b d and b s mixing at d Ø

06/20/2005 Beauty 2005, Tania Moulik (KU) 1

Bd and Bs mixing at DØ

BEAUTY 2005, Assisi, Perugia

Tania Moulik, University of Kansas

(For the DØ Collaboration)


Outline

IntroductionData taking, TriggersBd mixing measurement

ReconstructionFlavor Tagging

Bs mixing measurementDecay modesAmplitude scanSensitivity studies.


Introduction

Oscillations in the B-B system first observed by ARGUS in (18 years since then!)Signalled a large top massCP violation in B decays.

Many measurements on Bd mixing – LEP, SLD, CDF, DØ, Belle, BabarTevatron has unique opportunity to measure Bs mixing in 2 complementary analyses. ms (This talk) and s/s (Alberto Sanchez’s talk)


B mixing implies a B transition to Bsecond order weak interactions)

Light and heavy B meson mass eigenstates differ from flavor eigenstates:

Bd and Bs Mixing

W W

b

d(s) d(s)

t

00H

00L

BqBpB

BqBpB

(t)B

B(t)

iΓMiΓM

iΓMiΓM

(t)B

B(t)

dtd

i22222121

12121111

Time evolution follows the Schrodinger equation

VtbVtb

Vtd(s)Vtdt

t t

b

d(s)

b

d(s)Vtd(s)VtdW

VtbVtb W

122 qp

b


The case with mixed and unmixed decay probabilities become,

Extract mixing parameter m from asymmetry

Bd, Bs mixing

mtetP tmu cos1

2

1)(,

HLLH

LHLH

MMm

MMm

,2

,2

Time evolution of B and B states,


b

s

d

tbVtsVtdVcbVcsVcdVubVusVudV

b

s

d Wolfenstein parametrisation - expansion in ~ 0.22

1)(

1

)(1

23

22

32

AiA

A

iA

)21()21(

sin

2

2

c

0 tbtdcbcdubud VVVVVV

itdtdiubub eVVeVV ||||

complex 1

cbcd

tbtd

cbcd

ubud

VV

VV

VV

VV

Ultimate Goal – Constraing the CKM matrix - complex phase in the CKM matrix (CP violation).


md, ms, and CKM

(1,0)

()

cbcd

tbtdt

VV

VVR

cbcd

ubudu

VV

VVR

cb

ubu

V

VR

1

21

222

cb

tdt

V

VR

1

)1( 222

2*22

22

2

2

6tdtbBQCD

W

ttb

Fd VVfB

m

mFmm

Gm

ddB

2

2

2

td

ts

Bd

Bs

Bd

Bs

Bd

Bs

Bd

Bs

d

s

V

V

B

B

f

f

M

M

m

m

cbts VV


Data Taking TeV

TeV

Data taking

pb-1

pb-1


B physics triggers

Single muon Muon + track match at Level 1 and a muon at L2 Unbiased single muon triggers(PT>3,4,5) – Bd and Bs mixing, prescaled or turned off depending on luminosity.

Impact parameter biased triggers – Hadronic decays (Not being used yet).

Muon system Layers of drift chambers and scintillators.

Trigger (B mixing) Single inclusive muon trigger with || < , PT > GeV, Dimuon trigger (second muon for tagging)

Toroid

KBs KDs


Bd mixing – Motivation and Main ingredients

High statistics sample- determines charge of the B on reconstruction side.Flavor tagging – determine charge of opposite BSample composition – Other B decays contribute to the same final state. Validate flavor tagging to be used for main analysis, Bs mixing.

-

u(d)

b c

B-(B) DD*)

u(d)

D , D* D s

W


D0 and B+ selection

D selection:2 tracks, opposite charge, Pt>0.7, |<2.0 Displaced vertex:

d0/(d0) of tracks > 2Lxy/(lxy) > 4,

cos()> 0.9Good vertex fit.

D (B+) selection:If lxyB/lxyB) > 4, then cos(B ) > 0.95

lxyB < lxyD within 3 Does not form a D* with a soft pion.

K total in pb -1


Fit the 2 in VPDL bins to extract m and purity of tag

i i

eii

A

mAAm

)(

)),((),(

2

22

PT(B)

Bd mixing measurement

BT

BBXYB

T

BXY

BP

ML

βγ

Lc

Measured Expected

Visible Proper Decay Length:

LxyX

B vertex

Primary vtx

SSOS

SSOSi NN

NNA

Charge of B determined from charge on reconstructed side

Opposite B charge from Flavor Tag


Expected Asymmetry

Distribution of oscillated and non-oscillated events are function of K-factor,, m

B not fully reconstructed. Measure average k-factor K = Pt(D0)/Pt(B)

))cos()12(1(5.0)(, cKxmc

Kxn oscnonosc

d

),()()()()()( ,),,(

,,, KxnxKDdKxxxdxxN oscnonosc

sdujjMMoscnonosc

sud

VPDL resolutionK-factor

Reconstruction efficiencyof jth channel


6 Barrels – 4 layers, Double sided except for layers 1 and 3 of the outermost barrels.Interspersed F disks – double sided H disks – single sided, 24 wedges per h-disk

K readout channels

Barrel F-Disks H-disks

Bd mixing – Decay length resolution

m m


Flavor Tagging

----We have explored ---Jet charge, Soft muon, Same side tagging


Flavor Tagging Definitions

Flavor tagging merit (D2) B meson

PB+PtrkPtrel

Candidate track Ptrk

Same side Tagging

total

tag

N

N

WSRS

WSRS

NN

NND

)(

)(*)(

iP

iqiPQ

T

Tjet

Tagger D D2(%)

SLT

jetQ+SST

Jet Charge


Fitted asymmetry

Simultaneous fit to D* and D sample to extract m.

m = ps-1

(D*) – Bd contribution ~83%(D) – B+ contribution ~76%

B+D X Muon Tagger

JetQ+SST


Bs Mixing

Very similar analysis to the Bd mixing. Decay mode used: Bs Ds , Ds

1460pbdtL


For…Bs mixing observation

S = signal events D2 = tagging power S/B = signal/background t = proper time resolution


Normalized Tagging variable d Monotonic function between (-1,1)

d> (b) , d<(b)

Significant Improvements to flavor tagging

Add Secondary Vertex Charge Tagging

6.0||

6.0||

p

qpQSV

bb

Likelihood ratios for variables discriminating between b and b ptrel.q, svcharge,jetcharge

)(

)(;

ibi

ibi

i

n

ii

xf

xfyyy

y

yd

1

1


“Proof of principle” – md

measurement

md = 0.558+-0.048(stat.) ps-1

D2 = 1.0% (OST Tagging only)


Bs mixing limit – Amplitude fit method

Ideal non-osc/osc number of events as a function of VPDL (x) Fit for Amplitude A

Fit for A as a function of ms ( in steps of 1 ps-1)


Impact parameter resolution and tuning.

Tune track errors for data and MC taking taking into account dependence on:

Track momentumTrack anglesSilicon detector hit configurationSilicon cluster width

Variable scale factor for VPDL resolution (s.– Overall scale factor = 1.10


Sample composition

Decay Sample composition

Bs→Dsμν 20.6%

Bs→D*sμν 57.2%

Bs→D*0sμν 1.4%

Bs→D*1sμν 2.9%

Bs→DsDsX 11.3%

B0→DsDX 3.2%

B-→DsDX 3.4%


Bs mixing Limit (460 pb-1)Expect A=1, for freq = truems,

A=0 for freq truems

C.L smallest value of ms at which, A+1.645A = 1

Sensitivity:ms value with 1.645A = 1

ms > ps-1

Sensitivity = ps-1


To be Added…

Reconstructed candidates =


World averages for md world Bs mixing limit

ms > ps-1

Sensitivity = ps-1ps


Future Perspectives

With additionalChannels andImprovementsIn flavor tagging

ms upto 11 ps-1

Within reach at fb-1


Future perspectives

With increase in bandwidthms upto 18 ps-1

Addition of hadronic decay Modes and Layer + 50 Hz Bandwidth ms upto 26 ps-1


Conclusions and Summary

Bd mixing measurementWe can contribute to the Bd mixing measurement in a small way and an important cross check of the measurement in a hadron collider environment. It is mainly important as a validation tool for our flavor tagging.

Bs mixing measurementMore statisticsImprovements in flavor tagging, introduction of electron tagging (Almost ready!), Unbinned likelihood fitMore decay modes,

BsD s e XAddition of Ds K*KAddition of hadronic decay modes

Addition of Layer0 improvements in impact parameter resolutionWe are excited…. Lots more to come….


BACKUP


Inner Tracker


D0 Silicon – RunIIa disks


Silicon Alignment

b d and b s mixing at d Ø

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