Optimizing the W resonance in dijet mass

Optimizing the W resonance in dijet mass

Daniel AbercrombiePennsylvania 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 2

The Event


Characterizing the W peak

Searching for stable mean and smallest fractional width


200 GeV < pT < 225 GeV

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



• Jump in larger cones probably due pT cut for single jets



• ΔR = 0.4 gives narrowest width



• Reasonably constant responses from each cone size



• Again, ΔR = 0.4 gives the narrowest width

Comparing algorithms




• Grooming keeps mass relatively constant compared to anti-kT

ΔR = 0.5



ΔR = 0.5

• Trimming and filtering compete for best resolution



• Pruning may be too aggressive at low pileup

ΔR = 0.5



ΔR = 0.5

• Trimming and filtering compete for best resolution

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


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


Thank you!


Backup Slides


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.


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 pT jets with a invariant mass of 30 GeV < m < 250 GeV is picked




• 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

Other measures of efficiency


ΔR = 0.5

• All of the lines for each algorithm fall well withinthe uncertainties

Effects of PU


ΔR = 0.4

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

Effects of PU


ΔR = 0.5


Effects of PU


ΔR = 0.7


Effects of PU


ΔR = 0.9


PU jets simulation


𝑑𝜎𝑑𝑝𝑇

∝𝑝𝑇❑− 5 ;𝑝𝑇>3GeV

𝑑𝜎𝑑𝑝𝑇

=𝑚𝑝𝑇+𝑏 ;0GeV<𝑝𝑇<3GeV

Weighting:

𝑤 (𝑁𝑃𝑈 ,𝑛 𝑗𝑒𝑡𝑠 )= 𝑁𝑃𝑈 !(𝑁𝑃𝑈−𝑛 𝑗𝑒𝑡𝑠 ) !𝑛 𝑗𝑒𝑡𝑠 !

(0.0125 )𝑛 𝑗𝑒𝑡𝑠 (0.9875 )𝑁𝑃𝑈 −𝑛 𝑗𝑒𝑡𝑠

𝐴 𝑗𝑒𝑡

𝐴𝐶𝑀𝑆≈0.0125

PU jets simulation


NPU = 10

• Everything above 20 GeV can be mistakenfor a quark jet

PU jets simulation


NPU = 15


PU jets simulation


NPU = 20


PU jets simulation


NPU = 25


PU jets simulation


NPU = 30


PU jets simulation


NPU = 35


PU jets simulation


NPU = 40



ΔR = 0.3


ΔR = 0.4


ΔR = 0.5


ΔR = 0.6


ΔR = 0.7


ΔR = 0.8


ΔR = 0.9


ΔR = 1.0


ΔR = 0.7

175 GeV < pT < 200 GeV


ΔR = 0.7

200 GeV < pT < 225 GeV


ΔR = 0.7

225 GeV < pT < 250 GeV


ΔR = 0.7

250 GeV < pT < 275 GeV


ΔR = 0.7

275 GeV < pT < 300 GeV

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




ΔR = 0.5

• Grooming keeps mass relatively constant compared to anti-kT



ΔR = 0.5

• Anti-kT seems to have the smallest width



ΔR = 0.5

• Pruning may be too aggressive at low pileup



ΔR = 0.5

• Again, anti-kT has narrowest width


Top Mass


Top Mass Width

Optimizing the W resonance in dijet mass

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