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Khandaker, M.

Publications and source records attributed to Khandaker, M..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Ξ * photoproduction from threshold to W = 3.3 GeV

Here, the doubly-strange Ξ 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 Ξ 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 Ξ¯(1320) and first excited state Ξ¯(1530) are presented, extending significantly the center-of-mass energy range of previous data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Beam-target helicity asymmetry E in K 0 Λ and K 0 Σ 0 photoproduction on the neutron

Here, we report the first measurements of the $E$ beam-target helicity asymmetry for the $\vec{\gamma} \vec{n} \to K^{0}\Lambda$, and $K^{0}\Sigma^{0}$ channels in the energy range of 1.70$\leq W\leq$2.34 GeV. The CLAS system at Jefferson Lab used a circularly polarized photon beam and a target consisting of longitudinally polarized solid molecular hydrogen deuteride (HD) with low background contamination for the measurements. Comparisons with predictions from the KaonMAID, SAID, and Bonn-Gatchina models are presented. These results will help separate the isospin $I=0$ and $I=1$ photo-coupling transition amplitudes in pseudoscalar meson photoproduction.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Center of Mass Motion of Short-Range Correlated Nucleon Pairs studied via the A ( e , e ' p p ) Reaction

Short-Range Correlated (SRC) nucleon pairs are a vital part of the nucleus, accounting for almost all nucleons with momentum greater than the Fermi momentum (k F ). A fundamental characteristic of SRC pairs is having large relative momenta as compared to k F , and smaller center-of-mass (c.m.) which indicates a small separation distance between the nucleons in the pair. Determining the c.m. momentum distribution of SRC pairs is essential for understanding their formation process. We report here on the extraction of the c.m. motion of proton-proton (pp) SRC pairs in Carbon and, for the first time in heavier and ansymetric nuclei: aluminum, iron, and lead, from measurements of the A(e,e'pp) reaction. Here, we find that the pair c.m. motion for these nuclei can be described by a three-dimensional Gaussian with a narrow width ranging from 140 to 170 MeV/c, approximately consistent with the sum of two mean-field nucleon momenta. Comparison with calculations appears to show that the SRC pairs are formed from mean-field nucleons in specific quantum states.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Measurements of the γ v p → p ' π + π - cross section with the CLAS detector for 0.4 GeV 2 < Q 2 < 1.0 GeV 2 and 1.3 GeV < W < 1.825 GeV

New results on the single-differential and fully-integrated cross sections for the process $\gamma_{v} p \rightarrow p' \pi^{+} \pi^{-}$ are presented. The experimental data were collected with the CLAS detector at Jefferson Laboratory. Measurements were carried out in the kinematic region of the reaction invariant mass $W$ from 1.3 to 1.825 GeV and the photon virtuality $Q^2$ from 0.4 to 1.0~GeV$^2$. The cross sections were obtained in narrow $Q^{2}$ bins (0.05 GeV$^{2}$) with the smallest statistical uncertainties achieved in double-pion electroproduction experiments to date. The results were found to be in agreement with previously available data where they overlap. A preliminary interpretation of the extracted cross sections, which was based on a phenomenological meson-baryon reaction model, revealed substantial relative contributions from nucleon resonances. The data offer promising prospects to improve knowledge on the $Q^{2}$ evolution of the electrocouplings of most resonances with masses up to $\sim$1.8~GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Erratum: Polarization transfer observables in elastic electron-proton scattering at Q 2 =2.5 , 5.2, 6.8, and 8.5GeV 2 [Phys. Rev. C 96 , 055203 (2017)]

Subsequent to the release of our original paper, we discovered in the context of preparing our technical supplement [1] for journal publication that a typographical error had existed in the text file that the analysis program used to construct the beam polarization "database" for both the original analysis, published in Ref. [2], and our final analysis. The electron-beam polarization P e and the analyzing power A y cancel exactly in the ratio R, which is proportional to the ratio P t / P l of the transferred polarization components. On the other hand, the extraction of the relative e dependence of P l / P Born l relies on knowledge of the beam polarization. As such, data taking was interrupted roughly every two days during the GEp - 2γ experiment to perform invasive measurements of the beam polarization using the Hall C Moller polarimeter [3].

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Semi-inclusive π 0 target and beam-target asymmetries from 6 GeV electron scattering with CLAS

Here, we present precision measurements of the target and beam-target spin asymmetries from neutral pion electroproduction in deep-inelastic scattering (DIS) using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. We scattered 6-GeV, longitudinally polarized electrons off longitudinally polarized protons in a cryogenic 14 NH 3 target, and extracted double and single target spin asymmetries for ep → e'π 0 X in multidimensional bins in fourmomentum transfer (1.0 < Q 2 < 3.2 GeV 2 ), Bjorken-x (0.12 < x < 0.48), hadron energy fraction (0.4 < z < 0.7), transverse pion momentum (0 < P T < 1.0 GeV), and azimuthal angle Φh between the lepton scattering and hadron production planes. We extracted asymmetries as a function of both x and P T , which provide access to transverse-momentum distributions of longitudinally polarized quarks. The double spin asymmetries depend weakly on P T . The sin 2Φ h moments are zero within uncertainties, which is consistent with the expected suppression of the Collins fragmentation function. The observed sin Φ h moments suggest that quark gluon correlations are significant at large x.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Measurement of the beam asymmetry Σ and the target asymmetry T in the photoproduction of ω mesons off the proton using CLAS at Jefferson Laboratory

Here, the photoproduction of $\omega$ mesons off the proton has been studied in the reaction $\gamma p\to p\,\omega$ using the CEBAF Large Acceptance Spectrometer (CLAS) and the frozen-spin target (FROST) in Hall B at the Thomas Jefferson National Accelerator Facility. For the first time, the target asymmetry, $T$, has been measured in photoproduction from the decay $\omega\to\pi^+\pi^-\pi^0$, using a transversely-polarized target with energies ranging from just above the reaction threshold up to 2.8 GeV. Significant non-zero values are observed for these asymmetries, reaching about 30-40% in the third-resonance region. New measurements for the photon-beam asymmetry, $\Sigma$, are also presented, which agree well with previous CLAS results and extend the world database up to 2.1 GeV. These data and additional $\omega$-photoproduction observables from CLAS were included in a partial-wave analysis within the Bonn-Gatchina framework. Significant contributions from $s$-channel resonance production were found in addition to $t$-channel exchange processes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

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 $\gamma p$ -> $f_0 p$ -> $K_S^0 K_S^0 p$, 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.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Measurement of the Q 2 Dependence of the Deuteron Spin Structure Function g 1 and its Moments at Low Q 2 with CLAS

We measured the $g_{1}$ spin structure function of the deuteron at low $Q^{2}$, where QCD can be approximated with chiral perturbation theory ($\chi PT$). The data cover the resonance region, up to an invariant mass of $W\approx1.9$ GeV. The generalized GDH sum, the moment $\Gamma_{1}^{d}$ and the spin polarizability $\gamma_{0}^{d}$ are precisely determined down to a minimum $Q^2$ of 0.02 GeV$^2$ for the first time, about 2.5 times lower than that of previous data. We compare them to several $\chi PT$ calculations and models. In conclusion, these results are the first in a program of benchmark measurements of polarization observables in the $\chi PT$ domain.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Measurement of the helicity asymmetry E in ω → π + π - π 0 photoproduction

The double-polarization observable $E$ was studied for the reaction $\gamma p\to p\omega$ using the CEBAF Large Acceptance Spectrometer (CLAS) in Hall B at the Thomas Jefferson National Accelerator Facility and the longitudinally-polarized frozen-spin target (FROST). The observable was measured from the charged decay mode of the meson, $\omega\to\pi^+\pi^-\pi^0$, using a circularly-polarized tagged-photon beam with energies ranging from the $\omega$ threshold at 1.1 to 2.3 GeV. A partial-wave analysis within the Bonn-Gatchina framework found dominant contributions from the $3/2^+$ partial wave near threshold, which is identified with the sub-threshold $N(1720)\,3/2^+$ nucleon resonance. To describe the entire data set, which consisted of $\omega$ differential cross sections and a large variety of polarization observables, further contributions from other nucleon resonances were found to be necessary. Here, with respect to non-resonant mechanisms, $\pi$ exchange in the $t$-channel was found to remain small across the analyzed energy range, while pomeron $t$-channel exchange gradually grew from the reaction threshold to dominate all other contributions above $W \approx 2$ GeV.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗