Analysis of $\pi^{0},\eta$ and $\omega$ mesons in pp collisions with a high energy photon trigger at ALICE

High energy heavy ion collision is a powerful and unique tool to achieve the high density and temperature like the early universe. At normal temperature, partons are confined in nucleons and they can not move freely due to the asymp- totic freedom which is a property of the Quantum Chromo Dynamics (QCD). However, at high density and/or high temperature, they can be deconfined from nucleons. This phase is called the Quark Gluon Plasma (QGP). Hadron production measurements in proton-proton collisions at the Large Hadron Collider (LHC) energies can observe new phenomena which must be a frontier in the particle physics and allow validation of the predictive power of the QCD and can provide further constrains on pQCD theory for LHC energies. It is well known that the yield of high transvers momentum particles is suppressed in nucleus-nucleus collisions relative to that in proton-proton collisions. This effect is attributed to energy loss of parent partons or perhaps of hadrons after freeze-out. Since π 0 , η and ω consists of only light quarks but different masses, the com- parison of the suppression between them can provide systematically information whether the energy loss occurs at the parton level or not. This suppression can be observed at high p T region particles clearly because low p T particles are not only suppression but also recreation from soft processes. So, measurement of high p T particles is suitable to observe this effect. This energy loss measure- ment requires proton-proton collisions data for base line because this needs to compare between proton-proton and nucleus-nuclear results. In this thesis, π 0 and η mesons are observed via 2 photons decay channel and ω is measured via 3 π decay channel in proton-proton collisions at √ s = 8TeV. We use the Photon Spectrometer to measure photons and the Time Projection Chamber to measure charged tracks. We analyze high energy photon trigger data to measure higher p T mesons than the minimum bias data. This high energy photon trigger can measure selectively high energy photon events. This trigger is fired by a cluster has above threshold discriminated by the Trigger Region Unit (TRU). The method of analyzing this trigger data had not been established by anybody. However, I have done it and measured neutral mesons spectra in proton-proton collisions at √ s = 8TeV for the first time in the world.