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V. A. Khoze

Publications and source records attributed to V. A. Khoze.

At least 181 records · Page 10Linked to original sources
arXiv1998

Soft-Particle Spectra as a Probe of Interconnection Effects in Hadronic W^+ W^- Events

Cross-talk between the W^+ and W^- sources of hadron production at LEP2 offers a hope to learn about basic properties of QCD, but at the same time threatens high-precision measurements of the W boson mass. Directly visible effects are not expected to be large, however. It is, therefore, important to develop methods to measure the level of interconnection in the data --- `connectometers'. In this article we study one particular set of observables, namely the reduced rate of low-momentum particle production caused by reconnection. In realistic scenarios the expected signals are at the border of visibility, but not quite beyond reach. Special studies on kaons and protons, or with other subsets of the data, could provide supporting evidence. We also show how LEP1 Z$^0$ events could be used to define an alternative reference sample.

hep-ph↗
arXiv1998

Topology of Hadronic Flows for Higgs Production at Hadron Colliders

Hadronic radiation provides a tool to distinguish different topologies of colour flow in hard scattering processes. We study the structure of hadronic flow corresponding to Higgs production and decay in high-energy hadron-hadron collisions. In particular, the signal gg -> H -> b anti-b and background gg -> b anti-b processes are shown to have very different radiation patterns, and this may provide an useful additional method for distinguishing Higgs signal events from the QCD background.

hep-ph↗
arXiv1997

Dijet hadroproduction with rapidity gaps and QCD double logarithmic effects

We show that the hadroproduction of a pair of jets with large transverse energy in the central region bounded by rapidity gaps is an ideal process to see important double logarithmic QCD suppression effects. We compute the cross sections for both exclusive and inclusive double-diffractive dijet production at Tevatron and LHC energies for a range of rapidity configurations.

hep-ph↗
arXiv1997

The rapidity gap Higgs signal at LHC

We compare the WW and pomeron-pomeron fusion mechanisms for the double-diffractive production of a Higgs boson. We determine the suppression of the 'rapidity gap' pomeron-pomeron fusion events due to QCD radiative effects. In particular we use leading log techniques to estimate the cross sections for both exclusive and inclusive double-diffractive Higgs production at LHC energies. The same approach can be applied to the double-diffractive central production of large E_T dijets. These two processes provide one of the most justified applications of various aspects of leading logarithm QCD techniques.

hep-ph↗
arXiv1997

Higgs studies in polarized gamma-gamma collisions

The study of an intermediate mass Higgs boson, via the process gamma-gamma -> H -> bbbar from an initiallypolarized J_z = 0 state, has been advocated as an important feasible goal of a future photon linear collider. The crucial argument was the m_b^2/s suppression of the background process gamma-gamma (J_z = 0) -> bbbar. We critically review the contribution of the radiative background processes (in which the m_b^2/s suppression is absent) to the quasi-two-jet-like events with at least one, but preferably two, tagged energetic b jets. Within a complete study of the radiative processes, we find that a sizeable background contribution can come from the helicity-violating gamma-gamma (J_z = 0) -> bbbar process accompanied by soft gluon emission. These latter radiative corrections contain a new type of double logarithmic (DL) terms. We clarify the physical nature of these novel DL corrections. Despite the fact that the one-loop DL terms are comparable or even larger than the Born term, fortunately we find that the calculation of the cross section in the two-loop approximation is sufficient for a reliable evaluation of the background to the Higgs signal.

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↗
arXiv1996

Perturbative rates and colour rearrangement effects in four-jet events at LEP2

An important issue in the direct reconstruction method of determining the $W$ mass from $q\bar q Q\bar Q$ events at LEP2 concerns the impact of the relatively unknown QCD interconnection effects. It has been suggested that a study of `short string' states, in which colour singlet states are formed from $q \bar Q $ and $Q\bar q$ pairs with small phase--space separation, could shed important light on this issue. We show that such configurations can also be generated by conventional background $e^+e^-\ar 4$~parton processes, in particular QCD $q \bar q g g$ and $q \bar q Q \bar Q$ and non--resonant electroweak $q \bar q Q \bar Q$ production. We study the colour and kinematic structure of these background contributions, and estimate the event rate to be expected at LEP2. We find that the QCD processes are heavily suppressed, but that non--resonant $q \bar q Q \bar Q$ production may be comparable in rate to the expected `short string' signal from $W^+W^-$ production.

hep-ph↗
arXiv1996

Determination of the mass of the W boson

Previous studies of the physics potential of LEP2 indicated that with the design luminosity of 500 inverse picobarn one may get a direct measurement of the mass of the W-boson with a precision in the range 30 - 50 MeV. This report presents an updated evaluation of the estimated error on the mass of the W-boson based on recent simulation work and improved theoretical input. The most efficient experimental methods which will be used are also described.

hep-ph↗
arXiv1996

QCD

We discuss QCD studies that will be possible at LEP2. We examine both experimental and theoretical aspects of jets, fragmentation functions, multiplicities and particle spectra.

hep-ph↗
arXiv1995

$e^+e^- \to b\bar b W^+W^-$ events at the Next Linear Collider: colour structure of top signal and irreducible background

We examine the colour structure and charged particle yield for both the $t \bar t$ signal and the irreducible background processes contributing to \eebbww\ production close to the \ttb\ threshold. The charged particle multiplicity for the various components of the cross section is computed as a function of several kinematic variables. Our study may have important implications for recently proposed studies of interconnection phenomena in \ttb\ production at high--energy $e^+e^-$ colliders

hep-ph↗
arXiv1995

Higher-order Coulomb Corrections to the Threshold e+ e- --> W+ W- Cross Section

The QED Coulomb correction is one of the most important corrections to the e+ e- --> W+ W- total cross section near threshold. We calculate these corrections through second order, and discuss the implications for extracting M_W from a threshold cross section measurement at LEP2. Analytic expressions are derived in various kinematic limits.

hep-ph↗
arXiv1995

Specific Features of Heavy Quark Production. LPHD approach to heavy particle spectra

Perturbative QCD formula for inclusive energy spectra of heavy quarks from heavy quark initiated jets which takes into account collinear and/or soft logarithms in all orders, the exact first order result and two-loop effects is applied to distributions of heavy flavoured hadrons in the framework of the LPHD concept. Fits to experimentally measured charm and bottom mean energy losses result in $α_{\MSbar}(M_Z)=0.125\pm 0.003\pm 0.004$ and $(2\GeV)^{-1}\int_0^{2\GeV} dk α_s^{eff}(k)= 0.18\pm 0.01\pm 0.02$ with $α_s^{eff}$ an infrared finite effective QCD coupling.

hep-ph↗
arXiv1995

On the Coulomb Effects on the W Line Shape at LEP2

One of the most powerful methods for obtaining a precision measurement of M_W at LEP2 is from direct reconstruction of the invariant mass distribution of W bosons produced in e+e- --> W+W-. We investigate the effects on the W line shape, and in particular on the average invariant mass, of phase-space and first-order Coulomb corrections. The latter are shown to have a non-negligible effect on the reconstructed mass, inducing shifts of order -20 MeV at collision energies above threshold, compared to the Born approximation cross section. The sign and magnitude of the effect can be understood in a simple model calculation in which one of the W bosons is assumed to be stable.

hep-ph↗
arXiv1995

COULOMB EFFECTS IN W+ W- PRODUCTION

We calculate the Coulomb effects on the cross section for e+ e- --> W+ W- taking into account the instability of the W bosons. We carefully explain the consequences of instability throughout the energy range which will be accessible at LEP2. We present a formula which allows these effects to be easily implemented.

hep-ph↗
arXiv1994

Three-jet final states and measuring the $γγ$ width of the Higgs at a photon linear collider

The identification of the intermediate-mass Higgs process $γγ\to H \to b \bar b$ will be one of the most important goals of a future photon linear collider. Potentially important backgrounds from the continuum $γγ\to c \bar c, b \bar b$ leading-order processes can be suppressed by a factor $m_q^2/s$ by using polarized photon beams in the $J_z=0$ initial-state configuration. We show that the same $m_q^2/s$ suppressions do not necessarily apply to the radiative processes $γγ\to c \bar c g, b \bar b g$. These processes can mimic the two-jet topology of the Higgs signal when two of the three partons are collinear, or when one of the partons is soft or directed down the beam pipe. We calculate the contribution of these processes to the two-jet background in the $J_z=0$ channel. We investigate the effect of imposing additional event shape, jet width and secondary vertex cuts on both signal and background, and show that with reasonable detector capabilities it should be possible to reduce the background to a manageable level.

hep-ph↗