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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2010

The Search for Exotic Mesons in {gamma}p{yields}{pi}{sup +{pi}+{pi}-}n with CLAS at Jefferson Lab

In addition to ordinary qq-bar pairs, quantum chromodynamics (QCD) permits many other possibilities in meson spectra, such as gluonic hybrids, glueballs, and tetraquarks. Experimental discovery and study of these exotic states provides insight on the nonperturbative regime of QCD. Over the past twenty years, some searches for exotic mesons have met with controversial results, especially those obtained in the three-pion system. Prior theoretical work indicates that in photoproduction one should find gluonic hybrids at significantly enhanced levels compared to that found in pion production. To that end, the CLAS g12 run was recently completed at Jefferson Lab, using a liquid hydrogen target and tagged photons from a 5.71 GeV electron beam. The CLAS experimental apparatus was modified to maximize forward acceptance for peripheral production of mesons. The resulting data contains the world's largest 3{pi} photoproduction dataset, with {gamma}p{yields}{pi}{sup +{pi}+{pi}-}n events numbering in the millions. Early results describing the data quality, kinematics, and dysnamics will be shown.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

The Search for a π 1 (1400) Exotic Meson in the gammap-->Δ ++ ηπ - System with CLAS

Several experiments have reported evidence for the π 1 (1400) using pion production but the results have been controversial and its existence has yet to be seen in photoproduction. Theoretical works have implied that the production amplitude will be greatly increased in photoproduction in comparison to the pion production. The reaction gammap-->Λ ++ X-->pπ + π - (η) is being studied in the photon energy range 4.4 to 5.4 GeV as a possible method of producing the π1(1400) resonance. Data were collected at Jefferson Lab in Hall B. This reaction is being investigated by detecting the pπ + π - 2gamma and reconstructing the eta through the missing-mass of the p π + π - , and comparing the results to the 2γ composite. These data have yielded a 0 (980) and a 2 (1320) in the π - eta invariant mass spectrum. Further analysis is needed to untangle the possible π1(1400) resonance from the a2(1320).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Search for Strangeonia in Photoproduction using CLAS

The HyCLAS experiment at Jefferson Lab is a program to search for new and unusual mesons produced via photoproduction. The strangeonia sector is poorly known and a main component of this program is a search for new strangeonium states. The reaction {gamma}p{yields}p{phi}{eta} is an ideal channel to look for strangeonium states due to the strangeness content of both the {phi} and {eta}. The data was acquired at the JLAB CLAS facility using a 4-5.5 GeV tagged photon beam. The {phi} meson is identified via the K{sup +}K- decay. The recoil proton is observed in the CLAS spectrometer and the {eta} meson is identified through the missing mass. Also of interest is the search for strangeonia decaying to {phi}{pi}{sup 0} and {phi}{omega}. These channels are OZI suppressed for qq-bar mesons and an observation of a meson decaying to these channels would provide a strong evidence of mesons beyond qqa-bar. Preliminary results describing the data quality, kinematics and dynamics will be shown.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Study of {pi}{sup -}p{yields}{pi}{sup -{eta}p} and {pi}{sup -}p{yields}{pi}{sup -{eta}{eta}}p at {radical}(s) = 18.9 GeV with the COMPASS experiment

The COMPASS experiment at CERN studies diffractively produced states in the light quark sector with unprecedented statistics. The observation of f{sub 0}(1500)/f{sub 2}'(1525) decaying to {eta}{eta} in 2008 data with incoming negative pion beam at 190 GeV/c poses the question whether it is produced centrally or formed by the decay of a heavier diffractively produced {pi}{sub 1}(1800)/{pi}{sub 2}(1880). To decide, a dedicated amplitude analysis which includes different production mechanisms is formulated and compared with one which was used to fit centrally produced resonances including f{sub 0}(1500) by the WA102 experiment. Unbinned mass-dependent log-likelihood fitting methods may serve to solve the ambiguities which are present in binned, mass-independent partial wave analyses.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Study of Charged {kappa} Particle in J/{psi}{yields}K{sup {+-}K}{sub S{pi}}{sup {+-}{pi}0}

Based on a J/{psi} data sample of 58x10{sup 6} events at BESII, the decay of J/{psi}{yields}K{sup {+-}K}{sub S{pi}}{sup {+-}{pi}0} is studied. A low mass enhancement is visible in the sum of the K{sub S{pi}}{sup {+-}}and K{sup {+-}{pi}0} invariant mass spectra recoiling against K*(892){sup {+-}}. Partial wave analysis of this channel favors this low mass enhancement being a charged {kappa} particle with J{sup P} = 0{sup +} and with its pole locating at (849{+-}77{sub -14}{sup +18})-i(256{+-}40{sub -22}{sup +46}) MeV/c{sup 2} using a constant width Breit-Wigner. Also observed is J/{psi}{yields}K*(892){sup +}K*(892){sup -} with a branching fraction of (1.00{+-}0.19{sub -0.32}{sup +0.11})x10{sup -3}. All the above results are preliminary.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Systematic Study of Two-Pion Production in NN Collisions--from Single-Baryon to Di-Baryon Excitations

The two-pion production in nucleon-nucleon collisions has been studied by exclusive and kinematically complete experiments from threshold up to T{sub p} = 1.36 GeV at CELSIUS-WASA. At near-threshold energies the total and differential distributions for the {pi}{sup +{pi}-} and {pi}{sup 0{pi}0} channels are dominated by Roper excitation and its decay into N{sigma}s and {Delta}{pi} channels. At beam energies T{sub p}>1.1 GeV the {Delta}{Delta} excitation governs the two-pion production process. In the {pi}{sup +{pi}+} channel evidence is found for the excitation of a higher-lying I =3/2 resonance, favorably the {Delta}(1600). The isovector fusion processes leading to the deuteron and to quasi-stable {sup 2}He, respectively, exhibit no or only a modest ABC-effect, i.e. low-mass enhancement in the {pi}{pi}-invariant mass spectrum, and can be described by conventional t-channel {Delta}{Delta} excitation. On the other hand, the isoscalar fusion process to the deuteron exhibits a dramatic ABC-effect correlated with a narrow resonance-like energy dependence in the total cross section with a width of only 50 MeV and situated at a mass 90 MeV below the {Delta}{Delta} mass.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Kaon pair production in pp, pd and dd collisions at COSY

The near-threshold production of kaon-pairs has been investigated in proton-proton, proton-deuteron and deuteron-deuteron collisions at the Cooler Synchrotron COSY. The excitation function for the pp{yields}ppK{sup +}K{sup -} reaction and the invariant K{sup -}p, K{sup -}pp, and K{sup +}K{sup -} mass distributions indicate the presence of both K{sup -}p and K{sup +}K{sup -} final state interactions. Analogous final-state interactions of antikaons with deuterons has been found in the pp{yields}dK{sup +}K{sup 0}-bar reaction as well as in the pn{yields}dK{sup +}K{sup -} reaction, measured in the quasi-free pd{yields}p{sub sp}dK{sup +}K{sup -} process with a 'spectator' proton (p{sub sp}). The existing COSY data on the pd{yields}{sup 3}HeK{sup +}K{sup -} reaction are not yet sufficient to study the K{sup -3}He and K{sup +}K{sup -} final state interactions. A very small total cross section was found for the dd{yields}{sup 4}HeK{sup +}K{sup -} reaction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Hadron Spectroscopy in Double Pomeron Exchange Processes with the STAR Detector at RHIC

A new hadron spectroscopy program to study particle production at the central region through diffractive processes in polarized p+p collisions at {radical}(s) = 200-500 GeV has been initiated with the STAR detector at RHIC. Staged implementation of multiple Roman Pot stations for tagging forward protons in diffractive processes allows studying for the first time the dynamics of the particle production in the diffractive processes systematically at the RHIC energy regime. The STAR detector system with complete azimuthal coverage at the central region equipped with excellent particle reconstruction capabilities enables studies of the constituent gluonic degree of freedom in double Pomeron exchange processes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Hunting for a new {Sigma}*(1/2{sup -}) resonance around 1380 MeV

Quenched and unquenched quark models give very distinctive predictions for the lowest {Sigma}* with spin-parity J{sup P} = 1/2{sup -}. We report evidence for possible existence of a new {Sigma}* resonance with J{sup P} = 1/2{sup -} around 1380 MeV by re-examining data of various relevant reactions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Cascade Spectroscopy and Recent {Xi}* Photo-production Results from CLAS

Doubly-strange baryon resonances provide new insights into baryon structure. The standard QCD Lagrangian implies that for every N* and {Delta}* resonance, there should be a corresponding {Xi}(cascade resonance). This is due to the flavor symmetry of the strong force. Therefore, one can investigate baryon structure by observing aspects of the doubly-strange baryons like regularities such as parity doublets. At energies above approximately 1.5 GeV, the light-quark baryon resonances are broad and overlap while the cascades in this range are narrow and therefore more readily observed. An overview of the world cascade spectrum and a comparison to the lighter baryon spectra will be presented. Recent results from an on-going analysis from the G12 (5.4 GeV) photo-production experiment using the CLAS detector at JLab will be highlighted.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Photoproduction of the {Lambda}*(1520) Hyperon

The photoproduction of the {Lambda}*(1520) on both the proton and neutron have been studied by using the CLAS eg3 run data set. The reactions are {gamma}d{yields}K{sup +{Lambda}}*(n) and {gamma}d{yields}K{sup 0{Lambda}}*(p) with {Lambda}*{yields}pK{sup -}. Preliminary total and differential cross sections have been extracted in the photon energy region 1.75 GeV<E{sub {gamma}<}5.50 GeV. This is the first time that the photoproduction of {Lambda}*(1520) on the neutron is reported, and we will extend the results on the proton to higher energies than in previous studies.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Photoproduction of {Sigma}{sup +}K{sub s}{sup 0} with the CBELSA/TAPS-setup

Albeit quark models explain the known baryon spectrum reasonably well, they all overpredict the number of states significantly. This is often called the 'missing resonance' problem. It is speculated, that some of these resonances remained undetected in pi-induced reactions, but have a sizeable coupling to channels with strangeness involved. This provided our motivation to measure cross sections and polarisation observables in associated Kaon-Hyperon photoproduction with the focus on the {Sigma}{sup +}K{sub s}{sup 0} channel. Up to now, for this particular channel only limited data exists from the SAPHIR-, CLAS- and CBELSA/TAPS-collaboration for total and differential cross sections, and for recoil polarisation. Using the linearly polarised, energy tagged photon beam at the ELSA particle accelerator of Bonn University, data were taken with the combined photon spectrometers Crystal Barrel and TAPS. This setup is well suited to detect multi photon final states and therefore ideal to measure the reaction channel {gamma}p{yields}{Sigma}{sup +}K{sub s}{sup 0{yields}}p{pi}{sup 0{pi}0{pi}0{yields}}p6{gamma}. Here the extraction of cross sections, the recoil polarisation P and the photon asymmetry {Sigma}, which is measured for the first time, will be discussed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Exclusive Photoproduction of K + Σ* - (n) Off Deuteron

We are using the CEBAF Large Acceptance Spectrometer (CLAS) to study the exclusive photoproduction of K + Σ* - (1385) off the deuteron. It will be the first published total cross section of this reaction channel. We show the preliminary results of the total cross section, while we present all the key steps of achieving it. In order to study the reaction mechanism, we also study and show the angular distribution in the Gottfried-Jackson frame.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Measurement of the single polarization observables I{sup c} and I{sup s} in {pi}{sup 0{eta}} photoproduction

Meson photoproduction off the nucleon is a key tool in order to understand the structure of baryons and their excitation spectrum. Especially in the regime of high-lying resonances the photoproduction of multi-meson final states is of increasing importance, given that the cross sections for such processes exceed those for single-meson production. Additionally it gives a handle on sequential decays of such resonances via e.g. the {Delta}(1232) or the S{sub 11}(1535) in the intermediate state. For a complete understanding of the processes involved, the measurement not only of unpolarized cross sections but also of polarization observables is mandatory. With the Crystal Barrel/TAPS experiment, located at the ELSA accelerator facility in Bonn, it was possible to determine such observables using a linearly polarized photon beam impinging on a liquid hydrogen target. The beam asymmetries I{sup c} and I{sup s} are presented for the reaction gp {gamma}{sup {yields}p{yields}}p{pi}{sup 0{eta}}. The latter is a feature exclusive to the acoplanar kinematics of multi-meson final states and has been measured for the first time.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Measurements of the Polarization Observables I{sup s} and I{sup c} for {gamma}{sup {yields}p{yields}}p{pi}{sup +{pi}-} using the CLAS Spectrometer

Model predictions regarding the excited baryon spectrum provided by Constituent Quark Models show good agreement with experimental measurements in the low-energy region less than {approx_equal}1.8 GeV. The mass region above {approx_equal}1.8 GeV, however, contains many resonances which are predicted to exist by these models but have not been experimentally verified. The analysis of a double meson final state using linearly polarized photoproduction data allows access to two polarization observables, I{sup s} and I{sup c}(also known as the beam asymmetry {Sigma} for a single meson final state). It has been shown that measurements of these polarizaton observables can provide insight into this missing resonance problem. This analysis was carried out on data taken from the CLAS-g8b data run period conducted at Jefferson Lab in Newport News, Virginia. The analysis of this data and preliminary measurements of these obsevables will be dicussed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Beam Asymmetries in {pi}{sup 0} Photoproduction on the Proton

Polarization observables, such as the beam asymmetry {Sigma}, are vital to the study of the many N* and {Delta} resonances that decay to the p{pi}{sup 0} final state. Beam asymmetries in {pi}{sup 0} photoproduction off the proton have been determined using the Crystal Barrel CsI(Tl) calorimeter at ELSA, University of Bonn in Germany, in the energy range E{gamma} = 920 to 1680 MeV by analyzing the neutral decay mode {pi}{sup 0{yields}{gamma}{gamma}}. In this experiment, the BaF{sub 2} spectrometer TAPS was placed in the forward direction increasing the solid angle coverage to nearly 4{pi} and serving as a fast trigger. For the first time, these measurements include the most forward angles in {theta}{sub {pi}}{sup 0c{center_dot}m}. Additionally, this analysis provides new data points in the energy range E{gamma} = 1510 to 1680 MeV where few measurements have previously been made.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2010

Helicity Beam Asymmetry I{center_dot} in Two Neutral Pseudoscalar Photoproduction Reactions at the Crystal Barrel Experiment

A method for measuring the helicity beam asymmetry (I{sub {center_dot}}is shown and demonstrated using the reaction {gamma}p{yields}p{pi}{sup 0{eta}}. The very preliminary results for this channel are presented and suggest that the helicity beam asymmetry is small. The statistics for this channel in this analysis are limited making an analysis of angular dependencies difficult.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2010

Measurement of the Helicity Difference in γ → p → →pπ + π - with the CLAS Spectrometer at Jefferson Laboratory

The study of the properties of baryon resonances can provide us with hints to help us understand the structure of non-perturbative QCD and the effect of a particular resonance on polarization observables. The investigation of double-pion photoproduction data is needed to discover higher-lying states and their properties at and above W [approximate] 1.8 GeV. Therefore, the analysis of the helicity difference in gp γp→pπ + π - will help us in our understanding of QCD.The CLAS g9a (FROST) experiment, as part of the N* spectroscopy program at Jefferson Laboratory, has accumulated photoproduction data using linearly and circularly polarized photons incident on a longitudinally-polarized butanol target in the photon energy range 0.3 to 2.4 GeV. The FROST experiment provides an important step toward a “complete” experiment for the reaction gammaN-->KY.In this contribution, the method to calculate the helicity difference for the reaction γp→pπ + π - will be described and preliminary results will be discussed.

43 PARTICLE ACCELERATORS↗