IIHE topical seminar: Measurement of jet production in association with a Z boson at the LHC and jet energy correction and calibration at high level trigger in CMS
by
Fengwangdong Zhang(IIHE-ULB)
→
Europe/Brussels
Jacques Lemonne room (1G012) (IIHE, VUB)
Jacques Lemonne room (1G012)
IIHE, VUB
Description
abstract: This PhD public seminar talk presents the measurement of the cross section of jet production in association with a Z boson in proton-proton collisions at the Large Hadron Collider in CERN, with a center-of-mass energy of 8 TeV in 2012 and of 13 TeV in 2015. The data used for this analysis were collected by the Compact Muon Solenoid (CMS) detector, with an integrated luminosity of 19.6 fb-1 in 2012 and of 2.25 fb-1 in 2015. We measure the differential cross section as a function of jet multiplicity, jet transverse momentum and rapidity, and the scalar sum of jet transverse momenta. The rapidity correlations between the Z boson and jets are also measured benefiting from the large statistics of data taken in 2012. All distributions of measured observables are obtained after correcting detector effects, and the results of two leptonic decaying channels of Z boson are combined. Coming along with the systematic and statistical uncertainties, the measurements are compared to different theoretical predictions at different accuracy levels. The predictions are from MADGRAPH 5, SHERPA 2 (for
8 TeV analysis only), MADGRAPH_AMC@NLO, and fixed next-to-next-to-leading order (for 13 TeV analysis only). Through the precision measurement, in particular to the rapidity correlation measurement, we acquire a more accurate understanding of perturbative quantum chromodynamics. Thanks to the unprecedented high energy and the large statistics of data, we accomplished precision measurements in a physical phase space never reached before.
In this talk, the jet energy correction and calibration for the high level trigger system of CMS are also depicted. From 2012 to 2015, the Large Hadron Collider was upgraded, not only with the center-of-mass energy of the beams enlarged, but also with the instantaneous luminosity increased. The time distance between two particle bunches in a beam is reduced. As a result, the reconstructed momenta of the jets produced in each bunch crossing are significantly contaminated by multiple interactions. A dedicated technical approach has been developed for correcting the reconstructed jet momenta. The corrections have been calibrated for the data taking in 2015 and 2016.
