
0
0
ττ
π
πεπ
non
hID
bbhfractionGBhefficiency
Current systematic errors%3.1/ ππσ hh Br
Can be improved with
Large data
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Systematic ErrorSystematic Error
%3.1:
% 1.0: efficiency π* 0.51%:background *
negligible:dep.Run0.40%:Trigger*0.10%:resolutionπ
%0.35:statisticMC
)(:errorSystematic
0
0
All―――――――――――――――
00 hπhπ/Bσ
(%)33.0 0.0425.29)νπhBr(τ τ0
Numbers are preliminary.
systematics under investigation
(stat.) (sys.)
Many errors are canceled in the ratio
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b) τElectroDipole Momentb) τElectroDipole Moment (( EDM) EDM) d d ττ
• EDM : CP Violating observable
• Any CPV at τ production vertex can be parametrized by EDM
• current upper limit :
|d|< 3.1 10–16 ecm (LEP L3 ; e
e )
|Re(d)|< 4.6 10–16 ecm,
|Im(d)| < 1.8 10–16 ecm (ARGUS)
←CP violating effective lagradian
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Belle EDM analysisBelle EDM analysis
• 28.9 / fb• Use 8 combinations
• Criteria 1 - 1 prong , no sin
gleγ barrel part , high p
track e,μ , π : probability > 0.
95• 1.18M events
candidate
e+
–
e–
e+
ρρπππρμρρμππμ ,,,,,e,,ee
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001oct13-15
SelectedSelected datadata
ρ
μe
π
labP
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SelectedSelected datadata
labcosθe μ
πρ
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Observable Observable for EDM measurfor EDM measurementement
Use Optimal observable[PRD45,2405(1992)]
termpsskxssMe
R )()( xτ
termpsskssMe )()( --I
τ
Maximum Sensitivity
Mean value→ prop . to EDM
EDMSMprod MMM
Ambiguity of tau direction -> amplitude is avaraged
Most probable spin direction->determined from tau and decay
daughter
←CP violating terms
BESIII workshop 2
001oct13-15
ObservableObservable distributiondistribution
Dot: exp. data
Histogram:MC
Back. :blueORe=0.00520.0041 ORe=0.00600.0105
OIm= 0.0220.022OIm= –0.0130.008
μρ πρ
BESIII workshop 2
001oct13-15
EDMEDM vsvs ObservableObservableORe vs Re(d) from MC
In order take into account detector effect, coefficients are determined by MC
High sensitivity for hadronic decay
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001oct13-15
EDMEDM resultsresults
Weighted mean
Errors dominated by statistics
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001oct13-15
EDMEDM results results(2)(2)
..%[email protected]|)Im(|109.3|)Re(|
17
17
LCecmdecmd
τ
τ
current upper limit :|d|< 3.1 10–16 ecm (LEP L3 ; )|Re(d)|< 4.6 10–16 ecm, |Im(d)| < 1.8 10–16 ecm (ARGUS)
•O ne order of magnitude improvement
•Results are limitted by statistics
•Im: comparable to WDM results at LEP
28.9 / fb data
..%95@):(105.1|)Im(|
):(1056.0|)Re(|17
17
LCOPALPDGecmdOPALPDGecmd
w
w
τ
τc.f. WDM(Weak DipoleMoment ) limit :
ecmfewa 1810•Next Target
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001oct13-15
cc ) ) Rare`Forbidden` decay(LFV)Rare`Forbidden` decay(LFV)τ→μγτ→μγ
)200%,95(102.1)( 11 PDGeB γμ
n
mm
fortenhancemen
μ
τ
τ
model on dep. 2n -5=:
most at tenhancemen 10-10 65
).,.(10-10:)B(
predicts models based SUSY Some8-6-
HisanoJOkadaYorderμγτ
ettsBelle arg` :10-10Br 8-6-
●
●
●
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001oct13-15
τ→μγτ→μγ : : analysis based on 21/fb dataanalysis based on 21/fb data
Criteria• 2 - prong+ ≧1γ• Signal side
• Tag side track is not muon• Tau +missing
)1()1( GeVEGeVpmuon γ
150174.0||
8.0cos4.0
labmiss
labmiss GeVp
cm
θ
θμγ
))(5.4( trackeachGeVpt
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001oct13-15
3 candidates in the signal Box
GeVEGeVM1.025.0
85.17.1
Δμγ
GeVMμγ
EΔ
GeVData MCsignal )( μγτ
)( cmbeam
cmcm EEEE γμΔ
Signal BoxSignal Box
21/fb
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001oct13-15
BackgroundBackground evaluationevaluation
cut] d))[standar(MC( γττ cut] ardData[stand
side]-tagatvetoData[w/o μ ]/))[(( sidetagatvetoowMC μγττ
%)93...()(
exp..
IDofeffeiremainseemseventlikeee
EpositiveatexcesslainnotcanitbuteefromGBsome
μγγμμγ
ττγΔ
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001oct13-15
Background estimationBackground estimation and uppe and upper-limitr-limit
5.9 event
γττ ee:)(γγμμγee
# data( #B.G.)
•Efficiency = 9.4 %
↓
•# of signal at 95 % C. L. =3.5ev (Bayesian method)
..%90100.1)( 6
LCatB μγτ
regionEhighΔ
regionElowΔ•B.G. :tacking into account
and
B.G. in the signal box is estimated from data
(use muon-ID ineff. Value) to be
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001oct13-15
AchievableAchievable SensitivitySensitivity
+•Include Endcap (x1.35)
•Cuts optimization (x1.30)
•Improve res.(x1.6)
(use TOF/ ACC info.)
γE
?10:101:101
12358
7
machinescmaneedKEKcurrentwachievableBR
B
•High luninosity
Present condition
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001oct13-15
LFV: LFV: NeutrinoNeutrino less 3 charged deless 3 charged decaycay
0
1
1600
19mod18,23.).%90(108.1),(
MlfbwithesMMlMMlfbLCKeKBr
τ
μτ
@90 % C.L.
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001oct13-15
Neutrinoless 3 charged decayNeutrinoless 3 charged decay),( 00 eKKBr μτ :improve 2 order of
magnitude.
MarkIIOur target
Br=10-7
-10-8
90%C.L.
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001oct13-15
OutlooksOutlooks•KEKB/Belle achieved a luminosity of : 4.5x1033 cm - 1s - 1
•Belle accumulated 33 fb-1(30x106 ττ event) data
•10 times more data in next 5 years
•Precise measurement of spectrum function in
•Limit / find a Rear Decays of τ in the range 10-7—10-8
•Measure EDM target 10 - 17-10-18 ecm
•CPV in
•Tau decay to Kaon -> ms
•Michel parameters
•・・・・・
•Our PHYSICS targets are
γγμτ e,Mledch ,arg3τ
ττ νπνππτ 4,0
τνπτ K
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001oct13-15
KEKB : PlanKEKB : Plan
Limiting factors on KEKB : beam current limit to avoid arcing at masks and
bellows e+ blow up due to photoelectron cloud by
synchrotron light beam blow up due to beam-beam effect Near future : more tunings replacing masks and bellows
more bunch currentFuture possibilities : Reduce photoelectron effect
(1) Antechambers for e+ ring(2) Charge swap :
e-(8.0GeV)+e+(3.5GeV) e-(3.5GeV)+e+(8.0GeV)
Crab collision
BESIII workshop 2
001oct13-15
ττ physics at Bphysics at Belleelle
BESIII workshop 2001Oct13-1BESIII workshop 2001Oct13-155 ,, BeijingBeijing ,, ChinaChina
BESIII workshop 2
001oct13-15
World-Wide Activity Involving 50 Institutions
~300 members
The Belle CollaborationThe Belle Collaboration