A. Hovhannisyan
A5014399600- Particle physics theoretical and experimental studies
- Quantum Chromodynamics and Particle Interactions
- High-Energy Particle Collisions Research
- Black Holes and Theoretical Physics
- Cosmology and Gravitation Theories
- Dark Matter and Cosmic Phenomena
- Particle Accelerators and Free-Electron Lasers
- Neutrino Physics Research
A. Alikhanyan National Laboratory
2004-2022
RWTH Aachen University
2005-2008
Joint Institute for Nuclear Research
2003-2008
University of Birmingham
2008
National Center for Theoretical Sciences
2007-2008
National Taiwan University
2007-2008
Stanford University
2007
University of Bern
2007
European Organization for Nuclear Research
2007
Lund University
2005
Combining our results for various O(alpha[s]) corrections to the weak radiative B-meson decay, we are able present first estimate of branching ratio at next-to-next-to-leading order in QCD. We find B(B[over ]-->X[s]gamma)=(3.15+/-0.23) x 10(-4) Egamma>1.6 GeV B[over ]-meson rest frame. The four types uncertainties:nonperturbative (5%), parametric (3%), higher-order and m(c)-interpolation ambiguity (3%) have been added quadrature obtain total error.
A first measurement is reported of the longitudinal proton structure function F_L(x,Q^2) at ep collider HERA. It based on inclusive deep inelastic e^+p scattering cross section measurements with a positron beam energy 27.5 GeV and energies 920, 575 460 GeV. Employing dependence section, F_L measured in range squared four-momentum transfers 12 < Q^2 90 GeV^2 low Bjorken x 0.00024 0.0036. The values agree higher order QCD calculations parton densities obtained using data previously
We present next-to-next-to leading logarithmic (NNLL) results for the double differential decay width $d\ensuremath{\Gamma}(\stackrel{\ensuremath{\rightarrow}}{b}{X}_{s}{\mathcal{l}}^{+}{\mathcal{l}}^{\ensuremath{-}})/[d\ifmmode \hat{s}\else \^{s}\fi{}d\mathrm{cos}(\ensuremath{\theta})],$ where $s=\ifmmode \^{s}\fi{}{m}_{b}^{2}$ is invariant mass squared of lepton pair and \ensuremath{\theta} angle between momentum b quark ${\mathcal{l}}^{+},$ measured in rest frame pair. From these we also...
We present new contributions to the decay matrix element ${\mathrm{\ensuremath{\Gamma}}}_{12}^{q}$ of ${B}_{q}\ensuremath{-}{\overline{B}}_{q}$ mixing complex, where $q=d$ or $s$. Our results constitute order ${\ensuremath{\alpha}}_{s}^{2}{N}_{f}$ corrections penguin Wilson coefficients entering with full dependence on charm quark mass. This is first step toward prediction $CP$ asymmetry ${a}_{\mathrm{fs}}^{q}$ quantifying violation in at next-to-next-to-leading logarithmic (NNLO) quantum...
The process of charm quark fragmentation is studied using D * ± meson production in deep-inelastic scattering as measured by the H1 detector at HERA. parameters functions are extracted for QCD models based on leading order matrix elements and DGLAP or CCFM evolution partons together with string particle decays. Additionally, they determined a next-to-leading calculation fixed flavour number scheme independent quarks to mesons. Two different regions phase space investigated defined presence...
A search for excited electrons is performed using the full $e^{\pm}p$ data sample collected by H1 experiment at HERA, corresponding to a total luminosity of 475 pb$^{-1}$. The electroweak decays ${e}^{*}\to{e}{\gamma}$, ${e}^{*}\to{e}Z$ and ${e}^{*}{\to}\nu W$ with subsequent hadronic or leptonic $W$ $Z$ bosons are considered. No evidence electron production found. Mass dependent exclusion limits on $e^*$ cross sections ratio $f/{\Lambda}$ coupling compositeness scale derived within gauge...
The forward-backward asymmetry ${\mathcal{A}}_{\mathrm{FB}}$ in $B\ensuremath{\rightarrow}{K}^{*}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decay is a sensitive probe of new physics. Previous studies have focused on the sensitivity position zero. However, effective Wilson coefficients (short distance couplings) are principle complex, as illustrated by $B\ensuremath{\rightarrow}\ensuremath{\rho}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ within standard...
We propose formulas for computing the phase space integrals of $1\ensuremath{\rightarrow}3$ and $1\ensuremath{\rightarrow}4$ processes with massive particles in final states. As an application these formulas, we study state mass effects some interesting phenomenological cases, giving fully integrated analytic results corresponding spaces. consider also ${B}_{s}\ensuremath{-}{\overline{B}}_{s}$ process at next-to-next-to-leading order calculate one most complicated master integrals, which...
A bstract We calculate a class of three-loop Feynman diagrams which contribute to the next-to-next-to-leading logarithmic approximation for width difference ΔΓ s in $$ {B}_s-{\overline{B}}_s <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>B</mml:mi> <mml:mi>s</mml:mi> </mml:msub> <mml:mo>−</mml:mo> <mml:mover> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> system. The considered contain closed fermion loop gluon propagator and constitute order α 2 N f , where is...
In a recent paper we presented calculation of NNLL virtual corrections to the forward-backward asymmetries in $b\to X_s\ell^+\ell^-$ decay. That result does not include bremsstrahlung which are free from infrared and collinear singularities. present remaining ${\cal O}(\alpha_s)$ The numerical effect calculated contributions is found be below 1%.
The uncertainty of the theoretical prediction $\bar B \to X_s γ$ branching ratio at NLL level is dominated by charm mass renormalization scheme ambiguity. In this paper we calculate those NNLL terms which are related to $m_c$, in order get an estimate corresponding level. We find that these significantly reduce (by typically a factor two) error on ${BR}(\bar γ)$ induced definition $m_c$. Taking into account experimental accuracy around 10% and future prospects $B$ factories, conclude...
The first measurement of diffractive scattering quasi-real photons with large momentum transfer γp→γY, where Y is the proton dissociative system, made using H1 detector at HERA. performed for initial photon virtualities Q2<0.01GeV2. Single differential cross sections are measured as a function W, incident photon–proton centre mass energy, and t, square four-momentum transferred vertex, in range 175<W<247GeV 4<|t|<36GeV2. W dependence well described by model based on perturbative QCD leading...
The production of neutral strange hadrons is investigated using deep-inelastic scattering events measured with the H1 detector at HERA. measurements are made in phase space defined by negative four-momentum transfer squared photon 2 < Q^2 100 GeV^2 and inelasticity 0.1 y 0.6. K_s Lambda cross sections their ratios determined. compared to charged particles same region space. - anti-Lambda asymmetry also found be consistent zero. Predictions leading order Monte Carlo programs data.
We calculate the three-loop master integrals of Ref. [1] in analytic form.This allows us to present fermionic contributions ∆B = 2 Wilson coefficients B-B decay matrix next-to-next-to-leading order QCD with full dependence on mass charm quark loops.
The present NLL prediction for the decay rate of rare inclusive process B → X s γ has a large uncertainty due to charm mass renormalization scheme ambiguity.We estimate that this will be reduced by factor 2 at NNLL level.This is strong motivation on-going calculation, which thus significantly increase sensitivity observable possible new degrees freedom beyond SM.We also give brief status report calculation.