Enough Bs

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Enough Bs. Lets Talk about Top

• Florencia Canelli
• on behalf of the CDF Collaboration

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Over the TopPrecision Top Quark Mass
Measurements from CDF

• Florencia Canelli
• on behalf of the CDF Collaboration

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Outline

• State of the Art in CDF Mtop measurements
• CDF Mtop program
• New measurements
• New CDF combination
• Future

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The Top Quark

• The top quark was discovered only 10 years ago
• Existence is required by the SM, but striking
  characteristics its mass is surprisingly large
• Studied only at the Tevatron

The Standard Model
Particle Masses
t Z W b c s d u ?
? e ?? ?? ?e
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Why measure the Top Quark Mass?

• Related to standard model observables and
  parameters through loop diagrams
• Consistency checks of SM parameters
• Precision measurements of the Mtop (and MW)
  allow prediction of the MHiggs
• Constraint on Higgs mass can point to physics
  beyond the standard model

Summer 2005
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Tevatron Performance in ?Mtop/Mtop
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Production and Decay

• At Tevatron, mainly produced in pairs via the
  strong interaction
• Decay via the electroweak interactions
• Final state is characterized by the decay of the
  W boson
• Dilepton
• LeptonJets
• All-Jets

85

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Br(t ?Wb) 100
Different sensitivity and challenges in each
channel

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Dilepton Channel
Final State from Leading Order Diagram
What we measure

• Branching fraction 5 (lepton e or ?)
• Final state 2 leptons, 2 b quarks, 2 neutrinos
• Combinatorial background 2 combinations
• 2 neutrinos under constrained, kinematically
  complicated to solve Mtop
• SB 21 and 201 requiring 1? identified b tag

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LeptonJets Channel
Final State from Leading Order Diagram
What we measure

• Branching fraction 30 (lepton e or ?)
• SB 14 to 111 depending on the b-tagging
  requirement
• Combinatorial background 12 (0 b tag), 6 (1 b
  tag), and 2 (2 b tags)
• 1 neutrino over constrained
• Most precise Mtop measurements

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All Jets Channel
Final State from Leading Order Diagram
What we measure

• Branching fraction 44
• Huge amount of background SB 18 after
  requiring at least 1 b-tag jet
• Combinatorial background 90 combinations
• Backgrounds mainly from multi-jet QCD production

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Top Quark Mass at CDF
CDF Summer 2005 Results

• Robust program of top quark mass measurements
• Many measurements in all the different channels
  -gt consistency
• Different methods of extraction with different
  sensitivity -gt confidence
• Combine all channels and all methods -gt precision

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?Mtop

• Different statistical and systematical
  sensitivities in each channel
• Other sources arise from the assumptions employed
  to infer Mtop
• Initial state and final state radiation
• Parton distribution functions
• b-jet energy scale
• Generators
• Background modeling and composition
• b-tagging efficiency
• MC statistics
• Systematics dominated by the uncertainty on
  parton energies (Jet Energy Scale, JES)

CDF Measurement (350pb-1) Statistical (GeV/c2) JES (GeV/c2) Other syst. (GeV/c2)
Dilepton 6 3 2
LeptonJets 4 2 1
All Jets 5 4 2
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Jet Energy Scale

• Jet energy scale
• Determine the energy of the quarks produced in
  the hard scattered
• We use the Monte Carlo and data to derive the jet
  energy scale
• Jet energy scale uncertainties
• Differences between data and Monte Carlo from all
  these effects

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Jet Energy Scale Uncertainties
About 3 of Mtop when convoluted with ttbar pT
spectrum
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In-situ Measurement of JES

• Additionally, we use W?jj mass resonance (Mjj) to
  measure the jet energy scale (JES) uncertainty

Constrain the invariant mass of the non-b-tagged
jets to be 80.4 GeV/c2
Mjj
Measurement of JES scales directly with
statistics!
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Data and Monte Carlo
W-jet pT
b-jet pT
ttbar pT
Mttbar
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In this Talk

• Dilepton Matrix Element
• Lepton jets Template analysis
• Lepton jets Matrix Element
• Lepton jets Decay Length
• All Hadronic Ideogram

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Mtop Dilepton Results
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Method Overview

• Measurement with this method using 340 pb-1
• hep-ex/0512070, PRL accepted, PRD to be submitted
• Wine and Cheese August, 2005
• Likelihood is a linear combination of signal and
  background hypothesis
• Optimizes the use of information in the event
• Description of dominant backgrounds Drell-Yan,
  WWjets, fakes (instrumental)
• Updated measurement
• using 750 pb-1

Expected Events (750 pb-1)
DY, WWjets, fakes 15.7? 4.3
EW (WZ,WZ,ZZ) 3.6 ? 0.7
Total background 19.4 ? 3.4
tt (6.1 pb) 36.1 ? 1.2
Data 64
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Results

• Using 64 candidates events found in 750 pb-1 we
  measure
• Restrict sample to b-tagged events Mtop 162.7
  4.6 3.0 GeV/c2
• Comparable sensitivity to best
  leptonjets Run I measurements

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Mtop LeptonJets Results
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Template Analysis

• Measurement using this method with 318 pb-1
• PRL 96, 022004 PRD 72, 032003
• Used for Run I measurements
• Wine and Cheese April, 2005
• Reconstructed mtop and mjj from data are compared
  to templates of various true Mtop and ?JES (jet
  energy uncertainty shift) using an unbinned
  likelihood
• Uses four samples to increase sensitivity

2 b tags 1 b tag (T) 1 b tag (L) 0 b tag
Expected SB 101 41 11 0.61
Expected Number of Events ( ?tt 6.1pb) 47 104 64 no a priori estimate
Data (680 pb-1) 57 120 75 108
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Template Analysis Results

• Using 360 candidate events in 680 pb-1 we measure
• Using in-situ JES calibration results in 40
  improvement on JES

Better sensitivity than the previous world
average!
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Matrix Element Analysis Technique

• CDF adaptation of method used by D0
• Nature Vol 429, June 2004, D0 Run I
• Similar to the CDF Dynamical Likelihood Method
  PRL 96, 022004 PRD accepted, Wine and Cheese
  November, 2004
• D0 preliminary Run II result using 380 pb-1
• Optimizes the use of kinematic and dynamic
  information
• Build a probability for a signal and background
  hypothesis
• Likelihood simultaneously determines Mtop, JES,
  and signal fraction, Cs

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Matrix Element Analysis Technique

• For a set of set measured variables x
• JES sensitivity comes from W resonance
• All permutations and neutrino solutions are taken
  into account
• Lepton momenta and all angles are considered well
  measured

W(x,y) is the probability that a parton level set
of variables y will be measured as a set of
variables x (parton level corrections)
dn? is the differential cross section LO Matrix
element
f(q) is the probability distribution than a
parton will have a momentum q
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Monte Carlo Tests

• Calibrate method against MC samples
• Shows unbiased measurement
• Extracted errors are found to be underestimated
  by 6

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Event Selection

• Exactly 4 jets with with 1 b tags
• 1-b tag 4 jets ETgt15 GeV (SB51)
• 2-b tags 4 jets ETgt15 GeV (SB131)

Expected Events (680 pb-1)
W4 jets (Mistags) 4.39 ? 0.91
Non-W (QCD) 3.75 ? 1.86
Wbb 3.35 ? 1.54
Wcc 1.60 ? 0.76
Wc 1.00 ? 0.45
Single top 0.81 ? 0.19
EW (WZ,WZ,ZZ) 0.77 ? 0.17
Total background 15.67 ? 2.54
tt (6.1 pb) 78.89 ? 2.74
Data 118
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Results

• Using the 118 candidates in 680 pb-1 our Mtop is
  

with JES 1.019 ? 0.022 (stat)
Better sensitivity than the previous world
average!
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Results

• Compare Data and Monte Carlo calculating the
  invariant mass of 2 and 3 jets
• Signal probability evaluated at Mtop174.5 GeV/c2
  and JES1 and using the most probable
  configuration

Excellent agreement found between data and Monte
Carlo
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Decay Length Overview

• The method has been published by C. Hill et al.
  at PRD 71, 054029
• B hadron decay length ? b-jet boost ? Mtop
• Uses the average transverse decay length of the
  b-hadrons ltLxygt

Relies on tracking, no JES and uncorrelated with
other measurements
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Selection and Tests

• Event selection used to maximize the amount of
  signal in the sample
• 3 or more jets
• 1 b tag jet
• 375 events with SB 31

Expected Events (695 pb-1)
Total background 111.6 ? 12.5
Data 375

• Requires accurate simulation of Lxy
• Enriched heavy-flavor samples
• ltLxygt (data/Monte Carlo) 0.992 ? 0.012
• Major systematic uncertainty

• Data and Monte Carlo comparison in control sample

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Results

• Using the 375 candidates in 695 pb-1 our top
  quark mass measurement is
• ltLxygt 0.5808 0.0227 cm

Will carry more weight by the end of Run II
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Mtop All Jets Results
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All Jets

• Main challenges in this channel
• Small signal fraction SB 18 after requiring
  at least 1 identified b-jet
• Large combinatorial background 90 combinations
• Selection and events
• ET/ ? (? ET) lt 3 (GeV)1/2
• ?ET ? 280 GeV
• nb-tag ? 1
• Exactly 6 jets
• Ideogram method from the Delphi experiment for
  the W mass measurement, used in a Run II
  preliminary D0 for top mass measurement in
  leptonjets channel

Expected Events (310 pb-1)
Multi-jets (light) 182
Multi-jets (heavy flavor) 68
Total background 240
tt (6.1 pb) 40
Data 290
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Ideogram Overview

• Define a 2D event likelihood as
• Weight each combination with kinematical and
  b-tagging information wi
• Extract from kinematical fit to mtop and
  manti-top ? m1, m2, ?1,?2, ?2

Sm calculated convoluting Briet-Wigners and
Gaussian resolution functions
Scomb combinatorial background from Monte Carlo
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Template Shapes

• Template for combinatorial background

Template for background
Signal, correct combination
Using the two fitted masses gives a good
separation between signal and background
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Background Simulation
Data - Background MC
Region 2
Data - Background MC
Data - Background MC
Region 1
Region 3
Background is well understood
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Monte Carlo Tests

• From 290 observed events we estimate S/B by
  measuring the sample purity in data
• From data we fit a signal fraction Cs0.21 ? 0.07
• Results in 61 ? 20 signal events
• Compatible with all hadronic cross section
  measurements with 310 pb-1

• The Monte Carlo fitted purity is consistent
  with the purity obtained from data and
  independent of Mtop

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Monte Carlo Tests

• Estimation of the expected error is
  underestimated by 17
• We understand that this is caused by the
  background
• Inflate errors to take into account this effect
• Expected statistical errors 4 - 5 GeV/c2

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Results

• Using 310 pb-1 and 290 candidates we measure
• First Tevatron Run II all jets Mtop measurement
• Systematically limited!

Similar statistical sensitivity as the lepton
jets channel
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Summary of Mtop Results
CDF Measurement Extracted value (GeV/c2) Statistical (GeV/c2) JES (GeV/c2) Other syst (GeV/c2)
LeptonJets Template (680pb-1) 173.4 1.7 1.8 1.3
LeptonJets ME(680pb-1) 174.1 2.0 1.5 1.3
LeptonJets Decay Length (750pb-1) 183.9 15.7 -13.9 0.3 5.6
Dilepton Matrix Element (750pb-1) 164.5 4.5 2.6 1.7
All Jets Ideogram (310pb-1) 177.1 4.7 4.3 1.9
We compare (confidence and consistency) and
combine (precision)

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Combining Mtop Results

• Excellent results in each channel
• Combine them to improve precision
• Include Run-I results
• Account for correlations
• Use BLUE (NIM A270 110, A500 391)
• Matrix Element analysis in leptonjets not yet
  included. Working to understand statistical
  correlations with Template analysis

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Combining Mtop Results

• Are the channels consistent?
• We compare them taking into
• account their correlated
• systematics
• Discrepancy might reveal
• missing systematic?
• or New Physics?

Mtop(All Jets) 178.7 ? 5.5 GeV/c2
Mtop(Dilepton) 164.8 ? 4.8 GeV/c2
Mtop(LeptonJets) 173.5 ? 2.8 GeV/c2
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Future

• We surpassed our Run II goal of measuring to 3
  GeV/c2 precision
• Have made extrapolations based on present methods
• Upper limit Only ?(stat) improves with
  luminosity
• Lower limit Everything improves with luminosity
• Reality likely somewhere in between

With full Run-II dataset CDF should measure
Mtop to lt 1
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Conclusions

• CDF has robust program of Mtop measurements
• First Run-II determination in all-jets channel
• Multiple methods and channels
• Observed consistency builds confidence
• CDF combined
• CDF should reach 1 precision with full Run-II
  data set
• Tevatron combination better still

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Conclusions

• Present uncertainties on Mtop and MW help
  constrain MHiggs to about 40 ?MHiggs/ MHiggs
• Best fit favors light MHiggs
• where CDF/D0 are sensitive
• where difficult for LHC
• ?Mtop will continue to shrink
• New CDF/D0 MW expected soon...
• ?MW will also shrink