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Recent Results from the Tevatron. Alison Lister UC Davis. Outline. The Tevatron and Experiments CDF XFT Trigger Upgrade ‘Bread and Butter’ Physics Precision Measurements of SM Processes The ‘Known Knowns’ Recent Observations The ‘Unknown Knowns’ SM Higgs Searches The ‘Unknown Unknowns’

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recent results from the tevatron

Recent Results from the Tevatron

Alison Lister

UC Davis

Alison Lister, UC Davis

  • The Tevatron and Experiments
    • CDF XFT Trigger Upgrade
  • ‘Bread and Butter’ Physics
    • Precision Measurements of SM Processes
  • The ‘Known Knowns’
    • Recent Observations
  • The ‘Unknown Knowns’
    • SM Higgs Searches
  • The ‘Unknown Unknowns’
    • Beyond SM Searches

Alison Lister, UC Davis

tevatron performance


1500 pb-1


750 pb-1






Fiscal Years

Tevatron Performance
  • Many improvements over last year
      • More pbars, more reliably
        • Weekly integrated luminosity increased 25  45 pb-1
        • Peak luminosity increased 180e30  282e30 cm-2 s-1
  • Expect ~6-7 fb-1 by Oct. ‘09

Thanks to the Accelerator Division!

Alison Lister, UC Davis


Symmetric around beam axis

Front-back symmetric

1.4 Tesla solenoid

~100 tons

Dedicated silicon detector

for secondary vertex tagging

Muon coverage up to || ~ 1.1

Electron reconstruction up to || ~ 2.8

Alison Lister, UC Davis



Symmetric around beam axis

Front-back symmetric

Solenoid + Toroid magnets

Liquid argon compensating calorimeter

June 2006: Start of Run IIb

First data with L0 silicon detector

Alison Lister, UC Davis

cdf d

3.3 fb-1

2.7 fb-1

  • Integrated luminosity
    • ~3.3 fb-1 by July 2007
    • About half-way to expected data size by end 2009
  • Data taking efficiency
    • CDF + DØ ~87%
      • Starting/stopping runs
      • DAQ/hardware problems
      • Trigger dead-time
    • ~80% of delivered luminosity is used in analyses

Took >2 years of collisions to get to stable high efficiency

Alison Lister, UC Davis

cdf trigger upgrades
CDF Trigger Upgrades
  • Peak luminosity increasing
    • Close to design luminosity
    • Record is 282e30
  • Trigger rates grow rapidly with instantaneous luminosity
    • Mostly due to ‘fakes’ and not real physics


CMX inclusive high pT muons


  • CDF 3-tier trigger system limited by bandwidth at L2
  • Adding pre-scales to triggers to keep rates down compromises physics goals
  • Series of trigger upgrades to keep high efficiency while reducing rates

Alison Lister, UC Davis

xft trigger upgrade








Z in SL7





SL5 has opposite stereo angle






Z in SL5


XFT Trigger Upgrade
  • COT (Central Outer Tracker)
    • 4 axial superlayers
    • 4 stereo superlayers
  • eXtremely Fast Tracker (XFT)
    • Track triggering system
    • Affects ~80% of all CDF physics
  • Before upgrades
    • Only using axial superlayers
  • XFT L1 upgrade
    • Confirm axial track passes through stereo layers and rough alignment of track in 3D
    • Gain factor 3-4 in rate

Real tracks

Reject Fakes !

Commissioned October 2006

Alison Lister, UC Davis

xft l2 upgrade
XFT L2 Upgrade
  • Use full stereo information to reconstruct tracks in 3D and combine with information from outer detector components

CMX inclusive high pT muons

  • Rate reduction factor 4 - 3.4
  • Efficiency for well reconstructed muons ~99%
  • Combination of L1 and L2 XFT upgrades should take us safely beyond the Tevatron design luminosity






Fermilab Engineer S.Holm about the system: “The most difficult firmware in my 25-year experience”

Commissioning this autumn

Alison Lister, UC Davis

latest results for lp07
Latest Results for LP07
  • Just under 100 new results from CDF+DØ shown at LP07 conference
  • CDF: 31 using full data up to April 2007 (2.2 fb-1)
  • All areas covered from precision measurements of the W mass to MSSM Higgs searches
  • Many searches using “state of the art” techniques
    • Neural Networks
    • Matrix Element
    • Decision Trees

Alison Lister, UC Davis

tevatron sensitivities

More data

Better understanding of ‘backgrounds’

~9 orders

of magnitude

Tevatron Sensitivities
  • 1st Physics [few 100 pb-1]
    • Heavy flavor physics, inclusive W/Z, re-establish top
  • Now [1-2 fb-1]
    • Precision Mt, Bs-Mixing,Top properties, Observation of rare processes
  • Looking Ahead [? fb-1]
    • Even rarer processes, New Physics searches, Higgs
    • ‘The’ unexpected

The focus is now to uncover the unknown

Alison Lister, UC Davis

bread and butter physics

‘Bread and Butter’ Physics

Alison Lister, UC Davis

w c jet cross section

1.0 fb-1

W+ c-jet Cross-Section
  • Select W + jets sample from lepton + jets final state
  • W + c-jet sample
    • Jet tagged with muon
      • pT>20 GeV/c and ||<2.5
    • W→l (l=e, μ, where  decays leptonically)
      • Lepton pT>20 GeV/c and Missing transverse energy > 20 GeV
    • Exploit correlation between charges of leptons
      • Background: same sign
      • Signal: opposite sign

Important background for ttbar and Higgs

Can constrain s-quark PDF

W+c-jet fraction = 0.071 ±0.017

In agreement with LO theoretical predictions

Alison Lister, UC Davis

cp violation in b j k

1.6 fb-1

CP Violation in B±→J/ K±
  • Looking for charge asymmetry in b→c cbar bbar and conjugate
  • Asymmetry sensitive to new physics
  • Use kaon charge tag
  • Exploit polarity reversal of magnets to remove detector bias
  • Need careful modelling of kaon asymmetry due to different inelastic cross-sections in detector
    • K+N→ has no K-N counterpart
  • Unbinned fit to signal
  • Likelihood fit parametrisastion of backgrounds

ACP(B+→J/ K+)= 0.0067± 0.0074 (stat.) ± 0.0026 (syst)

Factor 2 better precision than world average

Consistent with SM predictions of ~1%

Alison Lister, UC Davis

w mass

0.2 fb-1

W Mass
  • Template fit to
    • Transverse Mass
    • Transverse Momentum
    • Transverse Missing Energy
  • Using their own fast MC simulation
  • Data driven shape constraints
  • 63 964 W→e events
  • 51 128 W→μ events

Momentum scale calibration

MW = 80413 ±34 (stat) ±34 (syst) MeV/c2

Alison Lister, UC Davis

top mass

1.2 fb-1

Top Mass
  • Many methods with improvements and more data
  • Some new ideas
    • e.g measuring the mass using cross-section constraint
  • In dilepton channel (l=e, μ)
  • Under-constrained system solved using ttbar longitudinal momentum
  • Replacing statistical with theoretical uncertainties
  • Sensitive to kinematics of events as well as number of events
  • 70 events pass all selection criteria

Mt =170.7 +4.2-3.9 (stat) ± 2.6 (syst) ± 2.4 (theory) GeV/c2

Alison Lister, UC Davis

top mass1

1.1-1.8 fb-1

Top Mass

March 2007

  • This autumn big CDF publication push for all analyses with 2.2 fb-1
  • Expect ~10 new measurements since latest combination

Is it looking less and less SM-like or is that just me?

DØ-CDF Joint Systematics Effort Underway!

New combinations will follow…

Alison Lister, UC Davis

finding the known knowns

Finding the ‘Known Knowns’

Alison Lister, UC Davis

diboson results
Diboson Results


Triple Gauge Couplings


Alison Lister, UC Davis

wz production

1.9 fb-1

WZ Production
  • WZ→l’ll
    • 3 isolated lepton
      • e,μ,→e,μ
      • One > 25 Gev, other 2 > 10 GeV
    • Missing ET (for the ) > 25 GeV
    • Clean signal but BR only 1.8%
  • 2 leptons
    • Opposite sign, same flavour, Z mass window
  • Fit using log likelihood ratio

(WZ) = 4.1 +1.3-1.0(stat) ± 0.2(syst) ± 0.3(lumi)

Lepton composition (t=track)

In agreement with NLO prediction

Alison Lister, UC Davis

wwz couplings

1.9 fb-1

WWZ Couplings
  • Anomalous coupling limits set using pT distribution of Z-boson
  • Fit data using binned log likelihood to 3 parameters , g and  for 2 different values of  (1.5 and 2.0 TeV)


Consistent with SM NLO

Alison Lister, UC Davis

b direct observation

1.3 fb-1

b-Direct Observation
  • Many new baryon discoveries this past year
  • b-(dsb) one quark from each generation
  • Fully reconstruct exclusive decay
    • Sign of charge of tracks
    • Reconstructed displaced vertices
    • Masses and impact parameter resolution of reconstructed vertices
    • Angular separation between tracks
    • Minimum pT requirements
  • Use + for background studies
    • Wrong-sign
  • Interpretation of peak as b- using unbinned likelihood

Peak: 5.5 significance

M(b-) =5.774 ± 0.011(stat) ± 0.015(syst)

Alison Lister, UC Davis

evidence for single top

0.9 fb-1

Evidence for Single Top
  • SM:  ~ 3 pb and rate |Vtb|2
  • Combine 3 analyses
    • Decision Tree
    • Matrix Element Method
    • Bayesian Neural Network
  • Best Linear Unbiased Estimate
  • Assume SM ratio between s- and t-channel cross-sections

Boosted Decision Trees

Combined: 3.6 significance

Multivariate techniques

can coax signal out

from large backgrounds

Alison Lister, UC Davis

sm higgs production decay
SM Higgs Production + Decay
  • Direct production gg→H
    • Highest Production rate
    • Largest background
  • Associated production ZH/WH
    • Leptonic vector boson decay helps for triggering and signal extraction

Decay modes

  • Low Mass (MH<135 GeV/c2)
    • H→bb mode dominates
  • High Mass (135<MH<200 GeV/c2)
    • H→WW mode dominates
  • Intermediate Mass (MH ~135 GeV/c2)
    • Particularly difficult

Alison Lister, UC Davis

sm h ww l l

1.9 fb-1

SM H→WW*→ll
  • Most sensitive channel for high mass Higgs
  • 2 leptons: e,,→e,
    • Must have opposite signs
  • Using Matrix Element Method
    • Event probability density from LO matrix elements from MCFM
  • Data compared to NNLL calculation for different mass hypotheses

Limit at 2.0*SM

for MH=160 GeV/c2

Looks like CDF was lucky this time…

Alison Lister, UC Davis

sm higgs limits

Run 1

0.1 fb-1

0.3-1.0 fb-1

1-2 fb-1

SM Higgs Limits

0.9-1.9 fb-1

The Tevatron experiments are doing much better than √(∫ lumi)

Alison Lister, UC Davis

sm higgs limits1
SM Higgs Limits

0.9-1.9 fb-1

  • Combining all limits from all channels as well as between CDF and DØ

Alison Lister, UC Davis

sm higgs limits2
SM Higgs Limits
  • Projections based on 2 x DØ results (for CDF + DØ)
  • Assuming better than √(∫ lumi)
    • Reducing systematics, increasing acceptance, including more channels ()

Alison Lister, UC Davis

deviations from sm
Deviations from SM
  • New CDF web-page “Discovery Watch” (soon to be made public)
    • < 2% match to SM or > 2 away from SM

Alison Lister, UC Davis

susy msugra
  • SUSY is one of the more popular extensions to the SM
  • mSUGRA
    • SUSY symmetry broken by gravity at GUT scale
    • 5 parameters: m0, m1/2, tan , A0, sign(µ)
  • Previous Tevatron squark/gluino searches using Jet and large MET
    • Mainly arising from decay of LSP
  • High tan 
    • Squarks decay to charginos and neutralinos
    • Final states with leptons
  • In some models stau might be lightest lepton
    • Enhanced cross-section to taus
    • Squarks lighter than gluinos

Alison Lister, UC Davis

susy squarks with jet h met

0.96 fb-1

tan = 15

A = -2m0


LEP slepton


LEP chargino searches

SUSY: Squarks with Jet, h, MET
  • ≥2 jets (∆12>165˚,ET>35 GeV, ||<0.8)
  • MET ≥ 175 GeV
  • At least one isolated hadronically decaying  (ET>15 GeV, ||< 2.5)
    • Separate hfrom jets and electrons using loose cuts to NN outputs
  • HT = ET + ETjet1+ ETjet2 ≥ 325 GeV
  • Main backgrounds: Z(→)+jets, ttbar,W+jets
    • Modeled by ALPGEN+PYTHIA
  • QCD negligible after selection
  • -decays simulated by TAUOLA
  • Dominant systematic Jet Energy Scale
  • 2 observed events

Alison Lister, UC Davis

t search

0.76 fb-1

t’ Search
  • Massive 4th generation top-like quark
  • Predicted by some SUSY models (beautiful mirrors), Little Higgs
  • Generic 4th chiral generation allowed by EWK data; can accommodate a heavy Higgs (~500 GeV) without any other new particles
  • Looking for interesting events on the tails of distributions
  • Analysis will be re-done with ~2.2 fb-1 making use of heavy-flavour tagging to hopefully increase sensitivity

Exclude with 95% CL t´ mass below 256 GeV/c2

Alison Lister, UC Davis


Couple of Strange Events…

Alison Lister, UC Davis

high mass resonances in ee
High Mass Resonances in ee

0.9 fb-1

  • Model independent search for high mass narrow resonances
  • Scan Mass region 150-500 GeV/c2 in 5 GeV/c2 steps
  • Assume narrow resonance
    • Model with Gaussian of width equal to detector resolution
  • Fit distribution to background only and background + narrow resonance
    • Estimate probability of background giving 2 as large as largest deviation: 1.7%


Excess around 240 GeV/c2

Alison Lister, UC Davis

model independent searches

0.9 fb-1

Model Independent Searches
    • Model independent approach that looks at gross features of the data
    • Sensitive to new large cross-section physics
    • Partitioning of events into exclusive final states
      • e,µ,,,jet,missing pT, …
  • Global comparison to SM predictions
  • 16’486 kinematic distributions from 344 exclusive final states
    • 409 distributions with deviation > 5
    • None believed to have new physics interpretation

Alison Lister, UC Davis


0.9 fb-1

  • Quasi-model independent approach emphasizes the high-ΣpT tails
  • Particularly sensitive to new electroweak scale physics
  • Looks at one variable: ΣpTfor all final states
  • Uses correction factors to SM predictions found by VISTA
  • SLEUTH determines most interesting region of tail
  • Same-sign e µ+ 2 jets + MET final state
  • 4 data events observed
  • 0.71 SM events predicted
  • 2.5 effect (stat only)

Alison Lister, UC Davis

status of the sm
Status of the SM
  • Very rich and diverse physics program
    • “Looking in most nooks and crannies”
  • Background understanding improving
    • Small systematic uncertainties in searches
  • Experiments found many new processes expected by SM
    • Sensitive to beyond SM
  • SM Higgs discovery potential looks much more exciting than it did a year ago
  • Model dependent and model independent searches showing “noise” above SM predictions but nothing concrete

EWK fit: MH<182 GeV/c2

(incl. LEP direct exclusion)

Alison Lister, UC Davis


We know something is out there but what and where?

Will we find “it” at the Tevatron or at the LHC?

Alison Lister, UC Davis

backup slides

Backup Slides

Alison Lister, UC Davis

evidence for zz

1.1-1.5 fb-1

Evidence for ZZ
  • ZZ→llll and ZZ→ll (l = e or )
  • Systematics
    • Mostly dominated by cross-section uncertainty of back-ground processes
    • Drell-Yan the missing ET is dominant
    • W+jets dominated by lepton fake rate

Likelihood ratio plot for ll

Measured: (ZZ) = 0.75 + 0.71- 0.54 pb

SM NLO: (ZZ) = 1.4 ± 0.1 pb

Consistent with SM without triple gauge coupling

Alison Lister, UC Davis

b baryon discoveries

1.1-2.2 fb-1

B Baryon Discoveries




Alison Lister, UC Davis