3,978 research outputs found

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

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

The peripheral heavy-ion collisions of $^{112, 124}Sn+ ^{86}Kr$ at $E_{b}=
25AMeV$ 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 $^{3}H$ and $^{3}He$ decrease with impact parameters and slope of the yield
of $^{3}H$ vs impact parameters as well as the ratio of Y($^{3}H$)/Y($^{3}He$)
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

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

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

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.

### Subleading Shape Functions in Inclusive B Decays

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 ($D_1$, $D^*_2$) in HQEFT

Exclusive semileptonic B decays into excited charmed mesons ($D_1$, $D^*_2$)
are studied up to the order of $1/m_Q$ in the framework of the heavy quark
effective field theory (HQEFT), which contains the contributions of both
particles and antiparticles. Two wave functions $\eta^b_0$ and $\eta^c_0$,
which characterize the contributions from the kinematic operator at the order
of $1/m_Q$, are calculated by using QCD sum rule approach in HQEFT. Zero recoil
values of other two wave functions $\kappa'_1$ and $\kappa'_2$ 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 $1/m_Q$ are analyzed. It is shown that the experimental measurements for the
branching ratios of $B \to D_1 l\nu$ and $B \to D^*_2 l\nu$ 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|

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

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

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