Top Quark Properties results and ongoing analyses at the Tevatron
Recent Results from the Tevatron
description
Transcript of Recent Results from the Tevatron
PSI seminar 5th November 2007 Alison Lister, UC Davis 1
Recent Results from the Tevatron
Alison ListerUC Davis
PSI seminar 5th November 2007 Alison Lister, UC Davis 2
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
PSI seminar 5th November 2007 Alison Lister, UC Davis 3
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
PSI seminar 5th November 2007 Alison Lister, UC Davis 4
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
PSI seminar 5th November 2007 Alison Lister, UC Davis 5
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
PSI seminar 5th November 2007 Alison Lister, UC Davis 6
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
PSI seminar 5th November 2007 Alison Lister, UC Davis 7
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
PSI seminar 5th November 2007 Alison Lister, UC Davis 8
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)
PSI seminar 5th November 2007 Alison Lister, UC Davis 9
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
PSI seminar 5th November 2007 Alison Lister, UC Davis 10
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 …
PSI seminar 5th November 2007 Alison Lister, UC Davis 11
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’
PSI seminar 5th November 2007 Alison Lister, UC Davis 12
‘Bread and Butter’ Physics
PSI seminar 5th November 2007 Alison Lister, UC Davis 13
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
PSI seminar 5th November 2007 Alison Lister, UC Davis 14
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
PSI seminar 5th November 2007 Alison Lister, UC Davis 15
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
PSI seminar 5th November 2007 Alison Lister, UC Davis 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-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
PSI seminar 5th November 2007 Alison Lister, UC Davis 17
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…
PSI seminar 5th November 2007 Alison Lister, UC Davis 18
Finding the ‘Known Knowns’
PSI seminar 5th November 2007 Alison Lister, UC Davis 19
Diboson Results
t-channel
s-channelTriple Gauge Couplings
PSI seminar 5th November 2007 Alison Lister, UC Davis 20
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
PSI seminar 5th November 2007 Alison Lister, UC Davis 21
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
PSI seminar 5th November 2007 Alison Lister, UC Davis 22
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)
PSI seminar 5th November 2007 Alison Lister, UC Davis 23
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
PSI seminar 5th November 2007 Alison Lister, UC Davis 24
Trying to find the ‘Unknown Knowns’
PSI seminar 5th November 2007 Alison Lister, UC Davis 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
PSI seminar 5th November 2007 Alison Lister, UC Davis 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-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…
PSI seminar 5th November 2007 Alison Lister, UC Davis 27
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
PSI seminar 5th November 2007 Alison Lister, UC Davis 28
SM Higgs Limits• Combining all limits from all channels as well as between CDF and DØ
0.9-1.9 fb-1
PSI seminar 5th November 2007 Alison Lister, UC Davis 29
SM Higgs Limits• Projections based on 2 x DØ results (for CDF + DØ)• Assuming better than √(∫ lumi)
Reducing systematics, increasing acceptance, including more channels ()
PSI seminar 5th November 2007 Alison Lister, UC Davis 30
Looking for the ‘Unknown Unknowns’
PSI seminar 5th November 2007 Alison Lister, UC Davis 31
Deviations from SM• New CDF web-page “Discovery Watch” (soon to be made public)
< 2% match to SM or > 2 away from SM
PSI seminar 5th November 2007 Alison Lister, UC Davis 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
• 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)
PSI seminar 5th November 2007 Alison Lister, UC Davis 33
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
PSI seminar 5th November 2007 Alison Lister, UC Davis 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/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
PSI seminar 5th November 2007 Alison Lister, UC Davis 35
Couple of Strange Events…
PSI seminar 5th November 2007 Alison Lister, UC Davis 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-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%
?
PSI seminar 5th November 2007 Alison Lister, UC Davis 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-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
PSI seminar 5th November 2007 Alison Lister, UC Davis 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-1
• Same-sign e µ+ 2 jets + MET final state
• 4 data events observed• 0.71 SM events predicted• 2.5 effect (stat only)
PSI seminar 5th November 2007 Alison Lister, UC Davis 39
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
PSI seminar 5th November 2007 Alison Lister, UC Davis 40
We know something is out there but what and where?
Will we find “it” at the Tevatron or at the LHC?
PSI seminar 5th November 2007 Alison Lister, UC Davis 41
Backup Slides
PSI seminar 5th November 2007 Alison Lister, UC Davis 42
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
PSI seminar 5th November 2007 Alison Lister, UC Davis 43
B Baryon Discoveries
b
b
b
1.1-2.2 fb-1