CDF での Top Flavor の物理

2008/02/22 20特定領域「フレーバーの物理の新展開」研究会08

1

CDF

CDF での Top Flavor の物理

戸村友宣( 筑波大学 )

2008/02/22 2008特定領域「フレーバーの物理の新展開」研究会 2

CDF

Introduction Top quark is the heaviest

known fundamental particle. Is this large mass related to

electroweak symmetry breaking? Relationship between

mt, mW, and mH

Top quark has very short lifetime

Decay before hadronization Momentum and spin are

transferred to decay products


CDF

Tevatron Run II Proton-Antiproton Collider

with CM energy of 1.96 TeV Peak luminosity: 2.91032

cm-2s-1

Delivered luminosity: > 3.5 fb-1


CDF

CDF II Detector

General Purpose solenoidal detector Efficiency: ~85% Recorded >2.9 fb-1


CDF

Top Pair Production

Top pair production through strong interaction

~85%

~15%


CDFTop Pair Production Cross Section

Measured using many different techniques

Good agreement Between measurements Between data and theory

LA bkgobs NN

ttpp

pb 7.6)GeV 175@( topMttppdilepton l+jets all hadronic


CDFForward Backward Asymmetry

Forward-backward asymmetry arises from interference between LO and higher order diagrams

syst04.0stat07.017.0fb A syst04.0stat13.024.0fb A

(NLO Theory: Afb = 0.04±0.01) (NLO Theory: Afb = 0.04—0.07)

Lab (ppbar-rest) frame

ttbar (parton) rest frame1.9 fb-1

frame lab

framerest parton

fb

fb

A

A


CDFttbar Production Mechanism

@95%CL38.0

07.015.007.0

ttpp

ttgg

Measure fraction of gg vs. qq top production

SM prediction: ~85% qq, ~15% gg Large theoretical uncertainty (~10%)

Two complementary approaches NN with production and decay kinematics Track multiplicity distributions

Combine two methods: ~6% improvement

1 fb-1


CDFttbar Differential Cross Section

Measure d/dMtt and test consistency with SM

Spectrum is sensitive to many BSM resonances (Z′, coloron, etc.)

ttbar invariant mass is reconstructed for l+jets events

Subtract background and correct the distribution using a regularized unfolding technique

Data is consistent with SM p-value = 0.45

1.9 fb-1

iMi

ii

tt

i

tt

NN

dM

d

LA

bkg


CDF

Search for Massive Gluon Search for heavy gluon-like

particle, Gttbar(color-octet model, etc.)

3 parameters Mass(M), Width(), coupling()

Event-by-event ttbar invariant mass reconstruction for l+jets with a Matrix Element technique (DLM)

Data is consistent with SM (<1.7) within 400M800, 0.05/M0.5

Set upper/lower limit for massive gluon coupling

Coloron model (=1, /M0.2) is excluded in the range, /M0.5 and M800

q Qg +

q QGgs gs qgs Qgs

SM interfere MG

1.9 fb-1


CDF

Top Quark Mass Many techniques were deployed for

top mass measurements Tevatron combination calculated 1 year

ago


CDFNew Mass Measurements (1)

Template Method Reconstruct top mass event-by-event and generate templates Use dijet mass from W daughters for in-situ jet energy calibration

Combined for dilepton and l+jets

all-hadronic

2top GeV syst6.1JESstat7.30.177 cM

2

2top

GeV 0.29.171GeV syst0.1

JESstat7.19.171

cc

M

Apply NN event-selection to improve S/B

1.9 fb-1


CDFNew Mass Measurement (2)

Matrix Element Method Calculate event-probability from the kinematics of decay

products using Matrix Element dilepton

lepton+jets

2top GeV syst2.1stat8.17.172 cM 2

top GeV syst9.2stat7.22.171 cM

Apply NN event-selection to optimize S/B

Cut lower tail of log-likelihood distribution

1.9 fb-1


CDF

Top Quark Width

Measure width of top quark directly using template method

Use 1-tag and 2-tag l+jets data

Calculate upper limit using Feldman-Cousin prescription

GeV 0.175CL @95% GeV 7.12

t

tM

1 fb-1


CDF

Top Quark Charge Measure the charge of “top” quark

SM top charge: +2/3 XM top charge: −4/3

D. Chang et. al. Phys. Rev. D59 (1999) 091503

tW+b or tW−b Charge of W (lepton charge) Pairing between W and b Flavor of b-jet

Use dilepton and l+jets data

Measured f+=0.87p-value=0.31

Exclude XM @87% CL

1.5 fb-1


CDF

W Helicity V−A character of the top decay

makes the helicity of W onlyF0=0.70, F−=0.30, F+=0.00(longitudinal, left-handed, right-handed)

syst05.0stat10.015.0

syst07.0stat21.038.00

F

F 0 and GeV175for

syst069.0stat084.0637.02

0

Fcm

F

t

l

l+

W+

b*

cos Method Matrix Element Technique

syst06.0stat10.066.00 F

CL%[email protected]

syst03.0stat05.001.0

F

F

1.9 fb-1

If F+ fixed to 0:

If F0 fixed to 0.7:


CDFSearch for FCNC Decay tZq

Top FCNC is extremely rare In SM, BR(tZq)=O(10-14) BSM, up to O(10-4)

Calculate 2 for FCNC top decay

1.9 fb-1

CL %95@

%7.3BR Zqt

2

rec,

2

rec,

2

PDG,rec,2

Zqt

tZqt

Wbt

tWbt

W

WW mmmmmm


CDF

Single Top Production Single top production through

weak interaction single top |Vtb|2

Sensitive to: 4-th generation H +

W′ FCNC Etc.

Background for WHlbbs-channelNLO = 0.88±0.07 pb

t-channelNLO = 1.98±0.21 pb

?

W,H+

Z

ct


CDF

Evidence for Single Top Multivariate Likelihood Function

7 input variables (kinematics, kinematic solver and ANN b-tag outputs)

Matrix Element Technique Ratio of event probability

densities for signal and bkg

pb0.12.13.1pb,1.1

4.11.1 ts

pb1.13.17.2ts

2.7 significance (2.9 expected)

pb9.00.19.1pb,8.0

0.11.1 ts

pb1.12.10.3ts

3.1 significance (3.0 expected)

1.5 fb-1


CDFDirect Measurement of |Vtb|

CKM Matrix Element |Vtb| Describes strength of Wtb vertex single top |Vtb|2

Assumes |Vtb|2+|Vtb|2<<|Vtb|2

Measured with Matrix Element Technique

Theory uncertainty arises from the cross-section dependence on

Top quark mass Factorization and

renormalization scales PDFs and s

(Z. Sullivan, Phys. Rev. D70 (2004) 114012)

theory07.0experiment18.002.1 tbV

1.5 fb-1


CDF

Search for W′ Resonance Search for resonance in tb channel using

MWJJ Many theories include new gauge boson

Extensions to the SM (GUT) Extra Dimensions (Kaluza-Klein)

Use massive W boson with SM-like couplings

Z. Sullivan, arXiv:hep-ph/0207290 Large branching fraction to tb

R

R

MMcM

MMcM

WW

WW

2

2

GeV825

GeV800@95%CL

1.9 fb-1


CDF

Summary CDF entered era of precision top measurements.

Mass and cross section No longer stat. dominant. Need revisit syst. Uncertainty.

New measurements for the properties of top quark.

Some of them are measurable only at Tevatron. Many improvements in analysis techniques. Top is a good probe for new physics. Good agreement with Standard Model, so far. New results will be coming!

CDF/Tevatron combination for top mass,including recent 2 /fb results.

Single top: 4~5 sigma w/ >2 /fb


CDF

Backups


CDFBackground Table @1.9 fb-

1

Dilepton Lepton+Jets


CDFExample of Syst. Err. for Mtop

Combined Template Method for dilepton and lepton+jets

2

2top

GeV 0.29.171GeV syst0.1

JESstat7.19.171

cc

M


CDF

b-jet Flavor Tagging

Jet Charge

Performance

xTT

xTT

pp

Qpp

jettrack

trackjettrackJetQ

Dil=87%, P=61%, D2=0.10

L+J: =98%, P=61%, D2=0.13

(x=0.5)

Jet axis

b tagged

Soft

PTrel

Away Jet

b tagged

SSOS

OSP


CDF

W Helicity


CDFForward-Backward Asymmetry

Interference between LO and NLO diagrams

ttqq

gttqq

CDF での Top Flavor の物理

Documents

Transcript of CDF での Top Flavor の物理