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Nuclear Theory·nucl-th

Monday·May 23, 2016

3 papers—1 primary·2 cross-listed

All3Primary1Cross-lists2
  1. 02

    [Submitted on 20 May 2016] (cross-list from hep-ph)

    Employing Helicity Amplitudes for Resummation in SCET

    Ian Moult🇺🇸 · Iain W. Stewart🇺🇸 · Frank J. Tackmann🇩🇪 · Wouter J. Waalewijn🇳🇱

    Helicity amplitudes are the fundamental ingredients of many QCD calculations for multi-leg processes. We describe how these can seamlessly be combined with resummation in Soft-Collinear Effective Theory (SCET), by constructing a helicity operator basis for which the Wilson coefficients are directly given in terms of color-ordered helicity amplitudes. This basis is crossing symmetric and has simple transformation properties under discrete symmetries.

    Comments:
    4 pages, 1 figures, to appear in the proceedings of the 51st Rencontres de Moriond (QCD and High Energy Interactions)
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1605.06226 [pdf]
    2 citations
  2. 03

    [Submitted on 20 May 2016] (cross-list from nucl-ex)

    Importance of lifetime effects in breakup and suppression of complete fusion in reactions of weakly bound nuclei

    K.J. Cook · E.C. Simpson · D.H. Luong · Sunil Kalkal · M. Dasgupta · D.J. Hinde

    Complete fusion cross sections in collisions of light, weakly bound nuclei and high Z targets show above-barrier suppression of complete fusion. This has been interpreted as resulting from breakup of the weakly bound nucleus prior to reaching the fusion barrier, reducing the probability of complete fusion. This paper investigates how these conclusions are affected by lifetimes of the resonant states that are populated prior to breakup. If the mean life of a populated resonance is much longer than the fusion timescale, then its breakup cannot suppress complete fusion. For short-lived resonances, the situation is more complex. This work includes the mean life of the short-lived 2+ resonance in 8Be in classical dynamical model calculations to determine its effect on energy and angular correlations of the breakup fragments and on predictions of fusion suppression. Coincidence measurements of breakup fragments produced in reactions of 9Be with 144Sm, 168Er, 186W, 196Pt, 208Pb and 209Bi at energies below the barrier are re-analysed. Predictions of breakup observables and of complete and incomplete fusion at energies above the fusion barrier are made using the classical dynamical simulation code PLATYPUS, modified to include the lifetimes of short-lived resonant states. The agreement of the breakup observables is improved when lifetime effects are included. The predicted suppression of complete fusion due to breakup is nearly independent of Z, with an average value of 9%, below the experimentally determined fusion suppression of 30% in these systems. This more realistic treatment of breakup leads to the conclusion that the suppression of complete fusion cannot be fully explained by breakup prior to reaching the fusion barrier. Other mechanisms that can suppress complete fusion must be investigated. A candidate is cluster transfer that produces the same nuclei as incomplete fusion.

    Comments:
    16 pages, 10 figures. Accepted as a Regular Article in Physical Review C
    Subjects:
    Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    1605.06237 [pdf]
    PRC(2016)·36 citations

Affiliations

first authorsco-authorsvia INSPIRE