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### 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 algorithms

Daniel Abercrombie

Comparing algorithms

ΔR = 0.5

- Grooming keeps mass relatively constant compared to anti-kT

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

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

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

Effects of PU

ΔR = 0.5

- Pileup decreases efficiency
- This is more prominent using larger cone sizes

Daniel Abercrombie

Effects of PU

ΔR = 0.7

- Pileup decreases efficiency
- This is more prominent using larger cone sizes

Daniel Abercrombie

Effects of PU

ΔR = 0.9

- Pileup decreases efficiency
- This is more prominent using larger cone sizes

Daniel Abercrombie

Daniel Abercrombie

Daniel Abercrombie

Daniel Abercrombie

Daniel Abercrombie

Daniel Abercrombie

Daniel Abercrombie

Daniel Abercrombie

Daniel Abercrombie

Cacciari, M., et al. JHEP04(2008)063

Daniel Abercrombie

Comparing algorithms

ΔR = 0.5

- Grooming keeps mass relatively constant compared to anti-kT

Daniel Abercrombie

Top Mass

Daniel Abercrombie

Top Mass Width

Daniel Abercrombie

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