3,978 research outputs found

    What is the Physics behind the 3He-4He Anomaly ?

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    We show that coalescence of nucleons emitted prior to thermalization in highly excited nuclei can explain the anomaly of kinetic energies of helium clusters. A new coalescence algorithm has been included into the statistical approach to nuclear reactions formerly used to describe intermediate mass fragment production.Comment: 5 pages, 4 figures, accepted at Eur. Phys.

    Probing the density dependence of the symmetry potential with peripheral heavy-ion collisions

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    The peripheral heavy-ion collisions of 112,124Sn+86Kr^{112, 124}Sn+ ^{86}Kr at Eb=25AMeVE_{b}= 25AMeV are studied by means of the Improved Quantum Molecular Dynamics Model(ImQMD). It is shown that the slope of the average N/Z ratio of emitted nucleons vs impact parameters for these reactions is very sensitive to the density dependence of the symmetry energy. Our study also shows that the yields of 3H^{3}H and 3He^{3}He decrease with impact parameters and slope of the yield of 3H^{3}H vs impact parameters as well as the ratio of Y(3H^{3}H)/Y(3He^{3}He) depend on the symmetry potential strongly for peripheral heavy-ion collisions.Comment: 10 pages,6 figures, accepted by Phys.Rev.

    Invariant Operators in Collinear Effective Theory

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    We consider processes which produce final state hadrons whose energy is much greater than their mass. In this limit interactions involving collinear fermions and gluons are constrained by a symmetry, and we give a general set of rules for constructing leading and subleading invariant operators. Wilson coefficients C(mu,P) are functions of a label operator P, and do not commute with collinear fields. The symmetry is used to reproduce a two-loop result for factorization in B -> D pi in a simple way.Comment: 11 pages, 2 figs, journal versio

    A Consistent Calculation of Heavy Meson Decay Constants and Transition Wave Functions in the Complete HQEFT

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    Within the complete heavy quark effective field theory (HQEFT), the QCD sum rule approach is used to evaluate the decay constants including 1/m_Q corrections and the Isgur-Wise function and other additional important wave functions concerned at 1/m_Q for the heavy-light mesons. The 1/m_Q corrections to the scaling law f_M \sim F/\sqrt{m_M} are found to be small in HQEFT, which demonstrates again the validity of 1/m_Q expansion in HQEFT. It is also shown that the residual momentum v.k of heavy quark within hadrons does be around the binding energy \bar{\Lambda} of the heavy hadrons. The calculations presented in this paper provide a consistent check on the HQEFT and shows that the HQEFT is more reliable than the usual HQET for describing a slightly off-mass shell heavy quark within hadron as the usual HQET seems to lead to the breakdown of 1/m_Q expansion in evaluating the meson decay constants. It is emphasized that the introduction of the `dressed heavy quark' mass is useful for the heavy-light mesons (Qq) with m_Q >> \bar{\Lambda} >> m_q, while for heavy-heavy bound states (\psi_1\psi_2) with masses m_1, m_2 >> \bar{\Lambda}, like bottom-charm hadrons or similarly for muonium in QED, one needs to treat both particles as heavy effective particles via 1/m_1 and 1/m_2 expansions and redefine the effective bound states and modified `dressed heavy quark' masses within the HQEFT.Comment: 20 pages, revtex, 22 figures, axodraw.sty, two irrelevant figures are moved awa

    Peculiarities of isotopic temperatures obtained from p+A collisions at 1 GeV

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    Nuclear temperatures obtained from inclusive measurements of double isotopic yield ratios of fragments produced in 1 GeV p + A collisions amount to about 4 MeV nearly independent from the target mass.Comment: 4 pages, 4 figures, to be submitted to Eur. Phys. J.

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    Subleading Shape Functions in Inclusive B Decays

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    The contributions of subleading shape functions to inclusive decay distributions of B mesons are derived from a systematic two-step matching of QCD current correlators onto soft-collinear and heavy-quark effective theory. At tree-level, the results can be expressed in terms of forward matrix elements of bi-local light-cone operators. Four-quark operators, which arise at O(g^2), are included. Their effects can be absorbed entirely into a redefinition of other shape functions. Our results are in disagreement with some previous studies of subleading shape-function effects in the literature. A numerical analysis of B->X_u+l+nu decay distributions suggests that power corrections are small, with the possible exception of the endpoint region of the charged-lepton energy spectrum.Comment: 22 pages, 2 figures; several typos corrected; version published in JHE

    Semileptonic B Decays into Excited Charmed Mesons (D1D_1, D2D^*_2) in HQEFT

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    Exclusive semileptonic B decays into excited charmed mesons (D1D_1, D2D^*_2) are studied up to the order of 1/mQ1/m_Q in the framework of the heavy quark effective field theory (HQEFT), which contains the contributions of both particles and antiparticles. Two wave functions η0b\eta^b_0 and η0c\eta^c_0, which characterize the contributions from the kinematic operator at the order of 1/mQ1/m_Q, are calculated by using QCD sum rule approach in HQEFT. Zero recoil values of other two wave functions κ1\kappa'_1 and κ2\kappa'_2 are extracted from the excited charmed-meson masses. Possible effects from the spin-dependent transition wave functions which arise from the magnetic operators at the order of 1/mQ1/m_Q are analyzed. It is shown that the experimental measurements for the branching ratios of BD1lνB \to D_1 l\nu and BD2lνB \to D^*_2 l\nu can be understood in the framework of HQEFT.Comment: 27 pages, RevTex, 4 figures, 3 tables, to be published in IJMP

    Proposal for a Precision Measurement of |Vub|

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    A new method for a precision measurement of the CKM matrix element |Vub| is discussed, which combines good theoretical control with high efficiency and a powerful discrimination against charm background. The resulting combined theoretical uncertainty on |Vub| is estimated to be 10%.Comment: 4 pages, 2 figures, RevTe

    Limits of complete equilibration of fragments produced in central Au on Au collisions at intermediate energies

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    Experimental data related to fragment production in central Au on Au collisions were analyzed in the framework of a modified statistical model which considers cluster production both prior and at the equilibrated stage. The analysis provides limits to the number of nucleons and to the temperature of the equilibrated source. The rather moderate temperatures obtained from experimental double-yield ratios of d,t,3He and 4He are in agreement with the model calculations. A phenomenological relation was established between the collective flow and the chemical temperature in these reactions. It was shown that dynamical mechanisms of fragment production, e.g. coalescence, dominate at high energies. It is demonstrated that coalescence may be consistent with chemical equilibrium between the produced fragments. The different meaning of chemical and kinetic temperatures is discussed.Comment: 13 pages, 10 figures, accepted at EPJ