arXiv subjects
Publications and source records attributed to D. V. Bandourin.
A neural network technique is used to discriminate between quark and gluon jets produced in the qg->q+photon and q q->g+photon processes at the LHC. Considering the network as a trigger and using the PYTHIA event generator and the full event fast simulation package for the CMS detector CMSJET we obtain signal-to-background ratios.
The artificial neural network approach is used for separation of signals from a single photon $γ$ and products of the $π^0,η, K^0_s$ meson neutral decay channels on the basis of the data from the CMS electromagnetic calorimeter alone. Rejection values for the three types of mesons as a function of single photon selection efficiencies are obtained for two Barrel and one Endcap pseudorapidity regions and initial $\Et$ of 20, 40, 60 and 100 GeV.
The possibility of separating the $π^0, η, ω$ and $K^0_s$ meson background from the signal photons produced directly in $pp$ collisions is analyzed. The rejection factors for two pseudorapidity regions 0.4<η<1.0$ and 1.6<η<2.0$ and six Et values, 20, 40, 60, 80, 100 and 200 GeV, are calculated for a case when only the calorimeter information is used. The cases of $η, ω$ and $K^0_s$ mesons decaying through the neutral and charged channels are considered separately.
It is shown in the paper that Pt activity limitation (modulus of the vector sum) of all particle beyond "photon+Jet" system Pt^out leads to the noticeable photon Pt - jet Pt disbalance decreasing. On a simultaneous restriction of the cluster Pt and Pt^out from above it is possible to reach an acceptable balance between photon Pt - jet Pt with a sufficient number of the photon Pt - jet Pt events for the jet energy scale setting and hadron calorimeter calibratiom of the CMS detector at LHC.
It is shown that "photon+Jet" events, being collected at LHC, would provide us with the data sufficient for an extraction of gluon distribution function in a proton using valence and s quark distributions measured in the same experiment with another physical proces A new region of 10^{-4}< x < 10^{-1} with 1.6x10^3< Q^2<10^5 ~(GeV/c)^2 can be covered. The rates of g c-> photon +Jet events are also given.
The possibilities of the background events suppression, based on the QCD subprocesses of qg-, gg-, qq- scattering with big cross sections, to the signal \gpj events are studied. Basing on the introduced selection criteria, the background suppression factors and signal events selection efficiencies and the number of the events, that can be collected at LHC with low luminosity L=10^{33}cm^2 s^{-1} during one month of continuous work, are determined.
In this paper the study of "photon+Jet" events is continued and the event number determination useful for jet energy scale setting with the possible CMS detector hadron calorimeter calibration at LHC is fulfiled. The sources of photon Pt and jet Pt disbalance are exposed. It is shown that the cluster Pt limitation, which is found in an event outside of the jet, can be a good criterion for this disbalance decreasing.
In this paper the study of "photon+Jet" events is continued, aimed at jet energy scale setting and hadron calorimeter calibration at LHC energies. The event number distribution over Pt and pseudorapidity eta in the barrel region of the photon is presented. The features of "photon+Jet" events in CMS detector |eta|<1.4 are exposed. Pt structure of the region in the eta-phi space inside and beyond jet is also shown.
"photon+Jet" events, based on the q~q-> g+photon and qg-> q+photon subprocesses, are proposed for jet energy scale setting and hadron calorimeter calibration at LHC energies. General features and selection criteria of "photon+Jet" events that would provide a good photon Pt - jet Pt balance are described. CMS detector geometry is taken as the basement.