Elementary Particles and Fields and String Theory Commons^™

Precision Measurements Of Aⁿ1 In The Deep Inelastic Regime, D. S. Parno, D. Flay, M. Posik, M. Canan, C. Hyde, The Jefferson Lab Hall A Collaboration

Physics Faculty Publications

We have performed precision measurements of the double-spin virtual-photon asymmetry A₁ on the neutron in the deep inelastic scattering regime, using an open-geometry, large-acceptance spectrometer and a longitudinally and transversely polarized ³He target. Our data cover a wide kinematic range 0.277 <= x <= 0.548 at an average Q² value of 3.078(GeV/c)², doubling the available high-precision neutron data in this xrange. We have combined our results with world data on proton targets to make a leading-order extraction of the ratio of polarized-to-unpolarized parton distribution functions for up quarks and for down quarks in the same kinematic range. Our data are consistent with …

Direct Observation Of Quark-Hadron Duality In The Free Neutron F2 Structure Function, I. Niculescu, G. Niculescu, W. Melnitchouk, J. Arrington, M. E. Christy, S. Kuhn

Physics Faculty Publications

Using the recently published data from the BONuS(Barely Off-shell Nucleon Structure) experiment at Jefferson Lab, which utilized a spectator tagging technique to extract the inclusive electron-free neutron scattering cross section, we obtain the first direct observation of quark-hadron duality in the neutron F₂ structure function. The data are used to reconstruct the lowest few (N = 2, 4, and 6) moments of F₂ in the three prominent nucleon resonance regions, as well as the moments integrated over the entire resonance region. Comparison with moments computed from global parametrizations of parton distribution functions suggest that quark-hadron duality holds locally …

Measurement Of The Emc Effect In The Deuteron, K. A. Griffioen, J. Arrington, M. E. Christy, R. Ent, N. Kalantarians, C. E. Keppel, S E. Kuhn

Physics Faculty Publications

We determined the structure function ratio R^d_EMC=F^d₂/(Fⁿ₂+F^p₂) from recently published Fⁿ₂/F^d₂ data taken by the BONuS experiment using CLAS at Jefferson Lab. This ratio deviates from unity, with a slope dR^d_EMC/dx=−0.10 ± 0.05 in the range of Bjorken x from 0.35 to 0.7, for invariant mass W>1.4 GeV and Q²>1 GeV² . The observed EMC effect for these kinematics is consistent with conventional nuclear physics models that include off-shell corrections, as well as with empirical analyses …

Towards A Resolution Of The Proton Form Factor Problem: New Electron And Positron Scattering Data, Clas Collaboration, D. Adikaram, L. B. Weinstein, R. P. Bennett, K. P, Adhikari, M. J. Amaryan, S. Careccia, L. El Fassi, C. E. Hyde, A. Klein, S E. Kuhn, M. Mayer, Z. W. Zhao

Physics Faculty Publications

There is a significant discrepancy between the values of the proton electric form factor, G^p_E, extracted using unpolarized and polarized electron scattering. Calculations predict that small two-photon exchange (TPE) contributions can significantly affect the extraction of G^p_Efrom the unpolarized electron-proton cross sections. We determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections using a simultaneous, tertiary electron-positron beam incident on a liquid hydrogen target and detecting the scattered particles in the Jefferson Lab CLAS detector. This novel technique allowed us to cover a wide range in virtual …

Measurements Of Ep → E'Π+N At 1.6 < W <2.0 Gev And Extraction Of Nucleon Resonance Electrocouplings At Clas, The Clas Collaboration, K. Park, K. P. Adhikari, M. J. Amaryan, L. El Fassi, Y. Prok, L. B. Weinstein

Physics Faculty Publications

Differential cross sections of the exclusive process ep -> e 'π⁺n were measured with good precision in the range of the photon virtuality Q² = 1.8-4.5 GeV² and the invariant mass range of the π⁺n final state W = 1.6-2.0 GeV using the Continuous Electron Beam Accelerator Facility Large Acceptance Spectrometer. Data were collected with nearly complete coverage in the azimuthal and polar angles of the n π⁺center-of-mass system. More than 37 000 cross-section points were measured. The contributions of the isospin I = ½ resonances N(1675) 5/2^-, N(1680) 5/2 …

Single And Double Spin Asymmetries For Deeply Virtual Compton Scattering Measured With Clas And A Longitudinally Polarized Proton Target, S. Pisano, A. Biselli, S. Niccolai, K. Adhikari, D. Adikaram, M. J. Amaryan, S. E. Kuhn, L. B. Weinstein, Z. W. Zhao, Clas Collaboration

Physics Faculty Publications

Single-beam, single-target, and double spin asymmetries for hard exclusive electroproduction of a photon on the proton ^→e^→p~ → e'p'γ are presented. The data were taken at Jefferson Lab using the CEBAF large acceptance spectrometer and a longitudinally polarized ¹⁴NH₃ target. The three asymmetries were measured in 165 four-dimensional kinematic bins, covering the widest kinematic range ever explored simultaneously for beam and target-polarization observables in the valence quark region. The kinematic dependences of the obtained asymmetries are discussed and compared to the predictions of models of generalized parton distributions. The measurement of three DVCS spin observables …

Resonant 𝜋⁺𝜸 → 𝜋⁺𝜋⁰ Amplitude From Quantum Chromodynamics, Raúl A. Briceño, Jozef J. Dudek, Robert G. Edwards, Christian J. Shultz, Christopher E. Thomas, David J. Wilson

Physics Faculty Publications

We present the first ab initio calculation of a radiative transition of a hadronic resonance within quantum chromodynamics (QCD). We compute the amplitude for 𝜋𝜋→𝜋𝜸^⋆, as a function of the energy of the 𝜋𝜋 pair and the virtuality of the photon, in the kinematic regime where 𝜋𝜋 couples strongly to the unstable ρ resonance. This exploratory calculation is performed using a lattice discretization of QCD with quark masses corresponding to m_π ≈ 400  MeV. We obtain a description of the energy dependence of the transition amplitude, constrained at 48 kinematic points, that we can analytically continue …

Temperature Mapping Of Nitrogen-Doped Niobium Superconducting Radiofrequency Cavities, Junki Makita, Gianluigi Ciovati, Pashupati Dhakal

Physics Faculty Publications

It was recently shown that diffusing nitrogen on the inner surface of superconducting radiofrequency (SRF) cavities at high temperature can improve the quality factor of the niobium cavity. However, a reduction of the quench field is also typically found. To better understand the location of rf losses and quench, we used a thermometry system to map the temperature of the outer surface of ingot Nb cavities after nitrogen doping and electropolishing. Surface temperature of the cavities was recorded while increasing the rf power and also during the quenching. The results of thermal mapping showed no precursor heating on the cavities …

Nitrogen Doping Study In Ingot Niobium Cavities, Pashupati Dhakal, Gianluigi Ciovati, Peter Kneisel, Ganapati Rao Myneni, Junki Makita

Physics Faculty Publications

Thermal diffusion of nitrogen in superconducting radio frequency cavities at temperatures around 800C has resulted in the increase in quality factor with a low-field Q-rise. However, the maximum accelerating gradients of these doped cavities often reduces below the values achieved by standard treatments. In this contribution, we present the results of the nitrogen diffusion into ingot niobium cavities subjected to successive material removal from the inner cavity surface by electropolishing in an effort to explore the underlying cause for the gradient degradation.

Semi-Inclusive Charged-Current Neutrino-Nucleus Reactions, O. Moreno, T. W. Donnelly, J. W. Van Orden, W. P. Ford

Physics Faculty Publications

The general, universal formalism for semi-inclusive charged-current (anti) neutrino-nucleus reactions is given for studies of any hadronic system, namely, either nuclei or the nucleon itself. The detailed developments are presented with the former in mind and are further specialized to cases where the final-state charged lepton and an ejected nucleon are presumed to be detected. General kinematics for such processes are summarized, and then explicit expressions are developed for the leptonic and hadronic tensors involved and for the corresponding responses according to the usual charge, longitudinal and transverse projections, keeping finite the masses of all particles involved. In the case …

Analytic Evolution Of Singular Distribution Amplitudes In Qcd, Asli Tandogan

Physics Theses & Dissertations

Distribution amplitudes (DAs) are the basic functions that contain information about the quark momentum. DAs are necessary to describe hard exclusive processes in quantum chromodynamics. We describe a method of analytic evolution of DAs that have singularities such as nonzero values at the end points of the support region, jumps at some points inside the support region and cusps. We illustrate the method by applying it to the evolution of a flat (constant) DA, antisymmetric flat DA, and then use the method for evolution of the two-photon generalized distribution amplitude. Our approach to DA evolution has advantages over the standard …

Investigation And Optimization Of A New Compact Superconducting Cavity For Deflecting And Crabbing Applications, Subashini Uddika De Silva

Physics Theses & Dissertations

Deflecting and crabbing structures have many applications in current accelerator systems. The primary use of a deflecting cavity is to separate a single beam into multiple beams. A crabbing cavity enables the head-on collision at the interaction point in particle colliders in order to increase the luminosity. The early uses of the deflecting structures have been in the early 1960s: these structures were disk loaded structures operating at room temperature. The crabbing structure which was installed at the NEK electron-positron collider was the first and only operational superconducting cavity of that kind. The most common design of superconducting deflecting and …

Direct Measurements Of Two Photon Exchange On Lepton-Proton Elastic Scattering Using Simultaneous Electron-Positron Beams In Clas, Dasuni Kalhari Adikaram

Physics Theses & Dissertations

The electric (GE) and magnetic ( GM) form factors of the proton are fundamental observables which characterize its charge and magnetization distributions. There are two methods to measure the proton form factors: the Rosenbluth separation method and the polarization transfer technique. However, the ratio of the electric and magnetic form factors measured by those methods significantly disagree at momentum transfer Q² > 1 GeV². The most likely explanation of this discrepancy is the inclusion of two-photon exchange (TPE) amplitude contributions to the elastic electron-proton cross section which significantly changes the extraction of GE from the …

Observation Of D⁰ Meson Nuclear Modifications In Au + Au Collisions At √SNn = 200 Gev, L. Adamczyk, J. K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, I. Alekseev, J. Alford, C. D. Anson, A. Aparin, D. Arkhipkin, E. C. Aschenauer, G. S. Averichev, A. Banerjee, D. R. Beavis, R. Bellwied, A. Bhasin, A. K. Bhati, P. Bhattarai, H. Bichsel, M. Zyzak, Et Al., Star Collaboration

Physics Faculty Publications

We report the first measurement of charmed-hadron (D⁰) production via the hadronic decay channel (D⁰→K⁻+π⁺) in Au+Au collisions at √s_NN=200  GeV with the STAR experiment. The charm production cross section per nucleon-nucleon collision at midrapidity scales with the number of binary collisions, N_bin, from p+p to central Au+Au collisions. The D⁰ meson yields in central Au+Au collisions are strongly suppressed compared to those in p+p scaled by N_bin, for transverse momenta p_T > 3  GeV/c, demonstrating significant energy loss of charm quarks in the hot …

Beam-Energy Dependence Of Charge Separation Along The Magnetic Field In Au + Au Collisions At Rhic, L. Adamczyk, J. K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, I. Alekseev, J. Alford, C. D. Anson, A. Aparin, D. Arkhipkin, E. C. Aschenauer, G. S. Averichev, A. Banerjee, D. R. Beavis, R. Bellwied, A. Bhasin, A. K. Bhati, P. Bhattarai, H. Bichsel, M. Zyzak, Et Al., Star Collaboration

Physics Faculty Publications

Local parity-odd domains are theorized to form inside a quark-gluon plasma which has been produced in high-energy heavy-ion collisions. The local parity-odd domains manifest themselves as charge separation along the magnetic field axis via the chiral magnetic effect. The experimental observation of charge separation has previously been reported for heavy-ion collisions at the top RHIC energies. In this Letter, we present the results of the beam-energy dependence of the charge correlations in Au+Au collisions at midrapidity for center-of-mass energies of 7.7, 11.5, 19.6, 27, 39, and 62.4 GeV from the STAR experiment. After background subtraction, the signal gradually reduces with …

Nuclear Electromagnetic Processes In Cheft, L. Girlanda, L. E. Marcucci, S. Pastore, M. Piarulli, R. Schiavilla, M. Viviani

Physics Faculty Publications

We review our recent work on the derivation of the nuclear electromagnetic charge and current operators in chiral perturbation theory, based on time-ordered perturbation theory. We then discuss the strategies for fixing the relevant low-energy constants, and compare the resulting predictions for the electric and magnetic form factors of the deuteron and trinucleons with experimental data, using as input accurate nuclear wave functions derived with realistic potentials.

Single Spin Asymmetries In Charged Kaon Production From Semi-Inclusive Deep Inelastic Scattering On A Transversely Polarized He-3 Target, Y. X. Zhao, Y. Wang, K. Allada, K. Aniol, J. R. M. Annand, T. Averett, F. Benmokhtar, W. Bertozzi, P. C. Bradshaw, M. Canan

Physics Faculty Publications

We report the first measurement of target single spin asymmetries of charged kaons produced in semi-inclusive deep inelastic scattering of electrons off a transversely polarized 3He target. Both the Collins and Sivers moments, which are related to the nucleon transversity and Sivers distributions, respectively, are extracted over the kinematic range of0.1 < x_bj < 0.4for K⁺ and K⁻ production. While the Collins and Sivers moments for K⁺ are consistent with zero within the experimental uncertainties, both moments for K⁻ favor negative values. The Sivers moments are compared to the theoretical prediction from a phenomenological fit to the world data. While …

Precision Measurement Of The Neutron Twist-3 Matrix Element D(2)(N): Probing Color Forces, M. Posik, D. Flay, D. S. Parrno, K. Allada, W. Armstrong, F. Benmokhtar, M. Canan, L. El Fassi, S. Golge, C. Hyde

Physics Faculty Publications

Double-spin asymmetries and absolute cross sections were measured at large Bjorken x (0.25 ≤ x ≤ 0.90), in both the deep-inelastic and resonance regions, by scattering longitudinally polarized electrons at beam energies of 4.7 and 5.9 GeV from a transversely and longitudinally polarized ³He target. In this dedicated experiment, the spin structure function g(2)(3He) was determined with precision at large x, and the neutron twist-3 matrix element d(2)(n) was measured at < Q²> of 3.21 and 4.32 GeV²/c², with an absolute precision of about 10^-5. Our results are found to be in agreement …

Progress On The Interaction Region Design And Detector Integration At Jlab's Meic, V. S. Morozov, P. Brindza, A. Camsonne, Ya S. Derbenev, R. Ent, D. Gaskell, F. Lin, P. Nadel-Turonski, M. Ungaro, Y. Zhang, C. E. Hyde, K. Park, M. Sullivan, Z. W. Zhao

Physics Faculty Publications

One of the unique features of JLab's Medium-energy Electron-Ion Collider (MEIC) is a full-acceptance detector with a dedicated, small-angle, high-resolution detection system, capable of covering a wide range of momenta (and charge-to-mass ratios) with respect to the original ion beam to enable access to new physics. We present an interaction region design developed with close integration of the detection and beam dynamical aspects. The dynamical aspect of the design rests on a symmetry-based concept for compensation of non-linear effects. The optics and geometry have been optimized to accommodate the detection requirements and to ensure the interaction region's modularity for ease …

Precision Measurements Of G¹ Of The Proton And The Deuteron With 6 Gev Electrons, Y. Prok, K. P. Adhikari, D. Adikaram, M. J. Amaryan, G. E. Dodge, N. Guler, A. Klein, S. Koirala, S. E. Kuhn, Clas Collaboration

Physics Faculty Publications

The inclusive polarized structure functions of the proton and deuteron, g^p₁ and g^d₁ , were measured with high statistical precision using polarized 6 GeV electrons incident on a polarized ammonia target in Hall B at Jefferson Laboratory. Electrons scattered at laboratory angles between 18 and 45 degrees were detected using the CEBAF Large Acceptance Spectrometer (CLAS). For the usual deep inelastic region kinematics, Q² > 1 GeV² and the final-state invariant mass W >2 GeV, the ratio of polarized to unpolarized structure functions g₁/F₁ is found to be nearly independent of Q …

Φ-Meson Photoproduction On Hydrogen In The Neutral Decay Mode, H. Seraydaryan, M. J. Amaryan, G. Gavalian, L. Weinstein, K. P. Adhikari, D. Adikaram, R. P. Bennett, S. Bültmann, N. Guler, C. E. Hyde, S. Koirala, S. E. Kuhn, L. B. Weinstein

Physics Faculty Publications

We report the first measurement of the photoproduction cross section of the ϕ meson in its neutral decay mode in the reaction γp→pϕ(K_SK_L) . The experiment was performed with a tagged photon beam of energy 1.6 ≤ E_γ ≤ 3.6 GeV incident on a liquid hydrogen target of the CLAS spectrometer at the Thomas Jefferson National Accelerator Facility. The pϕ final state is identified via reconstruction of K_S in the invariant mass of two oppositely charged pions and by requiring the missing particle in the reaction γp→pK_SX to be K_L. …

Measurement Of The Structure Function Of The Nearly Free Neutron Using Spectator Tagging In Inelastic ²H(E,E'Pˢ) X Scattering With Clas, S. Tkachenko, S. E. Kuhn, J. Zhang, K. P. Adhikari, M. J. Amaryan, A. Klein, S. Koirala, M. Mayer, L. Zana, Clas Collaboration

Physics Faculty Publications

Background: Much less is known about neutron structure than that of the proton due to the absence of free neutron targets. Neutron information is usually extracted from data on nuclear targets such as deuterium, requiring corrections for nuclear binding and nucleon off-shell effects. These corrections are model dependent and have significant uncertainties, especially for large values of the Bjorken scaling variable x . As a consequence, the same data can lead to different conclusions, for example, about the behavior of the d quark distribution in the proton at large x .

Purpose: The Barely Off-shell Nucleon Structure experiment at Jefferson …

Hom And Impedance Study Of Rf Separators For Lcls-Ii, S. U. De Silva, B.R.P. Gamage, R. G. Olave, J. R. Delayen, G. A. Krafft, T. Satogata

Physics Faculty Publications

The LCLS-II upgrade requires an rf spreader system to guide bunches into a switchyard delivering beam to two undulators and the primary beam dump. The beam pattern therefore needs a 3-way beam spreader. An rf deflecting cavity concept was proposed that includes both superconducting and normal conducting options. We characterize the higher order modes (HOM) of these rf separator cavities and evaluate beam dynamics effects due to potential HOM excitation. This study includes both short term wake and multi-bunch effects.

Employing Twin Crabbing Cavities To Address Variable Transverse Coupling Of Beams In The Meic, A. Castilla, V. S. Morozov, T. Satogata, J. R. Delayen

Physics Faculty Publications

The design strategy of the Medium Energy Electron-Ion Collider (MEIC) at Jefferson Lab contemplates both matching of the emittance aspect ratios and a 50 mrad crossing angle along with crab crossing scheme for both electron and ion beams over the energy range (√s=20-70 GeV) to achieve high luminosities at the interaction points (IPs). However, the desired locations for placing the crabbing cavities may include regions where the transverse degrees of freedom of the beams are coupled with variable coupling strength that depends on the collider rings’ magnetic elements (solenoids and skew quadrupoles). In this work we explore the feasibility of …

Induced Polarization Of Λ1116 In Kaon Electroproduction, Clas Collaboration, D. Adikaram, M. J. Amaryan, L. El Fassi, S. Koirala, S. E. Kuhn, M. Mayer

Physics Faculty Publications

We have measured. the induced polarization of the Λ (1116) in the reaction ep →e′K⁺Λ , detecting the scattered e′ and K⁺ in the final state along with the proton from the decay Λ → pπ⁻ . The present study used the CEBAF Large Acceptance Spectrometer (CLAS), which allowed for a large kinematic acceptance in invariant energy W (1.6≤ W ≤ 2.7 GeV) and covered the full range of the kaon production angle at an average momentum transfer Q² = 1.90GeV² . In this experiment a 5.50-GeV electron beam was incident upon …

Neutral Pion Cross Section And Spin Asymmetries At Intermediate Pseudorapidity In Polarized Proton Collisions At √ S = 200 Gev, L. Adamczyk, J. K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, I. Alekseev, S. Bültmann, I. Koralt, D. Plyku, Star Collaboration

Physics Faculty Publications

The differential cross section and spin asymmetries for neutral pions produced within the intermediate pseudorapidity range 0.8<η/c and is found to agree with a next-to-leading order perturbative QCD calculation. The longitudinal double-spin asymmetry A_LL is measured in the same pseudorapidity range and spans a range of Bjorken-x down to x≈0.01. The measured A_LL is consistent with model predictions for varying degrees of gluon polarization. The parity-violating asymmetry A_L is also measured and found to be consistent with zero. The transverse single-spin asymmetry AN is measured over a previously unexplored kinematic range in Feynman-x and P_T. Such measurements may aid our understanding of the onset and kinematic dependence of the large asymmetries observed …

High Precision Determination Of The Q² Evolution Of The Bjorken Sum, A. Deur, Y. Prok, V. Burkert, D. Crabb, F. X. Girod, K. A. Griffioen, N. Guler, S. E. Kuhn, N. Kvaltine

Physics Faculty Publications

We present a significantly improved determination of the Bjorken sum for 0.6 ≤ Q² ≤ 4.8 GeV² using precise new g^p₁ and g^d₁ data taken with the CLAS detector at Jefferson Lab. A higher-twist analysis of the Q² dependence of the Bjorken sum yields the twist-4 coefficient f ^p-n₂= -0.064 ± 0.009 ± ^0.032 _0.036. This leads to the color polarizabilities χ ^p-n _E= -0.032 ± 0.024 and χ^p-n_B= 0.032 ± 0.013. The strong force coupling is determined to be α ^MS_S (M²_{Z …}

Data Analysis Techniques, Differential Cross Sections, And Spin Density Matrix Elements For The Reaction 𝛾p → Φp, K. P. Adhikari, D. Adikaram, M. J. Amaryan, C. E. Hyde, S. Koirala, S. E. Kuhn, M. Mayer, I. Niculescu, Et Al., The Clas Collaboration

Physics Faculty Publications

High-statistics measurements of differential cross sections and spin density matrix elements for the reaction γp→ϕp have been made using the CLAS detector at Jefferson Lab. We cover center-of-mass energies (√s) from 1.97 to 2.84 GeV, with an extensive coverage in the ϕ production angle. The high statistics of the data sample made it necessary to carefully account for the interplay between the ϕ natural lineshape and effects of the detector resolution, that are found to be comparable in magnitude. We study both the charged- (ϕ→K⁺K⁻) and neutral- (ϕ→K⁰_SK⁰_L) K^{→ …}

Publisher’S Note: Data Analysis Techniques, Differential Cross Sections, And Spin Density Matrix Elements For The Reaction 𝛾p -> Φp (Phys. Rev. C. Vol 89, 055208, 2014), K. P. Adhikari, D. Adikaram, M. J. Amaryan, C. E. Hyde, A. Klein, S. Koirala, S. E. Kuhn, M. Mayer, I. Niculescu, J. Zhang, Et Al., The Clas Collaboration

Physics Faculty Publications

No abstract provided.

Photoproduction Of Π0 On Hydrogen With Clas From 1.1 Gev - 5.45 Gev Using E+E –Γ Decay, Michael C. Kunkel

Physics Theses & Dissertations

Photoproduction of the π⁰ meson was studied using the CLAS detector at the Thomas Jefferson National Accelerator Facility using tagged incident photon energies spanning the range E_γ = 1.1 GeV - 5.45 GeV. The measurement is performed on a liquid hydrogen target in the reaction γp → pe ⁺e^–(γ). The final state of the reaction is the sum of two subprocesses for π⁰ decay, the Dalitz decay mode of π⁰ → e ⁺e^–γ and conversion mode where one photon from π⁰ → γγ decay is converted into a …