Measurement of sin2φφ1Stephen L.Olsen
U. of Hawaii

LP01
RomeRepresenting the Belle Collaboration
July 23-28, 2001

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The Belle Collaboration

The Belle Collaboration

A World-Wide Activity Involving 50 Institutions
July 23-28, 2001

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The Belle Collaboration

The Belle Collaboration~300 Authors
July 23-28, 2001

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The Belle Collaboration

Outline! Introduction! KEKB/Belle performance! Measurement of sin2φ
φ1! Results & conclusions

July 23-28, 2001

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The Belle Collaboration

CPV ala Kobayashi-Maskawa
CPV due to complex phases in theQuark generation mixing matrix:

 d '  VudVusVub  d     s '  = VcdVcsVcb  s  b'  V V V  b    td ts tb  
Usually put in the Vtd and Vub corners
July 23-28, 2001

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The Belle Collaboration

sin2φ
φ1 from B→fCP + B↔B→fCP interf.
Sanda, Bigi & Carter:
Vcb

J/ψ
ψ

B0
KS+V*td

J/ψ
ψVtb

B02
∝V*
td

B0Vtb

July 23-28, 2001

KSV*tdLP01, Rome

The Belle Collaboration

Mixing-induced CPV asymmetry
ξf= ±1 for CP= ±1±B0

PDG notation!

B0t
July 23-28, 2001

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The Belle Collaboration

What do we measure?
Flavor-tag decay(B0 or B0 ?)ψJ/ψe+fCP

e−t=0
B-B
B+BKS

∆zmore B’s
more B’st ≈ ∆z/c β γφ= =(1-2w)sin2
1 φ(1-2w)sin2

1

July 23-28, 2001

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The Belle Collaboration

Previous result (using 10.5 fb-1)
+0.32
sin2φ
φ1 = 0.58 −0.34

+0.09
−0.10

Today:
Results from29.1 fb-1
4x more events

July 23-28, 2001

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The Belle Collaboration)

KEKB asymmetric e+e− collider
Lofo w ErP nos erg
itr y Roning(LRgyer
En trongh c
Hi r ElefoER

TSUKUBA Area (Belle)

HER
LER
Interaction Regiongin
RF

OHO Area
RFWIGGLER

RFRF(TRISTAN Accumulation Ring)

Rcna

July 23-28, 2001

LiRF
RF FUJI Area1034 cm-2s-1•achieved:4x1033cm-2s-1•target:•±11 mrad crossing angle•Small beam sizes:σy ≈3 µm; σx ≈ 100 µm-Positron/eElectron+ReHELE

WIGGLER)ER(HNIKKO Area

•Two separate ringse+ (LER) : 3.5 GeVe− (HER) : 8.0 GeV•ECM : 10.58 GeV at Υ(4S)•Luminosity

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The Belle Collaboration

What’s needed?
• Lots of B mesons(Br (B→fCP) ~ 10−3)– very high Luminosity

⇒

KEKB

• Find CP eigenstate decays
4π detector ⇒ Belle– high quality ~4π• Tag other B’s flavor– good particle id• Measure decay-time difference– Asymmetric energiesµm)– good vertexing (@KEKB: γ β cττ≈200µJuly 23-28, 2001

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The Belle CollaborationKEKB performance
225pb-1/day→Integrated luminosity/day

32.8fb-1→
Total accumulated luminosity

July 23-28, 2001

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The Belle Collaboration

Average luminosity during run〈L〉〉=3.5x1033/cm2s

All-time Lpeak = 4.5x1033/cm2s
July 23-28, 2001

LP01, Rome

The Belle CollaborationKEKB’s Special Features• Small beam sizes ⇒ low beam currents– 4.5x1033 with less than 1 Amp in each ring

• ± 11 mrad beam crossing angle

22mrade+e– No bending magnets near the IR– Fewer spent particles into Belle– Synchrotron X-rays easily expelled
July 23-28, 2001

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The Belle Collaborationψ Ks)The Belle detector: (B0 → J/ψ

July 23-28, 2001

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The Belle Collaborationψ Ks event vertex
B0 → J/ψ

July 23-28, 2001

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The Belle Collaboration

Detector Performance" Silicon Vertex Detector" σ ~ 55µµm 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 (σσ ∼95∼ ps)" Aerogel (n = 1.01 ~ 1.03)" γ, e± with CsI crystals" σE/Eγ ~ 1.8% @ 1GeV

" KL and µ± with KLM (RPCs)" µ± : effic. > 90% ; ~2% fakes
July 23-28, 2001

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The Belle CollaborationKEKB/Belle summary• World record luminosity– ~10 B mesons/sec• Backgrounds are tolerable:– SVD occupancy < 4%– CDC inner layer occupancy < 10%– CsI pedestals endcap < 1MeV; barrel <500keV• Headroom for improvement:– Plans: Lum ⇒ 1034 ;July 23-28, 2001

LP01, RomerIPpipe 2.0 ⇒ 1.5 cm
The Belle Collaboration

B##CP Eigenstate Decays
Use ~all low-background ccK0 modesψ KS(→π→π+π− & π0π0)
BCP → J/ψψ(2S)(→→l+l− & J/ψπψπ+π−) KS
dd χ (→o→J/ψγψγ)
ψγ KSc1PC
ηc(→→KSK+π−, K+K−π0) KSJ/ψψ
KLnev
0 (→0) (mostly)eπJ/ψψ
K*→KSCP
July 23-28, 2001

LP01, Rome

The Belle Collaboration

ξ f =-1
ξ f=+1ψ Ks(→π+π− )Golden mode: B0 → J/ψ
J/ψ→ψ→µψ→µ+µ−σ~10MeV/c2

Ks→π+π−σ~4MeV/c2Belle

J/ψ→
ψ→e
ψ→ +e−
σ~11MeV/c2Biggest contributor to the fcp event sample
July 23-28, 2001

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The Belle Collaboration

→π+π− ) (cont’d)ψ KS(→πB0 → J/ψ

457 events~3% bkgd
Energy difference:∆E ≡ E J /ψ + EK S − ECM 2
Beam-constrained mass:
mbc = ( ECM
July 23-28, 2001

rr 22) − ( p J /ψ + pK S )2

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The Belle Collaboration

For B→→J/ψ
ψKS; use KS#π0π0Total events = 76
Bkgd ≈ 9 evts (12%)

Mbc
July 23-28, 2001

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The Belle Collaboration

Other charmonium modesχc1χc21st observationof inclusive

B# χc2 X

M(l+l−γ) − M(l+l−)
July 23-28, 2001

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The Belle Collaboration

All CP-1 modes
B0 → other modes
290 candidates
46 background(Purity = 84%)

Belle

B0 → J/ψ
ψ Ks(→π+π− )457 candidates~12 background(Purity = 97%)
July 23-28, 2001

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The Belle Collaboration

ψ KL
B0 → J/ψψ →l+l− + KL
1) J/ψψ KL:
2) Assume B##J/ψ
compute PKL
3) Remove reconstructedψ K, J/ψ
ψ K*, …
B → J/ψ
4) Cut on a likelihood
based on kinematicaland shape quantities
5) Plot P*B =|P J/ψψ + PKL|

July 23-28, 2001

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The Belle Collaborationψ KL signal yield
B0 → J/ψ
BelleNsig = 346 events*ψ + PKL* |P*B =| PJ/ψNbkg = 223 evts

ψ KL
B0 → J/ψ
569 total events
346 signal(Purity = 61%)

PB(cms)July 23-28, 2001

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The Belle Collaboration

Flavor-tag the other B meson
Use inclusive flavor-specific properties:!Inclusive Leptons:
b# c l− ν!high-p l−s l+ ν!intermed-p l+!Inclusive Hadrons:
B0#D(*)− π+, D(*)− ρ+, etc.
!high-p π+π+π0K+ X,!intermed-p K+
D0 π −!low-p π−

Also need to consider correlations
July 23-28, 2001

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The Belle Collaboration

2-level Multi-dimensional flavor tagging

q = +1 ⇒ Btagq = −1 ⇒ Btag
r=(1-2w)MC

July 23-28, 2001

LP01, Rome

The Belle Collaboration

Determination of wrong tag fraction wl

get w from B⇔⇔Bmixing amplitude:∆md ∆t)(1-2wl)cos(∆

July 23-28, 2001

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The Belle Collaboration

Multi-dimensional Flavor Tagging• Uses all events

ε effective = 27.0 ± 1.2%
• Includes correlations• Use MC-r as a classifier• Use data-w for CP fits

1-2wl

– Efficiency > 99%rMC-determined r ≈ 1-2w measured from data
July 23-28, 2001

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The Belle Collaboration

Vertex Reconstruction
ψ#l+l−• For CP-side, use J/ψ
– Reject poorly fit events.
δzCP ≈ 75 µm (rms)• For Tag-side– use well fit tracks– iterate: discard worst track– δztag ≈ 140 µm (rms)• Require |zCP - ztag|<2mm (≈≈10τB)σ ∆t ≈ 1.5 ps• Tails ≈ 3%; Effic. ≈ 85%

1137 evts used in the CP fit.
July 23-28, 2001

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The Belle Collaboration

Validation: B lifetimes
B##D*lντB0 = 1.55 ± 0.02ps

PDG: 1.55 ± 0.03ps
July 23-28, 2001

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τB+ = 1.64 ± 0.03ps

PDG: 1.65 ± 0.03ps
The Belle Collaboration

Timeline• July 6: end Y(4S) running• July 9: finish data processing• July 11: find wl’s
• July 12: Open the box!!
• July 13: PRL draft # Collab• July 18: PRL submitted• July 23: Announce resultsJuly 23-28, 2001

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The Belle Collaboration

Combine q, ξf & ∆traw data

July 23-28, 2001

LP01, Rome

The Belle Collaboration

CP is violated in B decays!!
•Large effect•Apparent in the raw data
•Many σJuly 23-28, 2001

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The Belle Collaboration

Event-by-event Likelihood

July 23-28, 2001

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The Belle Collaboration

Event-by-event Likelihood

background frac.

From
Sidebands & MC

resolution function
B-lifetime studies
b-flavor tag

PDGξf= ±1 for CP= ±1
July 23-28, 2001

freeparameter
LP01, Romewrong-tag frac.
The Belle Collaboration

sin2φ
φ1 value that maximizes Πi Li

sin2φ
φ1 = 0.99 ± 0.14 (stat) ±0.06(sys)curvesfromunbinnedfit

July 23-28, 2001

LP01, Rome

The Belle Collaboration

Do the fits & errors make sense?
ourfit:

Use toy MC: run 1K similar expts
with sin2φφ1 (input)=0.99-0.14+0.14
low-sideerror

Toy MCmeans:
July 23-28, 2001

high-side
error+0.116-0.128LP01, Rome

The Belle Collaboration

asymmetry display
used binned data to examine “goodness of fit”

Plot:

ξfdivide data
into ∆t bins
July 23-28, 2001

NB−NBvs ∆t

weight eventsby their CPsensitivity

φ1fit for sin2φifor each ∆ti

plot:∆m∆∆ti
φ1isin∆
sin2φ

NB+NB

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The Belle Collaboration

NB−NBξf N +NB
B

asymmetry plot: all data

Result from global fit (sin2φφ1=0.99)
July 23-28, 2001

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The Belle Collaboration

Compare CP –1 and CP+1CP-1

sin2φ
φ1

NB−NB
NB+NB

0.84±±0.17
CP+1

opposite!

1.31±±0.23(statisticalerrors only)
July 23-28, 2001

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The Belle Collaboration

sin2φφ1 from various subsamples+1 560 evts
q=+q=−−1 577 evts
(statisticalerrors only)
July 23-28, 2001

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The Belle Collaboration

Control sample: B0→non-CP statesuse: B0#D(*)−−π+, D*−−ρ+, D*−−l+ν, J/ψ
ψK*(K+π−)~17K events“sin2φφ1”
0.05±±0.04(statisticalerror only)
July 23-28, 2001

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The Belle Collaboration

CP fit : Systematic Error
Vertex algorithm±0.04

Flavor tagging±0.03

Resolution function±0.02

KL background fraction ±0.02

July 23-28, 2001

Background shapes±0.01∆md and τB0 errors

±0.01

Total

±0.06

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The Belle Collaboration

Compare with CKM constraints
σ bandBelle’s 1σ(both sol’ns)

July 23-28, 2001

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The Belle Collaboration

1σ

95%1σ

Bellev a cen
lu t re s alCompare with constraints (cont’d)

95%

Ciuchini et al

July 23-28, 2001

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The Belle Collaboration

Conclusionsσ!!
$CP is violated in B decay >6σ!!
$sin 2φ
φ1 is large:
0.99 ± 0.14 ± 0.06

July 23-28, 2001

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The Belle Collaboration

Compare with other experiments

July 23-28, 2001

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The Belle Collaboration

Variations on a theme
Old data; old analysis: 0.58±±0.33
Old data; new analysis: 0.54±±0.34
New data; new analysis: 1.06±±0.14
Allow ∆md to float

φ1sin2φ∆md (PDG:0.472)±0.14 0.478±±0.057 ps-1
1.00±
Allow τB0 to float

φ1sin2φτΒ0 (PDG:1.550±0.14 1.66±±0.07 ps
1.00±July 23-28, 2001

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The Belle Collaboration

Resolution function
R = (1 − f tail )G ( ∆t ; µ main , σ main ) + f tailG ( ∆t ; µ tail , σ tail )′µ = m0 + m1σ tag

σ = f (σ CP , σ tag ;parcharm effect , parB T effect )pJ/ψKS data

µmain = –0.24ps
σmain = 1.49psµtail = 0.18ps
σtail = 3.85ps

resolutions (rms)δzCP ≈ 75 µm
δztag ≈ 140 µm

ftail = 0.03

July 23-28, 2001

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The Belle Collaboration

Combine q, ξf & ∆t
raw data

July 23-28, 2001

LP01, Rome

The Belle Collaboration

φ1 from various subsamples
sin2φ
1.4

sin2φ
φ11.2

0.99

10.8

Colum0.6
0.4
0.20q=+1q =-1

J/Y Ks(golden)

Other
CP-1

J/YKL

J/Y K*(statistical errors only)
July 23-28, 2001

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The Belle Collaboration

φ1 for different r values
sin2φ
1.8
1.6

sin2φ
φ1

1.4
1.2

0.99

10.8
0.6
0.4
0.2
00.5

July 23-28, 2001

0.75

LP01, Rome

0.875

1.0The Belle Collaborationr