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Title: Photoproduction and Radiative Decay of eta' Meson in CLAS at Jlab

Abstract

In this work the η' meson photoproduction cross sections as well as the distribution of the di-pion invariant mass, m(π+π-), in the radiative decay mode n' -> π+π-γ have been measured using the CLAS detector at the Thomas Jefferson National Accelerator Facility using tagged incident photons in the center-of-mass energy range 1.96 GeV - 2.72 GeV. The measurements are performed on a liquid hydrogen target in the reaction γ π -> π η'(η'-> π+π-γ). The analysis is based on the highest statistics collected in this decay channel in comparison to other experiments reported so far. The n' photoproduction cross sections measured with radiative decay are in a good agreement with results of previous publication from the same data set in CLAS obtained through η' -> π+π-γ decay mode. Two free parameters, α and Β, are extracted from a model-independent fit to the m(π+π-) distribution and their values are found to agree well with recent theoretical expectations. The results of both parameters confirm the existence of the box anomaly, ρ-ω mixing and effects of the a2(1320) tensor meson in the radiative decay of η'.

Authors:
 [1];  [2]
  1. Old Dominion Univ., Norfolk, VA (United States)
  2. (TJNAF), Newport News, VA (United States)
Publication Date:
Research Org.:
Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
OSTI Identifier:
1426886
Report Number(s):
JLAB-PHY-17-2646; DOE/OR/23177-4374
DOE Contract Number:
AC05-06OR23177
Resource Type:
Thesis/Dissertation
Country of Publication:
United States
Language:
English

Citation Formats

Mbianda Njencheu, Georgie, and Thomas Jefferson National Accelerator Facility. Photoproduction and Radiative Decay of eta' Meson in CLAS at Jlab. United States: N. p., 2017. Web. doi:10.2172/1426886.
Mbianda Njencheu, Georgie, & Thomas Jefferson National Accelerator Facility. Photoproduction and Radiative Decay of eta' Meson in CLAS at Jlab. United States. doi:10.2172/1426886.
Mbianda Njencheu, Georgie, and Thomas Jefferson National Accelerator Facility. Mon . "Photoproduction and Radiative Decay of eta' Meson in CLAS at Jlab". United States. doi:10.2172/1426886. https://www.osti.gov/servlets/purl/1426886.
@article{osti_1426886,
title = {Photoproduction and Radiative Decay of eta' Meson in CLAS at Jlab},
author = {Mbianda Njencheu, Georgie and Thomas Jefferson National Accelerator Facility},
abstractNote = {In this work the η' meson photoproduction cross sections as well as the distribution of the di-pion invariant mass, m(π+π-), in the radiative decay mode n' -> π+π-γ have been measured using the CLAS detector at the Thomas Jefferson National Accelerator Facility using tagged incident photons in the center-of-mass energy range 1.96 GeV - 2.72 GeV. The measurements are performed on a liquid hydrogen target in the reaction γ π -> π η'(η'-> π+π-γ). The analysis is based on the highest statistics collected in this decay channel in comparison to other experiments reported so far. The n' photoproduction cross sections measured with radiative decay are in a good agreement with results of previous publication from the same data set in CLAS obtained through η' -> π+π-γ decay mode. Two free parameters, α and Β, are extracted from a model-independent fit to the m(π+π-) distribution and their values are found to agree well with recent theoretical expectations. The results of both parameters confirm the existence of the box anomaly, ρ-ω mixing and effects of the a2(1320) tensor meson in the radiative decay of η'.},
doi = {10.2172/1426886},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon May 01 00:00:00 EDT 2017},
month = {Mon May 01 00:00:00 EDT 2017}
}

Thesis/Dissertation:
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  • This report presents the exclusive rho0 meson electroproduction on the nucleon at intermediate square momentum transfers Q 2 (1.5 < Q 2 < 3 GeV 2) and above the resonance region. The experiment has been taken place at the Jefferson laboratory with the CLAS detector, with a 4.2 GeV beam energy on a hydrogen target in the February-March 1999 period. They present the results and in particular the L/T separated cross sections. This experimentally unexplored domain experimentally is at the intersection between traditional ''soft'' hadronic physics models (VDM and Regge inspired models) and ''hard'' pQCD inspired approaches (recently introduced Generalizedmore » Parton Distribution). They discuss both approaches and their domain of validity.« less
  • The focus of this analysis is photoproduced η and η' mesons. The data were obtained in Hall B at Jefferson Lab using a photon beam at an endpoint energy of 4.016 GeV in the spring and summer of 2004. The Hall B photon tagging system and the CLAS spectrometer were used to collect the data. From this data, and in the course of analysis of the Nη and Nη' systems, measurements were made of the differential cross sections for η and η' photoproduction. The differential cross section measurements for the η improve the statistics and slightly improve the kinematic rangemore » for world data. The results for the η' represents an almost entirely new dataset which will allow for further analysis of the η' meson. The results of this measurement for the η' extend the statistics and kinematic range of world data dramatically.« less
  • The preliminary results discussed in this theses have been carried out with the Nuclear Physics group of the Department of Physics at the University of Rome Tor Vergata, under the supervision of Prof. A. D’Angelo.On March 2012 I joined the CLAS collaboration at the Thomas Jefferson National Laboratory, in Virginia, USA, and became a term member after a probation period of 9 months. As a member I could participate to the g14 data taking, started on November 18th 2011 and finished on May 18th 2012. In that period I was in charge of the timing calibration of the CLAS forwardmore » electromagnetic spectrometer. For the duration of the experiment, I was also responsible of the Raman laboratory located at the University of Rome Tor Vergata, where the Raman measurements were performed. The Raman measurements were crucial for determining the relative concentrations of H 2 and D 2 in the Hydrogen-Deuteride gas which was used for the target of the g14 experiment.« less
  • The work presented in this thesis describes the first experimental measurement of the photon asymmetry of the exclusivemore » $$\vec{γ}$$ → ρ 0p → π +π -p reaction. The data were gathered during the summer of 2001 as a proof of principle study using a polarized beam of photons with the CLAS detector in Hall B of Jefferson Lab for the first time. The aim of the g8a set of experiments is to improve the understanding of the underlying symmetry of the quark degrees of freedom in the nucleon, the nature of the parity exchange between the incident photon and the target nucleon, the mechanism of associated strangeness production in electromagnetic reactions, and to search for evidence for the existence of the so called missing resonances. A beam of tagged and collimated linearly polarized photons (energy range 1.8-2.2 GeV) in conjunction with the large solid angle coverage of CLAS make possible the extraction of polarization observables for the photoproduction of vector mesons. For example, the azimuthal distribution of the ρ 0 as a function of its polar angle in the ($$\vec{γ}$$p) c.m. system enables the measurement of the photon asymmetry parameter, Σ. This has been measured for θ c.m. ≤ 65°, the results of which are compared with the prediction of the quark model of Zhao for the ω vector meson. It has been found that the tensor coupling for the ρ 0 is quite different than that of the ω. The experimental technique of using a beam of linear polarized photons with the CLAS detector has been shown to be viable. By the end of the second phase of these experiments they expect to have a high quality data set which will allow the measurement of the spin density matrix elements for the ρ 0 and provide evidence relating to the existence of the missing resonances.« less
  • The study of baryon resonances provides a deeper understanding of the strong interaction because the dynamics and relevant degrees of freedom hidden within them are re ected by the properties of the excited states of baryons. Higher-lying excited states at and above 1.7 GeV/c2 are generally predicted to have strong couplings to final states involving a heavier meson, e. g. one of the vector mesons, ρ, ω φ, as compared to a lighter pseudoscalar meson, e. g. π and η. Decays to the ππΝ final states via πΔ also become more important through the population of intermediate resonances. We observemore » that nature invests in mass rather than momentum. The excited states of the nucleon are usually found as broadly overlapping resonances which may decay into a multitude of final states involving mesons and baryons. Polarization observables make it possible to isolate single resonance contributions from other interference terms. The CLAS g9 (FROST) experiment, as part of the N* spectroscopy program at Je?erson Laboratory, accumulated photoproduction data using circularly- & linearly-polarized photons incident on a transversely-polarized butanol target (g9b experiment) in the photon energy range 0:3-2:4 GeV & 0:7-2:1 GeV, respectively. In this work, the analysis of reactions and polarization observables which involve two charged pions, either in the fully exclusive reaction γρ -> ρπ+π- or in the semi-exclusive reaction with a missing neutral pion, γρ -> ρπ+π-(π0) will be presented. For the reaction ρπ+π-, eight polarization observables (Is, Ic, Px, Py, Psx; y, Pcx; y) have been extracted. The high statistics data rendered it possible to extract these observables in three dimensions. All of them are first-time measurements. The fairly good agreement of Is, Ic obtained from this analysis with the experimental results from a previous CLAS experiment provides support for the first-time measurements. For the reaction γρ -> ρω -> ρπ+π(π0, five polarization observables (T, Σ, F, H, P) have been extracted, four of which are first-time measurements at all energies. This analysis thus represents a comprehensive program on vector-meson photoproduction: The ω is observed and studied directly from the data and the polarization observables for the (broad) ω can be extracted from the double-pion reaction in a partial-wave analysis. The 13 polarization observables extracted in this analysis substantially augment the world database of polarization observables for these reactions and are expected to play a crucial role in identifying the contributing baryon resonances.« less