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Modified Fragmentation Function from Quark Recombination

Description: Within the framework of the constituent quark model, it isshown that the single hadron fragmentation function of a parton can beexpressed as a convolution of shower diquark or triquark distributionfunction and quark recombination probability, if the interference betweenamplitudes of quark recombination with different momenta is neglected.Therecombination probability is determined by the hadron's wavefunction inthe constituent quark model. The shower diquark or triquark distributionfunctions of a fragmenting jet are defined in terms of overlappingmatrices of constituent quarks and parton field operators. They aresimilar in form to dihadron or trihadron fragmentation functions in termsof parton operator and hadron states. Extending the formalism to thefield theory at finite temperature, we automatically derive contributionsto the effective single hadron fragmentation function from therecombination of shower and thermal constituent quarks. Suchcontributions involve single or diquark distribution functions which inturn can be related to diquark or triquark distribution functions via sumrules. We also derive QCD evolution equations for quark distributionfunctions that in turn determine the evolution of the effective jetfragmentation functions in a thermal medium.
Date: July 26, 2005
Creator: Majumder, A.; Wang, Enke & Wang, Xin-Nian
Partner: UNT Libraries Government Documents Department


Description: The 0-degree fragmentation products of {sup 16}O and {sup 12}C at 2.1-GeV/n and {sup 12}C at 1.05-GeV/n have been measured for targets ranging from H to Pb. They present a total of 464 partial-production cross sections for 35 isotopes. The cross sections are energy independent and can be factored into beam-fragment and target terms. The target factor, {gamma}{sub T} = A{sub T}{sup 1/4}, and other evidence, imply the isotopes are produced in peripheral interactions.
Date: February 1, 1975
Creator: Lindstrom, P.J.; Greiner, D.E.; Heckman, H.H.; Cork, Bruce & Bieser, F.S.
Partner: UNT Libraries Government Documents Department

System-size independence of directed flow at the RelativisticHeavy-Ion Collider

Description: We measure directed flow (v{sub 1}) for charged particles in Au + Au and Cu + Cu collisions at {radical}s{sub NN} = 200 GeV and 62.4 GeV, as a function of pseudorapidity ({eta}), transverse momentum (p{sub t}) and collision centrality, based on data from the STAR experiment. We find that the directed flow depends on the incident energy but, contrary to all available model implementations, not on the size of the colliding system at a given centrality. We extend the validity of the limiting fragmentation concept to v{sub 1} in different collision systems, and investigate possible explanations for the observed sign change in v{sub 1}(p{sub t}).
Date: September 20, 2008
Creator: Coll, STAR
Partner: UNT Libraries Government Documents Department

Systemsize dependence of associated yields in hadron-triggered jets

Description: We present results on the system size dependence of high transverse momentum di-hadron correlations at {radical}s{sub NN} = 200 GeV as measured by STAR at RHIC. Measurements in d+Au, Cu+Cu and Au+Au collisions reveal similar jet-like correlation yields at small angular separation ({Delta}{phi} {approx} 0, {Delta}{eta} {approx} 0) for all systems and centralities. Previous measurements have shown that the away-side yield is suppressed in heavy-ion collisions. We present measurements of the away-side suppression as a function of transverse momentum and centrality in Cu+Cu and Au+Au collisions. The suppression is found to be similar in Cu+Cu and Au+Au collisions at a similar number of participants. The results are compared to theoretical calculations based on the parton quenching model and the modified fragmentation model. The observed differences between data and theory indicate that the correlated yields presented here will provide important constraints on medium density profile and energy loss model parameters.
Date: July 5, 2010
Creator: Collaboration, STAR & Abelev, Betty
Partner: UNT Libraries Government Documents Department

The dihadron fragmentation function and its evolution

Description: Dihadron fragmentation functions and their evolution arestudied in the process of e+e- annihilation. Under the collinearfactorization approximation and facilitated by the cut-vertex technique,the two hadron inclusive cross section at leading order (LO) is shown tofactorize into a short distance parton cross section and a long distancedihadron fragmentation function. We provide the definition of such adihadron fragmentation function in terms of parton matrix elements andderive its DGLAP evolution equation at leading log. The evolutionequation for the non-singlet quark fragmentation function is solvednumerically with a simple ansatz for the initial condition and resultsare presented for cases of physical interest.
Date: February 24, 2004
Creator: Majumder, Abhijit & Wang, Xin-Nian
Partner: UNT Libraries Government Documents Department

Fragmentation Cross Sections of 290 and 400 MeV/nucleon 12C Beamson Elemental Targets

Description: Charge-changing and fragment production cross sections at 0circ have been obtained for interactions of 290 MeV/nucleon and 400MeV/nucleon carbon beams with C, CH2, Al, Cu, Sn, and Pb targets. Thesebeams are relevant to cancer therapy, space radiation, and the productionof radioactive beams. We compare to previously published results using Cand CH2 targets at similar beam energies. Due to ambiguities arising fromthe presence of multiple fragments on many events, previous publicationshave reported only cross sections for B and Be fragments. In this work wehave extracted cross sections for all fragment species, using dataobtained at three distinct values of angular acceptance, supplemented bydata taken with the detector stack placed off the beam axis. A simulationof the experiment with the PHITS Monte Carlo code shows fair agreementwith the data obtained with the large acceptance detectors, but agreementis poor at small acceptance. The measured cross sections are alsocompared to the predictions of the one-dimensional cross section modelsEPAX2 and NUCFRG2; the latter is presently used in NASA's space radiationtransport calculations. Though PHITS and NUCFRG2 reproduce thecharge-changing cross sections with reasonable accuracy, none of themodels is able to accurately predict the fragment cross sections for allfragment species and target materials.
Date: March 17, 2007
Creator: Zeitlin, C.; Guetersloh, S.; Heilbronn, L.; Miller, J.; Fukumura,A.; Iwata, Y. et al.
Partner: UNT Libraries Government Documents Department

Fragmentation cross sections of 28Si at beam energies from 290AMeV to 1200A MeV

Description: In planning for long-duration spaceflight, it will beimportant to accurately model the exposure of astronauts to heavy ions inthe Galactic Cosmic Rays (GCR). As part of an ongoing effort to improveheavy-ion transport codes that will be used in designing futurespacecraft and habitats, fragmentation cross sections of 28Si have beenmeasured using beams with extracted energies from 290A MeV to 1200A MeV,spanning most of the peak region of the energy distribution of siliconions in the GCR. Results were obtained for six elemental targets:hydrogen, carbon, aluminum, copper, tin, and lead. The charge-changingcross sections are found to be energy-independent within the experimentaluncertainties, except for those on the hydrogen target. Cross sectionsfor the heaviest fragments are found to decrease slightly with increasingenergy for lighter targets, but increase with energy for tin and leadtargets. The cross sections are compared to previous measurements atsimilar energies, and to predictions of the NUCFRG2 model used by NASA toevaluate radiation exposures in flight. For charge-changing crosssections, reasonable agreement is found between the present experimentand those of Webber, et al. and Flesch, et al., and NUCFRG2 agrees withthe data to within 3 percent in most cases. Fragment cross sections showless agreement between experiments, and there are substantial differencesbetween NUCFRG2 predictions andthe data.
Date: August 25, 2006
Creator: Zeitlin, C.; Fukumura, A.; Guetersloh, S.B.; Heilbronn, L.H; Iwata, Y.; Miller, J. et al.
Partner: UNT Libraries Government Documents Department

Fragmentation Cross Sections of Medium-Energy 35Cl, 40Ar, and 48TiBeams on Elemental Targets

Description: Charge-changing and fragment production cross sections at 0degrees have been obtained for interactions of 290, 400, and 650MeV/nucleon 40Ar beams, 650 and 1000 MeV/nucleon 35Cl beams, and a 1000MeV/nucleon 48Ti beam. Targets of C, CH2, Al, Cu, Sn, and Pb were used.Using standard analysis methods, we obtain fragment cross sections forcharges as low as 8 for Cl and Ar beams, and as low as 10 for the Tibeam. Using data obtained with small-acceptance detectors, we reportfragment production cross sections for charges as low as 5, corrected foracceptance using a simple model of fragment angular distributions. Withthe lower-charged fragment cross sections, we cancompare the data topredictions from several models (including NUCFRG2, EPAX2, and PHITS) ina region largely unexplored in earlier work. As found in earlier workwith other beams, NUCFRG2 and PHITS predictions agree reasonably wellwith the data for charge-changing cross sections, but do not accuratelypredict the fragment production cross sections. The cross sections forthe lightest fragments demonstrate the inadequacy of several models inwhich the cross sections fall monotonically with the charge of thefragment. PHITS, despite not agreeing particularly well with the fragmentproduction cross sections on average, nonetheless qualitativelyreproduces somesignificant features of the data that are missing from theother models.
Date: December 8, 2007
Creator: Zeitlin, C.; Guetersloh, S.; Heilbronn, L.; Miller, J.; Fukumura,A.; Iwata, Y. et al.
Partner: UNT Libraries Government Documents Department

Spectroscopic Evidence for Exceptional Thermal Contribution to Electron-Beam Induced Fragmentation

Description: While electron beam induced fragmentation (EBIF) has been reported to result in the formation of nanocrystals of various compositions, the physical forces driving this phenomenon are still poorly understood. We report EBIF to be a much more general phenomenon than previously appreciated, operative across a wide variety of metals, semiconductors and insulators. In addition, we leverage the temperature dependent bandgap of several semiconductors to quantify -- using in situ cathodoluminescence spectroscopy -- the thermal contribution to EBIF, and find extreme temperature rises upwards of 1000K.
Date: November 16, 2010
Creator: Caldwell, Marissa A.; Haynor, Ben; Aloni, Shaul; Ogletree, D. Frank; Wong, H.-S. Philip; Urban, Jeffrey J. et al.
Partner: UNT Libraries Government Documents Department

QGP and Modified Jet Fragmentation

Description: Recent progresses in the study of jet modification in hotmedium and their consequences in high-energy heavy-ion collisions are reviewed. In particular, I will discuss energy loss for propagating heavy quarks and the resulting modified fragmentation function. Medium modification of the parton fragmentation function due to quark recombination are formulated within finite temperature field theory and their implication on the search for deconfined quark-gluon plasma is also discussed.
Date: April 18, 2005
Creator: Wang, Xin-Nian
Partner: UNT Libraries Government Documents Department

Single Spin Asymmetry in Inclusive Hadron Production in pp Scattering from Collins Mechanism

Description: We study the Collins mechanism contribution to the single transverse spin asymmetry in inclusive hadron production in pp scattering p{up_arrow}p {yields} {pi}X from the leading jet fragmentation. The azimuthal asymmetric distribution of hadron in the jet leads to a single spin asymmetry for the produced hadron in the Lab frame. The effect is evaluated in a transverse momentum dependent model that takes into account the transverse momentum dependence in the fragmentation process. We find the asymmetry is comparable in size to the experimental observation at RHIC at {radical}s = 200GeV.
Date: April 14, 2008
Creator: Yuan, Feng & Yuan, Feng
Partner: UNT Libraries Government Documents Department

Reading the Ruptured Word: Detecting Trauma in Gothic Fiction from 1764-1853

Description: Using trauma theory, I analyze the disjointed narrative structure of gothic works from 1764-1853 as symptomatic of the traumatic experience. Gothic novels contain multiple structural anomalies, including gaps in experience that indicate psychological wounding, use of the supernatural to violate rational thought, and the inability of witnesses to testify to the traumatic event. These structural abnormalities are the result of trauma that characters within these texts then seek to prevent or repair via detection.
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Date: August 2016
Creator: Laredo, Jeanette A
Partner: UNT Libraries

Fragmentation pathwaysfor selected electronic states of theacetylene dication

Description: Coincident measurement of the Auger electron and fragmention momenta emitted after carbon core-level photoionization of acetylenehas yielded new understanding of how the dication fragments. Ab initiocalculations and experimental data, including body-frame Auger angulardistributions, are used to identify the parent electronic states andtogether yield a comprehensive map of the dissociation pathways whichinclude surface crossings and barriers to direct dissociation. The Augerangular distributions show evidence of core-holelocalization.
Date: December 18, 2007
Creator: Osipov, Timur; Rescigno, Thomas N.; Weber, Thorsten; Miyabe,Shungo; Jahnke, T.; Alnaser, A. et al.
Partner: UNT Libraries Government Documents Department

Anti-Hyperon polarization in high energy pp collisions withpolarized beams

Description: We study the longitudinal polarization of the {bar {Sigma}}{sup -}, {bar {Sigma}}{sup +}, {bar {Xi}}{sup 0} and {bar {Xi}}{sup +} anti-hyperons in polarized high energy pp collisions at large transverse momenta, extending a recent study for the {bar {Lambda}} antihyperon. We make predictions by using different parameterizations of the polarized parton densities and models for the polarized fragmentation functions. Similar to the {bar {Lambda}} polarization, the {bar {Xi}}{sup 0} and {bar {Xi}}{sup +} polarizations are found to be sensitive to the polarized anti-strange sea, {Delta}{bar s}(x), in the nucleon. The {bar {Sigma}}{sup -} and {bar {Sigma}}{sup +} polarizations show sensitivity to the light sea quark polarizations, {Delta}{bar u}(x) and {Delta}{bar d}(x), and their asymmetry.
Date: November 20, 2007
Creator: Chen, Ye; Liang, Zuo-tang; Sichtermann, Ernst; Xu, Qing-hua & Zhou, Shan-shan
Partner: UNT Libraries Government Documents Department

Azimuthal Asymmetric Distribution of Hadrons Inside a Jet atHadron Collider

Description: We study the azimuthal asymmetric distribution of hadronsinside a high energy jet in the single transverse polarized proton protonscattering, coming from the Collins effect multiplied by the quarktransversity distribution. We argue that the Collins function in thisprocess is the same as that in the semi-inclusive deep inelasticscattering. The experimental study of this process will provide usimportant information on the quark transversity distribution and test theuniversality of the fragmentation functions.
Date: September 20, 2007
Creator: Yuan, Feng
Partner: UNT Libraries Government Documents Department

A genomic analysis of the archael system Ignicoccus hospitalis-Nanoarchaeum equitans

Description: BACKGROUND: The relationship between the hyperthermophiles Ignicoccus hospitalis and Nanoarchaeum equitans is the only known example of a specific association between two species of Archaea. Little is known about the mechanisms that enable this relationship. RESULTS: We sequenced the complete genome of I. hospitalis and found it to be the smallest among independent, free-living organisms. A comparative genomic reconstruction suggests that the I. hospitalis lineage has lost most of the genes associated with a heterotrophic metabolism that is characteristic of most of the Crenarchaeota. A streamlined genome is also suggested by a low frequency of paralogs and fragmentation of many operons. However, this process appears to be partially balanced by lateral gene transfer from archaeal and bacterial sources. CONCLUSIONS: A combination of genomic and cellular features suggests highly efficient adaptation to the low energy yield of sulfur-hydrogen respiration and efficient inorganic carbon and nitrogen assimilation. Evidence of lateral gene exchange between N. equitans and I. hospitalis indicates that the relationship has impacted both genomes. This association is the simplest symbiotic system known to date and a unique model for studying mechanisms of interspecific relationships at the genomic and metabolic levels.
Date: September 1, 2008
Creator: Sun, Hui; Anderson, Iain; Makarova, Kira S.; Elkins, James G.; Ivanova, Natalia; Wall, Mark A. et al.
Partner: UNT Libraries Government Documents Department


Description: The catastrophic 'pancake' fragmentation process, proposed as being generally applicable to very large meteoroid entry in the early 1990's by a number of workers, has been carefully examined. In this effort, the transition from the traditional single-body dynamics and energetics model to a catastrophic 'pancake' fragmentation process has been delineated. The key parameters are the {mu} parameter originally proposed by Levin and the fragmentation scale height, Hf, which we have derived from {mu}. It has been found that this break-up process can only occur for an optimum set of circumstances.
Date: January 1, 2001
Creator: ReVelle, D. O. (Douglas O.)
Partner: UNT Libraries Government Documents Department

Ductile damage model with void coalescence

Description: A general model for ductile damage in metals is presented. It includes damage induced by shear stress as well as damage caused by volumetric tension. Spallation is included as a special case. Strain induced damage is also treated. Void nucleation and growth are included and give rise to strain rate effects. Strain rate effects also arise in the model through elastic release wave propagation between damage centers. Underlying physics of the model is the nucleation, growth, and coalescence of voids in a plastically flowing solid. Implementation of the model in hydrocodes is discussed.
Date: March 1, 1995
Creator: Tonks, D.L.
Partner: UNT Libraries Government Documents Department

Jet fragmentation properties at the Tevatron

Description: Preliminary CDF results on inclusive momentum distributions of charged particles in high transverse momentum jets produced in {anti p}p collisions at {radical}s=1.8 TeV at the Tevatron are presented and compared with QCD predictions based on the Modified Leading Log Approximation.
Date: May 16, 1997
Creator: Goulianos, K.
Partner: UNT Libraries Government Documents Department