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W. Ochs

Publications and source records attributed to W. Ochs.

13 recordsLinked to original sources
arXiv2008

Two-photon width and gluonic component of sigma/f_0(600)

We analyse data on pi pi and gamma gamma scattering below 700 MeV within an improved analytic K-matrix model. This model is based on an effective theory with couplings between resonances, hadrons and photons. The two-photon decay of a resonance can proceed through intermediate transition into charged hadrons (here: pi^+ pi^-) and their subsequent annihilation or through a ``direct'' transition into photons. Our analysis confirms the rather large total radiative width of the sigma/f_0(600) resonance which we find as (3.9 \pm 0.6) keV but suggests its dominance by the pi pi rescattering process. This process is not sensitive to the internal structure of the resonance contrary to the direct component which we find small, (0.13 \pm 0.05) keV, and well consistent with the expectations for an unmixed glueball according to the QCD sum rule calculations.

hep-ph↗
arXiv2008

Glueball nature of the sigma/f_0(600) from pi-pi and gamma-gamma scatterings

We estimate the I=0 scalar meson sigma/f_0(600) parameters from pi-pi and gamma-gamma scattering data below 700 MeV using an improved analytic K-matrix model. A fit of the hadronic data gives a complex pole mass M_sigma= 422-i290 MeV, while simultaneous best fits of the gamma-gamma to pi+pi-, pi0pi0 data give a direct width of (0.13+-0.05)keV, a rescattering component of (2.7+-0.4)keV and a total (direct+rescattering) width of (3.9+-0.6)keV. "Running" these results to the physical real axis, the small "direct" gamma-gamma and the large hadronic widths at the "on-shell" mass are compatible with QCD spectral sum rules (QSSR) and some low-energy theorems (LET) expectations for an unmixed lowest mass glueball/gluonium sigma_B of a mass around 1 GeV and a large OZI-violation decay into pi-pi.

hep-ph↗
arXiv2007

Can the gamma-gamma processes reveal the nature of the sigma ?

We reanalyse the gamma-gamma scattering data and conclude that in the mass region below 1 GeV the cross section for gamma-gamma to pi^0-pi^0 can be largely explained by the one pion exchange process with pi-pi rescattering. The radiative width of the sigma is estimated and a model dependent separation into contributions from direct gamma-gamma decay and decay through rescattering is obtained. We confront these findings with QCD spectral sum rule (QSSR) predictions and conclude that the sigma can have a large gluonium component in its wave function.

hep-ph↗
arXiv2005

Unifying the Fixed Order Evolution of Fragmentation Functions with the Modified Leading Logarithm Approximation

An approach which unifies the Double Logarithmic Approximation at small x and the leading order DGLAP evolution of fragmentation functions at large x is presented. This approach reproduces exactly the Modified Leading Logarithm Approximation, but is more complete due to the degrees of freedom given to the quark sector and the inclusion of the fixed order terms. We find that data from the largest x values to the peak region can be better fitted than with other approaches.

hep-ph↗
arXiv2005

Resummation of Soft Gluon Logarithms in the DGLAP Evolution of Fragmentation Functions

We define a general scheme for the evolution of fragmentation functions which resums both soft gluon logarithms and mass singularities in a consistent manner and to any order, and requires no additional theoretical assumptions. Using the Double Logarithmic Approximation and the known perturbative results for the splitting functions, we present our scheme with the complete contribution from the double logarithms, being the largest soft gluon logarithms. We show that the resulting approximation is more complete than the Modified Leading Logarithm Approximation even with the fixed order contribution calculated to leading order only, and find, after using it to fit quark and gluon fragmentation functions to experimental data, that this approximation in our scheme gives a good description of the data from the largest x_p values to the peak region in xi=ln (1/x_p), in contrast to other approximations. In addition, we develop a treatment of hadron mass effects which gives additional improvements at large xi.

hep-ph↗
arXiv2005

Generalizing the DGLAP Evolution of Fragmentation Functions to the Smallest x Values

An approach which unifies the Double Logarithmic Approximation at small x and the leading order DGLAP evolution of fragmentation functions at large x is presented. This approach reproduces exactly the Modified Leading Logarithm Approximation, but is more complete due to the degrees of freedom given to the quark sector and the inclusion of the fixed order terms. We find that data from the largest x values to the peak region can be better fitted than with other approaches.

hep-ph↗
arXiv2004

The Evolution of Hadron Spectra in the Modified Leading Logarithm Approximation

We perform fits of $Λ_{\rm QCD}$ and the gluon fragmentation function $D(x,Q)$ at initial scale $Q_0 \ggΛ_{\rm QCD}$ to charged light hadron momentum spectra data by evolving in the Modified Leading Logarithm Approximation. Without additional assumptions, we achieve a good description of the available data for $ξ=\ln(1/x)$ up to and around the Gaussian peak, and values of $Λ_{\rm QCD}$ acceptably close to those in the literature. In particular, we find that this procedure describes the position of the peak, and, in contrast to the Limiting Spectrum, also the normalization.

hep-ph↗
arXiv2002

Multiparticle Production in QCD Jets

We briefly summarise the main results presented at the IPPP Workshop on Multiparticle Production in QCD Jets, held in Durham in December 2001.

hep-ph↗
arXiv1997

Rapidity Gaps in e+e- Annihilation and Parton Hadron Duality

We calculate the probability for rapidity gaps in the parton cascade for different approximations within the perturbative QCD and compare the results with recent measurements. The aim is to find out whether the dual connection between the parton and hadron final states -- observed so far in various inclusive measurements -- holds as well for the extreme kinematic configurations with colour sources separated by large rapidity gaps. A description of the data is possible indeed choosing the parameters of the cascade in the range suggested by recent analyses of the energy spectra (the $k_\perp$ cutoff $Q_0~\gsim$ QCD scale $Λ\sim 250$ MeV).

hep-ph↗
arXiv1997

Perturbative QCD Approach to Multiparticle Production

In this review we discuss the analytical perturbative approach, based on perturbative QCD and Local Parton Hadron Duality (LPHD), and its application to multiparticle production in jets in the semisoft region. Analytical formulae are presented for various observables within the accuracy of the Modified Leading Logarithmic Approximation (MLLA), i.e. with terms of relative order $\sqrt{α_s}$ taken into account systematically, and in some cases with even higher accuracy. These predictions are confronted with existing experimental data. Many details of the perturbative approach to multiple hadroproduction have been consolidated in recent years, and the overall picture is remarkably healthy. The prospects of future studies of the semisoft jet physics are also discussed.

hep-ph↗
arXiv1996

Soft particle production and QCD coherence

We discuss the behaviour of the energy spectrum of particles in jets near the limit of small momenta of a few hundred MeV. In QCD parton cascades the soft gluons are coherently emitted from all faster partons in the jet and their production rate is predicted to scale. The observed charged and identified particle spectra follow this behaviour surprisingly well supporting of the hypothesis of the Local Parton Hadron Duality (LPHD) for this extreme limit. Further tests of this perturbative approach are discussed.

hep-ph↗
arXiv1996

QCD coherence and the soft limit of the energy spectrum

The analytical perturbative approach, if taken to the limit of its applicability, allows one to predict an energy independent limit for the one-particle invariant density in QCD jets E dn/d^3p at very small momenta p. This is a direct consequence of the colour coherence in soft gluon branching. The existing data on the charged and identified particle inclusive spectra follow this prediction surprisingly well. Further tests of the perturbatively based picture in the soft region are discussed.

hep-ph↗