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NLO BFKL and anomalous dimensions of light-ray operators

Description: This presentation covers: Regge limit in the coordinate space; “BFKL” representation of 4-point correlation function in N = 4 SYM; light-ray operators; “DGLAP” representation of 4-point correlation function; and anomalous dimensions from DGAP vs BFKL representations.
Date: May 1, 2013
Creator: Balitsky, Ian
Partner: UNT Libraries Government Documents Department

Measurements of transverse momentum in semi-inclusive deep-inelastic scattering at CLAS

Description: With mounting experimental evidence that only a small fraction of the proton's spin comes from the spins of its quarks and gluons, the quest for orbital angular momentum has begun. The parton distributions relevant to this depend on transverse quark momenta. Recent CLAS semi-inclusive deep-inelastic scattering measurements probe these new transverse-momentum-dependent parton distributions using longitudinally polarized beams and targets and detecting {pi}{sup +},{pi}{sup -} and {pi}{sup 0} in the final state.
Date: December 1, 2012
Creator: Griffioen, K.A.
Partner: UNT Libraries Government Documents Department

Measuring the charged pion polarizability in the gamma gamma -> pi+pi- reaction

Description: Development has begun of a new experiment to measure the charged pion polarizability $\alpha_{\pi}-\beta_{\pi}$. The charged pion polarizability ranks among the most important tests of low-energy QCD presently unresolved by experiment. Analogous to precision measurements of $\pi^{\circ}\rightarrow\gamma\gamma$ that test the intrinsic odd-parity (anomalous) sector of QCD, the pion polarizability tests the intrinsic even-parity sector of QCD. The measurement will be performed using the $\gamma\gamma\rightarrow\pi^{+{}}\pi^{-{}}$ cross section accessed via the Primakoff mechanism on nuclear targets using the GlueX detector in Hall D at Jefferson Lab. The linearly polarized photon source in Hall-D will be utilized to separate the Primakoff cross-section from coherent $\rho^{\circ}$ production.
Date: August 1, 2013
Creator: Lawrence, David W.; Miskimen, Rory A.; Mushkarenkov, Alexander Nikolaevich & Smith, Elton S.
Partner: UNT Libraries Government Documents Department

Nonperturbative short-range dynamics in TMDs

Description: This presentation covers: deep inelastic processes and transverse momentum distributions; chiral symmetry breaking, including the physical picture, the dynamical model, and parton distributions; partonic structures, including transverse momentum distributions, coordinate space correlator, and short range correlations; and measurements of semi-inclusive deep inelastic scattering, correlations, and multi-parton processes in pp interactions.
Date: May 1, 2013
Creator: Weiss, Christian
Partner: UNT Libraries Government Documents Department

Measuring the Weak Charge of the Proton and the Hadronic Parity Violation of the N -> {Delta} Transition

Description: Qweak will determine the weak charge of the proton, Q{sup p}{sub W}, via an asymmetry measurement of parity-violating elastic electron-proton scattering at low four momentum transfer to a precision of 4%. Q{sup p}{sub W} has a firm Standard Model prediction and is related to the weak mixing angle, sin{sup 2} {Theta}{sub W}, a well-defined Standard Model parameter. Qweak will probe a subset of new physics to the TeV mass scale and test the Standard Model. The details of how this measurement was performed and the analysis of the 25% elastic dataset will be presented in this thesis. Also, an analysis of an auxiliary measurement of the parity-violating asymmetry in the N -> {Delta} transition is presented. It is used as a systematic inelastic background correction in the elastic analysis and to extract information about the hadronic parity violation through the low energy constant, d{sub Delta}. The elastic asymmetry at Q{sup 2} = 0.0252 ± 0.0007 GeV{sup 2} was measured to be A{sub ep} = -265 ± 40 ± 22 ± 68 ppb (stat., sys., and blinding). Extrapolated to Q{sup 2} = 0, the value of the proton's weak charge was measured to be Q{sup p}{sub W} = 0.077 ± 0.019 (stat. and sys.) ± 0.026 (blinding). This is within 1 {sigma} of the Standard Model prediction of Q{sup p}{sub W} = 0.0705 ± 0.0008. The N -> {Delta} inelastic asymmetry at Q{sup 2} = 0.02078 ± 0.0005 GeV{sup 2} and W = 1205 MeV was measured to be A{sub inel} = -3.03 ± 0.65 ± 0.73 ± 0.07 ppm (stat., sys., and blinding). This result constrains the low energy constant to be d{sub {Delta}} = 5.8 ± 22g{sub {pi}}, and, if the result of the G0 experiment is included, d{sub {Delta}} = 5.8 ± 17g{sub {pi}}. This result rules out ...
Date: October 16, 2012
Creator: Leacock, John
Partner: UNT Libraries Government Documents Department

Study of Generalized Parton Distributions and Deeply Virtual Compton Scattering on the nucleon with the CLAS and CLAS12 detectors at the Jefferson Laboratory

Description: The exclusive leptoproduction of a real photon is considered to be the "cleanest" way to access the Generalized Parton Distribution (GPD). This process is called Deeply Virtual Compton Scattering (DVCS) lN {yields} lN{gamma} , and is sensitive to all the four GPDs. Measuring the DVCS cross section is one of the main goals of this thesis. In this thesis, we present the work performed to extract on a wide phase-space the DVCS cross-section from the JLab data at a beam energy of 6 GeV.
Date: November 1, 2012
Creator: Guegan, Baptiste
Partner: UNT Libraries Government Documents Department

Transverse momentum-dependent parton distribution functions in lattice QCD

Description: A fundamental structural property of the nucleon is the distribution of quark momenta, both parallel as well as perpendicular to its propagation. Experimentally, this information is accessible via selected processes such as semi-inclusive deep inelastic scattering (SIDIS) and the Drell-Yan process (DY), which can be parametrized in terms of transversemomentum-dependent parton distributions (TMDs). On the other hand, these distribution functions can be extracted from nucleon matrix elements of a certain class of bilocal quark operators in which the quarks are connected by a staple-shaped Wilson line serving to incorporate initial state (DY) or final state (SIDIS) interactions. A scheme for evaluating such matrix elements within lattice QCD is developed. This requires casting the calculation in a particular Lorentz frame, which is facilitated by a parametrization of the matrix elements in terms of invariant amplitudes. Exploratory results are presented for the time-reversal odd Sivers and Boer-Mulders transverse momentum shifts.
Date: August 1, 2013
Creator: Engelhardt, Michael G.; Musch, Bernhard U.; Haegler, Philipp G.; Negele, John W. & Schaefer, Andreas
Partner: UNT Libraries Government Documents Department

Study of the Two-pion Photoproduction on the Deuteron

Description: Understanding the structure of baryons in terms of the fundamental interaction of the constituent quarks and gluons is one of the primary challenges in strong interaction physics. This interaction is governed by Quantum Chromodynamics (QCD), which is a theory for understanding the dynamics of strong. QCD displays the asymptotic freedom of hadrons at very short distances and also the confinement of quarks and gluons inside hadrons. However, solutions of this QCD theory in the non-perturbative domain of the interaction are extremely difficult to achieve, mainly because confinement happens on the hadronic scale on which the coupling constant is large and prevents any perturbative approach. Thus leaving us with strategies such as lattice QCD or formulating QCD sum rules to get around this problem. In exclusive hadron production the yN interaction is recognized for being a powerful method for investigating hadrons and the mysteries that still exist within the strong interaction. From reactions with the nucleon, the strong interaction can be investigated through the transition amplitudes to the N and Delta resonances. More specifically, if an electromagnetic interaction is well known then the intermediate resonance states may be evaluated through meson photoproduction. To gain more detailed insight into this interaction, we look to probe the baryon structure of the nucleon and the photo-excited resonance decays through photon scattering off a deuteron producing two pions in the final state. This photoproduction process off the deuteron will be used to investigate known baryon resonances in the two pion channel. The two pion final state will be investigated for unraveling new information into the photo-coupling strengths. We want to explore final state interactions, search for properties of known resonances, and to explore the possibility of seeing missing states that are predicted by quark models but have not yet been found experimentally. Using the CEBAF ...
Date: December 1, 2012
Creator: Graham, Lewis P.
Partner: UNT Libraries Government Documents Department

Fourth Generation Parity

Description: We present a very simple 4th-generation (4G) model with an Abelian gauge interaction under which only the 4G fermions have nonzero charge. The U(1) gauge symmetry can have a Z_2 residual discrete symmetry (4G-parity), which can stabilize the lightest 4G particle (L4P). When the 4G neutrino is the L4P, it would be a neutral and stable particle and the other 4G fermions would decay into the L4P leaving the trace of missing energy plus the standard model fermions. Because of the new symmetry, the 4G particle creation and decay modes are different from those of the sequential 4G model, and the 4G particles can be appreciably lighter than typical experimental bounds.
Date: January 1, 2013
Creator: Lee, Hye-Sung & Soni, Amarjit
Partner: UNT Libraries Government Documents Department

First Determination of the Weak Charge of the Proton

Description: The Qweak experiment has measured the parity-violating asymmetry in polarized e-p elastic scattering at Q^2 = 0.025(GeV/c)^2, employing 145 microamps of 89% longitudinally polarized electrons on a 34.4cm long liquid hydrogen target at Jefferson Lab. The results of the experiment's commissioning run are reported here, constituting approximately 4% of the data collected in the experiment. From these initial results the measured asymmetry is A_e_p = -279 +- 35 (statistics) +- 31 (systematics) ppb, which is the smallest and most precise asymmetry ever measured in polarized e-p scattering. The small Q^2 of this experiment has made possible the first determination of the weak charge of the proton, Q^p_W, by incorporating earlier parity-violating electron scattering (PVES) data at higher Q^2 to constrain hadronic corrections. The value of Q^p_W obtained in this way is Q^p_W(PVES) = 0.064 +- 0.012, in good agreement with the Standard Model prediction of Q^p_W(SM) = 0.0710 +- 0.0007. When this result is further combined with the Cs atomic parity violation (APV) measurement, significant constraints on the weak charges of the up and down quarks can also be extracted. That PVES+APV analysis reveals the neutron's weak charge to be Q^n_W(PVES+APV) = -0.975 +- 0.010.
Date: October 1, 2013
Creator: Androic, D; Armstrong, D S; Asaturyan, A; Averett, T; Balewski, J; Beaufait, J et al.
Partner: UNT Libraries Government Documents Department

First JAM results on the determination of polarized parton distributions

Description: The Jefferson Lab Angular Momentum (JAM) collaboration is a new initiative aimed to the study of the angular-momentum-dependent structure of the nucleon. First results on the determination of spin-dependent parton distribution functions from world data on polarized deep-inelastic scattering will be presented and compared with previous determinations from other groups. Different aspects of global QCD analysis will be discussed, including effects due to nuclear structure, higher twist, and target-mass corrections, as well as the impact of different data selections.
Date: April 1, 2013
Creator: Jimenez-Delgado, Pedro
Partner: UNT Libraries Government Documents Department

Hard Exclusive Reactions at Jlab

Description: Dedicated experiments to study Deeply Virtual Compton Scattering (DVCS) and Deeply Virtual Meson Production (DVMP) have been carried out at Jefferson Lab. DVCS helicity--dependent and helicity--independent cross sections and beam spin asymmetries have been measured, as well as cross sections and asymmetries for the $\pi^0$, $\eta$, $\rho^0$, $\rho^+$, $\omega$ and $\phi$ for exclusive electroproduction. The data were taken in a wide kinematic range in $Q^2$=1--4.5 GeV$^2$, $x_B$=0.1--0.5, and $|t|$ up to 2 GeV$^2$. The presented results offer a unique opportunity to study the structure of the nucleon at the parton level as one has access to Bjorken $x_B$ and momentum transfer to the nucleon $t$ at the same time.
Date: September 20, 2011
Creator: Kubarovsky, Valery P.
Partner: UNT Libraries Government Documents Department

Helicity Asymmetry Measurement for pi^0 Photoproduction with FROST

Description: This thesis reports on the first helicity asymmetry measurement for single neutral pion photoproduction using the CLAS detector in Hall B at the Thomas Jefferson National Accelerator Facility (JLab). This measurement used longitudinally polarized protons and circularly polarized photons at energies between 350 MeV and 2400 MeV. The experimental results are compared to three available model calculations.
Date: August 1, 2011
Creator: Iwamoto, Hideko
Partner: UNT Libraries Government Documents Department

Simultaneous extraction of transversity and Collins functions from new semi-inclusive deep inelastic scattering and e{sup +}e{sup -} data

Description: We present a global re-analysis of the most recent experimental data on azimuthal asymmetries in semi-inclusive deep inelastic scattering, from the HERMES and COMPASS Collaborations, and in e{sup +}e{sup -} {yields} h{sub 1} h{sub 2} X processes, from the Belle Collaboration. The transversity and the Collins functions are extracted simultaneously, in the framework of a revised global analysis in which a new parameterisation of the unknown functions is also tested.
Date: May 1, 2013
Creator: U., Turin; U., Turin; Cagliari, INFN; Cagliari U., INFN Cagliari; Cagliari, INFN & JLAB
Partner: UNT Libraries Government Documents Department

The Sivers effect and the Single Spin Asymmetry A_N in p(transv. pol.) p --> h X processes

Description: The single spin asymmetry A_N, for large P_T single inclusive particle production in p(transv. pol.) p collisions, is considered within a generalised parton model and a transverse momentum dependent factorisation scheme. The focus is on the Sivers effect and the study of its potential contribution to A_N, based on a careful analysis of the Sivers functions extracted from azimuthal asymmetries in semi-inclusive deep inelastic scattering processes. It is found that such Sivers functions could explain most features of the A_N data, including some recent STAR results which show the persistence of a non zero A_N up to surprisingly large P_T values.
Date: September 1, 2013
Creator: Anselmino, Mauro; Boglione, Mariaelena; D'Alesio, Umberto; Melis, Stefano; Murgia, Francesco & Prokudin, Alexei
Partner: UNT Libraries Government Documents Department

Spin Physics with CLAS

Description: Inelastic scattering using polarized nucleon targets and polarized charged lepton beams allows the extraction of double and single spin asymmetries that provide information about the helicity structure of the nucleon. A program designed to study such processes at low and intermediate Q{sup 2} for the proton and deuteron has been pursued by the CLAS Collaboration at Jefferson Lab since 1998. Our inclusive data with high statistical precision and extensive kinematic coverage allow us to better constrain the polarized parton distributions and to accurately determine various moments of spin structure function g{sub 1} as a function of Q{sup 2}. The latest results are shown, illustrating our contribution to the world data, with comparisons of the data with NLO global fits, phenomenological models, chiral perturbation theory and the GDH and Bjorken sum rules. The semi-inclusive measurements of single and double spin asymmetries for charged and neutral pions are also shown, indicating the importance of the orbital motion of quarks in understanding of the spin structure of the nucleon.
Date: September 20, 2011
Creator: Prok, Yelena
Partner: UNT Libraries Government Documents Department

Recent Results of Target Single-Spin Asymmetry Experiments at Jefferson Lab

Description: We report recent results from Jefferson Lab Hall A “Neutron Transversity” experiment (E06-010). Transversely polarized target single-spin asymmetry AUT and beam-target double-spin asymmetry A{sub LT} have been measured in semi-inclusive deep-inelastic scattering (SIDIS) reactions on a polarized neutron ({sup 3}He) target. Collins-type and Sivers-type asymmetries have been extracted from A{sub UT} for charged pion SIDIS productions, which are sensitive to quark transversity and Sivers distributions, correspondingly. Double spin asymmetry A{sub LT} is sensitive to a specific quark transverse momentum dependent parton distribution (TMD), the so-called “ transverse helicity” (g{sub 1T} ) distributions. In addition, target single-spin asymmetries A{sub y} in inclusive electron scattering on a transversely polarized {sup 3}He target in quasi-elastic and deep inelastic kinematics were also measured in Hall A.
Date: August 1, 2013
Creator: Jiang, Xiaodong
Partner: UNT Libraries Government Documents Department

The GlueX experiment: Search for gluonic excitations via photoproduction at Jefferson Lab

Description: Studies of meson spectra via strong decays provide insight regarding QCD at the confinement scale. These studies have led to phenomenological models for QCD such as the constituent quark model. However, QCD allows for a much richer spectrum of meson states which include extra states such as exotics, hybrids, multi-quarks, and glueballs. First discussion of the status of exotic meson searches is given followed by an overview of the progress at Jefferson Lab to double the energy of the machine to 12 GeV, which will allow us to access photoproduction of mesons in search for gluonic excited states.
Date: July 1, 2013
Creator: Eugenio, Paul
Partner: UNT Libraries Government Documents Department

Guiding Center Equations of High Accuracy

Description: Guiding center simulations are an important means of predicting the effect of resistive and ideal magnetohydrodynamic instabilities on particle distributions in toroidal magnetically confined thermonuclear fusion research devices. Because saturated instabilities typically have amplitudes of δ#14;B/B of a few times 10-4 numerical accuracy is of concern in discovering the effect of mode particle resonances. We develop a means of following guiding center orbits which is greatly superior to the methods currently in use. In the presence of ripple or time dependent magnetic perturbations both energy and canonical momentum are conserved to better than one part in 1014, and the relation between changes in canonical momentum and energy is also conserved to very high order.
Date: March 29, 2013
Creator: R.B. White, G. Spizzo and M. Gobbin
Partner: UNT Libraries Government Documents Department

Measurement of the neutron spin structure function at low Q{sup 2}

Description: The spin dependent cross sections, {sigma}{sup T}{sub 1/2} and {sigma}{sup T}{sub 3/2}, and asymmetries, A{sub {parallel}} and A{sub {perp}}, for {sup 3}He have been measured at the Jefferson Lab's Hall A facility. The inclusive scattering process {sup 3}{vec He}({vec e},e)X was performed for initial beam energies ranging from 0.86 to 5.1 GeV, at a scattering angle of 15.5°. Data includes measurements from the quasielastic peak, resonance region, and the deep inelastic regime. An approximation for the extended Gcrasimov-Drell-Hcarn integral is presented at a 4-momentum transfer Q{sup 2} of 0.2-1.0 GeV{sup 2} . Also presented are results on the performance of the polarized {sup 3}He target. Polarization of {sup 3}He vvas achieved by the process of spin-exchange collisions with optically pumped rubidium vapor. The {sup 3}He polarization was monitored using the NMR technique of adiabatic fast passage (AFP). The average target polarization was approximately 35% and was determined to have a systematic uncertainty of roughly ±4% relative.
Date: August 1, 2000
Creator: Jensen, John Steffen
Partner: UNT Libraries Government Documents Department

Measurement of the neutron ({sup 3}He) spin structure functions at low Q{sup 2}: A CONNECTION BETWEEN THE BJORKEN AND GERASIMOV-DRELL-HEARN SUM RULE

Description: This dissertation presents results of experiment E94-010 performed at Jefferson Laboratory (simply known as JLab) in Hall A. The experiment aimed to measure the low Q{sup 2} evolution of the Gerasimov-Drell-Hearn (GDH) integral from Q{sup 2} = 0.1 to 0.9 GeV{sup 2}. The GDH sum rule at the real photon point provides an important test of Quantum Chromodynamics (QCD). The low Q{sup 2} evolution of the GDH integral contests various resonance models, Chiral Perturbation Theory ({chi}#31;PT) and lattice QCD calculations, but more importantly, it helps us understand the transition between partonic and hadronic degrees of freedom. At high Q{sup 2}, beyond 1 GeV{sup 2}, the difference of the GDH integrals for the proton and the neutron is related to the Bjorken sum rule, another fundamental test of QCD. In addition, results of the measurements for the spin structure functions g{sub 1} and g{sub 2}, cross sections, and asymmetries are presented. E94-010 was the first experiment of its kind at JLab. It used a high-pressure, polarized {sup 3}He target with a gas pressure of 10 atm and average target polarization of 35%. For the first time, the polarized electron source delivered an average beam polarization of 70% with a beam current of 15 {micro}#22;A. The limit on the beam current was only imposed by the target. The experiment required six different beam energies from 0.86 to 5.1 GeV. This was the first time the accelerator ever reached 5.1 GeV. Both High-Resolution Spectrometers of Hall A, used in singles mode, were positioned at 15.5#14;{deg} each.
Date: December 1, 2002
Creator: Djawotho, Pibero
Partner: UNT Libraries Government Documents Department