APR01 APS Recent results from Belle: Reflections on Beauty Kay Kinoshita University of Cincinnati...

APR01 APS

Recent results from Belle:Recent results from Belle: Reflections on Reflections on BeautyBeauty

Kay KinoshitaUniversity of Cincinnati

Belle Collaboration

2K. Kinoshita APR01 APS

OutlineOutline

•CP asymmetry in Standard ModelCP asymmetry in Standard Model•B decays and CPB decays and CP•Asymmetric eAsymmetric e++ee-- collisions at collisions at (4S)(4S)•KEKB and Belle:KEKB and Belle: time-dependent measurementtime-dependent measurement•Measurement of sin2Measurement of sin211

•SummarySummary


Belle CollaborationBelle Collaboration

274 authors, 45 institutions274 authors, 45 institutions many nationsmany nations


CP Asymmetry in Standard ModelCP Asymmetry in Standard Model

Weak interaction of quarks (u,c,t), (d,s,b){mass <- CKM matrix -> weak} eigenstates CKM - 3x3, unitary by definition -> 4 free

parameters

12/2 3A(i) 12/2 2A3A(1i) 2A 1

VVtdtdVVtbtb*+V*+VcdcdVVcbcb*+V*+VududVVubub*=0*=0““unitarity triangle”unitarity triangle”

irreducibly complexirreducibly complex-> CP violation-> CP violation

VudVusVubVcdVcsVcbVtdVtsVtbd s b u

ct=

V V *V V *cd cbtd tb

1.00.0

1.0(,)φ2

3φ 1φ *V V *V Vcd cbud ub


V V *V V *cd cbtd tb

1.00.0

1.0(,)φ2

3φ 1φ *V V *V Vcd cbud ub

CP phenomenologyCP phenomenology

••before 1998: seen only in K systembefore 1998: seen only in K system••predicted for b-hadrons in Standard Model, e.g.:predicted for b-hadrons in Standard Model, e.g.:

BB00->ππ->ππBB00->->ππ

BB00->J/->J/KKss

BB00->D->D((**) ) DD((**))BB00-> D*π-> D*πBB00->D*->D*

first resultfirst result


CP Asymmetry of B -> J/CP Asymmetry of B -> J/ K Kss

Decays to CP eigenstate: paths w/wo mixing interfere

CP-dependent oscillation in decay time distributions

No theoretical uncertainty

{cc}+{Ks,KL,π0}B CPeigenstatefCPB CP = ±1CP = ±1


Time measurement at Time measurement at (4S)(4S)

ee-- ee++

BB

22

t=0t=0z≈z≈ttcc

BB11

~200 µm~200 µmJ/J/

KKss

flavor tag: e, µ, Kflavor tag: e, µ, K±±, ..., ...

(4S): CP=-1, conserved(4S): CP=-1, conserved

++ee-- -> -> (4S)(4S)

BBidentify b/b {flavor tag}identify b/b {flavor tag}

until first B decay (t=0)until first B decay (t=0)

ReconstructReconstructCP=±1 mode @ t=CP=±1 mode @ t=tt

““CP side”CP side”


Experimental considerationsExperimental considerations

multiply by multiply by for lab lengthfor lab length(decay in flight)(decay in flight)

}}

Kaons W

b s

Wc

K–

b W ––e

cνleptons

• B0 lifetime = 1.548±0.032 ps, c=464±10 µmmixing m = 0.47±0.02 ps–1; cT~4.0 mmneed to distinguish B0 vs B0 (flavor tag), high efficiency

• True CP asymmetry is diluted:background to CP reconstructionincorrect flavor tag ratevertex resolution

• Bottom line: need >few x 10 fb–1 @ (4S) {>107 B events},vertexing@<40µm, hadron ID, lepton ID


Beams: KEKBBeams: KEKB

E*beam) = 2.6 MeVIP size = 77µm(x) x 2.0µm(y) x

4.0mm(z)Lmax = 3.4 X 1033 cm–2s–1 (design: 1x1034)

Data (6/1999–12/2000)Ldt = 10.5 fb–1@(4S), 0.6 fb–1off

ee –– 8.0 GeV

8.0 GeVee ++ 3.5 G

eV

3.5 GeV

22 mr

22 mr

= 0.425= 0.425


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


BB00 J/ J/ K Kss((++ ))as an exampleas an example

1lepton+1”not-hadron”Ks+

~4MeV/c2

Ks mass4

J/J/l l + + ll ))

CP mode reconstructionCP mode reconstruction


CP mode (continued)

~3MeV/c2

~10MeV

Kinematics for final selection:E E*cand–E*beam0 (E*beams0.5/2)

10-50 MeV res, depends on mode Mbc (Beam-constrained mass)

Mbc(E*beam2-p*cand

2 )0.5 Signal regionSignal region


J/J/ K KLL

Title: r404_f1_e61383_bdet_xy_ncol_nopt_stecl_nomom.ps (Portrait A 4)Creator: HIGZ Version 1.23/07Preview: This EPS picture was not saved with a preview (TIFF or PICT) included in itComment: This EPS picture will print to a postscript printer but not to other types of printers

• J/: {tight mass cut}1.42<p*<2.00 GeV/c

• KL: {KLM/ECL cluster w/o track,>1 KLM superlayers (resolution~ 3° (1.5° if ECL)} within 45˚ of expected lab direction

• Require cand to have B mass, calculate momentum in CMS (pB*) (~0.3 GeV for signal)

• backgrounds: random (from data), “feeddown,” knownmodes - estimate via MC


CP candidatesCP candidates

J/J/ K KLLFully reconstructed modesFully reconstructed modes


CP candidates - CP candidates - numbersnumbers


Flavor taggingFlavor tagging

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+}* all into multidimensional likelihoodSignificance of CP asymmetry depends on– tagging efficiency – wrong-tag fraction w (measured w data)- effective efficiency = (1-2w)


K-K-

z: vertex reconstructionz: vertex reconstruction

Constrained to measured IP in r-

• BCP: z~88 µm (rms)use only tracks from J/

• Btag: z~164 µm (rms)remaining tracks, excluding Ks;iterate, excluding tracks w. poor 2/nresolution includes physics (e.g. charm)

• Overall eff. = 87%


Prepare to fit: Wrong tag fractionPrepare to fit: Wrong tag fraction

Same fit method, but CP->flavor-specific• BD*-l+, D(*)-π+, D*-++flavor tag• separate same-, opp-flavor events• fit to z: mixing asymmetry, w:

• "effective tagging efficiency" eff=(1-2wl)2tag, l =(27.0±2.2)%

99.4% of candidates tagged(good agreement w MC)

Bins of dilution parameter (MC)Bins of dilution parameter (MC)


t resolution functiont resolution function

• Double Gaussian, parameters calculated event-by-event, includes effects of- detector resolution- poorly measured tracks- bias from e.g. charm- approximation of t=z/c

• form, params determined by- Monte Carlo- fits for D0K-π+, BD*l lifetimes

tail fraction: 1.8%tail fraction: 1.8%


Verifying Verifying t resolutiont resolution

t used in other measurements, serve as checks

• B0 mixing w. dileptonsmd=0.463±0.008±0.016 ps-1 (5.9 fb–1) PRL86,3228

(PDG2000: 0.472±0.017 ps-1)

• B lifetimesReconstructed B + flavor tag vertexBDX semileptonic+hadronic modes.

0=1.56±0.04 ps (PDG2000: 1.548±0.032 ps)

+=1.66±0.04 ps (PDG2000: 1.653±0.028 ps)


t resolutiont resolution

B0 mixing w. dileptonsSame sign- 2 primaries, mixed event- Primary+2ndary, unmixed & B+B-

- BackgroundsOpposite sign- 2 primaries, unmixed & B+B-

- Primary+2ndary, mixed&unmixed- Backgrounds Asymmetry in signal (2 primaries)

Nopp-Nsame

Nopp+Nsame

bb cc ssll-- ll++

Title: asymmetry.epsCreator: HIGZ Version 1.23/07Preview: This EPS picture was not saved with a preview (TIFF or PICT) included in itComment: This EPS picture will print to a postscript printer but not to other types of printers


Fitting Fitting t distributiont distribution

• distribution in t~z/c• unbinned max. likelihood fit, includes

- signal root distribution (analytic)

- wrong tag fraction (const)- background: right & wrong tag (MC,

parametrized) - detector & tagging resolution

(parametrized,evt-by-evt)


ResultsResults

binned in binned in tt

All modes combined : sin21=0.58+0.32-0.34


ResultsResults

Fit (stat. err.)Mod

e

36.41.82.0 +

−

075.0065.0 ±

60.004.0 ±−

57.60.10.0 +

−

40.47.21.1 +

−

CP = -1

CP = +1

SKB →

LKB →

Non-CP

32.34.58.0 +

−All CP

likelihoodlikelihood

Uncombined results are consistentUncombined results are consistent


Flavor tagging –0.07 +0.05

Physics parameters –0.04 +0.03

Background Fraction except KL

–0.02 +0.03

Background Fraction for KL

–0.05 +0.05

Background Shape –0.01 +0.01

Resolution Function –0.01 +0.01

IP measurement –0.01 +0.02

Total –0.10 +0.09

Systematic errorsSystematic errors


Result in context

sin21=0.58+0.32+0.09-0.34-0.10

• Feldman-Cousins confidence interval

• Probability of observing sin21>0.58 if CP is conserved: 4.9%

CKM, from rates

{PRL 86, 2509 (2001)}


Summary/ProspectsSummary/Prospects

Successful run of Belle in 2000Results onResults on• • sin 2sin 211: 10.5 fb: 10.5 fb–1 –1 on on (4S), 282 tagged events(4S), 282 tagged events• • + 17 papers at Osaka ICHEP 2000+ 17 papers at Osaka ICHEP 2000• • 2 publications, 4 submitted, more soon2 publications, 4 submitted, more soonNext• some improvements to analysis• data as of 4/01 - 20.5 fb–1; anticipate 30 fb–1 by summer• Luminosity: peak 3.41x1033cm–2s–1; 24 hrs 198 pb–1; month 4047 pb–1

• KEKB continuing to improve performance

APR01 APS Recent results from Belle: Reflections on Beauty Kay Kinoshita University of Cincinnati...

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