La Belle Epoque: A Midterm Reportmarlow/talks/cornell/cornell.pdf · 2004. 6. 11. · October 4,...

October 4, 2002 La Belle Epoque

La Belle Epoque: A Midterm Report

Particle Physics SeminarCornell University

Daniel Marlow Princeton University

October 4, 2002


Talk Outline

• Introduction• KEK-B & Belle• Mixing• Indirect CP Violation Measurement/Analysis

– Gold plated mode– Other sin2ϕ1 Modes

• B0→π+π-

• B→K(*)ll


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


The Unitarity Triangle

η

ρ

3λAVtd

( )ηρ ,

( )0,1

3λAVub

∗

2

*

λAVV tsus

1φ

2φ

3φ

The gold-plated mode determines the angle which is also called .

1φ

β

1≈≈ tbud VV


KEK B Asymmetric Collider

•Two separate ringse+ (LER) : 3.5 GeVe− (HER) : 8.0 GeV

•ECM : 10.58 GeV at Υ(4S)•Luminosity

•target: 1034 cm-2s-1

•achieved:7.2x1033cm-2s-1•±11 mrad crossing angle •Small beam sizes:

σy ≈3 µm; σx ≈ 100 µm

asymmetric e+e− collider


Machine Performance

Reported here

Integrated/day

Total Integrated ~80 fb-1

Summer shutdowns


KEKB/PEP II Luminosity Bakeoff

1789 pb-12207 pb-17 day

92.5 fb-193.3 fb-1Integrated

303 pb-1385 pb-124 hour

105 pb-1140 pb-1Shift

Peak

PEP-IIKEKB

1233 scm 102.7 −−× 1233 scm 106.4 −−×

As of ~Sept. 30, 2002 Comparisons not quite apples to apples.


µ / KL detection14/15 lyr. RPC+Fe

Tracking + dE/dxsmall cell + He/C2H5

CsI(Tl) 16X0

Aerogel Cherenkov cnt.n=1.015~1.030

Si vtx. det.3 lyr. DSSD

TOF counter

SC solenoid1.5T

8GeV e−

3.5GeV e+

Belle Detector


An international collaboration involving about 10 Countries, 50 Institutes, & 250 People

The BELLE Collaboration


Mixing

( ) ( )[ ]02202(0 sincos)( BeiBetB mimtmtimi φ−∆∆)/2Γ−− +×=Neutral B’s exhibit the fascinating phenomenon of mixing, which is where we will start the story.


Flavor TaggingAs noted, in IDCPV measurements, one needs to know the flavor of the spectator B0. This information can also be used for mixing studies.

• 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


Flavor Tagging: “Hamlet”

yreliabilit tag 10 ;1 ⇔


MixingBtdtb

W

tTWBB

Fd BVVm

mSmmfGm2*22

2

2

6 ⎟⎟⎠

⎞⎜⎜⎝

⎛=∆ η

π

[ ])cos(14

)(0

0

tmetP dB

t

OSB

∆∆+=∆

∆−

τ

τ

[ ])cos(14

)(0

0

tmetP dB

t

SSB

∆∆−=∆

∆−

τ

τ

Mixing measurements can be done by counting “same-sign” decays or by observing the timing distributions, or both.

XB +→ l0 XB −→ l0

mll±⇔""OS−−++⇔ llll or ""SS


MixingThere are various ways to determine the flavor of the decaying B0. In one method, one side of the event is fully reconstructed using known hadronic decay modes, such as B0→D*−π+and the other side is tagged using standard flavor tagging algorithm. Timing distributions are then plotted for same-flavor (SF) and opposite-flavor (OF) subsamples.


Mixing

The effect of the mixing is readily evident when the asymmetry is plotted as a function of ∆t.


Summary of Mixing Results

0.528±0.017±0.011HamletB0→D*-π+Hadronic

0.505±0.017±0.020High-pt l±

B0→D*-π+D*- →D0π-

Partial reconstruction

0.494±0.012±0.015HamletB0→D*-l+νSemi-leptonic

0.503±0.008±0.009High-pt l±High-pt l±Dilepton

∆md (ps-1)TagSignalMethod


But What About the CP Violating Phase?

( ) ( )[ ]02202(0 sincos)( BeiBetB mimtmtimi φ−∆∆)/2Γ−− +×=As noted, it is there, but we can’t get at it in a standard mixing measurement since it disappears when we “project out” the flavor eigenstates.


Indirect CP Violation

( ) ( )[ ]022020 sincos )( 1 BieBtB mtimt ∆−∆ +∝ φ( ) ( )[ ]020220 cos sin)( 1 BBietB mtmti ∆∆ +∝ φ

[ ]000 2

1 BBB ±≅±

LKJB Ψ→+ /0

CP Eigenstates

SKJB Ψ→− /0

CP odd CP even


Indirect CP ViolationIf we choose ϕ1=45o, then ie i ±=± 12 ϕ

( ) ( ) 0202

0

sincos

)(

BB

tBmtmt ∆∆ +

∝

( ) ( ) 0202

0

cossin

)(

BB

tBmtmt ∆∆ +−

∝


Indirect CP Violation

mt∆2π π

)(tΓ No mixing [ ]φξτ

τ

2sin)sin(1

)(/

mt

et

f

B

t B

∆±×

=Γ−

0B0B f

π mt∆2π

)(tA0B

0B

Mixing Coefficient

Interference from mixing.

CP eigenvalue


The Measurement

0B

+µ

−µ

0B

+µtag

CP

z∆

0DNeed to:

•Measure momenta

•ID leptons & K’s

•Measure vertices

−e +e

0K

Ψ/J


Analysis Flowchart


Muon Identification

µµµ

side- tagplus

/+−+

++

→

Ψ→

KKJB

The dilepton decay modes are a big part of the reason of why the “gold-plated” modes are given that name.

The gaps are instrumented with RPCs.


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.

29 fb-1


B Reconstruction

*beam

*cand EEE −≡∆

( )2

cand

2*beam ⎟

⎠

⎞⎜⎝

⎛−= ∑ pEmbc r

29 fb-1 sample


Ψ’ Modes

Both leptons tagged.

29 fb-1 sample


Other Charmonium Modes

M(l+l−γ) − M(l+l−)

1st observationof inclusiveB→ χc2 X

χc2

χc1

29 fb-1 sample


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 rr += Ψ


B→J/ΨKL Reconstruction

**/

*LKJB

ppp rr += Ψ

78 fb-1 Sample


Charmonium CP Mode Summary

78 fb-1 Sample


Flavor TaggingTwo measures of tagging performance:

• ε = efficiency

• w = wrong-tag fraction

• r = 1 – 2w

Amplitude of mixing oscillation depends on w

)21( w−01.027.0eff ±=ε


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.


Effect of Resolution

∆tThe resulting signature of CP violation is mainly a mean shift between the B0 and B0 samples.

∆t

Unsmeared theory Resolution

Smearing


Test of Vertex Resolution0*0 / KJB Ψ→


Fitting

)()'( sigsig tRttPLi ∆⊗∆−∆= )1( bgf−×

bgbgbg )()'( ftRttP ×∆⊗∆−∆+

[ ])sin(2sin)21(12

)( 1/

sig tmwqetP f

B

t B

∆∆−−=∆∆−

ϕξτ

τ

Signal

)()1(2

)(/

bkg tfeftP

bg

t bg

∆−+=∆∆−

δτ τ

τ

τ Background

Response function


The Fitted Result: 78 fb-1 Sample

035.0074.0719.02sin 1 ±±=ϕ

033.0067.0741.02sinBaBar cf ±±=β


Time-Dependent Asymmetry

One can plot the excess/deficit on a bin-by-bin basis. The plots to the right are notcorrected for dilution effects (wrong tagging, background, etc.).

78 fb-1 Sample


Subsample Dependence


What if |λ|≠1 ?

If |λ| is allowed to float, (i.e. a cos(∆m t) term)

074.0720.02sin 1 ±=φThe CPV asymmetry is ~unchanged.

026.0049.0950.0 ±±=λ

In general we have

Note: if |λ|≠1, then the gold-plated mode isn’t really gold plated.

78 fb-1 Sample


Other ϕ1 Modes b→sss

In the SM, the phase for these decays is ~0, so the IDCPV asymmetry should be ~sin2ϕ1 and no direct CPV. Given the anomalously large rate, however, there might be more to the story . . .

500 108.5)'( −×=→ KBB η


Other ϕ1 Modes b→sssπ+π−

B0 η’KSπ+π−η, ργ

γγ

π+π−B0 φKS

K+K−

π+π−B0 K+K−KS(K+K−≠φ)

Mbc (GeV/c2) Mbc (GeV/c2) Mbc (GeV/c2)

BELLE-CONF-0225


SφK = −0.73±0.64±0.18

AφK = −0.56±0.41±0.12

−SKKK = +0.52±0.46±0.11

AKKK = −0.42±0.36±0.09

+0.27−0.03+0.03−0.22

−Sη’K = +0.76±0.36

Aη’K = +0.26±0.22±0.03

+0.05−0.06

Uncertainty in CP ± fractionsw = (3 )%+16

−3

(−)S sin2φ1 in b ccs(=0.719±0.074±0.035)

Raw Asymmetries

PreliminaryPrelim

inary

Other ϕ1 Modes: b→sss


Other ϕ1 Modes: b→ccd

00 / πΨ→ JB 00 / ρΨ→ JB

Belle-Conf-0209


Other ϕ1 Modes: b→ccd

06.039.025.0 08.049.093.0

/

/

±±−=±±=−

Ψ

Ψ

π

π

J

J

AS78 fb-1 Sample


Measuring 2φ2=2(π- φ1- φ3)

)(2sin)sin(

)(2sin)sin( )()()()()(

31

00

00

φφξ

φφξ

+∆∆−=

+∆∆−=→Γ+→Γ→Γ−→Γ

=∆

tm

tmfBfBfBfBtA

f

DMf

CP−+= ππffor

With just one amplitude, CP violating phases will remain hidden. With two, they are revealed in a simple way. Three, alas, is not even better.Ideal Case


+

Measuring 2φ2

Interference between the tree level and penguin decay graphs is a little bit too much of a good thing!


[ ]) sin(1)(/

+∆∆±=∆Γ∆−

tmSet fB

t B

ππ

τ

ξτ

tmC ∆∆cosππ

Mean shift between q=+1 and q=-1 samples.

Population difference between the q=+1 and q=-1 samples.


After cut on Mbc

The background situation is more difficult.


0B

0B

0B0B

In the 42 fb-1 sample, we have observed an asymmetry in the rate for vs.At present, this is only a ~3σ effect, but if it persists with higher statistics, it will represent the first observation of direct CP violation in the B system.

−+→ ππ0B −+→ ππ0B


[ ]) sin(1)(/

+∆∆±=∆Γ∆−

tmSet fB

t B

ππ

τ

ξτ

tmC ∆∆cosππ

Mean shift between q=+1 and q=-1 samples.

Population difference between the q=+1 and q=-1 samples.


B→K(*)l+l-FCNC decays likeB→K(*)l+l- have a long and important history in particle physics. In the SM, they are forbidden at the tree level, but occur through penguins and loops, which are potentially sensitive to beyond-the-SM contributions.

60 fb-1 Sample


B→K(*)l+l-

610)06.016.058.0( )(

−

−+

×±±

=→ llKBBR

C.L. 90% 104.1 )(

6

*

−

−+

×<

→ llKBBR

Both results consistent with SM expectations.


Future Prospects

Oide


Summary & Conclusions• CP violation in the B system has been observed at the >6σ level.

• We see an indication of CP violation in B→π+π- decay.

•The KEKB accelerator is working very well and now holds the world record for instantaneous and integrated luminosity.

• There will be lots of good physics to come.

035.0074.0719.02sin 1 ±±=ϕ


Additional Slides


B→π+π- Checks


Likelihood Plots

12sin ϕ

ξξ


0LK Detection

Θ

LKP

missP

∑± =

−=hi

iS PPP,

4missγ

Inclusive “KL’s”


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|


Test of Vertex Resolution0*0 / KJB Ψ→


The Data

The first order effect is a mean shift between positively and negatively tagged samples (Summer ’01 sample).

30 fb-1sample


Sources of Systematic Error

±0.035Total

±0.007∆md and τB0 errors

±0.007Fit biases

±0.010KL background fraction

±0.014Resolution function

±0.015Flavor tagging

±0.022Vertex algorithm



r bin


Comparison to other sin2ϕ1Measurements

It looks like CDF had it right!

La Belle Epoque: A Midterm Reportmarlow/talks/cornell/cornell.pdf · 2004. 6. 11. · October 4,...

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