Search results for "Omero"

New Anomalous Exchange in Regge Phenomenology and Hard Diffraction

2001

A new mechanism for hard diffraction based on the anomalous $f_1$ trajectory exchange, which we identify as the odd signature partner of the Pomeron, is suggested. We calculate the contribution of the $f_1$ exchange to elastic and dissociative electromagnetic production of vector mesons and show that it gives a dominant contribution to the differential cross sections at large momentum transfers.

Minijet and transverse energy production in the BFKL regime

1996

Minijet production in hadronic and nuclear collisions through a BFKL pomeron ladder is studied for the energies of the future LHC heavy-ion collisions. We use unintegrated gluon densities compatible with the small-$x$ increase of parton distributions observed at HERA. We show that at LHC energies the BFKL minijet and transverse energy production is at most of the same order of magnitude as that in the collinear factorization approach.

Mechanism for the double-spin asymmetry in electromagnetic rho production at HERMES

2001

We calculate the contribution of meson and pomeron exchanges to the double-spin asymmetry in $\rho$-meson electromagnetic production at HERMES energies. We show that the observed double-spin asymmetries, which are large, can be explained by the interference between the natural parity $f_2$-secondary Reggeon and the unnatural parity anomalous $f_1$ exchanges.

Evidence for the flavor singlet axial anomaly related effects in phi meson electromagnetic production at large momentum transfers

2001

The gluonic contributions to the conventional PCAC formulas due to flavor singlet axial anomaly have been instrumental in explaining the mass of the $\eta^{\prime}$ and providing a plausible explanation for solving the spin crisis. We show that they also play an important role in the description of photo- and electroproduction of vector mesons at low energy and high momentum transfers. We calculate the contributions of this type to $\phi$ meson electromagnetic production in a model, which contains also a soft pomeron, and find agreement with recent CLAS data.

New anomalous trajectory in Regge theory

1999

We show that a new Regge trajectory with \alpha_{f_1} (0) \approx 1 and slope \alpha_{f_1}'(0) \approx 0 explains the features of hadron-hadron scattering and photoproduction of the rho and phi mesons at large energy and momentum transfer. This trajectory with quantum numbers P = C = +1 and odd signature can be considered as a natural partner of the Pomeron which has even signature. The odd signature of the new exchange leads to contributions to the spin-dependent cross sections, which do not vanish at large energy. The links between the anomalous properties of this trajectory, the axial anomaly and the flavor singlet axial vector f_1 (1285) meson are discussed.

DIS structure functions and the double-spin asymmetry inρ0electroproduction within a Regge approach

2003

The proton, neutron and deuteron structure functions ${F}_{2}{(x,Q}^{2})$ and ${g}_{1}{(x,Q}^{2}),$ measured at intermediate ${Q}^{2},$ are analyzed within a Regge approach. This analysis serves to fix the parameters of this scheme which are then used to calculate, in a unified Regge approach, the properties of ${\ensuremath{\rho}}^{0}$ meson electroproduction on the proton and the deuteron. In this way, the double-spin asymmetry observed at HERMES in ${\ensuremath{\rho}}^{0}$ electroproduction on the proton can be related to the anomalous behavior of the flavor-singlet part of the spin-dependent structure function ${g}_{1}{(x,Q}^{2})$ at small x.

Measurement of OZI rule violation and spin alignment inϕandωproduction at COMPASS

2012

The COMPASS collaboration at CERN dedicated the 2008 and 2009 run time to hadron spectroscopy measurements with emphasis on the mesonic sector. At 190 GeV/c beam momentum, diffractive and double-Reggeon/Pomeron production mechanisms contribute. Studying vector meson production allows to explore this relatively unknown transition domain. We present results on the ratio of production yields for p p → (1020) p p ϕ and p p → p p ω (782) and its xF dependence where we find an OZI rule violation in the order of a factor of 3. In addition, the spin alignment of ω and ϕ as a function of xF is investigated.

Photoproduction of η and η′ mesons with EtaMAID

2016

The unitary isobar model EtaMAID has been updated with an extended list of nucleon resonances, fitted to recent and new data for differential cross sections and polarization observables. The nonresonant background is described by Regge trajectories of ω,ρ and a 1 , b 1 mesons and in addition Regge cuts, where vector and axial vector mesons are exchanged together with Pomeron and f 2 mesons.

Kalmbergin kartasto R VI : List 8

1855

Massive Yang-Mills model and diffractive scattering

1998

We argue that the massive Yang-Mills model of Kunimasa and Goto, Slavnov, and Cornwall, in which massive gauge vector bosons are introduced in a gauge-invariant way without resorting to the Higgs mechanism, may be useful for studying diffractive scattering of strongly interacting particles. We perform in this model explicit calculations of S-matrix elements between quark states, at tree level, one loop, and two loops, and discuss issues of renormalisability and unitarity. In particular, it is shown that the S-matrix element for quark scattering is renormalisable at one-loop order and is only logarithmically non-renormalisable at two loops. The discrepancies in the ultraviolet regime between…