Energy Calibration of the JLab Bremsstrahlung Tagging System

In this report, we present the energy calibration of the Hall B bremsstrahlung tagging system at the Thomas Jefferson National Accelerator Facility. The calibration was performed using a magnetic pair spectrometer. The tagged photon energy spectrum was measured in coincidence with $e^+e^-$ pairs as a function of the pair spectrometer magnetic field. Taking advantage of the internal linearity of the pair spectrometer, the energy of the tagging system was calibrated at the level of $\pm 0.1$. The absolute energy scale was determined using the $e^+e^-$ rate measurements close to the end-point of the photon spectrum. The energy variations across the full tagging range were found to be $<3$ MeV.Comment: 15 pages, 12 figure

Hysteresis Effects During the Phase Transition in Solutions of Temperature Sensitive Polymers

It is demonstrated, for the first time,that well-known phase transitions induced by changes in temperature in solutions of polymers containing both hydrophilic and hydrophobic functional groups could be followed by noticeable hysteresis effects. A well-known phase transitions accompanied by a sharp change in fluid properties, in particular its optical density can be induced by many external influences, including temperature changes occurring in the solutions of polymers containing both hydrophilic and hydrophobic functional groups. Since intensification subsequent hydrophobic interactions, leading to loss of solubility of the polymer molecules, resulting, in particular, a significant increase in the turbidity of the medium and are accompanied by a pronounced hysteresis phenomena. Hysteresis phenomena in the processes of molecular-scale play an important theoretical and practical interest in linkage with the development of advanced nano-level technology. In particular, the issue of the development of molecular "trigger" switches, and other analog electronic systems, implemented on submolecular level was actively discussed. In fact, under the same physical conditions of the environment of macromolecules system can be in two different states, which resolves the issue of programming such molecules. State of these polymers depends on their way of formation and thermodynamic variables. Observed effect could be utilized directly for information recording into the structure on the basis of stimulus-sensitive macromolecular chains. In fact, it is a first step towards creating memory of quasi-biological elements

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.Comment: to be published in Physical Review

Induced polarization of {\Lambda}(1116) in kaon electroproduction

We have measured the induced polarization of the ${\Lambda}(1116)$ in the reaction $ep\rightarrow e'K^+{\Lambda}$, detecting the scattered $e'$ and $K^+$ in the final state along with the proton from the decay $\Lambda\rightarrow p\pi^-$.The present study used the CEBAF Large Acceptance Spectrometer (CLAS), which allowed for a large kinematic acceptance in invariant energy $W$ ($1.6\leq W \leq 2.7$ GeV) and covered the full range of the kaon production angle at an average momentum transfer $Q^2=1.90$ GeV$^2$.In this experiment a 5.50 GeV electron beam was incident upon an unpolarized liquid-hydrogen target. We have mapped out the $W$ and kaon production angle dependencies of the induced polarization and found striking differences from photoproduction data over most of the kinematic range studied. However, we also found that the induced polarization is essentially $Q^2$ independent in our kinematic domain, suggesting that somewhere below the $Q^2$ covered here there must be a strong $Q^2$ dependence. Along with previously published photo- and electroproduction cross sections and polarization observables, these data are needed for the development of models, such as effective field theories, and as input to coupled-channel analyses that can provide evidence of previously unobserved $s$-channel resonances.Comment: 13 figure

Absorption of the ω\omega and ϕ\phi Mesons in Nuclei

Due to their long lifetimes, the $\omega$ and $\phi$ 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.Comment: 6 pages, 4 figure

Measurement of the nuclear multiplicity ratio for Ks0K^0_s hadronization at CLAS

The influence of cold nuclear matter on lepto-production of hadrons in semi-inclusive deep inelastic scattering is measured using the CLAS detector in Hall B at Jefferson Lab and a 5.014 GeV electron beam. We report the $K_s^0$ multiplicity ratios for targets of C, Fe, and Pb relative to deuterium as a function of the fractional virtual photon energy $z$ transferred to the $K_s^0$ and the transverse momentum squared $p_{T}^2$ of the $K_s^0$. We find that the multiplicity ratios for $K^0_s$ are reduced in the nuclear medium at high $z$ and low $p_{T}^2$, with a trend for the $K^0_s$ transverse momentum to be broadened in the nucleus for large $p_{T}^2$.Comment: Submitted to Phys. Lett.