Jet energy correction with charged particle tracks in CMS

Abstract

The performance of a jet-energy-correction algorithm using reconstructed charged particle tracks is presented. The jet energy correction allows the jet energy scale to be restored and improves the energy resolution for jets with energies up to 120 GeV. For low energy jets (20 GeV) it improves the resolution by a factor 1.7 with respect to uncorrected jets. For 100 GeV jets the resolution improves by 15%. The deviation from unity of the ratio of the reconstructed to the generated jet transverse energies decreases by a factor two for low-¤ ¦ ¥

Jet results in heavy-ion collisions from CMS

“…These particle flow objects are then clustered using the anti-k T [10] algorithm, with a resolution parameter of 0.3, encoded in the FastJet [11] framework. In pPb and PbPb jet events the underlying event is removed with the iterative pileup subtraction technique [12]. The b-jets are tagged by using a discriminator which uses the information of the flight distance of the reconstructed secondary vertices with respect to the nominal collision interaction point.…”

Systematic shifts in jet energy scale from the process $$W \to q\bar q$$ in CMS detector

“…Jet energy correction done by using events (1) is based on the usage of the relationship between the mass of a W boson and the invariant mass of cali brated jets produced in W decay: (4) With accuracy up to / (m q and E q are the mass and energy of quarks produced in W decay), the W boson mass can be represented as follows: (5) Here f qq denotes an angular factor expressed via pseu dorapidities and azimuthal angles of quarks. A similar relationship can be written for the invariant mass of jets: (6) It can be rewritten for the energies, corrected by some calibration factors k 1 and k 2 , in the following way:…”

“…This factor can be used to correct the ener gies of calibrated jets, for example, after "γ + jet" [1,2] or "jet + track" correction [3][4][5], for which the ratio / is appreciably independent of the jet transverse energy.…”

“…(iii) "ZSP + JPT" jets are those with the cone size R = 0.5 found by applying the algorithm that uses reconstructed energies released in cells of calorime ters, track parameters, and ZSP corrections [3][4][5]. …”

Jet energy measurements in CMS

“…[5]. For each track reaching the calorimeter surface within the reconstruction jet area, the expected response is subtracted from the calorimeter jet energy and the track momentum is used instead.…”