Searcharxiv⌕ Search

arXiv subjects

Wolfgang Ochs

Publications and source records attributed to Wolfgang Ochs.

At least 37 records · Page 2Linked to original sources
arXiv2005

Multiplicity Difference between Heavy and Light Quark Jets Revisited

The perturbative QCD approach to multiparticle production predicts a characteristic suppression of particle multiplicity in a heavy quark jet as compared to a light quark jet. In the Modified Leading Logarithmic Approximation (MLLA) the multiplicity difference δ_{Q\ell} between heavy and light quark jets is derived in terms of a few other experimentally measured quantities. The earlier prediction for b-quarks needs revision in the light of new experimental results and the improvement in the understanding of the experimental data. We now find δ_{b\ell}=4.4\pm0.4. The updated MLLA results on δ_{b\ell} and δ_{c\ell} are compared with the present data from e^+e^- annihilation. Their expected energy independence is confirmed within the energy range between 29 and 200 GeV; the absolute values are now in better agreement with experiment than in the previous analysis, and the remaining difference can be attributed largely to next-to-MLLA contributions, an important subset of which are identified and evaluated.

hep-ph↗
arXiv2005

QCD evolution of hadron and jet multiplicity moments

We describe recent applications of the MLLA evolution equations to the calculation of mean multiplicities in quark and gluon jets and the higher moments of hadron and sub-jet multiplicity distributions in $e^+e^-$-annihilation as function of c.m.s. energy $Q$ and resolution parameter $y_{cut}$. The transition from jets to hadrons with increasing jet resolution is considered.

hep-ph↗
arXiv2004

Multiparticle Dynamics 2004

We summarize results presented at this conference with special emphasis on hard processes with jets and heavy quarks, soft particle production, small x structure functions and diffraction as well as heavy ion collisions and quark gluon plasma.

hep-ph↗
arXiv2004

B decays into light scalar particles and glueball

The recent observations of f_0(980) in charmless B-decays motivate further studies of scalar particle and glueball production in these processes. Amplitudes for charmless 2-body B decays involving the members of the scalar nonet are presented based on the symmetries of the dominant penguin contribution. Different scenarios for the lightest scalar nonet are investigated in view of the presently available data. We describe the evidence from B-decays for f_0(1500) with a flavour octet like mixing and the hints towards the members of the q qbar nonet of lowest mass. There is further support for the hypothesis of a broad 0^{++} glueball acting as coherent background especially in B -> K Kbar K. The estimated B decay rates into gluonic mesons represent a sizable fraction of the theoretically derived decay rate for b -> sg.

hep-ph↗
arXiv2004

Gluonic Meson Production

The existence of glueballs is predicted in QCD, the lightest one with quantum numbers J^{PC}=0^{++}, but different calculations do not well agree on its mass in the range below 1800 MeV. Several theoretical schemes have been proposed to cope with the experimental data which often have considerable uncertainties. Further experimental studies of the scalar meson sector are therefore important and we discuss recent proposals to study leading clusters in gluon jets and charmless B-decays to serve this purpose.

hep-ph↗
arXiv2003

Oscillating Hadron and Jet Multiplicity Moments

Recently, the moments of multiplicity distributions in e+e- annihilation and the ratios H_q (cumulant over factorial moments K_q/F_q) have been determined both for the hadronic final state and for jets at variable resolution. These ratios show an oscillatory behaviour as function of q with strong dependence of the amplitude and length of oscillation on the jet resolution parameter y_{cut}. The recent explanation of this phenomenon based on perturbative QCD calculations is discussed.

hep-ph↗
arXiv2003

The scalar meson sector and the sigma, kappa problem

In the light scalar meson sector (M < 1.8 GeV) one expects at least one q qbar nonet and a glueball, possibly also multi-quark states. We discuss the present phenomenological evidence for sigma and kappa particles; if real, they could be members of the lightest (quark or multi-quark) nonet together possibly with a_0(980) and f_0(980). Alternatively, the lightest nonet could include f_0(980) but not sigma and kappa. Future decisive experimental studies, concerning tests of symmetry relations, especially in B-decays, are outlined.

hep-ph↗
arXiv2003

QCD explanation of oscillating hadron and jet multiplicity moments

Ratios of multiplicity moments, H_q (cumulant over factorial moments K_q/F_q), have been observed to show an oscillatory behaviour with respect to order, q. Recent studies of e^+e^- annihilations at LEP have shown, moreover, that the amplitude and oscillation length vary strongly with the jet resolution parameter y_{cut}. We study the predictions of the perturbative QCD parton cascade assuming low non-perturbative cut-off (Q_0\sim Λ_{QCD}\sim few 100 MeV) and derive the expectations as a function of the cms energy and jet resolution from threshold to very high energies. We consider numerical solutions of the evolution equations of gluodynamics in Double Logarithmic and Modified Leading Logarithmic Approximations (DLA,MLLA), as well as results from a parton MC with readjusted parameters. The main characteristics are obtained in MLLA, while a more numerically accurate description is obtained by the MC model. A unified description of correlations between hadrons and correlations between jets emerges, in particular for the transition region of small y_{cut}.

hep-ph↗
arXiv2003

Scalar mesons and glueball in B-decays and gluon jets

We discuss the recent observation of f_0(980) in charmless B-decays and in gluon jets which hints toward a gluonic coupling of this meson similar to eta'. Further predictions on B-decays into scalar particles are presented. Charmless B decays also show a broad K Kbar (and possibly pi pi) S-wave enhancement which we relate to the 0^{++} glueball. These gluonic mesons represent a sizable fraction of the theoretically derived decay rate for b -> sg.

hep-ph↗
arXiv2003

Angular Distribution of Particle Flows and Perturbative QCD Predictions

We discuss the predictions of perturbative QCD for angular flows of final state particles in two and three jet events including their cms energy and jet resolution (y_{cut}) dependence. The simple analytical formulae for gluon bremsstrahlung from primary partons, modified for gluon cascading, reproduce the main features of the experimental data well. For y_{cut}-selected events, the particle flow is derived from a superposition of colour dipoles in much the same way that photon radiation is derived from electric dipoles.

hep-ph↗
arXiv2002

On the scalar nonet lowest in mass

The hypothesis that there exists a nonet of scalars mainly composed of a valence quark-antiquark pair and mixed according to near singlet-octet separation : f_0 (980) singlet, a_0^{+,0,-} (980), K^{* +,0}_0 (1430), \bar K^{* -,0}_0 (1430), f_0 (1500) octet, is put to further tests from the three body decays D^{\pm}, D_{s}^{\pm} -> PS^{\pm} pi^+ pi^- with PS^{\pm} = pi^{\pm}, K^{\pm}. The analysis of decay phases supports the singlet nature of f_0 (980).

hep-ph↗
arXiv2002

The glueball among the light scalar mesons

In our phenomenological analysis of the spectroscopy of light scalar mesons we do not find compelling evidence for the existence of the low mass κ(900) or σ(600) states nor for f_0(1370) as single resonance. If the f_0(980) and and f_0(1500) are taken as members of the q qbar nonet there remains a broad object formed by f_0(400-1200) and f_0(1370) which is a glueball candidate gb(1000).

hep-ph↗
arXiv2001

QCD Description of Angular Correlations

We review the predictions on angular correlations and their recent experimental tests at LEP and HERA. Power behaviour of correlation functions appear for large angles and reflect the underlying fractal structure in jet evolution. Asymptotic scaling laws work rather well for the low momentum particles. For angular correlations the predictions work at least qualitatively, sometimes quantitatively, at LEP and the higher HERA energies. Some limitations of the approach and possible improvements are discussed.

hep-ph↗
arXiv2001

Light scalar meson spectrum

We discuss the classification of the light scalar mesons with mass below 2 GeV into q qbar nonets and glueballs. The information on production and decay of these states, in particular recent information on f_0(980), f_0(400-1200) (or sigma(600)) and f_0(1500) is considered. Although the data are not yet very precise the recent information is in favour of the previously developed scheme which includes f_0(980), a_0(980), K_0^*(1430), f_0(1500) into the lightest scalar nonet. The glueball in this approach appears as broad object around 1 GeV. Alternative schemes find the glueball at somewhat higher mass or suggest his mixing with q qbar states spread over a similar mass range. We do not see sufficient evidence yet for a light scalar nonet below 1 GeV around a sigma(600) resonance.

hep-ph↗
arXiv2001

Theory of Multiparticle Production in the Soft Region

We review theoretical and experimental advances in the application of the perturbative QCD approach to the description of particle distributions in jets in the (semi) soft region with particular emphasis on HERA physics.

hep-ph↗
arXiv2001

Search for Gluonic Mesons in Gluon Jets

We present a short survey of the theoretical expectations on glueballs and hybrids as well as of the present phenomenological status. The possibility to obtain new information on gluonic mesons from the study of gluon jets in comparison to quark jets is discussed.

hep-ph↗
arXiv2000

Analytical QCD and multiparticle production

We review the perturbative approach to multiparticle production in hard collision processes. It is investigated to what extent parton level analytical calculations at low momentum cut-off can reproduce experimental data on the hadronic final state. Systematic results are available for various observables with the next-to-leading logarithmic accuracy (the so-called modified leading logarithmic approximation - MLLA). We introduce the analytical formalism and then discuss recent applications concerning multiplicities, inclusive spectra, correlations and angular flows in multi-jet events. In various cases the perturbative picture is surprisingly successful, even for very soft particle production.

hep-ph↗