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Measure η_c Mass and Width and Reconstruction Efficiency of Low Momentum π~0

Author: ZhangSuRong
Tutor: YangYongZuo;ZhangJingZhi
School: Guangxi Normal University
Course: Theoretical Physics
Keywords: Charmonium ψ (2S) η_c quality η_c physical width The soft π ~ 0 reconstruction efficiency
CLC: O572.33
Type: Master's thesis
Year: 2011
Downloads: 1
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Physicists have found a series of charmonium J / ψ, ψ (2S), ψ (3770) particles, etc., and would like to the charmonium family's efforts to find new members. Charmonium is the ideal place to research and find new hadron production and decay properties of the testing and development of quantum chromodynamics (QCD) theory has a very important significance. QCD theory is used to describe the basic theory of strong interactions, QCD theory test and development of great significance for us to further understand the nature of the strong interaction law. Nature has found Hadron by two or three quarks, the QCD theory predicts that multi-quark states with more than three quarks, the quark - anti-quark and gluon or three quarks and gluons (qqg qqg) consisting of mixed state and pure gluon (gg, ggg) glueball new hadron composed exist. But so far, the experiment also never confirmed the existence of the new hadron states. Therefore, the observed glueball new hybrid state and multi-quark state hadron state and determine the nature of the testing and development of QCD theory is of great significance, has been one of the the world's most important to a lot of high energy physics experiment on the physical target. Ηc various studies for many, but obtained in the different experimental ηc resonance curve, the quality and the width of the description there is a big difference. Precise the M1 transitions measurement factor not only be able to verify our understanding of the theory, and standardized ηc branching ratio ηc branching ratio is a key measure other characteristics. At the same time the the ηc quality and accurate measurement of the physical width of the accurate measurement of the premise and guarantee of ηc branching ratio. Currently the CLEO_c research group has collected using CLEO_c detector 24.5 million ψ (2S) decay data, accurate measurements of a the charmonium system of magnetic dipole radiation. They measured J / ψ and ψ (2S) decays to η from the magnetic dipole radiation. The branching ratio. Later they measured the following thirds of the decay channels: B (ψ (2S) → γηc) = (4.32 ± 0.16 ± 0.60) × 10-3, B (J / ψ → γηc) / B (ψ ( 2S) → γηc) = 4.59 ± 0.23 ± 0.64, B (J / ψ → γηc) = (1.98 ± 0.09 ± 0.30)%. In these studies they observed due to the photon energy is dependent on the rate of magnetic dipole radiation, thereby ηc the shape distorted. The radiative transition process with other mechanisms in the measurement of the quality of ηc differences. Based experimental study of CLEO_c, we use the BES Ⅲ about $ ψ (2S) case data via the decay channel ψ '→ γηc intensive research ηc resonance parameters accurate measurement method, the signal fitting method, and error handling method , thereby accurately measuring ηc mass and width. Diao same time. Distortions further physical interpretation is given, that resonant states between successive amplitude interference may be asymmetrical in shape. For this reason plus Since ηc itself widths wide (about 30MeV), cause it may be the end of the direct decay of ψ (2S) ηc resonance state decay (background) state form an interference, so the in ηc quality spectrum fitting We used the signal and the background coherent method, taking into account the efficiency correction and mass resolution effects. In many physical analysis π0 either as a signal or background are systematic errors of the main source of π0 reconstruction efficiency precision measurement can accurately estimate the systematic errors brought it, especially in the low-momentum π0. We sample decay channels ψ (2S) → π0π0J of / ψ, J / ψ → μ μ-/ e e-measured low momentum π0 reconstruction efficiency. The experimental analysis of this thesis is the upgraded Beijing Spectrometer (BES Ⅲ) 106 MB ψ (2S) data collected for the first time on the Beijing Electron Positron Collider (BEPC Ⅱ), the data sample is the the BES Ⅱ ψ (2S) seven times the data (14 million), CLEO-c experiment group at Cornell University collected samples (27 million), about four times the data sample collected on the world's largest ψ (2S) formant.

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CLC: > Mathematical sciences and chemical > Physics > Nuclear physics,high energy physics > High-energy physics > Particle types > Meson
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