arXiv subjects

Roman Pasechnik

Publications and source records attributed to Roman Pasechnik.

154 records · Page 9Linked to original sources

arXiv2010

Finite-width effects in the near-threshold ZZZ and ZWW production at ILC

We calculate the cross-section of the near-threshold off-shell $ZZZ$ and $ZW^+W^-$ production at the International Linear Collider taking into account their instability and the principal part of NLO corrections. The calculations are performed in the framework of the model of unstable particles with smeared mass-shell. We show that the contribution of the finite $Z/W$ and $H$ widths (their instability) is large in the Higgs resonance range and should be taken into account in the Higgs boson searches at future colliders.

hep-ph↗

arXiv2010

Diffractive deep inelastic scattering from multiple soft gluon exchange in QCD

Diffractive hard scattering is interpreted as the effect of soft gluon exchanges between the emerging energetic quarks and the nucleon's color field, resulting in an overall color singlet exchange. Summing multiple gluon exchanges to all orders leads to exponentiation and an amplitude in analytic form. Numerical evaluation reproduces the precise HERA data and gives new insights on the density of gluons in the proton.

hep-ph↗

arXiv2010

Polarisation effects in the central exclusive $χ_c$ production and the $J/ψ$ angular distributions

We discuss exclusive elastic double diffractive axial-vector $χ_c(1^+)$ and tensor $χ_c(2^+)$ mesons production for different meson polarisations in proton-(anti)proton collisions at the Tevatron energy. The amplitude for the process is derived within the $k_t$-factorisation approach using unintegrated gluon distributions (UGDFs). Differential cross sections for different $χ_c$ polarisations are calculated. Angular distributions of $J/ψ$ meson from the radiative $χ_c(1^+,2^+)$ decays are derived. Prospects for experimental selection of different spin states of $χ_c$ mesons are discussed.

hep-ph↗

arXiv2010

Spin effects in diffractive charmonia production

We consider exclusive double diffractive production of polarised axial-vector $χ_c(1^+)$ and tensor $χ_c(2^+)$ charmonia in proton-(anti)proton collisions at Tevatron energy. The corresponding amplitudes for these processes are derived within the $k_t$-factorisation approach. Contributions from different polarisation states of axial-vector and tensor charmonia are quantified. Corresponding experimental consequences are discussed.

hep-ph↗

arXiv2010

Nucleon spin structure at low momentum transfers

The generalized Gerasimov-Drell-Hearn (GDH) sum rule is known to be very sensitive to QCD radiative and power corrections. We improve the previously developed QCD-inspired model for the $Q^2$-dependence of the GDH sum rule. We take into account higher order radiative and higher twist power corrections extracted from precise Jefferson Lab data on the lowest moment of the spin-dependent proton structure function $Γ_1^{p}(Q^2)$ and on the Bjorken sum rule $Γ_1^{p-n}(Q^2)$. By using the singularity-free analytic perturbation theory we demonstrate that the matching point between chiral-like positive-$Q^2$ expansion and QCD operator product $1/Q^2$-expansion for the nucleon spin sum rules can be shifted down to rather low $Q\simeqΛ_{QCD}$ leading to a good description of recent proton, neutron, deuteron and Bjorken sum rule data at all accessible $Q^2$.

hep-ph↗

arXiv2010

QCD rescattering mechanism for diffractive deep inelastic scattering

We present a QCD-based model where rescattering between final state partons in deep inelastic scattering leads to events with large rapidity gaps and a leading proton. In the framework of this model the amplitude for multiple gluon exchanges is calculated in the eikonal approximation to all orders in perturbation theory. Both large and small invariant mass M_X limits are considered. The model successfully describes the precise HERA data on the diffractive deep inelastic cross section in the whole available kinematical range and gives new insight into the density of gluons at very small momentum fractions in the proton.

hep-ph↗

arXiv2010

Diffractive exclusive production of heavy quark pairs at high energy proton-proton collisions

We discuss exclusive double diffractive (EDD) production of heavy quark - heavy antiquark pairs at high energies. Differential distributions for $c \bar c$ at $\sqrt{s}$ = 1.96 GeV and for $b \bar b$ at $\sqrt{s}$ = 14 TeV are shown and discussed. Irreducible leading-order $b \bar b $ background to Higgs production is calculated for the first time in several kinematical variables. The signal-to-background ratio is shown and several improvements are suggested.

hep-ph↗

arXiv2009

Exclusive double-diffractive production of open charm in proton-proton and proton-antiproton collisions

We calculate differential cross sections for exclusive double diffractive (EDD) production of open charm in proton-proton and proton-antiproton collisions. Sizeable cross sections are found. The EDD contribution constitutes about 1 % of the total inclusive cross section for open charm production. A few differential distributions are shown and discussed. The EDD contribution falls faster both with transverse momentum of the $c$ quark/antiquark and the $c \bar c$ invariant mass than in the inclusive case.

hep-ph↗

arXiv2005

Higgsinos as carriers of SUSY residual effects

New version of the MSSM scales is discussed. In this version mu << M_{SUSY} ~ M_0 ~ M_{1/2}, where mu is the Higgsino mass, M_0 is the mass scale of sleptons and squarks, M_{1/2} is the mass scale of gaugino. Renormalization group motivation of this MSSM version is proposed. The radiation corrections give main contribution to the splitting of neutralino and chargino masses if M_{SUSY} > 10^7 GeV. Calculation of the mass difference has led to the value M_{chi_1^\pm}-M_{chi_{1,2}^0} ~ 360 MeV at M_{chi} ~ mu ~ 3 TeV. The mean life time of charged Higgsino in this model is tau_{chi_1^\pm} ~ 0.4 * 10^{-9} s. The analysis of the residual neutralino concentration in the cosmological plasma is developed and the value of Higgsino mass is estimated: M_{chi} ~ 3 TeV. Formation of the residual neutralino concentration occurs in the high symmetric phase of the cosmological plasma. Problems of the relic Higgsinos searches at the underground laboratory NUSEL and Galactic neutralino annihilation radiation at the satellite detector GLAST are discussed.

hep-ph↗

arXiv2005

Split Light Higgsino from Split Supersymmetry

New version of MSSM scales is discussed. In this version mu << M_{SUSY} ~ M_0 \~ M_{1/2}, where mu is the Higgsino mass, M_0 is the mass scale of sleptons and squarks, M_{1/2} is the mass scale of gaugino. Renormalization group motivation of this MSSM version is proposed. Analysis of Split Supersymmetry ideas in this case together with the Dark Matter arguments results in the statement that the formation of residual neutralino concentration occurs in the high symmetric phase of cosmological plasma. The value of Higgsino mass is estimated. The recharging process for high energy neutralinos in the neutralino-nucleus scattering is considered. There has been reported the possibility to check-up of the model predictions at modern experimental facilities NUSEL and GLAST.

hep-ph↗