A simulation study of the rapidity distributions of leptons from W boson decays at ATLAS Laura...

14
A simulation study of the rapidity distributions of leptons from W boson decays at ATLAS Laura Gilbert q q W l l
  • date post

    21-Dec-2015
  • Category

    Documents

  • view

    213
  • download

    0

Transcript of A simulation study of the rapidity distributions of leptons from W boson decays at ATLAS Laura...

Page 1: A simulation study of the rapidity distributions of leptons from W boson decays at ATLAS Laura Gilbert.

A simulation study of the rapidity distributions of leptons from W

boson decays at ATLAS

Laura Gilbert

q

qW

l

l

Page 2: A simulation study of the rapidity distributions of leptons from W boson decays at ATLAS Laura Gilbert.

Simulation

• Pythia: One million of each W→eνe and W→ μνμ events generated. W mass and CTEQ5 pdfs assumed.

• ATLFAST – “fast” detector simulation: uses smearing to model detector efficiency: ntuples produced and studied for two million events.

• GEANT4 – “full” detector simulation, gives accurate detector efficiencies: 100 fully simulated muon events. Hits can be seen but tracks are not reconstructed.

Page 3: A simulation study of the rapidity distributions of leptons from W boson decays at ATLAS Laura Gilbert.

Why ?llWqq

• Reconstructed transverse masses can be used with MC studies to constrain real W mass

• W± rapidity asymmetry constrains pdfs and test evolution equations at low x.

• Simulations can be used to study GEANT detector efficiencies

Page 4: A simulation study of the rapidity distributions of leptons from W boson decays at ATLAS Laura Gilbert.

Rapidity Distributions

z

W+

VALENCE QUARK SEA QUARK

d

W+ production:

W- production:

Balances out with max at 0 for leptons

Sea quarks less x than valence?

u

udW-

-l

l

l+υl

l+

υl

l-

l

Page 5: A simulation study of the rapidity distributions of leptons from W boson decays at ATLAS Laura Gilbert.

Rapidity DistributionsGenerator-only results from Dittmar et al (1997). Plots are symmetric about 0 rapidity.

Peak: double the number of valence us

contribute to W+ than ds to W-

Central rapidities: xvalence = xsea ~10-3:

Two sea quarks, ~ even densities

xvalence>10-3; xsea<10-3:

Valence quark + sea antiquark

Page 6: A simulation study of the rapidity distributions of leptons from W boson decays at ATLAS Laura Gilbert.

Preliminary ATLFAST results – lepton pseudorapidity

Muon rapidity, constructed with and without a rapidity cut:

Cuts:

•Muon transverse momentum > 20GeV

•Missing energy > 20GeV

•|recoil| > 20GeV

•|muon pseudorapidity| < 2.4

Page 7: A simulation study of the rapidity distributions of leptons from W boson decays at ATLAS Laura Gilbert.

W transverse mass

• Longitudinal momentum of the neutrino cannot be measured

• Calculate transverse mass of W from transverse momenta (pT) of the neutrino and of the charged lepton

• Lepton pT is measured, whereas the transverse momentum of the neutrino is obtained from the pT of the lepton and the recoil

• The trailing edge of the spectrum is sensitive to the W mass. Compare real data to MC with difference values of MW.

)cos1(2 TlT

WT ppm

|| uppl

TT

Page 8: A simulation study of the rapidity distributions of leptons from W boson decays at ATLAS Laura Gilbert.

W transverse mass

• Trailing edge smeared by W intrinsic width and the detector resolution.

• Red plot is at the generator level, blue includes energy and momentum resolution as implemented in ATLFAST.

Page 9: A simulation study of the rapidity distributions of leptons from W boson decays at ATLAS Laura Gilbert.

Preliminary ATLFAST results – W transverse mass

W transverse mass, excluding (left) and including (right) cuts as before – red are W-, black are W+.

Page 10: A simulation study of the rapidity distributions of leptons from W boson decays at ATLAS Laura Gilbert.

GEANT4 ResultsReconstruction currently incomplete, but visualisationpossible:

Page 11: A simulation study of the rapidity distributions of leptons from W boson decays at ATLAS Laura Gilbert.

GEANT4 ResultsReconstruction currently incomplete, but visualisationpossible:

Page 12: A simulation study of the rapidity distributions of leptons from W boson decays at ATLAS Laura Gilbert.

GEANT4 ResultsReconstruction currently incomplete, but visualisationpossible:

Page 13: A simulation study of the rapidity distributions of leptons from W boson decays at ATLAS Laura Gilbert.

Grid at Dell

• Currently involved in investigating virtualisation of Atlas software on a Dell grid cluster in Austin, Tx.

• Should make it possible to run far larger simulations – will be able to analyse “real” data once reconstruction is complete (~1 month?)

Page 14: A simulation study of the rapidity distributions of leptons from W boson decays at ATLAS Laura Gilbert.

Future Work – W asymmetry

• Reconstruct W rapidities as far as possible

• Consider how far pdfs can be constrained at rapidities allowed by the detector

• Use GEANT4 datasets to study detector efficiencies

• Background Studies