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Title: STUDY OF BEAM SPIN ASYMMETRY IN EXCLUSIVE Π° PRODUCTION

Abstract

Describing and understanding atomic nuclei is a puzzle that has intrigued scientists for decades. Approximately ten years ago, a description of nucleon structure, referred to as Generalized Parton Distribution (GPD), was introduced. GPDs are a way of describing scattering and production processes in a single framework. Deeply Virtual Compton Scattering (DVCS) is a process that scatters a photon from a proton and detects a scattered electron, a proton, and one photon in the fi nal state. From DVCS, GPDs can be extracted in order to lead us to a more complete picture of nucleon structure. The focus of this study is to understand the beam spin asymmetry (BSA) of the neutral π° meson, a main source of background during the DVCS process. To calculate the BSA, the number of π° events with positive helicity (spin) and negative helicity were counted by integrating histograms with Gaussians fi ts. It is shown that there is a signifi cant non-zero BSA in production of exclusive π°, namely 0.0655±0.0022. In the analysis of previous experiments, the BSA of π° was assumed to be zero and therefore ignored. Now, future analyses of DVCS data may incorporate this evidence of BSA. A deeper understanding of backgroundmore » processes (π°) in the DVCS will allow precision measurements of GPDs, providing new insight concerning the structure of nucleons.« less

Authors:
;
Publication Date:
Research Org.:
DOESC (USDOE Office of Science (SC) (United States))
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1051821
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Undergraduate Research; Journal Volume: 7
Country of Publication:
United States
Language:
English

Citation Formats

Howley, I., and Avagyan, H.. STUDY OF BEAM SPIN ASYMMETRY IN EXCLUSIVE Π° PRODUCTION. United States: N. p., 2007. Web.
Howley, I., & Avagyan, H.. STUDY OF BEAM SPIN ASYMMETRY IN EXCLUSIVE Π° PRODUCTION. United States.
Howley, I., and Avagyan, H.. Mon . "STUDY OF BEAM SPIN ASYMMETRY IN EXCLUSIVE Π° PRODUCTION". United States. doi:. https://www.osti.gov/servlets/purl/1051821.
@article{osti_1051821,
title = {STUDY OF BEAM SPIN ASYMMETRY IN EXCLUSIVE Π° PRODUCTION},
author = {Howley, I. and Avagyan, H.},
abstractNote = {Describing and understanding atomic nuclei is a puzzle that has intrigued scientists for decades. Approximately ten years ago, a description of nucleon structure, referred to as Generalized Parton Distribution (GPD), was introduced. GPDs are a way of describing scattering and production processes in a single framework. Deeply Virtual Compton Scattering (DVCS) is a process that scatters a photon from a proton and detects a scattered electron, a proton, and one photon in the fi nal state. From DVCS, GPDs can be extracted in order to lead us to a more complete picture of nucleon structure. The focus of this study is to understand the beam spin asymmetry (BSA) of the neutral π° meson, a main source of background during the DVCS process. To calculate the BSA, the number of π° events with positive helicity (spin) and negative helicity were counted by integrating histograms with Gaussians fi ts. It is shown that there is a signifi cant non-zero BSA in production of exclusive π°, namely 0.0655±0.0022. In the analysis of previous experiments, the BSA of π° was assumed to be zero and therefore ignored. Now, future analyses of DVCS data may incorporate this evidence of BSA. A deeper understanding of background processes (π°) in the DVCS will allow precision measurements of GPDs, providing new insight concerning the structure of nucleons.},
doi = {},
journal = {Journal of Undergraduate Research},
number = ,
volume = 7,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • Beam-target double-spin asymmetries and target single-spin asymmetries in exclusive pi(+) and quasiexclusive pi(-) electroproduction were obtained from scattering of 1.6- to 5.7-GeV longitudinally polarized electrons from longitudinally polarized protons (for pi(+)) and deuterons (for pi(-)) using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The kinematic range covered is 1.1 < W < 2.6 GeV and 0.05 < Q(2) < 5 GeV2, with good angular coverage in the forward hemisphere. The asymmetry results were divided into approximately 40 000 kinematic bins for pi(+) from free protons and 15 000 bins for pi(-) production from bound nucleons in the deuteron.more » The present results are found to be in reasonable agreement with fits to previous world data for W < 1.7 GeV and Q(2) < 0.5 GeV2, with discrepancies increasing at higher values of Q(2), especially for W > 1.5 GeV. Very large target-spin asymmetries are observed for W > 1.6 GeV. When combined with cross-section measurements, the present results can provide powerful constraints on nucleon resonance amplitudes at moderate and large values of Q(2), for resonances with masses as high as 2.3 GeV.« less
  • Cited by 2
  • Here, beam-target double-spin asymmetries and target single-spin asymmetries in exclusive π + and quasiexclusive π electroproduction were obtained from scattering of 1.6- to 5.7-GeV longitudinally polarized electrons from longitudinally polarized protons (for π +) and deuterons (for π ) using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The kinematic range covered is 1.1 < W < 2.6 GeV and 0.05 < Q 2 < 5GeV 2, with good angular coverage in the forward hemisphere. The asymmetry results were divided into approximately 40 000 kinematic bins for π + from free protons and 15 000 bins for πmore » production from bound nucleons in the deuteron. The present results are found to be in reasonable agreement with fits to previous world data for W < 1.7 GeV and Q 2 < 0.5GeV 2, with discrepancies increasing at higher values of Q 2, especially for W > 1.5 GeV. Very large target-spin asymmetries are observed for W > 1.6 GeV. When combined with cross-section measurements, the present results can provide powerful constraints on nucleon resonance amplitudes at moderate and large values of Q 2, for resonances with masses as high as 2.3 GeV.« less
  • Beam-target double-spin asymmetries and target single-spin asymmetries were measured for the exclusive π + electroproduction reaction γ*p→nπ +. The results were obtained from scattering of 6-GeV longitudinally polarized electrons off longitudinally polarized protons using the CEBAF Large Acceptance Spectrometer at Jefferson Laboratory. The kinematic range covered is 1.1 < W < 3 GeV and 1 < Q 2 < 6GeV 2. Results were obtained for about 6000 bins in W, Q 2, cos(θ*), and Φ*. Except at forward angles, very large target-spin asymmetries are observed over the entire W region. Reasonable agreement is found with phenomenological fits to previous datamore » for W < 1.6 GeV, but very large differences are seen at higher values of W. A generalized parton distributions (GPD)-based model is in poor agreement with the data. As a result, when combined with cross-sectional measurements, the present results provide powerful constraints on nucleon resonance amplitudes at moderate and large values of Q 2, for resonances with masses as high as 2.4 GeV.« less