recent results from the tevatron

EPFL seminar 29th October 2007

Alison Lister, UC Davis

1

Recent Results from the Tevatron

Alison Lister

UC Davis



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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’ Beyond SM Searches



3

Thanks to the Accelerator Division!Thanks to the Accelerator Division!

• Many improvements over last year• More pbars, more reliably

Monthly integrated luminosity increased 25 45 pb-1

Peak luminosity increased 180e30 292e30 cm-2 s-1

• Expect ~6-7 fb-1 by Oct. ‘09

2007

20062005 2004

2003

Design

Base

Fiscal Years

1500 pb-1

750 pb-1

Tevatron Performance



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CDF IISymmetric around beam

axis

Front-back symmetric

1.4 Tesla solenoid

Dedicated silicon detector

for secondary vertex tagging

~100 tons

Electron reconstruction up to || ~ 2.8Muon coverage up to || ~ 1.1



5

DØ IISymmetric around beam

axis

Front-back symmetricSolenoid + Toroid

magnets

Liquid argon compensating calorimeter

June 2006: Start of Run IIb

First data with L0 silicon detector



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CDF + DØ

• Data taking efficiency CDF + DØ ~87%

• Starting/stopping runs• DAQ/hardware problems• Trigger dead-time

~80% of delivered luminosity is used in analyses

• Integrated luminosity ~3.3 fb-1 by July 2007 About half-way to expected data

size

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

3.3 fb-1

2.7 fb-1



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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

300e30

• 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

default

CMX inclusive high pT muons



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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

Commissioned Oct 2006Commissioned Oct 2006

Real tracks

Reject Fakes !

Z in SL7

+

-

- +Z in SL5

• 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

SL5

SL6

SL7pixel (SL7)

SL5 has opposite stereo angle

pixel (SL5)

SL3

SL4

pixel (SL3)

(stereo)

(stereo)

(stereo)

(axial)

(axial)



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XFT L2 Upgrade

default L1 confirmed

L2 pointing

• Use full stereo information to reconstruct tracks in 3D and combine with information from outer detector components

• 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

Commissioning this autumnCommissioning this autumn

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



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Latest Results for LP07• 51 (42) new results from CDF

(DØ) shown at LP07 conference• 31 from CDF 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 …



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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 unknownThe focus is now to uncover the unknown

~9 ordersof magnitude

More dataBetter understanding of ‘backgrounds’



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‘Bread and Butter’ Physics



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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

1.0 fb-11.0 fb-1

W+c-jet fraction = 0.071 ± 0.017W+c-jet fraction = 0.071 ± 0.017

In agreement with LO theoretical predictionsIn agreement with LO theoretical predictions

Important background for ttbar and HiggsImportant background for ttbar and Higgs Can constrain s-quark PDFCan constrain s-quark PDF



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1.6 fb-11.6 fb-1CP 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 modeling of kaon

asymmetry due to different inelastic cross-sections in detector K+N→ has no K-N counterpart

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

Consistent with SM predictions of ~1%Consistent with SM predictions of ~1%

Factor 2 better precision than world averageFactor 2 better precision than world average

• Unbinned fit to signal• Likelihood fit parametrisastion of

backgrounds



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W Mass• Template fit to

Transverse Mass Transverse Momentum Transverse Missing Energy

• Using their own fast MC simulation• Data driven shape constraints

MW = 80413 ± 34 (stat) ± 34 (syst) MeV/c2MW = 80413 ± 34 (stat) ± 34 (syst) MeV/c2

0.2 fb-10.2 fb-1

• 63 964 W→e events• 51 128 W→μ eventsMomentum scale calibration



16

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

1.2 fb-11.2 fb-1

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

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

• Replacing statistical with theoretical uncertainties

• Sensitive to kinematics of events as well as number of events

• 70 events pass all selection criteria



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Top Mass• This autumn big CDF publication

push for all analyses with 2.2 fb-1

• Expect ~10 new measurements since latest combination

1.1-1.8 fb-11.1-1.8 fb-1

March 2007

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

DØ-CDF Joint Systematics Effort Underway!New combinations will follow…

DØ-CDF Joint Systematics Effort Underway!New combinations will follow…



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Finding the ‘Known Knowns’



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Diboson Results

t-channel

s-channel

SM

Triple Gauge Couplings?



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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%

1.9 fb-11.9 fb-1

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

Lepton composition (t=track)

• 2 leptons opposite sign, same flavour, Z mass

window

• Fit using log likelihood ratio

In agreement with NLO predictionIn agreement with NLO prediction



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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 without triple gauge couplingConsistent with SM NLO without triple gauge coupling

NLO MCFM

1.9 fb-11.9 fb-1



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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

1.3 fb-11.3 fb-1

• Use + for background studies wrong-sign

• Interpretation of peak as b-

using unbinned likelihood

Peak: 5.5 significancePeak: 5.5 significance

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



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Evidence for Single Top 0.9 fb-10.9 fb-1

Combined: 3.6 significanceCombined: 3.6 significance

• 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

Multivariate techniques can coax signal out from large backgrounds

Multivariate techniques can coax signal out from large backgrounds



24

Trying to find the ‘Unknown Knowns’



25

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



26

SM H→WW*→ll• 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

1.9 fb-11.9 fb-1

Limit at 2.0*SM

for MH=160 GeV/c2

Limit at 2.0*SM

for MH=160 GeV/c2

• Data compared to NNLL calculation for different mass hypotheses

Looks like CDF was lucky this time…Looks like CDF was lucky this time…



27

SM Higgs Limits 0.9-1.9 fb-10.9-1.9 fb-1

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

0.3-1.0 fb-1

1-2 fb-1

Run 10.1 fb-1



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SM Higgs Limits• Combining all limits from all channels as well as between CDF and D0

0.9-1.9 fb-10.9-1.9 fb-1



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SM Higgs Limits• Projections based on 2 x D0 results (for CDF + D0)• Assuming better than √(∫ lumi)

Reducing systematics, increasing acceptance, including more channels ()

0.9-1.9 fb-10.9-1.9 fb-1



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Looking for the ‘Unknown Unknowns’



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Deviations from SM• New CDF web-page “Discovery Watch” (soon to be made public)



32

SUSY + mSUGRA

• 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

• Some models stau might be lightest lepton Enhanced cross-section to taus Squarks lighter than gluinos

• 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)



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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 h from jets and electrons using

loose cuts to NN outputs

HT = ET + ET

jet1+ ETjet2 ≥ 325 GeV

0.96 fb-10.96 fb-1

• 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

LEP chargino searchesL

EP

sle

pto

n s

ea

rch

es

tan = 15A = -2m0

µ<0



34

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

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Exclude with 95% CL t´ mass below 256 GeV/c2Exclude with 95% CL t´ mass below 256 GeV/c2

0.76 fb-10.76 fb-1

• 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



35

Couple of Strange Events… Couple of Strange Events…



36

High Mass Resonances in ee• 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

0.9 fb-10.9 fb-1

Excess around 240 GeV/c2Excess around 240 GeV/c2

• Fit distribution to background only and background + narrow resonance Estimate probability of background

giving 2 as large as largest deviation: 1.7%

?



37

Model Independent Searches

• VISTA 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, …

0.9 fb-10.9 fb-1

Global comparison to SM predictions from PYTHIA, MADEVENT and/or HERWIG

16’486 kinematic distributions from 344 exclusive final states

• 409 distributions with deviation > 5

• None believed to have new physics interpretation



38

SLEUTH• Quasi-model independent approach emphasizes the high-ΣpT tails

• Particularly sensitive to new electroweak scale physics

• Looks at one variable: ΣpT for all final states

• Uses correction factors to SM predictions found by VISTA• SLEUTH determines most interesting region of tail

0.9 fb-10.9 fb-1

• Same-sign e mu + 2 jets + MET final state

• 4 data events observed• 0.71 SM events predicted• 2.5 sigma effect (stat only)



39

Status of the SM

EWK fit: MH<182 GeV/c2

(incl. LEP direct exclusion)

EWK fit: MH<182 GeV/c2

(incl. LEP direct exclusion)

• 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

• Higgs discovery at Tevatron looks much exciting than it did a year ago New results expected in next year

• Model dependent and model independent searches showing “noise” above SM predictions but nothing concrete

We know something is out there but what and where?

We know something is out there but what and where?



40

Backup Slides



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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

1.1-1.5 fb-11.1-1.5 fb-1

Measured: (ZZ) = 0.75 + 0.71 - 0.54 pbSM NLO: (ZZ) = 1.4 ± 0.1 pb

Likelihood ratio plot for ll

Consistent with SM without triple gauge couplingConsistent with SM without triple gauge coupling



42

B Baryon Discoveries

b

b

b

1.1-2.2 fb-11.1-2.2 fb-1

recent results from the tevatron

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