Top Quark Mass Measurements at Hadron Colliders

1. Top Quark Mass Measurements at Hadron Colliders G. Watts (UW/Seattle, CPPM) For the DZERO, CDF, CMS, and ATLAS collaborations July 15, 2014

2. The Top Quark Just like other Fermions Except: The next heaviest quark! G. Watts (UW/Seattle) FFP 2014 - Marseille The Mass gives the top quark a special role in the Standard Model • Only fermion which has a significant coupling to the Higgs • Plays key roll in many important physics processes • Flavor physics, Electro-weak processes • It plays a special roll in a number of Beyond the Standard Model theories as well

3. The Top Mass We have known almost since it was discovered. By far the most precisely measured quark mass! While it behaves like any other quark in the Standard Model, its mass gives it a unique role. • Only version for which the coupling to the Higgs is important • Stability of the SM Higgs potential at high scales G. Watts (UW/Seattle) FFP 2014 - Marseille A consistency check for the Standard Model! • Shows up in a number of production loops • at the LHC contains a top loop • Heavy Flavor physics (e.g. ) production

4. Top Mass Is A Precision Measurement Current World Average: 173.3 GeV. Known to better than 0.5 %!! G. Watts (UW/Seattle) FFP 2014 - Marseille Higgs mass is known to better than 0.3% Each measurement deserves at least a seminar Top is easier to discover: at TeV at TeV Top is harder to reconstruct: I have chosen a few extra results No clean easy to see peak l! All final states involve jets

5. Tevatron G. Watts (UW/Seattle) FFP 2014 - Marseille LHC

6. Decays Classified by the Ws’ decay Dilepton events Clean, but low statistics ~4% Lepton + Jet events G. Watts (UW/Seattle) FFP 2014 - Marseille Good compromise Reasonable background ~30% All Hadronic events Huge multi-jet background ~44% Top mass has been measured in all decay channels.

7. The Tevatron & The LHC The Tevatron is coming out with its final results • of data at TeV • Well understood detector • Sophisticated analysis techniques The LHC is just coming online in the world G. Watts (UW/Seattle) FFP 2014 - Marseille • TeV results well developed • 8 TeV results just appearing • Statistics are much better due to the much higher The much larger statistics will eventually open the door to new measurement techniques.

8. Extracting from Data Detector gives you 4-vectors. Use Griffiths! • Does not always give you 4-vectors (neutrinos!) • Detector/Object resolutions (e.g. Jet Energy Scale) • Background contamination • Incorrect reconstruction (e.g. bad jet assignment) • Top mass width • Etc. G. Watts (UW/Seattle) FFP 2014 - Marseille Two common methods to address this: Uses all the information Computationally veryexpensive Matrix Element Flexible, subsets the information used “Fairly easy” to implement Template Method What do we measure? The Pole mass? The MC mass?

9. The Jet Energy Scale Lepton+Jets Common curse for all methods • Experiments normally measure in independent control sample. • Resolution not good enough for a state-of-the-art top mass measurement. G. Watts (UW/Seattle) FFP 2014 - Marseille In situ Jet Energy Scale measurement Many techniques will constrain to be as part of the global fitting process. Two poorly measured objects • Global fit over the full sample • Scale all jets by a constant factor to achieve constraint One very well measured object Flavor Jet Energy Scale

10. The Matrix Element Approach A reverse Monte Carlo Distributions of kinematic variables for all objects MC Generates 100K events G. Watts (UW/Seattle) FFP 2014 - Marseille “Map of kinematic phase space” Turn that around Given a single event in data, how dense a part of kinematic phase space is it in? Repeat for all major backgrounds and signal:

11. ME – Multiple Steps 4 vectors of reconstructed objects Detector Simulation Reconstruction ALPGEN + Pythia G. Watts (UW/Seattle) FFP 2014 - Marseille • A weight reflecting the probability of those jet assignments • -tagging probabilities Normalization • Sum over all possible jet assignments • Which jet is the first tops? • Which jets belong to the W?

12. ME – Multiple Steps 4 vectors of reconstructed objects Detector Simulation Reconstruction ALPGEN + Pythia G. Watts (UW/Seattle) FFP 2014 - Marseille • 10 dimensional integral over phase space • Mass of the tops, W’s • Directions of the b-quarks • Lepton and neutrino direction Note no mention of data 4-vectors yet!

13. ME – Multiple Steps 4 vectors of reconstructed objects Detector Simulation Reconstruction ALPGEN + Pythia G. Watts (UW/Seattle) FFP 2014 - Marseille • The Leading Order Matrix Element • Given all the phase space parameters • Weight for the kinematics values • Uses all available information • At leading order Sum over incoming parton flavors All neutrino solutions

14. ME – Multiple Steps 4 vectors of reconstructed objects Detector Simulation Reconstruction ALPGEN + Pythia G. Watts (UW/Seattle) FFP 2014 - Marseille PDF’s Phase Space Factor Transverse momenta of incoming partons

15. ME – Multiple Steps 4 vectors of reconstructed objects Detector Simulation Reconstruction ALPGEN + Pythia G. Watts (UW/Seattle) FFP 2014 - Marseille • Transfer Functions • Given a generated jet with what is the probability DZERO will reconstruct values x and y? • Detector and reconstruction resolution

16. DZERO using the ME Method In used at DZERO since Run I • Use different top mass in the Matrix Elements • Vary the Jet Energy Scale in the transfer functions G. Watts (UW/Seattle) FFP 2014 - Marseille GeV 3 years of work (old result): Total error is equivalent to March world average! GeV 3.6

17. What Did 3 years get? • Speed (CPU) to allow better MC stats • X100 increase means MC stats error drops from ~0.25 GeV to ~0.05 GeV. • New Jet Energy Scale Calibrations • ISR modeling • Constrain by studies in Drell-Yan data G. Watts (UW/Seattle) FFP 2014 - Marseille The variable is sensitive to Z boson recoil (). Gives an experimental bound to ISR mis-modeling Systematic error on reduced from ~0.25 to 0.06 GeV • General modeling improvements

18. Template Method Using a distribution sensitive to : Make it for each sample Simulated sample at GeV Simulated sample at GeV G. Watts (UW/Seattle) FFP 2014 - Marseille Simulated sample at GeV Use a likelihood to estimate template compatibility • Can do in two dimension • Jet energy scale • Top mass

19. Top Mass In Dilepton Events 4% of all decays, split into , and . Very little SM background! G. Watts (UW/Seattle) FFP 2014 - Marseille CDF’s basic selection: Observe 520 events, expect 78% purity ATLAS’ basic selection: Observe 2913, expect 96% purity Really excellent top lab Except… There are no 4-vectors for the two!! For 2 !!!

20. Template Method Need distributions that are strongly correlated with the top mass Template method to figure out the top mass ATLAS G. Watts (UW/Seattle) FFP 2014 - Marseille The average in the event Two permutations (take smallest) Avoid the missing resolution Good separation power

21. CDF Template Variables Fully reconstruct the top mass Problem: detector measures missing There are not enough constraints to solve for solution! The weighting method Grid in the azimuthal angles G. Watts (UW/Seattle) FFP 2014 - Marseille • Fit for the top mass at each grid location. • Resulting is the template variable. • Weight by fit . • The fit includes terms for: • All the measurements (2 leptons, two jets, missing ) • Top mass and the (constrained) W mass

22. Statistics Isn’t The Problem… Broad peak, but decent separation power. Leading systematic: Jet Energy Scale! This measurement is statistics limited. Can something be done? G. Watts (UW/Seattle) FFP 2014 - Marseille

23. Statistics Isn’t The Problem… Broad peak, but decent separation power. Leading systematic: Jet Energy Scale! This measurement is statistics limited. Can something be done? G. Watts (UW/Seattle) FFP 2014 - Marseille CDF creates a second template variable: GeV • Depends on 4-vector of leptons • Direction of jets • No Jet Energy Scale, no Missing And combines the two, optimizing for minimal error

24. Dilepton Top Mass Results Standard Template Method Jet Energy Scale isn’t fit: not enough constraints G. Watts (UW/Seattle) FFP 2014 - Marseille Statistics already making a big difference here

25. Top Mass in All Hadronic Decays (CDF & CMS) 44% of all decays. Largest single decay class. Overwhelmed by SM QCD background! G. Watts (UW/Seattle) FFP 2014 - Marseille 6 Jets After CMS requires 6 jets 4 jets with GeV 5th with GeV 6th with GeV Estimated signal purity is 3% Signal Efficiency is 3.5%!

26. Improving the Purity Unique Handles: Look for -tagged jets 2 -jets • Perform kinematic fit: • Know • The two are the same 2 2 G. Watts (UW/Seattle) FFP 2014 - Marseille (CDF) Mass of the pairs of light quark jets Mass of the pairs of light quark jets free parameters is the well measured value of 80.4 GeV Every jet permutation is tried Minimum is kept

27. Improving the Purity Requiring the fit to converge Very basic cuts on the Raise CMS’s purity to 39% G. Watts (UW/Seattle) FFP 2014 - Marseille Additional kinematic selection Raise CMS’s purity to 54% CDF has a purity of 57% CMS: CDF: Neural Network

28. Extracting the Mass The Template Method Fit for both Jet Energy Scale and G. Watts (UW/Seattle) FFP 2014 - Marseille

29. Lepton + Jets From CMS Analysis is very similar to the All-Jets analysis from CMS Full TeV result: Initial selection is > 100K events and 94% pure QCD background is negligible! A simple kinematic fit to clean up incorrect jet assignments • Each possible jet assignment gives • Each is weighted by the fit probability G. Watts (UW/Seattle) FFP 2014 - Marseille Largest systematic error is the flavor dependent Jet Energy Scale (0.41 GeV)

30. Conclusions • Field is still rapidly evolving • World average submitted in March • CDF dilptons and all-hadronic • DZERO matrix element • CMS all-hadronic and lepton+jets • What is next? • Tevatron will finish putting out “final” mass measurements • LHC’s statistics and purity mean it should quickly surpass the Tevatron. • LHC Run 2 projections • Other measurements with the quark mass • Top and anti-top have consistent masses • measurements that can clarify which mass we measure. • Becoming like the W mass… G. Watts (UW/Seattle) FFP 2014 - Marseille If you believe BICEP2!

31. Awaiting the next world Combination… G. Watts (UW/Seattle) FFP 2014 - Marseille Current World Combination CMS Combination Tevatron Combination

32. Systematic Errors G. Watts (UW/Seattle) FFP 2014 - Marseille

33. ATLAS Lepton+Jets Template G. Watts (UW/Seattle) FFP 2014 - Marseille

34. CDF dilepton ATLAS dilepton 7 TeV G. Watts (UW/Seattle) FFP 2014 - Marseille

35. CMS all jets CDF all jets G. Watts (UW/Seattle) FFP 2014 - Marseille

36. CMS All Jets 7 TeV G. Watts (UW/Seattle) FFP 2014 - Marseille

37. DZERO Lepton+Jets ME Tevatron Combination G. Watts (UW/Seattle) FFP 2014 - Marseille