3,230 research outputs found
Flow Study in Relativistic Nuclear Collisions by Fourier Expansion of Azimuthal Particle Distributions
We propose a new method to study transverse flow effects in relativistic
nuclear collisions by Fourier analysis of the azimuthal distribution on an
event-by-event basis in relatively narrow rapidity windows. The distributions
of Fourier coefficients provide direct information on the magnitude and type of
flow. Directivity and two dimensional sphericity tensor, widely used to analyze
flow, emerge naturally in our approach, since they correspond to the
distributions of the first and second harmonic coefficients, respectively. The
role of finite particle fluctuations and particle correlations is discussed.Comment: 14 pages, 3 figures included as figures.uu at the end, REVTE
Hadronic Transition chi(c1)(1P) to eta(c) plus two pions at the Beijing Spectrometer BES and the Cornell CLEO-c
Hadronic transitions of the chi(cj)(1P) states have not been studied yet. We
calculate the rate of the hadronic transition chi(c1)(1P) to eta(c) plus two
pions in the framework of QCD multipole expansion. We show that this process
can be studied experimentally at the upgraded Beijing Spectrometer BES III and
the Cornell CLEO-c.Comment: 6 pages RevTex4(two-column). Version published in Phys. Rev. D 75,
054019 (2007
Particle decay in false vacuum
We revisit the problem of decay of a metastable vacuum induced by the
presence of a particle. For the bosons of the `master field' the problem is
solved in any number of dimensions in terms of the spontaneous decay rate of
the false vacuum, while for a fermion we find a closed expression for the decay
rate in (1+1) dimensions. It is shown that in the (1+1) dimensional case an
infrared problem of one-loop correction to the decay rate of a boson is
resolved due to a cancellation between soft modes of the field. We also find
the boson decay rate in the `sine-Gordon staircase' model in the limits of
strong and weak coupling.Comment: 19 pages, 2 figure
Large Component QCD and Theoretical Framework of Heavy Quark Effective Field Theory
Based on a large component QCD derived directly from full QCD by integrating
over the small components of quark fields with , an
alternative quantization procedure is adopted to establish a basic theoretical
framework of heavy quark effective field theory (HQEFT) in the sense of
effective quantum field theory. The procedure concerns quantum generators of
Poincare group, Hilbert and Fock space, anticommutations and velocity
super-selection rule, propagator and Feynman rules, finite mass corrections,
trivialization of gluon couplings and renormalization of Wilson loop. The
Lorentz invariance and discrete symmetries in HQEFT are explicitly illustrated.
Some new symmetries in the infinite mass limit are discussed. Weak transition
matrix elements and masses of hadrons in HQEFT are well defined to display a
manifest spin-flavor symmetry and corrections. A simple trace
formulation approach is explicitly demonstrated by using LSZ reduction formula
in HQEFT, and shown to be very useful for parameterizing the transition form
factors via expansion. As the heavy quark and antiquark fields in HQEFT
are treated on the same footing in a fully symmetric way, the quark-antiquark
coupling terms naturally appear and play important roles for simplifying the
structure of transition matrix elements, and for understanding the concept of
`dressed heavy quark' - hadron duality. In the case that the `longitudinal' and
`transverse' residual momenta of heavy quark are at the same order of power
counting, HQEFT provides a consistent approach for systematically analyzing
heavy quark expansion in terms of . Some interesting features in
applications of HQEFT to heavy hadron systems are briefly outlined.Comment: 59 pages, RevTex, no figures, published versio
Transition Form Factors and Decay Rates with Extraction of the CKM parameters , ,
A systematic calculation for the transition form factors of heavy to light
mesons () is carried out
by using light-cone sum rules in the framework of heavy quark effective field
theory. The heavy quark symmetry at the leading order of expansion
enables us to reduce the independent wave functions and establish interesting
relations among form factors. Some relations hold for the whole region of
momentum transfer. The meson distribution amplitudes up to twist-4 including
the contributions from higher conformal spin partial waves and light meson mass
corrections are considered. The CKM matrix elements , and
are extracted from some relatively well-measured decay channels. A
detailed prediction for the branching ratios of heavy to light meson decays is
then presented. The resulting predictions for the semileptonic and radiative
decay rates of heavy to light mesons () are found to be compatible with the current experimental data
and can be tested by more precise experiments at B-factory, LHCb, BEPCII and
CLEOc.Comment: 23 pages, 32 figures, 25 tables,published version, minor corrections
and references adde
Ultrasoft contribution to heavy-quark pair production near threshold
We compute the third-order correction to the heavy-quark current correlation
function due to the emission and absorption of an ultrasoft gluon. Our result
supplies a missing contribution to top-quark pair production near threshold and
the determination of the bottom quark mass from QCD sum rules.Comment: 10 pages, LaTe
A Remark on Supersymmetric Bubbles and Spectrum Crossover
Using an exact expression for the domain wall tension in a supersymmetric
model we show that a spectrum crossover takes place in passing from weak to
strong coupling. In the weak coupling regime elementary excitations are the
lightest states, while in the strong coupling regime solitonic objects of a
special type -- bubbles -- assume the role of the lightest states. The
crossover occurs at \lambda^2/(4\pi) \sim 0.4.Comment: 6 p., 1 fi
Directed and Elliptic Flow in Pb+Pb collisions at 40 and 158 AGeV
Directed and elliptic flow are reported for charged pions and protons as a
function of transverse momentum, rapidity, and centrality in 40 and 158 AGeV Pb
+ Pb collisions. The standard method of correlating particles with an event
plane is used. The directed flow of protons is small and shows little variation
near to midrapidity, but rises fast towards projectile rapidity in the 40 AGeV
data. For most peripheral collisions the flat region becomes negative resulting
in changing sign three times. Elliptic flow doesn't seem to change very
much from 40 AGeV to 158 AGeV. The difference is smaller than anticipated from
the overall energy dependence from AGS to RHIC.Comment: Presented at 16th International Conference on Ultrarelativistic
Nucleus-Nucelus Collisions, Quark Matter 2002 (QM 2002), Nantes, France,
18-24 Jul 2002, 4 pages, 3 figure
Characterization and analysis of azimuthally sensitive correlations
A unified framework for describing the azimuthal dependence of two-particle
correlations in heavy-ion collisions is introduced, together with the methods
for measuring the corresponding observables. The generalization to azimuthal
correlations between more than two particles is presented.Comment: 7 pages; talk given at Hot Quarks 2004, Taos (NM), July 18-24,200
Once again on electromagnetic properties of a domain wall interacting with charged fermions
The response to a magnetic flux is considered of the vacuum state of charged
Dirac fermions interacting with a domain wall made of a neutral spinless field
in (3+1) dimensions with the fermion mass having a phase variation across the
wall. It is pointed out that due to simple C parity arguments the spontaneous
magnetization for this system is necessarily zero, thus invalidating some
claims to the contrary in the literature. The cancellation of the spontaneous
magnetization is explicitly demonstrated in a particular class of models. The
same calculation produces a general formula for the electric charge density
induced by the magnetic flux -- an effect previously discussed in the
literature for axionic domain walls. The distribution of the induced charge is
calculated in specific models.Comment: 15 page
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