Recent Results from the Tevatron

PSI seminar 5th November 2007 Alison Lister, UC Davis 1

Recent Results from the Tevatron

Alison ListerUC 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’

Beyond SM Searches


Thanks to the Accelerator Division!

• 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

2007

20062005 2004

2003

Design

Base

Fiscal Years

1500 pb-1

750 pb-1

Tevatron Performance


CDF IISymmetric around beam

axisFront-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


DØ IISymmetric around beam

axisFront-back symmetric

Solenoid + Toroid magnets

Liquid argon compensating calorimeter

June 2006: Start of Run IIbFirst data with L0 silicon

detector


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 by end 2009

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

3.3 fb-1

2.7 fb-1


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


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 October 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)


XFT L2 Upgrade• 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 autumn

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

default

L2 pointing

L1 confirmed

CMX inclusive high pT muons


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 …


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

~9 ordersof magnitude

More dataBetter understanding of ‘backgrounds’


‘Bread and Butter’ Physics


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-1

W+c-jet fraction = 0.071 ± 0.017

In agreement with LO theoretical predictions

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


1.6 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 modelling 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)

Consistent with SM predictions of ~1%

Factor 2 better precision than world average

• Unbinned fit to signal• Likelihood fit parametrisastion of

backgrounds


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/c2

0.2 fb-1

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


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-1

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


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-1

March 2007

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

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


Finding the ‘Known Knowns’


Diboson Results

t-channel

s-channelTriple Gauge Couplings


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-1

(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 prediction


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

NLO MCFM

1.9 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

1.3 fb-1

• 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)


Evidence for Single Top 0.9 fb-1

Combined: 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-sectionsBoosted Decision Trees

Multivariate techniques can coax signal out from large backgrounds


Trying to find the ‘Unknown Knowns’


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


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-1

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…


SM Higgs Limits 0.9-1.9 fb-1

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

0.3-1.0 fb-1

1-2 fb-1

Run 10.1 fb-1


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

0.9-1.9 fb-1


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

Reducing systematics, increasing acceptance, including more channels ()


Looking for the ‘Unknown Unknowns’


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

< 2% match to SM or > 2 away from SM


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

• In 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)


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-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 searchesLE

P s

lept

on s

earc

hes

tan = 15A = -2m0

µ<0


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/c2

0.76 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


Couple of Strange Events…


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-1

Excess 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%

?


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-1

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


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-1

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

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


Status of the SM

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

• 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


We know something is out there but what and where?

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


Backup Slides


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-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 coupling


B Baryon Discoveries

b

b

b

1.1-2.2 fb-1

Recent Results from the Tevatron

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