| Our human being has never been stopping in the exploration of the virgin field in understanding ourselves and our surroundings. In the 20th century, great achieve-ments have been obtained in particle physics. Our knowledge on the fundamental matter has reached the quark level (R～10-18m), which in turn improve our un-derstanding on the origin of universe. Standard Model is one of the best theories to predict the new phenomena and explain the experiment results in these fields. It explains that the fundamental particles are 3 generations of quarks,3 generations of leptons and four force carriers (γ-electromagnetic interaction; gluon-strong interac-tion; Z0 and W±-weak interaction). However, there arc also still a number of puzzles remaining, such as existence of Higgs boson and super-symmetry particles, neutrino mass puzzle, which within or beyond the Standard Model, need to be answered. Be-sides, whether there are new particles/quarks/leptons unexpected? These questions are the first driving force to motivate physics scientists.As a part of Standard Model, Lattice Quantum ChromoDynamics (1QCD) predicts a phase transition from hadronie matter to the deconfined QCD matter called Quark Gluon Plasma (QGP) at extreme high energy and density. Probing of the QGP and exploring its thermal properties and dynamic evolution are the main topics in ultra-relativistic heavy-ion collisions. In addition, the probe of QGP also plays an important role in direction of astrophysical observation. However, there are no direct way to measure the QCD matter but by the measurement of final hadron spectrum. Several observables have been well built, such as the high PT hadron suppression and jet quenching, enhancement of the strangeness particles, suppression of the quarkonia production and the hydrodynamic collective flow etc. Among these observables, in my study I will employ the electromagnetic probe to build the connections to the hot-dense matter, because the interaction between the photon and medium is weak when the photon goes through thus can carry the origin information when it was created.Up to now, a great of results have been obtained at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory with a top center-of-mass energy 200 GeV. The results are critical reference for the experiments at Large Hadron Collider (LHC) at CERN. A Large Ion Collider Experiment (ALICE) is one of the four main experiments at the LHC, which is dedicated on the heavy-ion collisions at a top center-of-mass energy (?)SNN= 5.5 TeV. The initial runs with proton-proton collisions at 900 GeV (2009) and 7 TeV (2010) arc useful reference points for the Pb-Pb collisions at a (?)SNN of 2.76 TeV (2010) and 5.5 TeV (2013). Firstly, the raw yield of neutral mesons byπ0(η)→2γandω(782)→π0γ→3γwith the realistic geometrical configuration were estimated. It gives us an important reference before the ALICE data-taking at nominal energy. For PHOS, the study proves the possibility to measure theηandω(782) despite of its limited acceptance.I would like to say it was my fortunate that I caught the moment of ALICE data-taking in the course of my PhD, which makes the thesis a bit rich of "EXPERI-MENTAL", and not only of "SIMULATION". Besides, from the experience of shifts on Data Acquisition (DAQ), Central Trigger Processing (CTP) and Detector Control System (DCS) I get to know how the LHC works and its complexity.However, the experiment is not like phenomenology which can get the expected results as they want by adjusting the parameters properly. Especially at the beginning running, we need to understand the detectors and then to get the convincing physics results. Thus the data processing chain from raw data to the physics analysis oriented arc studied and presented, which includes the clusterization, detector calibration and particle identification.In this thesis, the neutral mesons measurement with ALICE electromagnetic calorimeters (PHOS and EMCAL) at the LHC is presented. Depending on the differ-ent technical design of the PHOS and EMCAL, the strategies of the neutral mesons extraction by invariant mass analysis, shower shape analysis and isolation cut method arc studied. The only reason is the detector granularity so that the clusters start to merge which push us to unfold the cluster and identify the particle species according to their shower shape parameters. At very high PT, the isolation cut method was developed to identify the direct photons, and also for the extraction of neutral pion indirectly.For EMCAL, we need further investigations on the calibration and geometrical problems left at the moment. More results with PHOS are included in the current analysis. Here I do not intent to claim that all the results are the final results, but present my contributions and what I obtained.From the current statistics with pp collisions at 7 TeV,～390 million min-bias events are analyzed. By using the invariant mass analysis, theπ0 spectrum is ex-tracted to a PT range of 25 GeV/c with PHOS. While for EMCAL, due to the cluster overlap it can measure theπ0 spectrum with PTx range to 15 GeV/c. The 77 peak is also can be observed and measured up to 10 GeV/c, but not included in this analysis. As for theω→π0γ, there is no evidence of this channel in PHOS because of the small acceptance and bad channels, but for EMCAL it can be seen at high PT>10 GeV/c with the help of special unfolding algorithm. An additional method with the assumption that high PT clusters areπ0 without cluster unfolding was developed forωmeasurement, which had been studied in simulation and being validated in real data.For the corrections of the raw spectrum, we take into account the geometrical acceptance and the reconstruction efficiency together by a full simulation with a uniform singleπ0 per event. The systematic uncertainties are estimated due to the absolute energy scale calibration, non-linearity response of the detector, bad channels andπ0 loss. The finalπ0 production yield are obtained. The scaling behavior of xT and mT are studied by comparing the world-wide data set. Finally,π0 cross section arc compared with QCD next-lcading-order calculation.What I want to emphasis is that the first measurement of the neutral mesons channels are crucial for the calibration of electromagnetic calorimeters. It is also related to almost all the photon physics, such as direct photon access, flow measure-ment and jet physics etc. In the coming years, the ALICE will continue with the data taking with pp and PbPb collision and the LHC will reach the designed luminosity. More statistics and more physics results will come forth.Finally, I would like to say "it is an accomplishment of my PhD study, but just a beginning of ALICE physics activities."...
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