CDF Mjj anomaly in CMS data

Minimal plan:

Immediate goal is to produce a statement on the CDF bump for the summer conferences, ideally already for EPS.

  • Apply diboson selection for lnujj
  • Fit the Mjj spectrum with the V+jets background shape taken from a MC template. (Should eventually be taken from data, this is an obvious point to improve upon, but that needs more time).
  • Extract W+Jets Mjj templates from Madgraph/Alpgen/MCFM/Sherpa MC generators and compare effect in fit to data.
  • If using both lepton flavors proves to require too much time, concentrate on muon channel

Urgent list of tasks for minimal plan:

  • As a very first step, to get an idea how sensitive the W+jets Mjj spectrum is to the actual generator, compare Mjj on gen level between the various generators.
  • For sys checks: Understand from MC authors which MC parameters may impact the Mjj spectrum and what their possible range is. Extract W+jets templates with MC parameters varied within possible range.
  • Monitor in steadily increasing data set the effect of the diboson selection
  • Monitor in steadily increasing data set the effect of changing trigger conditions

Tasks list

Monte Carlo generation:

Produce W+jets MC samples of 10x the data statistics expected by July 1 for

  • Madgraph
  • Alpgen
  • MCFM
  • Sherpa

Cut optimization:

Study impact of CDF like cuts

For reference:

Cuts used in current diboson lnujj analysis:

W→lν reconstruction

  • ET > 25 GeV, |η| <2.5 (2.1) for electron (muon)
  • Passing Top PAG recommended isolation/Id criteria
  • W transverse mass: mT > 50 GeV, PF MET > 25 GeV
  • Z veto

Require two PF jets in the event

  • each jet with corrected pT >20 GeV and |η| <2.4
  • |cosθ*|< 0.4, |Δϕ(jet1, jet2)| > 1.5
  • |Δϕ(jet1, MET)| > 0.6
  • |Δϕ(W, W) − π| < 0.2
  • No b-tagged jets

Cuts used in W+jets 2010 selection for electron channel:

Gsf electrons:

  • pT > 20 GeV
  • |η| < 2.5, exclu. 1.4442 < |η| < 1.566
  • WP80 cuts
  • No other electrons forming Z mass with 1st, i.e. ! ( 60 < mll < 120 GeV )
  • No muons with pT > 15
  • Transverse impact parameter δxy < 0.035
  • HLT object match
  • MT > 20 GeV (MT calculated from gsfElectron and PF MET)

Particle Flow Jets

  • Loose PFlow JetID applied
  • L1FastJet, L2+L3+L2L3Residual corrections
  • ET > 30 GeV
  • |eta| < 2.4
  • If selected electron is within ΔR < 0.5, remove

CDF cuts

  • ET (pT ) lepton > 20 GeV
  • MET > 25 GeV
  • MT > 30 GeV/c2
  • Number of jets .ge. 2
  • ET of two leading jets > 20 GeV
  • Opening angle in eta between two leading jets .le. 2.5
  • Opening angle in the transverse plane between MET and leading jet ET .ge.0.4
  • Transverse momentum of dijet system, ptjj > 40 GeV

Template fit to Mjj spectrum:

In addition to those tasks listed above for minimal plan, prepare machinery for Q^2 reweighting of Alpgen samples


Study impact of triggers on Mjj spectrum, look at single lepton triggers, lepton+jets triggers and lepton+dijet+x triggers (x can be missingHT); emulate relevant trigger menus for that purpose; point is to make sure that we understand possible bias introduced to Mjj spectrum by the trigger


Estimate impact of JES uncertainty and JER on Mjj spectrum

Pile up subtraction:

Study impact of different subtraction methods on Mjj spectrum

Cross check Mjj spectrum from W+jets with Z+jets events

Advantage: Can use dilepton triggers, no missingET or MT cuts

-- MonikaGrothe - 01-Jun-2011

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Topic revision: r2 - 2011-06-03 - MonikaGrothe
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