Invariant mass distribution of jet pairs produced in association with a W boson

in pp collisions at √s=1.96 TeV

CDF

• Layer 1: Beam Pipe

• Layer 2: Silicon Detector

• Layer 3: Central Outer Tracker

• Layer 4: Solenoid Magnet

• Layer 5: Electromagnetic Calorimeters

• Layer 6: Hadronic Calorimeters

• Layer 7: Muon Detectors

Two jets:ET > 30 GeV|η|< 2.4Dijet system pT>40 GeV/cThe two jets must be separated by |η|<2.5. Direction of pT and of the most energetic jet are separated azimuthally by |Δφ|>0.4.

Electron (muon):pT>20 GeV/c|η|<1.0Missing transverse energy ET>25 GeVThe transverse mass of the lepton +ET systemmust be greater than 30 GeV/c2.

The dijet invariant mass distribution. The sum of electron and muon events is plotted. The band in the subtracted plots represents the sum of all background shape systematic uncertainties described in the text. The distributions are shown with a 8GeV/c2 binning, while the actual fit is performed by using a 4GeV/c2 bin size.

The dijet invariant mass distribution for the sum of electron and muon events. The fit χ²/ndf is 62.0/81. Rjj distribution for events with Mjj< 115 and Mjj > 175 GeV/c2 of the data compared to the background estimation that corresponds to the same systematic combination of. The uncertainty band corresponds to background statistical uncertainty.

Variation with ET threshold

Increasing the jet ET threshold in steps of 5 GeV. The result is compatible with the expectation from a Monte Carlo simulation of a W boson plus a particle with a mass of 150 GeV/c2 and decaying into two jets.If the ET threshold is reduced to 20 GeV the significance of the excess is reduced and becomes 1.1 sigma.

"Inclusive" distributions without Njets=2 cut The MJJ and background subtracted MJJ distributions are shown below when the Njets=2 cut is relaxed.

High pT sample. The significance of the excess for the subsample of events selected with pT> 60 GeV is 2.2 σ.

Resonant production

Distribution of the total mass of the event and Q = Ml ν+ JJ - MJJ -MW distribution. The pZ of the neutrino is obtained by constraining the W mass to the PDG value and extracting the two solutions. The plots thus have two entries per event. The distributions are compatible with the background-only hypothesis.