2,415 research outputs found
The initial energy density of gluons produced in very high energy nuclear collisions
In very high energy nuclear collisions, the initial energy of produced gluons
per unit area per unit rapidity, , is equal to , where is proportional to the gluon density per unit
area of the colliding nuclei. For an SU(2) gauge theory, we perform a
non--perturbative numerical computation of the function . It
decreases rapidly for small but varies only by %, from
to , for a wide range 35.36--296.98 in , including the range relevant for collisions at RHIC and LHC. Extrapolating
to SU(3), we estimate the initial energy per unit rapidity for Au-Au collisions
in the central region at RHIC and LHC.Comment: 11 pages, Latex, 3 figures; revised version-includes additional
numerical data; reference adde
Forward Quark Jets from Protons Shattering the Colored Glass
We consider the single-inclusive minijet cross section in pA at forward
rapidity within the Color Glass Condensate model of high energy collisions. We
show that the nucleus appears black to the incident quarks except for very
large impact parameters. A markedly flatter p_t distribution as compared to QCD
in the dilute perturbative limit is predicted for transverse momenta about the
saturation scale, which could be as large as Q_s^2 ~ 10 GeV^2 for a gold
nucleus boosted to rapidity ~10 (as at the BNL-RHIC).Comment: 9 pages, no figure
Hard Parton Rescatterings and Minijets in Nuclear Collisions at LHC
The average number of minijets and the corresponding transverse energy
produced in heavy ion collisions are evaluated by including explicitly
semi-hard parton rescatterings in the dynamics of the interaction. At the LHC
semi-hard rescatterings have a sizable effect on global characteristics of the
typical inelastic event. An interesting feature is that the dependence on the
cutoff which separates soft and hard parton interactions becomes less critical
after taking rescatterings into account.Comment: 14 pages, 3 figures. Enlarged discussion in sect.1 and 4; 1 figure
added. To be published in Phys.Rev.
The lifespan method as a tool to study criticality in absorbing-state phase transitions
In a recent work, a new numerical method (the lifespan method) has been
introduced to study the critical properties of epidemic processes on complex
networks [Phys. Rev. Lett. \textbf{111}, 068701 (2013)]. Here, we present a
detailed analysis of the viability of this method for the study of the critical
properties of generic absorbing-state phase transitions in lattices. Focusing
on the well understood case of the contact process, we develop a finite-size
scaling theory to measure the critical point and its associated critical
exponents. We show the validity of the method by studying numerically the
contact process on a one-dimensional lattice and comparing the findings of the
lifespan method with the standard quasi-stationary method. We find that the
lifespan method gives results that are perfectly compatible with those of
quasi-stationary simulations and with analytical results. Our observations
confirm that the lifespan method is a fully legitimate tool for the study of
the critical properties of absorbing phase transitions in regular lattices
Non-linear evolution in CCFM: The interplay between coherence and saturation
We solve the CCFM equation numerically in the presence of a boundary
condition which effectively incorporates the non-linear dynamics. We retain the
full dependence of the unintegrated gluon distribution on the coherence scale,
and extract the saturation momentum. The resulting saturation scale is a
function of both rapidity and the coherence momentum. In Deep Inelastic
Scattering this will lead to a dependence of the saturation scale on the photon
virtuality in addition to the usual x-Bjorken dependence. At asymptotic
energies the interplay between the perturbative non-linear physics, and that of
the QCD coherence, leads to an interesting and novel dynamics where the
saturation momentum itself eventually saturates. We also investigate various
implementations of the "non-Sudakov" form factor. It is shown that the
non-linear dynamics leads to almost identical results for different form
factors. Finally, different choices of the scale of the running coupling are
analyzed and implications for the phenomenology are discussed.Comment: 37 pages, 21 figure
From colored glass condensate to gluon plasma: equilibration in high energy heavy ion collisions
The initial distribution of gluons at the very early times after a high
energy heavy ion collision is described by the bulk scale of gluon
saturation in the nuclear wavefunction. The subsequent evolution of the system
towards kinetic equilibrium is described by a non-linear Landau equation for
the single particle distributions \cite{Mueller1,Mueller2}. In this paper, we
solve this equation numerically for the idealized initial conditions proposed
by Mueller, and study the evolution of the system to equilibrium. We discuss
the sensitivity of our results on the dynamical screening of collinear
divergences. In a particular model of dynamical screening, the convergence to
the hydrodynamic limit is seen to be rapid relative to hydrodynamic time
scales. The equilibration time, the initial temperature, and the chemical
potential are shown to have a strong functional dependence on the initial gluon
saturation scale .Comment: 34 pages, 10 figure
The Eruption from a Sigmoidal Solar Active Region on 2005 May 13
This paper presents a multiwavelength study of the M8.0 flare and its
associated fast halo CME that originated from a bipolar active region NOAA
10759 on 2005 May 13. The source active region has a conspicuous sigmoid
structure at TRACE 171 A channel as well as in the SXI soft X-ray images, and
we mainly concern ourselves with the detailed process of the sigmoid eruption
as evidenced by the multiwavelength data ranging from Halpha, WL, EUV/UV,
radio, and hard X-rays (HXRs). The most important finding is that the flare
brightening starts in the core of the active region earlier than that of the
rising motion of the flux rope. This timing clearly addresses one of the main
issues in the magnetic eruption onset of sigmoid, namely, whether the eruption
is initiated by an internal tether-cutting to allow the flux rope to rise
upward or a flux rope rises due to a loss of equilibrium to later induce tether
cutting below it. Our high time cadence SXI and Halpha data shows that the
first scenario is relevant to this eruption. As other major findings, we have
the RHESSI HXR images showing a change of the HXR source from a confined
footpoint structure to an elongated ribbon-like structure after the flare
maximum, which we relate to the sigmoid-to-arcade evolution. Radio dynamic
spectrum shows a type II precursor that occurred at the time of expansion of
the sigmoid and a drifting pulsating structure in the flare rising phase in
HXR. Finally type II and III bursts are seen at the time of maximum HXR
emission, simultaneous with the maximum reconnection rate derived from the
flare ribbon motion in UV. We interpret these various observed properties with
the runaway tether-cutting model proposed by Moore et al. in 2001.Comment: 10 pages, 10 figures, The Astrophysical Journal, accepted July, 200
Saturation and Wilson Line Distributions
We introduce a Wilson line distribution function bar{W}_tau(v) to study gluon
saturation at small Feynman x_F, or large tau=ln(1/x_F). This new distribution
can be obtained from the distribution W_tau(alpha) of the Color Glass
Condensate model and the JIMWLK renormalization group equation. bar{W}_tau(v)
is physically more relevant, and mathematically simpler to deal with because of
unitarity of the Wilson line v. A JIMWLK equation is derived for bar{W}_tau(v);
its properties are studied. These properties are used to complete Mueller's
derivation of the JIMWLK equation, though for bar{W}_tau(v) and not
W_tau(alpha). They are used to derive a generalized Balitsky-Kovchegov equation
for higher multipole amplitudes. They are also used to compute the unintegrated
gluon distribution at x_F=0, yielding a completely flat spectrum in transverse
momentum squared k^2, with a known height. This is similar but not identical to
the mean field result at small k^2.Comment: One reference and two short comments added. To appear in Physical
Revies
Coherent gluon production in very high energy heavy ion collisions
The early stages of a relativistic heavy-ion collision are examined in the
framework of an effective classical SU(3) Yang-Mills theory in the transverse
plane. We compute the initial energy and number distributions, per unit
rapidity, at mid-rapidity, of gluons produced in high energy heavy ion
collisions. We discuss the phenomenological implications of our results in
light of the recent RHIC data.Comment: 4 pages, 2 figure
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