arXiv subjects

Martin Maul

Publications and source records attributed to Martin Maul.

9 recordsLinked to original sources

arXiv2003

Integral equation for spin dependent unintegrated parton distributions incorporating double ln^2(1/x) effects at low x

In this paper we derive an integral equation for the evolution of unintegrated (longitudinally) polarized quark and gluon parton distributions. The conventional CCFM framework is extended at small x in order to incorporate the QCD expectations concerning the double ln^2(1/x) resummation at low x for the integrated distributions. Complete Altarelli-Parisi splitting functions are included, that makes the formalism compatible with the LO Altarelli-Parisi evolution at large and moderately small values of x. The obtained modified polarized CCFM equation is shown to be partially diagonalized by the Fourier-Bessel transform. Results of the numerical solution for this modified CCFM equation for the non-singlet quark distributions are presented.

hep-ph↗

arXiv2003

Center-Vortex Solutions of the Yang-Mills Effective Action in Three and Four Dimensions

We calculate the one-loop effective action of the SU(2) Yang-Mills theory for center-vortex configurations, both in 3d and 4d. We find that in both cases there are minima of the effective action, corresponding to vortices of the transverse size approximately 4/g_3^2 and 1.7/Lambda_MS, respectively. The values of the effective actions at the minima are negative, suggesting that the Euclidian vacuum may be unstable with respect to creation of vortices.

hep-lat↗

arXiv2002

Effective Field Theoretical Approach to Black Hole Production

A field theoretical description of mini black hole production at TeV energies is given taking into account the quantization of black holes in discrete resonances. The unknown quantum gravitational effects are absorbed in effective couplings, black hole masses and the Hawking temperature. The evaporation is described in terms of thermal field theory.

hep-ph↗

arXiv2002

A polarized version of the CCFM equation for gluons

A derivation for a polarized CCFM evolution equation which is suitable to describe the scaling behavior of the the unintegrated polarized gluon density is given. We discuss the properties of this polarized CCFM equation and compare it to the standard CCFM equation in the unpolarized case.

hep-ph↗

arXiv2001

Semi-leptonic B-decays and the two-pion distribution amplitudes

We show that the semi-leptonic decay B+ -> pi+ pi- l+ ν_l can be used as a source of information for two-pion distribution amplitudes. The connection between these amplitudes and the B-meson decay width is achieved by the light cone sum rule method. We show the relevant distribution amplitudes and give the formula for the decay width.

hep-ph↗

arXiv2001

Quarkonium Production through Hard Comover Rescattering in Polarized and Unpolarized pp Scattering

In this paper hadroproduction of charmonium states in polarized pp collisions is discussed. A thermal picture for the gluonic cloud of comovers is given making contact between the formalism and the measured unpolarized cross sections. The experimentally observed non-polarization of the final J/psi states leads to the consequence that no correlations between the initial proton spin and the final charmonium spin should be existent. Hence the single spin asymmetries vanish to leading order in that model.

hep-ph↗

arXiv2001

Semi-classical Description of Exclusive Meson Pair Production in $γ^*γ$ Scattering

A semi-classical picture is given for the production of exclusive meson pairs in γγ^* scattering using elements of the Lund string fragmentation model, spin and C-parity conservation. The model can be generalized to the production of any few meson states in scattering reactions at intermediate momentum transfers. As an example we show that we get a consistent description for the time-like pion form factor. For the reaction γγ^*\to π^+π^- we find a seizable cross section at LEP2 energies.

hep-ph↗

arXiv2000

Large Extra Dimensions in Rare Decays

The prospect of experimental verification of the large extra dimension scenario in rare decays is discussed. The case of J/Ψand Υto photon + missing energy is calculated in detail, and it is shown that the limit on the compactification scale M_S lies at present in the ten GeV range. In contrast to the quarkonium systems, signals in Kaon and Pion decays will be small.

hep-ph↗

arXiv2000

Semi-Exclusive Production of Photons at HERA

We study the feasibility of measuring semi-exclusive photon production γ+ p \to γ+ Y at HERA. The cross section of photons produced at large transverse momenta, recoiling off an inclusive system Y of limited mass, can without photon isolation cuts be simply expressed in terms of hard pQCD subprocesses and standard target parton distributions. With the help of event generators we identify the kinematic region where quark and gluon fragmentation processes can be neglected. The cross section in this semi-exclusive region is large enough to be measured with an upgraded HERA luminosity of L = 100/pb. The subprocesses of lowest order in α_s are suppressed at low recoil masses M_Y, compared to higher order gluon exchange, i.e. BFKL contributions. The distinct M_Y-dependence makes it possible to determine experimentally the kinematic range where the higher order processes dominate.

hep-ph↗