11 research outputs found
Local charge compensation from colour preconfinement as a key to the dynamics of hadronization
If, as is commonly accepted, the colour-singlet, `preconfined', perturbative
clusters are the primary units of hadronization, then the electric charge is
necessarily compensated locally at the scale of the typical cluster mass. As a
result, the minijet electric charge is suppressed at scales that are greater
than the cluster mass. We hence argue, and demonstrate by means of Monte Carlo
simulations using HERWIG, that the scale at which charge compensation is
violated is close to the mass of the clusters involved in hadronization, and
its measurement would provide a clue to resolving the nature of the dynamics.
We repeat the calculation using PYTHIA and find that the numbers produced by
the two generators are similar. The cluster mass distribution is sensitive to
soft emission that is considered unresolved in the parton shower phase. We
discuss how the description of the splitting of large clusters in terms of
unresolved emission modifies the algorithm of HERWIG, and relate the findings
to the yet unknown underlying nonperturbative mechanism. In particular, we
propose a form of that follows from a power-enhanced beta function,
and discuss how this that governs unresolved emission may be related
to power corrections. Our findings are in agreement with experimental data.Comment: 37 pages, 20 figure
Survival probability for high mass diffraction
Based on the calculation of survival probabilities, we discuss the problem of
extracting the value of , the triple Pomeron 'bare' coupling constant,
by comparing the large rapidity gap single high mass diffraction data in
proton-proton scattering and photo and DIS production. For p-p
scattering the calculation in a three amplitude rescattering eikonal model,
predicts the survival probability to be an order of magnitude smaller than for
the two amplitude case. The survival probabilities calculation for photo and
DIS production is made in a dedicated model. In this process we show
that, even though its survival probability is considerably larger than in p-p
scattering, its value is below unity and cannot be neglected in the data
analysis. We argue that, regardless of the uncertainties in the suggested
procedure, its outcome is important both with regards to a realistic estimate
of , and the survival probabilities relevant to LHC experiments.Comment: 17 pages, 8 pictures and one tabl
Total photoproduction cross-section at very high energy
In this paper we apply to photoproduction total cross-section a model we have
proposed for purely hadronic processes and which is based on QCD mini-jets and
soft gluon re-summation. We compare the predictions of our model with the HERA
data as well as with other models. For cosmic rays, our model predicts
substantially higher cross-sections at TeV energies than models based on
factorization but lower than models based on mini-jets alone, without soft
gluons. We discuss the origin of this difference.Comment: 13 pages, 9 figures. Accepted for publication in EPJC. Changes
concern added references, clarifications of the Soft Gluon Resummation method
used in the paper, and other changes requested by the Journal referee which
do not change the results of the original versio
Gauge invariant sub-structures of tree-level double-emission exact QCD spin amplitudes
In this note we discuss possible separations of exact, massive, tree-level
spin amplitudes into gauge invariant parts. We concentrate our attention on
processes involving two quarks entering a color- neutral current and, thanks to
the QCD interactions, two extra external gluons. We will search for forms
compatible with parton shower languages, without applying approximations or
restrictions on phase space regions. Special emphasis will be put on the
isolation of parts necessary for the construction of evolution kernels for
individual splittings and to some degree for the running coupling constant as
well. Our aim is to better understand the environment necessary to optimally
match hard matrix elements with partons shower algorithms. To avoid
complications and ambiguities related to regularization schemes, we ignore, at
this point, virtual corrections. Our representation is quite universal: any
color-neutral current can be used, in particular our approach is not restricted
to vector currents only.Comment: 27 pages, formula in section 5 correcte
Formation of dense partonic matter in relativistic nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX collaboration
Extensive experimental data from high-energy nucleus-nucleus collisions were
recorded using the PHENIX detector at the Relativistic Heavy Ion Collider
(RHIC). The comprehensive set of measurements from the first three years of
RHIC operation includes charged particle multiplicities, transverse energy,
yield ratios and spectra of identified hadrons in a wide range of transverse
momenta (p_T), elliptic flow, two-particle correlations, non-statistical
fluctuations, and suppression of particle production at high p_T. The results
are examined with an emphasis on implications for the formation of a new state
of dense matter. We find that the state of matter created at RHIC cannot be
described in terms of ordinary color neutral hadrons.Comment: 510 authors, 127 pages text, 56 figures, 1 tables, LaTeX. Submitted
to Nuclear Physics A as a regular article; v3 has minor changes in response
to referee comments. Plain text data tables for the points plotted in figures
for this and previous PHENIX publications are (or will be) publicly available
at http://www.phenix.bnl.gov/papers.htm
Jets and QCD: A Historical Review of the Discovery of the Quark and Gluon Jets and its Impact on QCD
The observation of quark and gluon jets has played a crucial role in establishing Quantum Chromodynamics [QCD] as the theory of the strong interactions within the Standard Model of particle physics. The jets, narrowly collimated bundles of hadrons, reflect configurations of quarks and gluons at short distances. Thus, by analysing energy and angular distributions of the jets experimentally, the properties of the basic constituents of matter and the strong forces acting between them can be explored. In this review, which is primarily a description of the discovery of the quark and gluon jets and the impact of their observation on Quantum Chromodynamics, we elaborate, in particular, the role of the gluons as the carriers of the strong force. Focusing on these basic points, jets in e+e− collisions will be in the foreground of the discussion and we will concentrate on the theory that was contemporary with the relevant experiments at the electron-positron colliders. In addition we will delineate the role of jets as tools for exploring other particle aspects in ep and \hbox{} collisions − quark and gluon densities in protons, measurements of the QCD coupling, fundamental 2-2 quark/gluon scattering processes, but also the impact of jet decays of top quarks, and W ± , Z bosons on the electroweak sector. The presentation to a large extent is formulated in a non-technical language with the intent to recall the significant steps historically and convey the significance of this field also to communities beyond high energy physics
Jet physics in electron--proton scattering
Hadronic jets in electron–proton collisions at HERA have been used for some considerable time as a tool for tests of the theory of strong interactions, quantum chromodynamics. Using jet final states, basic concepts like the factorisation ansatz for cross-section calculations, the perturbative approach to the cross section and the universality of the proton parton distribution functions can be examined. More concretely, jet measurements provide ready access to the strong coupling of QCD, α
s
, and to the parton distributions. In this report, an overview of jet results from the HERA experiments H1 and ZEUS and their interpretation is given together with a description of the theoretical foundations of jet physics in electron–proton collisions and of the experimental environment at HERA. Special emphasis is put on extractions of α
s
values and on the influence of jet data on fits of the proton parton distribution functions. Where useful, the HERA results are also discussed in the light of results from other colliders like LEP, the Tevatron or the LHC. The central message from these studies is that QCD does not only describe most of the measurements very well, but that QCD at HERA has achieved the status of a precision theory. On the other hand it is shown that further understanding of problematic issues relies critically on theoretical progress in the form of improved models or of increased precision in analytical calculations
Measurement of the production rates of charged hadrons in e+ e- annihilation at the Z0
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