Recent Results from the Tevatron

Recent Results from the Tevatron

Mary ConveryFermilab

for the CDF and DØ Collaborations

ALCPG11 – Linear Collider Workshop of the AmericasEugene, Oregon

March 19-23, 2011

Mary Convery (Fermilab) ALCPG11 2

Outline

• Introduction• Recent Tevatron highlights

– New particles observed– CP violation– Precision measurements– Higgs searches

• Conclusions

Main Injector /Recycler

Tevatron( ~4 miles circumf)

CDF

DØ

Antiproton source

Chicago

Proton source

The Fermilab Tevatron Collider Run II

Proton-antiproton collisions at √s=1.96 TeV


The Fermilab Tevatron Collider Run II


yearInte

gra

ted

lum

ino

sity

(p

b-1)

/ 1

013 a

ntip

roto

ns

Tevatron has performed well the last few years

Optimized use of antiprotons

Luminosity performance and projections


real data for FY02-FY08

7.8 fb-1

Inte

gra

ted

lum

ino

sity

(fb

-1)

---------

FY04 FY05 FY06 FY07 FY08 FY09 FY10 FY11

~12 fb-1

9.305 fb-1 deliveredthru FY10

have achieved design parameter goals of Run II

on track for ~12 fb-1 through FY11, experiments would acquire ~10 fb-1

9.3 fb-1

currently ~10.5 fb-1


CDF and DØ Run II detectors

L2 trigger on displaced vertices Excellent tracking resolution Excellent muon ID and acceptanceExcellent tracking acceptance || < 2-3

Both detectors•Silicon microvertex tracker•Solenoid•High rate trigger/DAQ•Calorimeters and muons

The Tevatron research program

Precision, New Research Discoveries

• Mixing, CKM Constraints and CP Violation

• Heavy Flavor Spectroscopy• New Heavy Baryon States• Tests of Quantum

Chromodynamics• Precise measurement of Top-

quark and W-boson Masses• Top Quark Properties• Di-Boson production and SM

Gauge Couplings• New Exclusive/Diffractive

Processes

Unique Window into the unknown• Searches for Supersymmetry,

Extra Dimensions, Exotica• Probing the Terascale as the

luminosity increases

• Standard Model Higgs Boson is within reach!

Mary Convery (Fermilab) 7ALCPG11

8

Observation of new heavy baryons

ddb

uub

dsb

2006 2007

2009Mary Convery (Fermilab) ALCPG11

ddbuub

dsb ssb

9

With more data: emergence of a new particle (CDF)

2009 YY(4140)(4140) unknown composition

These new discoveries yield a few events/fb-1 new areas of research @ 10 fb-1These new discoveries yield a few events/fb-1 new areas of research @ 10 fb-1

Mary Convery (Fermilab) ALCPG11

m = 4143.4+2.9-3.0 (stat) ± 0.6(syst) MeV/c2

= 15.3+10.4-6.1 (stat) ± 2.5(syst) MeV/c2

statistical significance > 5

CP violation• Charge-conjugation – Parity conservation: a process in

which all particles are exchanged with their antiparticles is equivalent to the mirror image of the original process

• The weak interaction does not conserve C, P, or CP, so the Standard Model predicts CP violation

• Cabibbo-Kobayashi-Maskawa matrix contains information on the strength of flavor-changing weak decays, important in the understanding of CP violation

• CKM matrix unitary in the SM


SM levels of CP violation do not explain apparent matter-antimatter asymmetry of the universe

CP violation in Bs→ J/

• The mass eigenstates are a superposition of Bs and Bs

• Width difference between mass eigenstates is correlated with s

– Measure simultaneously

• CP violation in the interference between decay w/ and w/o Bs - Bs mixing

• Measure by statistical determination of CP even and odd contribution using angular analysis

• New physics can have large

effect on CP violation


Bs0

Bs0

_J/

J/

Bs

0

,t’

,t’

Bs0=sb

Bs0=sb

_

_

_

_

_

_

Precision: CP Violation in s

12

Both CDF and D0 measure the CP violating parameter s in Bs in J/


Dimuon charge asymmetry (D0)

• Measure CP violation in mixing using the dimuon charge asymmetry of semileptonic B decays:

– Nb++, Nb

−− : number of events with two b hadrons decaying semileptonically and producing two muons of same charge

– One muon comes from direct semileptonic decay b → μ−X

– Second muon comes from direct semileptonic decay after neutral B meson mixing

bb

bbbsl NN

NNA

X

X

0B0B


Evidence for anomalous like-sign dimuon charge asymmetry

• Asl is 3.2 from Standard Model predictions

• First evidence for Beyond the Standard Model CP Violation

0B

XlBB

XlBB

sdsd

sdsd)(0

,0

,

0,

0,

)(

• Double semileptonic decay of BB results in OS lepton pair when no mixing; LS lepton pair when one meson undergoes mixing

• Use impact parameters of muon pairs with template fits to identify source of muons: b, c, prompt

• Correct for other sources of dimuons

=0.126±0.008, consistent with LEP average =0.1259±0.0042, smaller than previous Tevatron measurements (CDF’s used looser silicon-track requirements)

Measurement of time-integrated mixing probability of B hadrons


__

_

μ+ μ+

μ+ μ

μ μ

Search for new dielectron resonances and Randall-Sundrum gravitons

• Common approach to search for new particles – look for bump in mass of combined objects

• No significant excess over SM observed• Combined with 5.4 fb-1 diphoton analysis,

RS-graviton mass limit for the coupling k/MPl=0.1 is 1055 GeV/c2 – strongest limit to date


Highest-mass dielectron ever observed (960 GeV/c2)

Signature-based Search: γ + missing-ET + b-jet + lepton

• Search for new physics by looking for anomalies in kinematic distributions, rather than limiting search to specific model

• Leading background is Standard Model tt • No excess observed• Measure cross section σ(tt) =0.18 ± 0.07 pb• R(tt/tt) = 0.024 ± 0.009

16Mary Convery (Fermilab) ALCPG11

Towards the Higgs


W mass summary

Mw = 80.399 0.023 GeV

Tevatron has world’s best measurement


Top quark pair production and decay• Top quark existence required by the SM,

partner of the bottom quark• Discovered in 1995 at Tevatron • Only SM fermion with mass at the EW scale

~40x heavier than the bottom quark• Top decays before hadronization – provides

unique opportunity to study a "bare" quark • Pair produced via strong interaction

• Top quark decays ~100% to W+b• t-tbar events classified by decay of W’s:

– All-hadronic (44%, large background)– Dilepton (5% excl , small background)– Lepton+Jet (30% excl , manageable

background)


Summary of Top Mass

We now know the mass of the top quark with better precision (<1%) than any other quark


new!

updated

http://www-cdf.fnal.gov/physics/new/top/2009/mass/tevcombination_march/topmass_tev0309v1.eps

Constraints from precision top quark mass measurement

• SM Higgs Mass constrained by Mtop and MW through loop correction of W mass

• Precision top quark mass measurement– Predict SM Higgs mass– Constraints for physics

beyond standard model

X ??


Where is the Higgs hiding?

MH < 157 GeV at 95% C.L. preferred MH – 87+35

-26 GeV

Mw vs Mtop


Standard Model Higgs production and decay

• Higgs are produced in several different ways

– gg→H, qq → WH, qq → ZH biggest cross sections

– Also qq → qqH, bb → H, gg,qq→ ttH

• The Higgs decays into different “final states” depending on its mass

• To find it, we need to look at all these final decay states and combine the results


The Challenge

These are production numbers – trigger, acceptance etc. not yet factored in…

# of Events produced/exp in 1 fb-1


W/Z + jets

• Test of perturbative QCD• Background for W/Z+H and other new physics

– Test Monte-Carlo modeling


Di-bosons WW, WZ, ZZ

• Background to Higgs searches: W/Z H, H->WW, H->ZZ• Similar techniques as used for Higgs searches

– dijet mass, matrix element, neural networks– Discrimination in kinematics of final state (???)


• Using mjj and matrix element techniques with 4.3-4.6fb-1

• Observed with >5 significance

WW/WZ → lepton + jets

5.2 σ5.4 σ

σ = 18.1 ± 3.3stat ± 2.5sys pb

σ = 16.5 +3.3-3.0 ± 3.5sys pbSM = 15.1 ± 0.9 pb


WZ→lll, ZZ→ll

• Using neural networks


3.7±0.6(stat.). +0.6-0.4 (syst.)

ZZ → eeee, ee,

• 10 events

• σ = 1.35+0.50-0.40(stat) ± 0.15(syst) pb

• SM prediction 1.4±0.1 pb


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Single top

• Test s vs t channel [new physics]• Direct measurement of Vtb [precision]• Lifetime [new physics]

• Wbb similar final state as Higgs– Similar tools

• Test s vs t channel [new physics]• Direct measurement of Vtb [precision]• Lifetime [new physics]

• Wbb similar final state as Higgs– Similar tools


SM Higgs: HWW (high mass channel)

• HWWll - signature: Two high pT leptons and MET

– Primary backgrounds: WW and top in di-lepton decay channel– Key issue: Maximizing signal acceptance– Excellent physics-based discriminants

• Most sensitive Higgs search channel at the Tevatron

HHμ+

ν

W-

W+

e-

ν

W-

W+

Spin correlation: Charged leptons go in the same direction


Limits from HWW

• First time CDF and D0 independently exclude mass range for Standard Model Higgs at 95% CL

• D0 excludes MH=165 GeV/c2

• CDF excludes 158<MH<168 GeV/c2


Combine experiments

Fac

tor

away

in s

ensi

tivity

fro

m S

M

Neither experiment has sufficient power to span the entire mass range using the luminosity we expect to acquire in Run II

SM Higgs Excluded: mH = 163-166 GeV


We are making steady progress…

• Some projected improvements:• Combine all channels• Maximize signal acceptance• Improve b-tagging to reduce

W/Z+jets background• Improve dijet mass

reconstruction (resolution)• Improve di-tau mass

reconstruction• Improve signal vs background

separation (neural networks, boosted decision trees, matrix element methods, combining different kinematic variables


How well can we do?


Forward-backward tt production asymmetry

• QCD t-tbar production symmetric at leading order, positive and negative contributions to asymmetry at next-to-leading order

• Asymmetry seen in previous measurements by CDF and D0 and dilepton channel

• New CDF measurements show 2 excess in both lepton+jets and dilepton channel


low mass high mass

high massl -

high massl +

_

BF

BFAfb

Evidence for mass dependence of Afb

• Significant asymmetry at large y, Mtt

• Consistent with CP conservation (l + vs l - = t vs t)


low mass high mass

high massl -

high massl +

_

Conclusions

• The Tevatron has a broad program

– Precision measurements• Mixing, CKM Constraints and CP Violation• Precise measurement of top-quark and W-boson

masses– Searches for Higgs and beyond SM physics– B hadron spectroscopy

• Once new particles observed, studies of their properties

– Tests of Quantum ChromoDynamics• Stay tuned as the Tevatron continues to produce

important results in many areas of HEP


Recent Results from the Tevatron

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