ICHEP 2008, 7/30/08 B. Jayatilaka (Duke) Top quark mass in dilepton and all jets channels Bo Jayatilaka Duke University/CDF On Behalf of the CDF and D∅ Collaborations 34 th International Conference on High Energy Physics July 30, 2008 Philadelphia, PA 1
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ICHEP 2008, 7/30/08 B. Jayatilaka (Duke)
Top quark mass in dilepton and all jets channels
Bo JayatilakaDuke University/CDF
On Behalf of the CDF and D∅ Collaborations
34th International Conference on High Energy PhysicsJuly 30, 2008
Philadelphia, PA
1
DØnote 4725-CONF
Measurement of the Top Quark Mass in the Dilepton Channel
The DØ CollaborationURL http://www-d0.fnal.gov(Dated: February 25, 2005)
We present a preliminary measurement of the top quark mass in the dilepton channel based onabout 230 pb!1 of data collected by the DØ experiment during Run II of the Fermilab Tevatroncollider. We show that the method used obtains consistent results using ensemble tests of eventsgenerated with the DØ Monte Carlo simulation. We apply this technique to a total of 13 dileptonevents selected in the collider data to obtain mt = 155+14
!13(stat) ± 7(syst) GeV.
Preliminary Results for Winter 2005 Conferences
ICHEP 2008, 7/30/08 B. Jayatilaka (Duke)
Why measure the top mass?• Top mass is a fundamental parameter in SM
• Important in radiative corrections
• Why so massive?
• Only fermion with mass near EW scale
• Yukawa coupling of ~1
• Constrains SM Higgs mass and SUSY models
2
80.3
80.4
80.5
150 175 200
mH [GeV]114 300 1000
mt [GeV]m
W [
GeV
]
68% CL
!"
LEP1 and SLDLEP2 and Tevatron (prel.)
March 2008
Measurement in different decay channels
• Important to check consistency between channels (is it SM top?)
• Discrepancy could indicate new physics
ICHEP 2008, 7/30/08 B. Jayatilaka (Duke)
Dilepton decay channel• 2 leptons, 2 jets, large missing ET
• Mostly electroweak background
• Drell-Yan, Diboson
• Instrumental background (fakes)
• Kinematically underconstrained
• Two neutrinos
• Make assumptions and integrate over at least one variable
• Advantages
• Clean: little background without need for b-tagging
• Least jets of any channel (less reliant on JES, less ambiguity in jets)
Disadvantages
• Low statistics
• 2 νs escape undetected– underconstrained system
3
ICHEP 2008, 7/30/08 B. Jayatilaka (Duke)
Alljets decay channel
4
• Look for 6 jets
• Dominated by QCD multijet background
• Require b-tags to have appreciable signal
• Reconstructable final state
• Many permutations of jet combinations
• Advantages
• High statistics
• Hadronic Ws allow for in situ jet energy scale (JES) calibration as in l+jets channel
Disadvantages
• Large background
ICHEP 2008, 7/30/08 B. Jayatilaka (Duke)
Reconstructing the mass
5
Reconstruct mass for each event
Form “templates” for signal (varying Mtop) and background using simulated events
Perform maximum likelihood fit to extract measured Mtop
Form per-event probability using matrix element
Integrate over unmeasured quantities
Form ensemble probability and calibrate using simulated events
1. Template-based
Advantages: Less CPU bound (systematic uncertainties less likely to be limited by CPU)Disadvantages: Only single number (recon. mass) per event in final Likelihood, all events have equal weight
Advantages: More statistical power, probability curve rather than single mass per event, events weighted naturally
• 2nd lepton is only required to be an isolated track
• More statistics at expense of background
6
Source CDF D∅
tt (Mt=175 GeV/c2) 164.3±5.1 86.9±3.8
Drell-Yan 50.1±7.2 12.8±1.4
Fakes 81.0±15.9 7.1±1.2
WW/WZ 15.4±1.0 4.0±0.6
Total 311.8±18.7 110.8±5.0
Data 330 107
Expected Signal Fraction 53% 78%
CDF [lepton+isolated track]
- 1 lepton with pT >20 GeV/c- 1 isolated, well-measured track with pT >20 GeV/c- 2 jets with ET >20 GeV, |η|<2- ET >25 GeV
D∅ [two identified leptons]
- 2 leptons with pT >15 GeV/celectrons up to |η|<2.5
- 2 jets with pT >20 GeV/c, |η|<2.5- HT >115 GeV
DØnote 4725-CONF
Measurement of the Top Quark Mass in the Dilepton Channel
The DØ CollaborationURL http://www-d0.fnal.gov(Dated: February 25, 2005)
We present a preliminary measurement of the top quark mass in the dilepton channel based onabout 230 pb!1 of data collected by the DØ experiment during Run II of the Fermilab Tevatroncollider. We show that the method used obtains consistent results using ensemble tests of eventsgenerated with the DØ Monte Carlo simulation. We apply this technique to a total of 13 dileptonevents selected in the collider data to obtain mt = 155+14
!13(stat) ± 7(syst) GeV.
Preliminary Results for Winter 2005 Conferences
ICHEP 2008, 7/30/08 B. Jayatilaka (Duke)
Advanced event selection: ENN
• Most selections used in top mass measurements were designed for x-section measurements
• Optimized for S:B
• Devise selection optimized for uncertainty in top mass
• Evolutionary neural net
• Evaluate “fitness function” (Mt stat. error from pseudoexperiments)
• Select best networks and breed
• Best networks do not have best S:B
• 20% improvement in CDF ME analysis over cut-based selection
• Matrix element probabilities for both signal and dominant backgrounds
• Use sample selected using evolving neural net
• 2.0 fb-1 (344 events)
• Measure Mt=171.2±2.7(stat.)±2.9(syst.) GeV/c2
8
)2
(GeV/ct
M155 160 165 170 175 180 185 190 195
-ln
(P)
0
2
4
6
8
10
12
14
16
18
20
)-1
CDF Run II Preliminary (2.0 fb
ICHEP 2008, 7/30/08 B. Jayatilaka (Duke)
Matrix element dilepton mass: D∅
• Measurement performed in eμ channel only
• Reduces Drell-Yan background
• Expect 87 tt events out of 107 data events
• Uses 2.8 fb-1 of data
• Measure Mt=172.9±3.6(stat)±2.3(syst) GeV/c2
9
DØnote 4725-CONF
Measurement of the Top Quark Mass in the Dilepton Channel
The DØ CollaborationURL http://www-d0.fnal.gov(Dated: February 25, 2005)
We present a preliminary measurement of the top quark mass in the dilepton channel based onabout 230 pb!1 of data collected by the DØ experiment during Run II of the Fermilab Tevatroncollider. We show that the method used obtains consistent results using ensemble tests of eventsgenerated with the DØ Monte Carlo simulation. We apply this technique to a total of 13 dileptonevents selected in the collider data to obtain mt = 155+14
!13(stat) ± 7(syst) GeV.
Preliminary Results for Winter 2005 Conferences
(GeV)topm160 165 170 175 180
-ln L
0
0.5
1
1.5
/ ndf 2! 6.353 / 4
p0 0.02861! -0.06246
p1 0.08874! 4.707
p2 0.08088! 170.2
/ ndf 2! 6.353 / 4
p0 0.02861! -0.06246
p1 0.08874! 4.707
p2 0.08088! 170.2
4.7 GeV!=170.2top
m
-1DØ RunII Preliminary, L=1.1fb
(GeV)topm170 175 180
-ln L
0
1
2
/ ndf 2! 7.744 / 4
p0 0.04575! -0.007383
p1 0.07768! 3.799
p2 0.09391! 175.6
/ ndf 2! 7.744 / 4
p0 0.04575! -0.007383
p1 0.07768! 3.799
p2 0.09391! 175.6
3.8 GeV!=175.6top
m
-1DØ RunII Preliminary, L=1.7fb
ICHEP 2008, 7/30/08 B. Jayatilaka (Duke)
Template dilepton mass: CDF
• Template method integrating over neutrino φ
• Combined background template
• Use lepton+isolated track sample
• Use 2.8 fb-1 of CDF data
• Measure
10
Mtop = 165.1 (stat.)±3.1(syst.)GeV/c2+3.3-3.2
0
20
40
60
80
100
100 150 200 250 300 3500
20
40
60
80
100
100 150 200 250 300 350
Data (330 ev.)
CDF RunII Preliminary (2.8 fb-1
)
Constrained fit
ttbar+Backgr.Backgr.
Reconstructed mass (GeV/c2)
Even
ts/(
10 G
eV
/c2) -!
Ln
(L)
0
0.5
1
1.5
2
2.5
3
160 165 170
ICHEP 2008, 7/30/08 B. Jayatilaka (Duke)
Template dilepton mass: D∅
• Template method integrating over neutrino rapidity
• Include looser lepton+track selection
• Measure Mt=176.0±5.3(stat.)±2.0(syst.) GeV/c2
• Combine all Run II measurements of dilepton mass at D0
• Matrix Element eμ and Template ee, μμ, and l+track
• Mt=174.4±3.2(stat.)±2.1(syst.) GeV/c2
• χ2/dof=1.3/3
11
DØnote 4725-CONF
Measurement of the Top Quark Mass in the Dilepton Channel
The DØ CollaborationURL http://www-d0.fnal.gov(Dated: February 25, 2005)
We present a preliminary measurement of the top quark mass in the dilepton channel based onabout 230 pb!1 of data collected by the DØ experiment during Run II of the Fermilab Tevatroncollider. We show that the method used obtains consistent results using ensemble tests of eventsgenerated with the DØ Monte Carlo simulation. We apply this technique to a total of 13 dileptonevents selected in the collider data to obtain mt = 155+14
!13(stat) ± 7(syst) GeV.
Preliminary Results for Winter 2005 Conferences
[GeV]top
m140 150 160 170 180 190 200 210
-lo
gL
160
165
170
175
180
185
DØ Preliminary -1 1 fb
ICHEP 2008, 7/30/08 B. Jayatilaka (Duke)
Systematics: dilepton channel
• Systematic uncertainty in dilepton channel is dominated by JES error
• Cannot do in situ calibration
12
Source CDF (ME) GeV/c2 CDF (Template) GeV/c2
D∅(ME) GeV/c2
[Run IIb only]D∅(Template)
GeV/c2
Jet Energy Scale 2.5 2.9 2.3 1.7b Jet Energy Scale 0.4 0.4 0.3 0.5
Measurement of the Top Quark Mass in the Dilepton Channel
The DØ CollaborationURL http://www-d0.fnal.gov(Dated: February 25, 2005)
We present a preliminary measurement of the top quark mass in the dilepton channel based onabout 230 pb!1 of data collected by the DØ experiment during Run II of the Fermilab Tevatroncollider. We show that the method used obtains consistent results using ensemble tests of eventsgenerated with the DØ Monte Carlo simulation. We apply this technique to a total of 13 dileptonevents selected in the collider data to obtain mt = 155+14
• Templates for signal and background constructed using per-event likelihoods
• ME-like calculation for likelihoods
• Signal purity is a free parameter
• Use 1.9 fb-1 of CDF data
• Mt=165.2±4.4(stat.+JES)±1.9(syst.) GeV/c2
15
)2
(GeV/ct
M150 155 160 165 170 175 180
)JE
S!
JE
S (
-0.5
0
0.5
1
1.5
2
2.5
3
)-1
CDF Run II Preliminary (1.9 fb
Measured values
)!) = 0.5 (1 max-Ln(L/L
)!) = 2.0 (2 max-Ln(L/L
)!) = 4.5 (3 max-Ln(L/L
)-1
CDF Run II Preliminary (1.9 fb
)2
(GeV/ct
M100 150 200 250 300
2E
ve
nts
/6.8
Ge
V/c
0
5
10
15
20
25
30
35
40
)-1
CDF Run II Preliminary (1.9 fb
Data2
=165 GeV/ct
Signal, M
Background
/nDof = 24.9/262!
KS Prob = 0.854
)2
(GeV/ct
M100 150 200 250 300
2E
ve
nts
/6.8
Ge
V/c
0
5
10
15
20
25
30
35
40
)-1
CDF Run II Preliminary (1.9 fb
ICHEP 2008, 7/30/08 B. Jayatilaka (Duke)
Systematics: alljets
• Alljets channel systematics lower since JES is handled in situ
16
Source CDF (Template) GeV/c2
CDF (Template) [JES]
CDF(Ideogram) GeV/c2
Residual Jet Energy Scale 0.8 N/A 0.7
b Jet Energy Scale 0.6 0.09 0.3
Pileup 0.3 0.03 0.7
MC Statistics 1.1 0.05 0.1
PDFs 0.4 0.11 0.4
Generator 0.5 0.26 0.8
Background Shape N/A N/A 0.4
ISR/FSR 0.5 0.10 1.2
Method 0.5 0.12 0.2
Sample Composition N/A N/A 0.5
Total 1.7 0.36 1.9
ICHEP 2008, 7/30/08 B. Jayatilaka (Duke)
Impact and conclusions
• 2.8/fb combination from July 2008
• Includes dilepton: CDF(ME), D0(combined)
• Includes template alljets
• Dilepton and alljets measurements contribute ~12% weight
• Compare measurements across channels
• Agree... for now.
• Both CDF and D0 continue analyses in these channels
• Alljets result from D0 imminent
17
DØnote 4725-CONF
Measurement of the Top Quark Mass in the Dilepton Channel
The DØ CollaborationURL http://www-d0.fnal.gov(Dated: February 25, 2005)
We present a preliminary measurement of the top quark mass in the dilepton channel based onabout 230 pb!1 of data collected by the DØ experiment during Run II of the Fermilab Tevatroncollider. We show that the method used obtains consistent results using ensemble tests of eventsgenerated with the DØ Monte Carlo simulation. We apply this technique to a total of 13 dileptonevents selected in the collider data to obtain mt = 155+14
!13(stat) ± 7(syst) GeV.
Preliminary Results for Winter 2005 Conferences
)2
(GeV/ctop
M
150 160 170 180 190 2000
15
CDF March’07 2.2! 1.5 !12.4
Tevatron July’08*
1.0! 0.7 !172.4 (syst.)!(stat.)
CDF-II trk*
3.0! 6.2 !175.3
CDF-II all-j*
3.3! 2.6 !176.9
CDF-I all-j 5.7!10.0 !186.0
D0-IIb l+j*
1.7! 1.3 !173.0
D0-IIa l+j*
1.5! 1.5 !171.5
CDF-II l+j*
1.0! 1.3 !172.2
D0-I l+j 3.6! 3.9 !180.1
CDF-I l+j 5.3! 5.1 !176.1
D0-II di-l*
2.1! 3.2 !174.4
CDF-II di-l*
2.9! 2.7 !171.2
D0-I di-l 3.6!12.3 !168.4
CDF-II di-l 4.9!10.3 !167.4
Mass of the Top Quark (*Preliminary)
/dof = 6.9/11.0 (81%)2!
Figure 1: A summary of the input measurements and resulting world average mass of the topquark.