Testing partonic charge symmetry at a high-energy electron collider

We examine the possibility that one could measure partonic charge symmetry violation (CSV) by comparing neutrino or antineutrino production through charged-current reactions induced by electrons or positrons at a possible electron collider at the LHC. We calculate the magnitude of CSV that might be expected at such a facility. We show that this is likely to be a several percent effect, substantially larger than the typical CSV effects expected for partonic reactions.     

New results from fluctuation analysis in NA49 at the CERN SPS

The exploration of the phase diagram of strongly interacting matter, particularly the study of the phase transition from hadronic to partonic matter and the search for a hypothetical critical endpoint of the first order transition line, is one of the most challenging tasks in present heavy ion physics. New results on chemical (particle ratio), transverse momentum, multiplicity and azimuthal angle fluctuations are presented. We also discuss their connection to the onset of deconfinement and to the critical endpoint.     

Possible signatures of the hadronisation scale in parton jets

Models for hadron production in hard collisions differ widely in the energy scale characteristic of the transition from the primary partonic to the secondary hadronic phase of jet evolution. We investigate possible experimental signatures for the existence of both phases. In particular, we consider multiplicity and energy moments, long range charge correlations and angular correlations as a function of total energy or near the exclusive two body limit ine ⁺ e ^? annihilation and deep inelastic scattering processes. The possibility of a dual correspondence between hadronic and partonic states is discussed.     

THE CHARGED PARTICLE MULTIPLICITY IN PROTON-ANTIPROTON ANNIHILATION

Using the three-chain diagram based on the dual partonic scheme, combining with the FF quark fragmentation mechanism, the charged particle multiplicity, the productions of Л and K mesons, the single-particle inclusive distribution and the central plateau particle density of soft high energy pp annihilation are calculated and compared with pp experiments on CERN SPS.     

Nuclear-like effects in proton–proton collisions at high energy

We show that several effects considered nuclear effects are not nuclear in the sense that they do not only occur in nucleus–nucleus and hadron–nucleus collisions but, as well, they are present in hadron–hadron (proton–proton) collisions. The matter creation mechanism in hh, hA and AA collision is always the same. The p _T suppression of particles produced in large multiplicity events compared to low multiplicity events, the elliptic flow and the Cronin effect are predicted to occur in pp collisions at LHC energies as a consequence of the high density partonic medium obtained.     

Self-similarity in one and two dimension of 800 GeV proton interactions with AgBr nuclei

The normalized multiplicity moments in one and two dimensions were investigated for secondary particles produced in 800 GeV proton interactions with AgBr nuclei in nuclear emulsion. The fluctuations are found to be more in two dimensions as compared to one dimension. It has been shown that the self-similar cascade model describes well the observed fluctuations. The multiplicity shows a weaker dependence of moments for high multiplicity events in comparison to all multiplicity events. The slope ratios (r _q) are not different in one and two dimensions and are found to be independent of the multiplicity. Ther _q distribution is well represented by the logbinomial and Levy-stable distributions which follows from the self-similar cascade model.     

The Lund fragmentation process for a multi-gluon string according to the area law

The Lund area law describes the probability for the production of a set of colourless hadrons from an initial set of partons, in the Lund string fragmentation model. It was derived from classical probability concepts but has later been interpreted as the result of gauge invariance in terms of the Wilson gauge loop integrals. In this paper {we will present a general method to implement the area law for a multi-gluon string state}. In this case the world surface of the massless relativistic string is a geometrically bent (1+1)-dimensional surface embedded in the (1+3)-dimensional Minkowski space. The partonic states are in general given by a perturbative QCD cascade and are consequently defined only down to a cutoff in the energy-momentum fluctuations. We will show that our method defines the states down to the hadronic mass scale inside an analytically calculable scenario. We will then show that there is a differential version of our process which is closely related to the generalized rapidity range , which has been used as a measure on the partonic states. We identify as the area spanned between the directrix curve (the curve given by the parton energy-momentum vectors laid out in colour order, which determines the string surface) and the average curve (to be called the -curve) of the stochastic X-curves (curves obtained when the hadronic energy-momentum vectors are laid out in rank order). Finally {we show that from the X-curve corresponding to a particular stochastic fragmentation situation it is possible to reproduce the directrix curve} (up to one starting vector and a set of sign choices, one for each hadron). This relationship provides an analytical formulation of the notion of parton–hadron duality. The whole effort is made in order to get a new handle to treat the transition region between where we expect perturbative QCD to work and where the hadronic features become noticeable. Received: 3 July 2001 / Published online: 31 August 2001     

Fluctuations and anomalous dimensions in QCD cascades

A recently proposed multiplicity measure is used to study the properties of QCD cascades. We show that it is possible to define anomalous dimensions locally in rapidity space for the QCD cascade ine ⁺ e ^–-annihilation events and in deep inelastic lepton scattering. In this way it will be possible to differentiate between different suggested models for multiple gluon emission. We also show that the properties of an event are to a surprisingly large degree deterimined by the first one or two gluons. Thus e.g. the multiplicity fluctuations ine ⁺ e ^–-annihilation at theZ ⁰-pole are to about 90% determined by the hardest gluon. This implies that it may be principally difficult to make a distinct separation between the hard perturbative phase and the soft hadronization phase.     

Partonic energy loss and the Drell-Yan process

We examine the current status of the extraction of the rate of partonic energy loss in nuclei from A-dependent data. The advantages and difficulties of using the Drell-Yan process to measure the energy loss of a parton traversing a cold nuclear medium are discussed. The prospects of using relatively low energy proton beams for a definitive measurement of partonic energy loss are presented.     

Multifractal dimensions in QCD cascades

Particle production in small rapidity or angular intervals have fractal structures similar to a Cantor dust. In this paper we present analytical result for multifractal dimensions valid for high energies. For high moments the dimension is given by \(\sqrt {6\alpha _s /\pi } \) . The scaling properties seen in the partonic state are not so well reflected in the hadronic multiplicity moments or factorial moments. We show how to define new observables on the final hadronic state, which do scale well. This means that the multifractal dimensions can be well determined and compared with results from QCD.     

Multiplicity dependence of intermittency in one and two dimensions in proton-nucleus interactions at 800 GeV

The intermittency effect has been observed in interactions of 800 GeV protons with emulsion-nuclei in one-(pseudorapidity/azimuthal angle) and two-dimensional (pseudorapidity and azimuthal angle) phase spaces in different multiplicity intervals. The intermittency strength is found to decrease with increasing multiplicity. Compared to one dimension, the two dimensional distribution is found to reflect better the intermittent behavior of the interactions. The dependence of various intermittency parameters on order of moment gives clear evidence of self-similar cascade mechanism in the interactions but there is no definite indication of the presence of different phases in the cascade.     

The extent of strangeness equilibration in quark gluon plasma

The evolution and production of strangeness from chemically equilibrating and transversely expanding quark gluon plasma which may be formed in the wake of relativistic heavy-ion collisions is studied with initial conditions obtained from the self screened parton cascade (SSPC) model. The extent of partonic equilibration increases almost linearly with the square of the initial energy density, which can then be scaled with the number of participants.     

The construction of gauge-links in arbitrary hard processes

Transverse momentum dependent parton distribution and fragmentation functions are described by hadronic matrix elements of bilocal products of field operators off the light-cone. These bilocal products contain gauge-links, as required by gauge-invariance. The gauge-links are path-ordered exponentials connecting the field operators along a certain integration path. This integration path is process-dependent, depending specifically on the short-distance partonic subprocess. In this paper we present the technical details needed in the calculation of the gauge-links, and a calculational scheme is provided to obtain the gauge invariant distribution and fragmentation correlators corresponding to a given partonic subprocess. PACS 12.38.-t; 13.85.Ni; 13.88.+e     

Signatures of the handbag mechanism in wide-angle photoproduction of pseudoscalar mesons

Wide-angle photoproduction of pseudoscalar mesons is investigated under the assumption of dominance of the handbag mechanism, considering both quark helicity flip and non-flip. The partonic subprocess, meson photoproduction off quarks, is analysed with the help of a covariant decomposition of the subprocess amplitudes which is independent of a specific meson generation mechanism. As examples of subprocess dynamics, however, the twist-2 as well as two-particle twist-3 contributions are explicitly calculated. Characteristic features of the handbag approach are discussed in dependence upon the relative magnitudes of the invariant functions. Differential cross sections and spin correlations are predicted to show a characteristic behaviour which allows one to test the underlying assumption of handbag dominance.Received: 15 September 2003, Revised: 2 December 2003, Published online: 29 January 2004     

Pseudorapidity dependence of short-range correlations from a multi-phase transport model

Using a multi-phase transport model(AMPT) that includes both initial partonic and hadronic interactions, we study neighboring bin multiplicity correlations as a function of pseudorapidity in Au+Au collisions at (sNN)~(1/2) = 7.7- 62.4 GeV.It is observed that for (sNN)~(1/2) 19.6 GeV Au+Au collisions, the short-range correlations of final particles have a trough at central pseudorapidity, while for (sNN)~(1/2) 19.6 GeV AuAu collisions,the short-range correlations of final particles have a peak at central pseudorapidity. Our findings indicate that the pseudorapidity dependence of short-range correlations should contain some new physical information, and are not a simple result of the pseudorapidity distribution of final particles. The AMPT results with and without hadronic scattering are compared. It is found that hadron scattering can only increase the short-range correlations to some level, but is not responsible for the different correlation shapes for different energies. Further study shows that the different pseudorapidity dependence of short-range correlations are mainly due to partonic evolution and the following hadronization scheme.     

<Emphasis Type="Italic">Z</Emphasis><Superscript>0</Superscript>-tagged quark jets at the large hadron collider

The Large Hadron Collider will allow studies of hard probes in nucleus-nucleus collisions which were not accessible at the Relativistic Heavy Ion Collider—even the study of small cross-section Z ⁰-tagged jets becomes possible. Going beyond the measurement of back-to-back correlations of two strongly interacting particles to measure plasma properties, we replace one side by an electromagnetic probe which propagates through the plasma undisturbed and therefore provides a measurement of the energy of the initial hard scattering. We show that at sufficiently high transverse momentum the Z ⁰-tagged jets originate predominately from the fragmentation of quarks and anti-quarks while gluon jets are suppressed. We propose to use lepton-pair tagged jets to study medium-induced partonic energy loss and to measure in-medium parton fragmentation functions to determine the opacity of the quark gluon plasma.     

Structure functions

Structure functions are a measure of the partonic structure of hadrons, which is important for any process which involves colliding hadrons. They are a key ingredient for deriving partons distributions in nucleons. In recent years dramatic progress has been made in the understanding of the nucleon structure and the precision of its partonic content, due to vast theoretical progress, and the availability of new high precision measurements. This review gives an overview on present structure functions and related data, and on the most recent techniques used to extract parton distribution functions to describe the structure of the proton. Special attention is given to the determination of the uncertainties on the parton distributions.     

Multiplicity structure of the hadronic final state in diffractive deep-inelastic scattering at HERA

The multiplicity structure of the hadronic system X produced in deep-inelastic processes at HERA of the type , where Y is a hadronic system with mass GeV and where the squared momentum transfer at the pY vertex, t, is limited to , is studied as a function of the invariant mass of the system X. Results are presented on multiplicity distributions and multiplicity moments, rapidity spectra and forward-backward correlations in the centre-of-mass system of X. The data are compared to results in annihilation, fixed-target lepton-nucleon collisions, hadro-produced diffractive final states and to non-diffractive hadron-hadron collisions. The comparison suggests a production mechanism of virtual photon dissociation which involves a mixture of partonic states and a significant gluon content. The data are well described by a model, based on a QCD-Regge analysis of the diffractive structure function, which assumes a large hard gluonic component of the colourless exchange at low . A model with soft colour interactions is also successful. Received: 27 April 1998 / Published online: 3 September 1998     

Fractals in one and two dimensions of medium energy particles in 800 GeV p-AgBr interactions

We present the first experimental results on self-similar nature of fluctuations of one and two-dimensional density distributions of medium energy particles in 800 GeV p-AgBr interactions. The density fluctuations as measured by 1?D _q are found to be more in two dimensions as compared to those in one dimension, whereas the fluctuations decrease with increase in multiplicity. It has been found that the self-similar cascade model with multifractal properties describes well the observed fluctuations. The ratios of multifractal power law indices are found to be independent of the dimensionality of phase space and of multiplicity.     

Universal scaling of kinetic freeze-out parameters across different collision systems at LHC energies

In this study, we perform Tsallis Blast-Wave analysis on the transverse momentum spectra of identified hadrons produced in a wide range of collision systems at the Large Hadron Collider (LHC) including pp, pPb, XeXe, and PbPb collisions. The kinetic freeze-out properties varying with event multiplicity are investigated across these systems. We find that the extracted kinetic freeze-out temperature, radial flow velocity, and non-extensive parameter exhibit a universal scaling behavior for these systems with very different geometric sizes, especially when the independent baryon Tsallis non-extensive parameter is considered. This universality may indicate the existence of a unified partonic evolution stage in different collision systems at the LHC energies.