1. From Tevatron to the LHC: W/Z and top physics
Craig Buttar
University of Glasgow
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

2. Topics
Outline
Focus on some electroweak and top quark measurements at the Tevatron and LHC, other topics were covered by Emily
Can LHC extend precision of measurements
What does Tevatron tell us?
W/Z cross-section
Top mass
Top cross-section
Single top
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

3. LHC 14TeV  10TeV Gain at 14TeV (10TeV)
W/Z production LHC ~x8 (x5) Tevatron
Top production LHC~x100 (x50) Tevatron
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

4. W/Z xsect
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

5. Tevatron W/Z cross-sections
sW(m)
2768±16±64±166
sW(e)
2780±14±60±167
sW(e+m)
2775±10±53±167
sW(NLLO)
2687±54
sZ(m)
248.0±5.9±7.6±14.9
sZ(e)
255.8±3.9±5.5±15.4
sZ(e+m)
254.9±3.3±4.6±15.2
sZ(NLLO)
251.3±5.0
R(m)
11.12±0.27±0.18
R(e)
10.82±0.18±0.16
R(e+m)
10.92±0.15±0.14
R(NNLO)
10.69±0.08
Precision measurement of cross-section with statistical errors ~ % and systematic errors ~2-3% Acceptance uncertainties dominated by PDF ~1.5%
Limiting factor is luminosity ~6%
For 8fb-1 statistical error ~ %
Both luminosity and PDF systematic error are reduced in the ratio statistical error ~1.3% systematic error ~1.3%
NNLO theoretical errors on cross-section at the level of 2% on the ratio error~0.7% as PDF uncertainties cancel
PDF error changes with acceptance region
CDF cross-sections (pb) for 72pb-1
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

6. Tag & Probe
Muon reconstruction efficiency
Electron identification
Tag and probe methods used to determine reconstruction and trigger efficiencies from data
Improve systematics with increased data
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

7. LHC W/Z cross-sections
50pb-1
1fb-1
sW(m)
±0.2%±3%
±0.04%±2.3%
sW(e)
±0.2%±5%
±0.04%±2.5%
sZ(m)
±0.7%±4%
±0.2%±2.4%
sZ(e)
Luminosity ~5-10% at start-up
Dedicated experiments eg ALFA will reduce lumi error
Remember CDF?
statistical errors ~ % and systematic errors ~2-3%
Early running
W-channels
Higher statistics
Systematic dominated by background at 50pb-1
Z-channels
Lower statistics
systematic dominated by efficiency (2-leptons)
background suppressed (2-leptons)
Systematic uncertainty at 1fb-1 dominated by theoretical uncertainties in acceptance: ISR~2.0%, 0.4% KT, UE 0.2%, PDF 0.9%
Likely to improve with measurements at LHC – difficult to quantify
Uncertainty on efficiencies improve 2-0.4% from 50b-1 to 1fb-1 as efficiencies are based on data eg tag and probe
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

8. W/Z cross-section
Tevatron precision measurements dominated by systematics ~2-3% and luminosity ~6%
LHC statistical error at 1fb-1 ~ Tevatron at 8fb-1
Systematics comparable to Tevatron due to theoretical uncertainty on acceptance
This may improve but difficult to quantify
Tag & Probe allows for robust efficiency estimates with data, scales with luminosity
LHC luminosity ~2-3% using dedicated forward physics expts
Systematics limited by luminosity and the effect of PDF uncertainty on the acceptance
What do measure from W/Z cross-sections: PDFs, luminosity…?
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

9. Top
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

10. Top mass
Precision top mass measurement is required for EW fits to predict MH and then confirm consistency of Standard Model
For equal contribution to MH uncertainty:
DMt < 2 GeV  DMW < 15 MeV
Can get dMH/MH~30%
Important cross-check with direct measurements
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

11. Top mass Tevatron Most precise CDF top mass measurement
3.2fb-1 using ME and in-situ Wjj
0.3%stat 0.6% syst
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

12. Colour reconnection
Colour reconnection is part of the soft part of the underlying event
Implemented in new PYTHIA MPI model (6.3 onwards)
Not in conventional tevatron UE tunes
Will be critical to tune from data eg <Nch> vs pt
Will disappear from Tevatron mass measurements?
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

13. Top mass from cross-section
What top mass is measured?
Input to EW fits is the pole mass
Fits from templates and matrix elements are related to MC variables
Not well defined mass, same for all generators?
Can define mass as a function of cross-section in well defined renormalisation scheme,  well defined measurement of pole mass
Current measurements give dmt~4% cf 1%
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

14. How well can the Tevatron do?
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

15. LHC top mass measurement
Semi-leptonic
Channel with b-tagging
L > 1fb-1
Initial JES ~ 5%
b-jet JES systematic ~3.5GeV
Light-jet JES systematic ~ 1GeV
Use W-jj to get 1% light jet and model difference to get b JES
Ultimately get to ~ 0.2GeV light quark JES
~0.7GeV for b-quark JES (total JES ~ 0.7GeV
cf CDF analysis with W->jj in-situ ~0.6GeV
Geometric method
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

16. Top mass via J/Y
Method measures direction and momentum of b-quark from Y
Reconstruct M(Y+l)
Uses well measured leptons and avoids JES systematics
Limited in statistics
Relies on simulation to determine Mt M(Y+l)
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

17. High-pt top PT>200GeV ~2% for stt ~15k events/10fb-1
Reconstruct collimated hadronic decay top in large cone directly from calorimeter cells (
Calibrate the mass using W->jj
Sensitive to the underlying event
Can be removed by looking at UE in data
Avoids effects of jet reconstruction but still subject to calibration errors
dMt
ISR
0.1
FSR
b-fragmentation
0.3
UE estimate
1.3
Mass scale calibration
0.9
1.6GeV
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

18. LHC Top mass summary
dMt GeV
Dominant error
Semileptonic (kinematic fit)
~1 (~3.5GeV)
FSR+light and b-jet energy scales~1% (5%)
Semileptonic high pt
1.6
Calibration+UE
Di-leptons
PDFs (statistical~0.3GeV)
Multijet
3.0
JES ISR/FSR
J/Y
1.5
Statistics 50fb-1+theoretical errors
Semileptonic channels we have already discussed.
Di-leptons are characterised by tow high pt isolated leptons, large Et-miss and two b-jets.
Get ~400k events for 10fb-1
Cuts are:
two opposite leptons with pt>35Gev and 25Gev in eta<2.5, et-miss>40GeV and two jets with pt>25GeV.
Get 80K signal with a S/B~10
Backgrounds are Drell-Yan, Z->tautau+jets, WW+jets and bbbar production.
To find top mass do kinematic fit using various input top masses. The weights of the best solution for a given top mass are found. For each top mass the mean weight over all events is found, the maximum average weight corresponds to the measured mass.
Efficiency-purity is 97.6%-73%.
Constraints are conservation of pt in ttbar system assuming pt=0; lnu systems are constrained to Mw; lnuj systems are constrained to Mtop, used as an input.
Multi-jet channel, S/B=3x10-8 at production. Kinematic cuts get to S/B=1/19 and after kinematic fit and x-sq cut get 1/2.6, and finally limiting the mass window to GeV, get 6/1. The efficiency for ttbar is 0.18% but large statisitcs allow for this still giving 6660 events/10fb-1.
The top mass can be measured in a number of different ways, that mostly have different dominant systematic errors so that combinations of these measurements, and combinations of the expts should certainly allow the top mass error to get below ~1 GeV.
Can achieve results comparable to the Tevatron, but need control JES
Larger cross-section allows some techniques to be used that avoid JES
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

19. Top mass from cross-section at the LHC
Need to measure cross-section ~3% to get mass at 0.6% (1GeV)
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

20. Tevatron Top xsect CDF combined xsect Stat 4.3% Sys 5.7% Lumi 5.7%
Total ~9%
Sys dominated by
JES
Heavy flavour model in MC
B-tagging in MC
lumi
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

21. Top Cross-section at the LHC
Dilepton channel for 10fb-1
Semi-leptonic channel
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

22. Top summary and conclusions
Top well understood at Tevatron
Top mass constrained ~1GeV  for EW fits the issue is now Mw
Top mass needs to be understood
LHC with 1fb-1/expt can achieve dmt~3.5GeV with JES 5% (dmt~1GeV JES 1%)
LHC has access to rare methods that may help understand mass better
The issue of what top mass is measured
Cross-section measurements can provide well defined mass measurements
Cross-section errors are too large for precision
Tevatron has given LHC a new precision “standard candle”
Can we use this measure the b-jet JES for other analyses?
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

23. Single top at the Tevatron
Use multivariate discriminators to identify different channels
Combination gives 5s discovery
Key channel for Higgs searches
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

24. Single top observation at Tevatron
Use multivariate discriminators to identify different channels
Combination gives 5s discovery
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

25. Single top at LHC Background are:
W+jets Tt
As at Tevatron require multivariate analysis to reduce backgrounds
ln+2b+X
Sensitive to NP
ln+b+jets
tt-like
ln+b+jets
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

26. Single top at LHC t-channel results for 1fb-1
Principal systematic, background from tt background
Use BDT
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

27. Single top at the LHC s-channel Most challenging, small signal
W+jet and tt background
t-channel
tt-like signal
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

28. Single Top summary
Tevatron has observed single top making a combined measurement of s and t channels and using multivariate analysis
At LHC can observe individual channels, with varying degrees of precision
LHC has carried over multivariate analysis techniques
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

29. Summary and conclusions
Increased cross-sections help with
Rare processes: Single top
Avoiding JES: top mass from high PT and M(Yl)
Tevatron has provided LHC with another “standard candle” -- top
Mass well known
Can LHC use it to measure b-JES
Cross-section measurements may be needed to determine the mass
Tevatron has observed single top with combined measurement
LHC can observe individual channels, with varying precision
Many LHC systematics currently based on uncertainties in models: ISR, UE etc, likely to come down with data
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

30. Good ideas help
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

31. Backup slides
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

32. Principal References Tevatron References: LHC
CDF public pages:
D0 public pages:
LHC
ATLAS: Expected performance of the ATLAS experiment: detector, trigger and physics: arXiv (All results for 14TeV unless otherwise stated)
CMS: Physics TDR
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

33. Determining the jet energy scale
Determine jet-energy scale (JES) uncertainty using in-situ methods
Z-jets 10GeV<Pt< GeV 1% statistical uncertainty on JES with 300pb-1 Systematics: ISR/FSR+UE ~5-10% at low Pt, reducing to 1-2% for Pt~ GeV
g-jets <Pt<500GeV 1-2% statistical uncertainty on JES with 100pb-1 systematics from physics effects: ISR/FSR+UE ~ 1-2%
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

34. DIS09 top review
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

35. W and Z inclusive production
Well understood theoretically
Dominant uncertainty is due to PDFs
For 1fb-1
Ds/s(ppZ+Xmm+X)=0.13±2.3±10%
Ds/s(ppW+Xmn+X)=0.04±3.3±10%
Tracker efficiency
PT (LONLO)
Muon efficiency
Trigger efficiency
MET
PT(LONLO)
Stat sys lumi
Equivalently can use to evaluate luminosity at the level of 6-7%
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

36. Z-afb
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

37. Measurement of Afb in Z-decays and determination of sin2θefflept(MZ2 )
AFB = b { a - sin2θefflept( MZ2 ) }
Measure Afb with leptons in Z0 DY events
Can fit with Mt to constrain MH
a, b calculated to NLO QED and QCD.
Need to define direction
At the Tevatron -- well defined
qq pdfs  low z-boost
Match q+l+ q
qbar
At LHC no asymmetry wrt beam
Assume that there is a
Q-qbar collision  large Z-boost
quark direction from y(ll)
Requires measurement at high y(ll) Q
qbar
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

38. Why measure Afb
Precision measurement of Afb can give precison measurement of sintheta – which contains higher order terms – , together with a precison measurement of mt, this provides a constraint on the Higgs mass
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

39. D0 Run-II Afb result and sin2θefflept(MZ2 )
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

40. ATLAS study of Afb 100fb-1 measurement
Not a day-1 measurement
2 classes
C-C central electrons with tracker
C-F central electron and forward electron
Need forward electrons for statistics
2.5<|h|<3.2
No tracking information
Select only |h|>1 to reduce Sq-Sqbar background Q
qbar
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

41. ATLAS sinthetaW C-F one central electron |h|<2.5
+ forward electron |h|<4.9
C-C two central electrons |h|<2.5
Statistical error for LHC with 100fb-1 (1yr at 1034cm-2s-1) x10 better than Tevatron
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

42. Effect of underlying event in jet reconstruction
Z+jets Events
Fragmentation reduces the amount of energy in jet cone
UE adds energy to the hadron level jet
Underlying event and fragmentation have the opposite effect
Precise behaviour depends on the jet algorithm used
Frag. corrections for Cone DR=0.7 jets smaller than for Cone DR=0.4 jets, UE corrections larger due to the larger cone size
KT D=0.4 shows the lowest combined corrections (Frag. and UE effects cancel out).
KT D=0.6 jets is comparable to Cone DR=0.4 jets.
(Except for Cone DR=0.7 jets), non-perturbative effects are negligible for jets with pT>40 GeV (PYTHIA).
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

43. Top Physics -
Main goal, so far, has been to estimate uncertainties on reconstructed top parameters from UE (MPI) and ISR/FSR (coupled together)
variations on UE, ISR/FSR affect observables on which selections cuts are applied: jet multiplicity, particles pT etc.
potentially a serious impact on top reconstructed parameters (e.g. Mtop, stT)
ISR and FSR PYTHIA parameters have been varied to give smallest and largest values of reconstructed top mass
Max ISR, Min FSR (LISR*2, ISR cutoff -0.5*ISR cutoff, LFSR*0.5) → Max Mtop
Min ISR, Max FSR (LISR*0.5, ISR cutoff +0.5*ISR cutoff, LFSR*2) → Min Mtop
up to ~10% change in the Selection Efficiency from Min-Max Mtop samples
contributing ~10% on syst. uncertainty on early data stT
visible effect on reconstructed Mtop:
MC-Truth: ~5 GeV (hadronic Mtop) and ~1-2 GeV (leptonic Mtop)
Mtop [GeV]
PYTHIA Params
max. mass:
parp(61)=0.384, mstp(70)= 0 and parp(62)=1.0, parj(81)=0.07
min. mass:
parp(61)=0.096, mstp(70)=0 and parp(62)=3.0, parj(81)=0.28.
AcerMC+PYTHIA
AcerMC+PYTHIA
MC-Truth
MC-Truth
MC-level Plots
For semi-leptonic tt events
(Cone DR=0.4 truth jets) _
UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009