The HEP group, in colloboration with the experimental particle physics team in IUT, is now part of the CMS collaboration of the LHC.

At moment we are involved in two projects, which is briefly descibe below:

Search for an exotic decay of the Higgs boson to a pair of light pseudo scalar in proton-proton   collisions at 13 TeV

The Higgs boson discovered in 2012 was the last missing particle predicted in the standard model (SM) of particle physics. Although the fundamental properties of the Higgs particle have been studied since its discovery, the uncertainties on the measured parameters still allow us to search for the signals of the new physics. In this search, we study an exotic decay of the Higgs boson to a pair of light pseudo scalar particles a1, assuming that one of the pseudoscalars decays to a pair of opposite sign muons and the other decays to a pair of opposite sign b-quarks. Such signatures are predicted in a number of extensions of the standard model (BSM), including NMSSM and 2HDM+S. The studies will be based on a data set of proton-proton collisions corresponding to an integrated luminosity of 137 fb^-1 , accumulated with the CMS experiment at the CERN LHC within 2016-2018 at a center-of-mass energy of 13 TeV.

CMS luminosity measurement using nucleus-nucleus collisions at sqrt(s_NN) = 5.02 TeV in 2015

In particle physics experiments the energy available for the production of new effects is the most important parameter. The required large centre of mass energy can only be provided with colliding beams where little or no energy is lost in the motion of the centre of mass system. Besides the energy, the number of useful interactions (events), is important. This is especially true when rare events with a small production cross section are studied. The quantity that measures the ability of a particle accelerator to produce the required number of interactions is called the luminosity. In practice the luminosity is determined based on some special scans, called van-der-Meer (vdM) scans, which involve scanning the two incident beams across each other and monitoring the interaction rate. In this project we try to measure the luminosity based on the lead-lead collision data collected by the CMS detector in 2015.

High Energy Physics Research Group

Department of Physics

Sharif University of Technology