arXiv subjects

D. P. Weygand

Publications and source records attributed to D. P. Weygand.

16 recordsLinked to original sources

arXiv2019

High Precision Measurement of Compton Scattering in the 5 GeV region

The cross section of atomic electron Compton scattering $γ+ e \rightarrow γ^\prime + e^\prime $ was measured in the 4.40--5.475 GeV photon beam energy region by the {\em PrimEx} collaboration at Jefferson Lab with an accuracy of 2\% and less. The results are consistent with theoretical predictions that include next-to-leading order radiative corrections. The measurements provide the first high precision test of this elementary QED process at beam energies greater than 0.1 GeV.

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arXiv2018

Study of Xi Photoproduction from Threshold to W = 3.3 GeV

The doubly-strange Xi baryons provide an effective way to study a puzzle called the missing-baryons problem, where both quark models and lattice gauge theory predict more baryon excited states than are seen experimentally. However, few of these excited states have been observed with any certainty. Here, high-mass Xi states have been searched for in photoproduction with the CLAS detector, and upper limits for the total cross sections have been established from threshold to W = 3.3 GeV. In addition, the total cross sections of the ground state Xi(1320) and first excited state Xi(1530) are presented, extending significantly the center-of-mass energy range of previous data.

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arXiv2017

Double $K_S^0$ Photoproduction off the Proton at CLAS

The $f_0$(1500) meson resonance is one of several contenders to have significant mixing with the lightest glueball. This resonance is well established from several previous experiments. Here we present the first photoproduction data for the $f_0$(1500) via decay into the $K_S^0 K_S^0$ channel using the CLAS detector. The reaction $γp$ -> $f_0 p$ -> $K_S^0 K_S^0 p$, where J = 0, 2, was measured with photon energies from 2.7 to 5.1 GeV. A clear peak is seen at 1500 MeV in the background subtracted invariant mass spectra of the two kaons. This is enhanced if the measured 4-momentum transfer to the proton target is restricted to be less than 1.0 GeV2. By comparing data with simulations, it can be concluded that the peak at 1500 MeV is produced primarily at low t, which is consistent with a t-channel production mechanism.

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arXiv2012

Comment on the narrow structure reported by Amaryan et al

The CLAS Collaboration provides a comment on the physics interpretation of the results presented in a paper published by M. Amaryan et al. regarding the possible observation of a narrow structure in the mass spectrum of a photoproduction experiment.

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arXiv2010

Absorption of the $ω$ and $ϕ$ Mesons in Nuclei

Due to their long lifetimes, the $ω$ and $ϕ$ mesons are the ideal candidates for the study of possible modifications of the in-medium meson-nucleon interaction through their absorption inside the nucleus. During the E01-112 experiment at the Thomas Jefferson National Accelerator Facility, the mesons were photoproduced from $^{2}$H, C, Ti, Fe, and Pb targets. This paper reports the first measurement of the ratio of nuclear transparencies for the $e^{+}e^{-}$ channel. The ratios indicate larger in-medium widths compared with what have been reported in other reaction channels.

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arXiv2008

Search for the photo-excitation of exotic mesons in the pi+pi+pi- system

A search for exotic mesons in the $π^{+}π^{+}π^{-}$ system photoproduced by the charge exchange reaction $γp\to π^{+}π^{+}π^{-}(n)$ was carried out by the CLAS collaboration at Jefferson Lab. A tagged-photon beam with energies in the 4.8 to 5.4 GeV range, produced through bremsstrahlung from a 5.744 GeV electron beam, was incident on a liquid-hydrogen target. A Partial Wave Analysis (PWA) was performed on a sample of 83,000 events, the highest such statistics to date in this reaction at these energies. The main objective of this study was to look for the photoproduction of an exotic $J^{PC} = 1^{-+}$ resonant state in the 1 to 2 GeV mass range. Our PWA analysis, based on the isobar model, shows production of the $a_{2}(1320)$ and the $π_{2}(1670)$ mesons, but no evidence for the $a_{1}(1260)$, nor the $π_{1}(1600)$ exotic state at the expected levels. An upper limit of 13.5 nb is determined for the exotic $π_1(1600)$ cross section, less than 2% of the $a_2(1320)$ production.

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arXiv2008

Light Vector Mesons in the Nuclear Medium

The light vector mesons ($ρ$, $ω$, and $ϕ$) were produced in deuterium, carbon, titanium, and iron targets in a search for possible in-medium modifications to the properties of the $ρ$ meson at normal nuclear densities and zero temperature. The vector mesons were detected with the CEBAF Large Acceptance Spectrometer (CLAS) via their decays to $e^{+}e^{-}$. The rare leptonic decay was chosen to reduce final-state interactions. A combinatorial background was subtracted from the invariant mass spectra using a well-established event-mixing technique. The $ρ$ meson mass spectrum was extracted after the $ω$ and $ϕ$ signals were removed in a nearly model-independent way. Comparisons were made between the $ρ$ mass spectra from the heavy targets ($A > 2$) with the mass spectrum extracted from the deuterium target. With respect to the $ρ$-meson mass, we obtain a small shift compatible with zero. Also, we measure widths consistent with standard nuclear many-body effects such as collisional broadening and Fermi motion.

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arXiv2007

Search for medium modification of the $ρ$ meson

The photoproduction of vector mesons on various nuclei has been studied using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Laboratory. The vector mesons, $ρ$, $ω$, and $ϕ$, are observed via their decay to $e^+e^-$, in order to reduce the effects of final state interactions in the nucleus. Of particular interest are possible in-medium effects on the properties of the $ρ$ meson. The $ρ$ spectral function is extracted from the data on various nuclei, carbon, iron, and titanium, and compared to the spectrum from liquid deuterium, which is relatively free of nuclear effects. We observe no significant mass shift for the $ρ$ meson; however, there is some widening of the resonance in titanium and iron, which is consistent with expected collisional broadening.

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arXiv2007

Confirmation of a pi_1^0 Exotic Meson in the ηπ^0 System

The exclusive reaction $π^- p \to ηπ^0 n$, $η\to π^+ π^- π^0$ at 18 GeV$/c$ has been studied with a partial wave analysis on a sample of 23~492 $ηπ^0 n$ events from BNL experiment E852. A mass-dependent fit is consistent with a resonant hypothesis for the $P_+$ wave, thus providing evidence for a neutral exotic meson with $J^{PC} = 1^{-+}$, a mass of $1257 \pm 20 \pm 25$ MeV$/c^2$, and a width of $354 \pm 64 \pm 60$ MeV$/c^2$. New interpretations of the meson exotics in neutral $ηπ^0$ system observed in E852 and Crystal Barrel experiments are discussed.

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arXiv2007

Cascade production in the reactions gamma p --> K+ K+ (X) and gamma p --> K^+ K^+ pi- (X)

Photoproduction of the cascade resonances has been investigated in the reactions $γp \to K^+ K^+ (X)$ and $γp \to K^+ K^+ π^- (X)$. The mass split of the $Ξ$ doublet is measured to be $5.4\pm 1.8$ MeV/c$^2$, consistent with existing measurements. The differential (total) cross sections for the $Ξ^{-}$ have been determined for photon beam energies from 2.75 to 3.85 (4.75) GeV, and are consistent with a possible production mechanism of $Y^*\to K^+Ξ^-$ through a $t$-channel process. The reaction $γp \to K^+ K^+ π^-[Ξ^0]$ has also been investigated in search of excited cascade resonances. No significant signal of excited cascade states other than the $Ξ^-(1530)$ is observed. The cross section results of the $Ξ^-(1530)$ have also been obtained for photon beam energies from 3.35 to 4.75 GeV.

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arXiv2006

Search for the $Θ^+$ pentaquark in the reactions $γp \to \bar K^0K^+n$ and $γp \to \bar K^0K^0p$

The exclusive reactions $γp \to \bar K^0 K^+ n$ and $γp \to \bar K^0 K^0 p$ have been studied in the photon energy range 1.6--3.8 GeV, searching for evidence of the exotic baryon $Θ^+(1540)$ in the decays $Θ^+\to nK^+$ and $Θ^+\to p K^0$. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility. The integrated luminosity was about 70 pb$^{-1}$. The reactions have been isolated by detecting the $K^+$ and proton directly, the neutral kaon via its decay to $K_S \to π^+ π^-$ and the neutron or neutral kaon via the missing mass technique. The mass and width of known hyperons such as $Σ^+$, $Σ^-$ and $Λ(1116)$ were used as a check of the mass determination accuracy and experimental resolution. Approximately 100,000 $Λ^*(1520)$'s and 150,000 $ϕ$'s were observed in the $\bar K^0 K^+ n$ and $\bar K^0 K^0 p$ final state respectively. No evidence for the $Θ^+$ pentaquark was found in the $nK^+$ or $pK_S$ invariant mass spectra. Upper limits were set on the production cross section of the reaction $γp \to Θ^+ \bar K^0$ as functions of center-of-mass angle, $nK^+$ and $pK_S$ masses. Combining the results of the two reactions, the 95% C.L. upper limit on the total cross section for a resonance peaked at 1540 MeV was found to be 0.7 nb. Within most of the available theoretical models, this corresponds to an upper limit on the $Θ^+$ width, $Γ_{Θ^{+}}$, ranging between 0.01 and 7 MeV.

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arXiv2006

Search for $Θ^{++}$ Pentaquarks in the Exclusive Reaction $γp\to K^+K^-p$

The reaction $γp \to pK^+K^-$ was studied at Jefferson Lab with photon energies from 1.8 to 3.8 GeV using a tagged photon beam. The goal was to search for a $Θ^{++}$ pentaquark, a narrow doubly charged baryon state having strangeness S=+1 and isospin I=1, in the $pK^+$ invariant mass spectrum. No statistically significant evidence of a $Θ^{++}$ was found. Upper limits on the total and differential production cross section for the reaction $γp \to K^-Θ^{++}$ were obtained in the mass range from 1.5 to 2.0 GeV/c$^2$, with an upper limit of about 0.15 nb, 95% C.L. for a narrow resonance with a mass $M_{Θ^{++}}=1.54$ GeV/c$^2$. This result places a very stringent upper limit on the $Θ^{++}$ width.

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arXiv2006

Photoproduction of $K^{*+}Λ$ and $K^+Σ(1385)$ in the reaction $γ\lowercase{p} \to K^+ Λπ^0 $ at Jefferson Lab

The search for missing nucleon resonances using coupled channel analysis has mostly been concentrated on $Nπ$ and $KY$ channels, while the contributions of $K^*Y$ and $KY^*$ channels have not been investigated thoroughly mostly due to the lack of data. With an integrated luminosity of about 75 $pb^{-1}$, the photoproduction data using a proton target recently collected by the CLAS Collaboration at Jefferson Lab with a photon energy range of 1.5-3.8 GeV provided large statistics for the study of light hyperon photoproduction through exclusive reactions. The reaction $γp \to K^+ Λπ^0$ has been investigated. Preliminary results of the $K^{*+}Λ$ and $K^+Σ(1385)$ cross sections are not negligible compared with the $KY$ channels. The $Λπ^0$ invariant mass spectrum is dominated by the $Σ(1385)$ signal and no significant structure was found around the $Σ(1480)$ region.

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arXiv2006

$Ξ$ spectroscopy in photoproduction on a proton target at Jefferson Lab

The CLAS Collaboration at Jefferson Lab conducted a photoproduction experiment on a proton target using a tagged photon beam with an energy range of 1.5-3.8 GeV during May-July 2004. With an integrated luminosity of about 75 $pb^{-1}$, this experiment provides the largest data set for photon-proton reactions ever collected. The reaction $γp \to K^+K^+Ξ^{-}(1320)$ has been investigated and the preliminary results of the cross section measurement of $Ξ^-(1320)$ for the photon energy range of 2.7-3.8 GeV have been obtained. In a search for excited cascade states, the reaction of $γp \to K^+K^+π^-(Ξ^0(1320))$ has also been explored.

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arXiv2005

Search for $Θ^+(1540)$ pentaquark in high statistics measurement of $γp \to \bar K^0 K^+ n$ at CLAS

The exclusive reaction $γp \to \bar K^0 K^+ n$ was studied in the photon energy range between 1.6-3.8 GeV searching for evidence of the exotic baryon $Θ^+(1540)\to nK^+$. The decay to $nK^+$ requires the assignment of strangeness $S=+1$ to any observed resonance. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility corresponding to an integrated luminosity of 70 $pb^{-1}$. No evidence for the $Θ^+$ pentaquark was found. Upper limits were set on the production cross section as function of center-of-mass angle and $nK^+$ mass. The 95% CL upper limit on the total cross section for a narrow resonance at 1540 MeV was found to be 0.8 nb.

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arXiv1995

Search for Exotic Mesons in pi- P Interactions at 18 GeV/c

The recent search for non $q \bar{q}$ mesons in $π^{-}p$ interactions at Brookhaven National Laboratory is summarized. Many final states such as $ηπ$, $η' π^{-}$, $a_{0} π$, $f_{1} π$, $a_{2} π$, $b_{1} π$, which are favored decay modes of exotics, are under investigation.

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