Optimizing the W resonance in dijet mass

Optimizing the W resonance in dijet mass Daniel Abercrombie Pennsylvania State University 8 August 2013 Advisors: Phil Harris and Andreas Hinzmann

The Goal of the Project • Compare jet cone sizes and algorithms • Identify the algorithm and parameters that givesa stable W mass and narrowest resonance • Results will be used in talks with ATLAS to determine a common set of parameters for jet reconstruction between the experiments Daniel Abercrombie

The Event Daniel Abercrombie

Characterizing the W peak Searching for stable mean and smallest fractional width 200 GeV < pT < 225 GeV Daniel Abercrombie

Comparing cone sizes • Using the anti-kT algorithm gives the most conic shape and is resistant to soft radiation • Scanned through cone sizes from ΔR = 0.4 to ΔR = 0.8 with a resolution of 0.1 Daniel Abercrombie

Comparing cone sizes • Jump in larger cones probably due pT cut for single jets Daniel Abercrombie

Comparing cone sizes • ΔR = 0.4 gives narrowest width Daniel Abercrombie

Comparing cone sizes • Reasonably constant responses from each cone size Daniel Abercrombie

Comparing cone sizes • Again, ΔR = 0.4 gives the narrowest width Daniel Abercrombie

Comparing algorithms Daniel Abercrombie

Comparing algorithms ΔR = 0.5 • Grooming keeps mass relatively constant compared to anti-kT Daniel Abercrombie

Comparing algorithms ΔR = 0.5 • Trimming and filtering compete for best resolution Daniel Abercrombie

Comparing algorithms ΔR = 0.5 • Pruning may be too aggressive at low pileup Daniel Abercrombie

Comparing algorithms ΔR = 0.5 • Trimming and filtering compete for best resolution Daniel Abercrombie

Conclusions • Smaller cone sizes give the best mass resolution with a reasonably small response • Pruning looks like it might be too aggressive • Current plots should be improved by finding ways to increase the efficiency of picking the correct jets Daniel Abercrombie

Future work • Explore additional parameter space of the algorithms • Look at the effects of jet reconstruction onthe top quark mass • Work on selection cuts and parameters to increase the efficiency of selecting the correct jet Daniel Abercrombie

Thank you! Daniel Abercrombie

Backup Slides Daniel Abercrombie

Selection criteria jets • Events must have at least two b tagged jets and one isolated muon with pT > 10 GeV and |η| < 2.4 • Two jets with pT > 20 GeV and the highest combined secondary vertex values were selected as the b jets • Other jets were in the opposite hemisphere from the muon, MET, and b tagged jet closer to the muon i.e. Daniel Abercrombie

Selection criteria jets (cont.) • Single jets were picked with the following cuts:p > 200 GeV; mass > 60 GeV; MET > 30 GeV • MET cut helps ensure boosted tops • If there were no single jets, the dijet system with the highest pTjets with a invariant mass of 30 GeV < m < 250 GeV is picked Daniel Abercrombie

Comparing algorithms • Pruningtight: nsubjets=2, zcut=0.1, dcut factor=0.5, algo = CAloose: nsubjets=2, zcut=0.1, dcut factor=0.2, algo = CA • Filteringtight: rfilt=0.2, nfilt=3, algo = CA loose: rfilt=0.3, nfilt=3, algo = CA • Trimmingtight: rtrim=0.2, pTfrac=0.05, algo = CA loose: rtrim=0.2, pTfrac=0.03, algo = CA Daniel Abercrombie

Other measures of efficiency ΔR = 0.5 • All of the lines for each algorithm fall well withinthe uncertainties Daniel Abercrombie

Effects of PU ΔR = 0.4 • Pileup decreases efficiency • This is more prominent using larger cone sizes Daniel Abercrombie

PU jets simulation Weighting: Daniel Abercrombie

PU jets simulation NPU = 10 • Everything above 20 GeV can be mistakenfor a quark jet Daniel Abercrombie

Daniel Abercrombie

ΔR = 0.3 Daniel Abercrombie

ΔR = 0.7 175 GeV < pT < 200 GeV Daniel Abercrombie

Optimizing the W resonance in dijet mass