共查询到20条相似文献,搜索用时 31 毫秒
1.
We investigate the properties of qq and
states in hot and dense quark matter in the framework of light-front finite-temperature field theory. Presently we use the Nambu–Jona-Lasinio model of QCD and derive the gap equation at finite temperature and density. We study pionic and scalar diquark dynamics in quark matter and calculate the masses and the Mott dissociation as a function of the temperature T and the chemical potential μ. For the scalar diquark we determine the critical temperature of color superconductivity. 相似文献
2.
Di-jet production is studied in collisions of quasi-real photons at e + e- centre-of-mass energies
from 189 to 209 GeV at LEP. The data were collected with the OPAL detector. Jets are reconstructed using an inclusive
-clustering algorithm for all cross-section measurements presented. A cone jet algorithm is used in addition to study the different structure of the jets resulting from either of the algorithms. The inclusive di-jet cross-section is measured as a function of the mean transverse energy
of the two leading jets, and as a function of the estimated fraction of the photon momentum carried by the parton entering the hard sub-process,
, for different regions of
. Angular distributions in di-jet events are measured and used to demonstrate the dominance of quark and gluon initiated processes in different regions of phase space. Furthermore the inclusive di-jet cross-section as a function of
and
is presented, where
is the jet pseudo-rapidity. Different regions of the
-
-space are explored to study and control the influence of an underlying event. The results are compared to next-to-leading order perturbative QCD calculations and to the predictions of the leading order Monte Carlo generator PYTHIA.Received: 20 December 2002, Published online: 17 October 2003 相似文献
3.
A. Morsch 《The European Physical Journal C - Particles and Fields》2005,43(1-4):333-336
In central Pb-Pb collisions at the LHC, jet rates are expected to be high at energies at which ALICE can reconstruct jets
over the background of the underlying event. This will open the possibility to quantify the effect of partonic energy loss
through medium induced gluon radiation, jet quenching, by detailed measurement of the modification of the longitudinal and transverse structure of identified jets. In order to
obtain probes sensitive to the properties of the QCD medium, it is mandatory to measure the high-
parton fragments together with the low-
particles from the radiated gluons. Hence, the excellent charged particle tracking capabilities of ALICE combined with the
proposed electromagnetic calorimeter for ALICE, EMCAL, represent an ideal tool for jet quenching studies at the LHC.
Electronic Supplementary Material Supplementary material is available for this article at
PACS:
25.75.Nq, 24.85. + p, 13.87.-a 相似文献
4.
R. Arnaldi 《The European Physical Journal C - Particles and Fields》2005,43(1-4):167-172
The study of dilepton production in heavy-ion collisions at the CERN SPS provided some of the most interesting observations
done so far in the search for the quark gluon plasma. However, several aspects of the understanding of these measurements
need to be clarified. For example, the study of the J/
production in different colliding systems should help to disentangle which is the variable driving the J/
suppression. The NA60 experiment, with a new radiation tolerant Silicon pixel detector, studied Indium-Indium interactions
in the year 2003. In this paper, we present the J/
/ DY ratio, integrated over all the centralities of the collisions, together with a first study of the J/
transverse momentum and polarization.
Arrival of the final proofs: 1 July 2005
PACS:
25.75.Dw, 25.75.Nq, 13.20.Gd 相似文献
5.
We analyze electroproduction of light vector mesons (
) at small Bjorken-x in an approach that includes the gluonic generalized parton distributions and a partonic subprocess,
,
. The subprocess is calculated to lowest order of perturbative QCD taking into account the transverse momenta of the quark and antiquark as well as Sudakov suppressions. Our approach allows us to investigate the transition amplitudes for all kinds of polarized virtual photons and polarized vector mesons. Modeling the generalized parton distributions through double distributions and using simple Gaussian wavefunctions for the vector mesons, we compute the longitudinal and transverse cross sections at large photon virtualities as well as the spin-density matrix elements for the vector mesons. Our results are in fair agreement with the findings of recent experiments performed at HERA.Received: 3 February 2005, Revised: 9 May 2005, Published online: 28 June 2005 相似文献
6.
Measurements of on-shell ZZ production are described, using data from the DELPHI experiment at LEP in e
+
e
- collisions at centre-of-mass energies between 183 and 209 GeV, corresponding to an integrated luminosity of about 665 pb-1. Results obtained in each of the final states
,
,
,
,
, l
+
l
-
l
+
l
-, and
(with
) are presented. The measured production cross-sections are consistent with the Standard Model expectations. These results update and supersede those already published at 183 and 189 GeV.Received: 3 March 2002, Revised: 28 May 2003, Published online: 19 September 2003 相似文献
7.
Diffractive W + 2 jet production: a backgroundto exclusive $H\to W W$ production at hadron colliders
Central exclusive double-diffractive Higgs-boson production,
, is now recognised as an important search scenario for the LHC. We consider the case when the Higgs boson decays to two W bosons, one of which may be off-mass-shell, that subsequently decay to the
final state. An important background to this is from the QCD process
, where the two gluons are required to be in a Jz = 0, colour-singlet state. We perform an explicit calculation and investigate the salient properties of this potentially
important background process.
Received: 21 April 2005, Revised: 4 July 2005, Published online: 30 August 2005 相似文献
8.
9.
10.
We discuss the angular distribution of the lepton pair in the Drell-Yan process,
. This process gives information on the spin-density matrix
of the annihilating quark-antiquark pair in
. There is strong experimental evidence that even for unpolarised initial hadrons
is non-trivial, and therefore the quark-antiquark system is polarised. We discuss the possibilities of a general
- which could be entangled - and a factorising
. We argue that instantons may lead to a non-trivial
of the type indicated by experiments.Received: 6 December 2004, Published online: 9 February 2005 相似文献
11.
A model describing the leptoproduction of
mesons is considered. For the amplitude of the photon dissociation into a
pair, the light-cone wave function is used. Scattering of the colorless
pair off the nucleon is computed within reggeon exchange phenomenology. The transition of the scattered quark and antiquark into the final
meson is treated with the aid of the parton-hadron duality concept. Numerical calculations of
and r0400 describe the world data at Q2 < 4 GeV2 rather reasonably. The calculations of the
meson spin density matrix show that the computed matrix elements except r0400 are in good agreement with the available experimental data at Q2 up to 8 GeV2 and the total mass of the
system greater than 4 GeV. The Regge phenomenology predictions at the highest experimentally available energies agree with both the HERA data and calculations performed within the perturbative QCD approach even for very high Q2 (
-20 GeV2). The predicted scale of the S-channel helicity non-conservation is in reasonable agreement with the experimental data.Received: 18 September 2003, Revised: 17 December 2003, Published online: 13 February 2004 相似文献
13.
A study of Z-boson pair production in e + e- annihilation at center-of-mass energies between 190 GeV and 209 GeV is reported. Final states containing only leptons, (
and
), quark and lepton pairs, (
,
) and only hadrons (
) are considered. In all states with at least one Z boson decaying hadronically, lifetime, lepton and event-shape tags are used to separate
pairs from
final states. Limits on anomalous ZZ
and ZZZ couplings are derived from the measured cross sections and from event kinematics using an optimal observable method. Limits on low scale gravity with large extra dimensions are derived from the cross sections and their dependence on polar angle.Received: 14 July 2003, Published online: 18 December 2003 相似文献
14.
It has recently been pointed out that a new class of subleading shape functions involving B-meson matrix elements of non-local four-quark operators contributes at order
to
decay distributions in the endpoint region. The corresponding functions
and
are estimated using the vacuum-insertion approximation. A numerical analysis of various
decay spectra suggests that these power corrections are very small, below present theoretical uncertainties due to other
subleading shape-function contributions.
Received: 29 June 2005, Published online: 13 September 2005 相似文献
15.
The ZEUS inclusive differential cross-section data from HERA, for charged and neutral current processes taken with e + and e- beams, together with differential cross-section data on inclusive jet production in e + p scattering and dijet production in
scattering, have been used in a new NLO QCD analysis to extract the parton distribution functions of the proton. The input of jet-production data constrains the gluon and allows an accurate extraction of
at NLO;
An additional uncertainty from the choice of scales is estimated as
. This is the first extraction of
from HERA data alone. 相似文献
16.
Inclusive cross-sections for gluon jet production are studied numerically in the perturbative QCD pomeron model for pA and central AA collisions at high energies. Two forms for the inclusive cross-sections, with and without emission from the triple pomeron vertex, are compared. The difference was found to reduce to a numerical factor
for momenta below the saturation momentum Q
s. Above Q
s no difference was found at all. For pA collisions the gluon spectrum was found to be
at momenta k below Q
s and
above it. For central AA collisions it was found to be
at momenta k below Q
s and
above it. At large k the spectrum goes like
, flattening with energy. The multiplicities turned out to be proportional to A
0.7 for pA collisions and A for central AA collisions with a good precision. In the latter case they are becoming more peaked at the center with the growth of energy. Their absolute values are high and grow rapidly with energy in accordance with the high value of the BFKL intercept.Received: 12 October 2004, Revised: 22 November 2004, Published online: 21 January 2005 相似文献
17.
U. P. Sukhatme 《Zeitschrift fur Physik C Particles and Fields》1979,2(4):321-324
We compute observable quantities like the multiplicity and momentum distributions of hadrons in gluon and quark jets in the framework of a recursive cascade model, which is strongly motivated by the fundamental interactions of QCD. Fragmentation occurs via 3 types of breakups: quark → meson+ quark, gluon→meson+gluon, gluon→quark+ antiquark. In our model gluon jets are softer than quark jets. The ratio of gluon jet to quark jet multiplicity is found to be 2 asymptotically, but much less at lower energies. Some phenomenological consequences for λ decay are discussed. 相似文献
18.
G. Martens C. Greiner S. Leupold U. Mosel 《The European Physical Journal A - Hadrons and Nuclei》2003,18(2-3):223-226
We calculate color electric fields of quark/antiquark (
) and 3-quark (qqq) systems within the Chromodielectric Model (CDM). We explicitly evaluate the string tension of flux tubes in the
-system and analyze their profile. To reproduce results of lattice calculations we use a bag pressure
from which an effective strong-coupling constant
follows. With these parameters we get a Y-shaped configuration for large qqq-systems.Received: 30 September 2002, Published online: 22 October 2003PACS:
11.10.Lm Field theory: Nonlinear or nonlocal theories and models - 11.15.Kc Gauge field theories: Classical and semiclassical techniques - 12.39.Ba Phenomenological quark models: Bag model 相似文献
19.
The production of forward jets has been measured in deep inelastic ep collisions at HERA. The results are presented in terms of single differential cross sections as a function of the Bjorken
scaling variable (xBj) and as triple differential cross sections d3σ/dxBjdQ2
, where Q2 is the four momentum transfer squared and
is the squared transverse momentum of the forward jet. Also cross sections for events with a di-jet system in addition to
the forward jet are measured as a function of the rapidity separation between the forward jet and the two additional jets.
The measurements are compared with next-to-leading order QCD calculations and with the predictions of various QCD-based models. 相似文献
20.
We calculate, to first order in QCD, the probability for a fast hadron observed at laboratory angle θ h from the virtual photon directionq, to originate from the quark of a quark-gluon final state. Given this probability, the average gluon energy and angle with respect toq are then calculated. This approach provides a method for gluon jet direction in forthcoming experiments. 相似文献