Atomic mass dependence of hadron production in semi-inclusive deep inelastic lepton-nucleus scattering

Hadron production in lepton-nucleus deep inelastic scattering is studied in a quark energy loss model. The leading-order computations for hadron multiplicity ratios are presented and compared with the selected HERMES pions production data with the quark hadronization occurring outside the nucleus by means of the hadron formation time. It is found that the obtained energy loss per unit length is 0.440 ± 0.013 GeV/fm for an outgoing quark by the global fit. It is confirmed that the atomic mass number dependence of hadron attenuation is theoretically and experimentally in good agreement with the A^2/3 power law for quark hadronization occurring outside the nucleus.     

A general model for jet fragmentation

We present a general condition on quark fragmentation which gives a hadron distribution satisfying Lorentz invariance and causality. The hadronization can be described as an iterative cascade process, symmetric with respect to iteration from the quark and the antiquark ends. The possible particle distributions are strongly restricted, with few free parameters related to the total multiplicity and corelations in rapidity. These parameters can be given an appealing interpretation in terms of the expected area and perimeter dependence of Wilson loop integrals.     

Nonextensive boltzmann equation and hadronization

We present a novel nonextensive generalization of the Boltzmann equation. We investigate the evolution of the one-particle distribution in this framework. The stationary solution is exponential in a nonlinear function of the original energy. The total energy is composed using a general, associative nonextensive rule. We propose that for describing the hadronization of quark matter such rules may apply.     

Heavy flavor hadrons in statistical hadronization of strangeness-rich QGP

We study b and c quark hadronization from QGP. We obtain the yields of charm and bottom flavored hadrons within the statistical hadronization model. The important novel feature of this study is that we take into account the high strangeness and entropy content of QGP, conserving the strangeness and entropy yields at hadronization. PACS 25.75.Nq; 12.38.Mh; 25.75.-q; 24.10.Pa     

e~＋e~－湮没中不同味道夸克喷注带电粒子多重数差别

利用“夸克产生律”与“夸克组合律”计算了ｅ＋ｅ－湮没中重夸克喷注事例的带电粒子多重数，结果与实验符合．并与轻夸克喷注事例及平均夸克味道喷注事例的多重数做了比较．     

Lepton pair emission as a probe for the spacetime scenario of quark-hadron phase transition

The correlation between thermal lepton pair emission and hadronic multiplicity is explored to clear up the spacetime picture of quark matter hadronization phase transition in ultrarelativistic nuclear collisions.     

Hadronization from color interactions

A quark coalescence model, based on semi-relativistic molecular dynamics with color interactions among quarks, is presented and applied to pp collisions. A phenomenological potential with two tunable parameters is introduced to describe the color interactions between quarks and antiquarks. The interactions drive the process of hadronization that finally results in different color neutral clusters, which can be identified as hadrons based on some criteria. A Monte Carlo generator PYTHIA is used to generate quarks in the initial state of hadronization, and different values of tunable parameters are used to study the final state distributions and correlations. Baryon-to-meson ratio, transverse momentum spectra, pseudorapidity distributions and forward-backward multiplicity correlations of hadrons produced in the hadronization process, obtained from this model with different parameters, are compared with those from PYTHIA.     

Search for scalar bottom quarks from gluino decays in collisions at

We searched for scalar bottom quarks 156 pb(-1) of pp collisions at radicalS = 1.96 recorded by the Collider Detector at Fermilab II experiment at the Tevatron. Scalar bottom quarks can be produced from gluino decays in -parity conserving models of supersymmetry when the mass of the gluino exceeds that of the scalar bottom quark. Then, a scalar bottom quark can decay into a bottom quark and a neutralino. To search for this scenario, we investigated events with large missing transverse energy and at least three jets, two or more of which were identified as containing a secondary vertex from the hadronization of quarks. We found four candidate events, where 2.6 +/- 0.7 are expected from standard model processes, and placed 95% confidence level lower limits on gluino and scalar bottom quark masses of up to 280 and 240 GeV/c(2), respectively.     

Parton transverse momentum distribution at the moment of hadronization at RHIC

We extract the transverse momentum distribution of effective partons using the spectra of Ω, Ξ, Λ and ϕ hadrons measured by the STAR Collaboration from Au + Au collisions at $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 200 GeV at RHIC. The extracted momentum distribution of strange quarks is flatter than that of up/down quarks consistent with hydrodynamics expansion in partonic phase prior to hadronization. Consistency in quark ratios derived from various hadron spectra gives clear evidence for hadron production as suggested by quark coalescence or recombination model.     

Geometric interpretation of a new hadronization model

It is shown that the phenomenological potential, used in the context of a recent successful hadronization scheme to realize an effective quark confinement, can be reproduced by coupling, to first order, the quark field to the geometry of an anti-de Sitter vacuum. This seems to suggest a geometric interpretation whith could explain and justify the manifest Lorentz noninvariance of the original effective hadronization model.     

Geometric interpretation of hadronization model

A hadronization model termed as geometric dielectric confinement model is described. The model describes the charmed meson decays quite successfully. In the model we assume that the non-abelian gauge field describing the colour force simulates the effect of a medium having space-dependent dielectric constant. The quarks produced in weak decays move in the dielectric medium such that they are free in limited region of space (r⋍0) and cannot appear as asymptotic states resulting in hadronization. It is found that the dielectric medium resembles anti-desitter microuniverse and the quarks behave essentially as free particles damped by gaussian distribution. The model reproduces from a single Lagrangian the quark motion as well as the form of dielectric function.     

Gluon and quark jets in a recursive model motivated by quantum chromodynamics

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.     

Mechanism of crossover between hadron gas and QGP and the liquid property of sQGP

We raise for the first time the highly important question that the hadronization of partons one by one as assumed in current models for crossover in QCD, contradicts color confinement. A possible mechanism — molecule-like hadron aggregation — is proposed for crossover compatible with color confinement. A toy model to realize this mechanism is constructed. A kind of grape-shape quark gluon plasma (gQGP) is obtained. Pair distribution function for gQGP is calculated which exhibits the character of liquid.     

Application of the heat-kernel method to the constituent quark model at finite temperature

The heat-kernel method is applied to the constituent quark model. We calculate the effect of thermal quark fluctuations on the meson action and the resulting quark condensate and ππ-scattering amplitude at finite temperature. The quarks produce a chiral phase transition only by their effect on the mesonic coupling constants. The s-wave isospin zero ππ-scattering amplitude diverges near the phase transition showing the necessity for a more sophisticated treatment of meson fluctuations.     

Search for Higgs bosons decaying to bb and produced in association with W bosons in pp collisions at square root of s = 1.96 TeV

We present a search for Higgs bosons decaying into bb and produced in association with W bosons in pp collisions at square root of s = 1.96 TeV. This search uses 320 pb(-1) of the data set accumulated by the upgraded Collider Detector at Fermilab. Events are selected that have a high-transverse momentum electron or muon, missing transverse energy, and two jets, at least one of which is consistent with the hadronization of a b quark. Both the number of events and the dijet mass distribution are consistent with standard model background expectations, and we set 95% confidence level upper limits on the production cross section times branching ratio for the Higgs boson or any new particle with similar decay kinematics. These upper limits range from 10 pb for mH = 110 GeV/c2 to 3 pb for mH = 150 GeV/c2.     

Resonances and fluctuations at SPS and RHIC

We perform an analysis of preliminary data on hadron yields and fluctuations within the statistical hadronization ansatz. We describe the theoretical disagreements between different statistical models currently on the market and show how the simultaneous analysis of yields and fluctuations can be used to determine if one of them can be connected to underlying physics. We perform such an analysis on preliminary RHIC and SPS A–A data that includes particle yields, ratios and event-by-event fluctuations. We show that the equilibrium statistical model can not describe the K/π fluctuation measured at RHIC and SPS, unless an unrealistically small volume is assumed. Such a small volume then makes it impossible to describe the total particle multiplicity. The non-equilibrium model, on the other hand, describes both the K/π fluctuation and yields acceptably due to the extra boost to the π fluctuation provided by the high pion chemical potential. We show, however, that both models significantly over-estimate the p/π fluctuation measured at the SPS and speculate for the reason behind this. PACS 25.75.-q; 24.60.-k; 24.10.Pa     

Intermittency and jets

We show that intermittency, i.e. unlimited growth of multiplicity fluctuations with increasing resolution, is obtained in hadron cascade models with scale invariant branching structure. Strong effects are expected if in a multiparticle event not only the rapidity but simultaneously the azimuthal angle around the beam axis is analysed. The occurrence of narrow jets (“pencil jets”) is expected. The relevance of this type of study for models of hadronization is pointed out.     

Energy dependence of transverse quark flow in heavy ion collisions

Energy dependence of quark transverse flow carries information about dynamical properties (equation of state, initial conditions) of deconfined matter produced in heavy ion collisions. We assume quark-antiquark matter formation in Pb+Pb collisions at CERN SPS and Au+Au collisions at RHIC energies and determine quark transverse flow at the critical temperature of the quark-hadron phase transition. Coalescence of massive quarks is calculated in the MICOR hadronization model and hadronic final state effects are considered using the GROMIT cascade program. Comparing theoretical results to data, transverse flow values are determined and energy dependence is discussed.