Single spin asymmetry in inclusive pion production, Collins effect and the string model

We calculate the single spin asymmetry in the inclusive pion production in proton-proton collisions. We generate the asymmetry at the level of fragmentation function (Collins effect) by the Lund coloured string mechanism. We compare our results with the Fermilab E704 data from polarized proton-proton collisions at 200 GeV. We show that the transversely polarized quark densities at high Bjorken x strongly differ from these predicted by the SU(6) proton wave function.Comment: (11 pages in TeX; 7 figures in PS files available upon request) LYCEN/9423, TPJU 12/9

Exclusive ηc\eta_c photo- and electroproduction at HERA as a possible probe of the odderon singularity in QCD

Theory and phenomenology of the eta_c photo- and electroproduction is developed from the point of view of probing the odderon singularity in QCD which corresponds to the three gluon exchange mechanism. This mechanism leads to the cross-sections which are independent of W^2 for the exchange of three non-interacting gluons or exhibit increase with increasing W^2 (or 1/x) for the odderon intercept above unity. The \eta_c electroproduction in the three gluon exchange mechanism is shown to be entirely controlled by the transversely polarised virtual photons. The magnitude of the eta_c photoproduction cross-section is estimated to be around 11-45pb. The t-dependence of the differential cross-section is also discussed.Comment: 9 pages, LaTeX, uses epsfig.sty; Numerical error corrected. A factor of 1/3 missing in amplitude in Eq.(8) added. Obtained gamma p -> eta_c p cross-section smaller by a factor of 9 than in the original version of the paper. Figures 4 and 5 changed accordingl

Nuclear Attenuation of high energy two-hadron system in the string model

Nuclear attenuation of the two-hadron system is considered in the string model. The two-scale model and its improved version with two different choices of constituent formation time and sets of parameters obtained earlier for the single hadron attenuation, are used to describe available experimental data for the $z$-dependence of subleading hadron, whereas satisfactory agreement with the experimental data has been observed. A model prediction for $\nu$-dependence of the nuclear attenuation of the two-hadron system is also presented.Comment: 8 page

Agreement between prospective diary data and retrospective questionnaire report of abdominal pain and stooling symptoms in children with irritable bowel syndrome

BACKGROUND: In functional gastrointestinal disorders, patient recall of symptoms drives diagnostic decisions and evaluation of treatment response, and research conclusions about potential treatments. In pediatrics, parent report also impacts assessment and care. Hence, identifying methods for accurately capturing patient and parent report of irritable bowel syndrome (IBS) symptoms is important. This study evaluated correspondence between retrospective questionnaire (parent and child report) and prospective diary data for children and adolescents with IBS. METHODS: Participants included 50 children/adolescents with IBS per Rome III criteria. Children completed a 2-week pain and stool diary. Children and parents subsequently completed a 2-week recall questionnaire, reporting number of pain days, maximum pain, days without bowel movement, and days with diarrhea during the diary interval. Intraclass correlation coefficients and Bland-Altman plots assessed agreement. KEY RESULTS: For pain and days without bowel movement, overall agreement between child recall questionnaire and child diary was strong, although under conditions likely to facilitate agreement and with individual variation observed. Parent recall and child diary were less concordant, and agreement about diarrhea was poor for parent and child. Age did not significantly correlate with agreement. CONCLUSIONS & INFERENCES: Child questionnaire with short recall interval may be a reasonable approximation for diary data, although this varies by individual and replication/investigation of lengthier recall are needed. Relying on parent questionnaire does not appear a suitable proxy, and recall of stool form by both parent and child appears more problematic. These results combined with existing literature support use of diary data whenever possible

A global reanalysis of nuclear parton distribution functions

We determine the nuclear modifications of parton distribution functions of bound protons at scales $Q^2\ge 1.69$ GeV$^2$ and momentum fractions $10^{-5}\le x\le 1$ in a global analysis which utilizes nuclear hard process data, sum rules and leading-order DGLAP scale evolution. The main improvements over our earlier work {\em EKS98} are the automated $\chi^2$ minimization, simplified and better controllable fit functions, and most importantly, the possibility for error estimates. The resulting 16-parameter fit to the N=514 datapoints is good, $\chi^2/{\rm d.o.f}=0.82$. Within the error estimates obtained, the old {\em EKS98} parametrization is found to be fully consistent with the present analysis, with no essential difference in terms of $\chi^2$ either. We also determine separate uncertainty bands for the nuclear gluon and sea quark modifications in the large-$x$ region where they are not stringently constrained by the available data. Comparison with other global analyses is shown and uncertainties demonstrated. Finally, we show that RHIC-BRAHMS data for inclusive hadron production in d+Au collisions lend support for a stronger gluon shadowing at $x<0.01$ and also that fairly large changes in the gluon modifications do not rapidly deteriorate the goodness of the overall fits, as long as the initial gluon modifications in the region $x\sim 0.02-0.04$ remain small.Comment: 33 pages, 14 figure

Estimate of the Collins fragmentation function in a chiral invariant approach

We predict the features of the Collins function, which describes the fragmentation of a transversely polarized quark into an unpolarized hadron, by modeling the fragmentation process at a low energy scale. We use the chiral invariant approach of Manohar and Georgi, where constituent quarks and Goldstone bosons are considered as effective degrees of freedom in the non-perturbative regime of QCD. To test the approach we calculate the unpolarized fragmentation function and the transverse momentum distribution of a produced hadron, both of which are described reasonably well. In the case of semi-inclusive deep-inelastic scattering, our estimate of the Collins function in connection with the transversity distribution gives rise to a transverse single spin asymmetry of the order of 10%, supporting the idea of measuring the transversity distribution of the nucleon in this way. In the case of e+ e- annihilation into two hadrons, our model predicts a Collins azimuthal asymmetry of about 5%.Comment: 12 pages, 15 figures. Figs. 11-14 changed, minor changes in discussion, few typos fixed and some references added. Final version to appear in PR

Transverse polarization of quark pairs created in string fragmentation

Classical arguments predict that the quark and the antiquark of a pair created during string fragmentation are both transversely polarized in the direction of \hat z \times \vec q_T, where z is the direction of the pull exerted by the string on the antiquark and \vec q_T (-\vec q_T) is the transverse momentum of the quark (antiquark). The existence of this effect at the quantum-mechanical level is investigated by considering two analogous processes involving the tunnel effect in a strong field: (1) dissociation of the positronium atom (2) electron pair creation. In case (1) the positronium is taken in the 3P_0 state to simulate the vacuum quantum numbers J^PC = 0^++. Using the nonrelativistic WKB method, the final electron and positron are indeed found to be transversely polarized along \hat z \times \vec p_T. On the contrary, case (2), treated with the Dirac equation, shows no correlation between transverse polarization and transverse momentum both when the field is uniform and when it depends on z and t. The pair is nevertheless produced in a triplet spin state. The difference between these two results and their relevance to transverse spin asymmetry in inclusive reactions is discussed.Comment: 13 pages, 5 figures, uses epsfig.sty, to be published in Acta Physica Polonica

Nuclear Hadronization: Within or Without?

Nuclei are unique analyzers for the early stage of the space-time development of hadronization. DIS at medium energies is especially suitable for this task being sensitive to hadronization dynamics, since the production length is comparable with the nuclear size. This was the driving motivation to propose measurements at HERMES using nuclear targets, and to provide predictions based on a pQCD model of hadronization [1]. Now when the first results of the experiment are released [2,3], one can compare the predictions with the data. The model successfully describes with no adjustment the nuclear effects for various energies, zh, pT, and Q2, for different flavors and different nuclei. It turns out that the main source of nuclear suppression of the hadron production rate is attenuation of colorless pre-hadrons in the medium. An alternative model [4] is based upon an ad hoc assumption that the colorless pre-hadron is produced outside the nucleus. This model has apparent problems attempting to explain certain features of the results from HERMES. A good understanding of the hadronization dynamics is important for proper interpretation of the strong suppression of high-pT hadrons observed in heavy ion collisions at RHIC. We demonstrate that the production length is even shorter in this case and keeps contracting with rising pT.Comment: Latex 34 p. Based on talks given by B.Z.K. at the Fourth International Conference on Perspectives in Hadronic Physics, Trieste, Italy, May 12-16, 2003; and at the EuroConference on Hadron Structure Viewed with Electromagnetic Probes, Santorini, Greece, October 7-12, 200

ETHICS INSTRUCTION AND CULTURAL DIFFERENCES IN AN MBA MANAGEMENT ACCOUNTING COURSE

This article discusses a study designed to yield improvements in student moral reasoning when specific instructional strategies and materials for teaching ethical decision making were utilized in a non-ethics MBA management accounting course taught by an instructor who was not formally trained in business ethics. The study reported in this article was conducted in a graduate management accounting course with domestic and foreign students. The specific intervention strategies and instructional materials utilized were developed through several iterations of developmental research that were carried out over a four-year period at a mid-sized Midwestern university. The measurement of moral reasoning used in all of the research was the revised version of the Defining Issues Test, the DIT-2 (Rest, Narvaez, Bebeau & Thoma, 1999). This research was originally funded by a grant from the Lilly Endowment