arXiv subjects

N. V. Krasnikov

Publications and source records attributed to N. V. Krasnikov.

At least 109 records · Page 6Linked to original sources

arXiv1999

Search for SUSY at LHC in Jets + E^{miss}_T final states for the case of nonuniversal gaugino masses

We investigate squark and gluino pair production at LHC (CMS) with subsequent decays into quarks and LSP for the case of nonuniversal gaugino masses. Visibility of signal by an excess over SM background in (n > 1)jets + E^{miss}_T events depends rather strongly on the relation between LSP, gluino and squark masses and it decreases with the increase of LSP mass. For relatively heavy LSP mass closed to squark or gluino masses and for (m_{\tilde{q}}, m_{\tilde{g}}) > 1.5 TeV signal is too small to be observable. For the case when only third generation squarks and LSP are relatively light signal is not visible without b-tagging.

hep-ph↗

arXiv1999

Gaugino pair production at LHC for the case of nonuniversal gaugino masses

We investigate χ^{+/-}_1 χ^0_2 pair production at LHC (CMS) with subsequent decays into leptons for the case of nonuniversal gaugino masses. Visibility of signal by an excess over SM background in 3 leptons + no jet + E^{miss}_T events depends rather strongly on the relation between LSP mass χ^0_1 and χ^{+/-}_1 mass. We also give some preliminary results on the investigation of squark and gluino production at LHC for the case of nonuniversal gaugino masses.

hep-ph↗

arXiv1999

Is it always possible to discover supersymmetry broken at TeV scale at LHC?

We show that the search for supersymmetry at LHC will be very problematic for the particular case of nonuniversal relations among gaugino masses. Namely, if gluino, first chargino and LSP masses are closed to each other it would be very difficult to discover supersymmetry even if sparticle masses are lighter than 1 TeV.

hep-ph↗

arXiv1999

Limits on the magnetic moment of sterile neutrino and two-photon neutrino decay

It is shown that the non-zero transition magnetic moment ($μ_{tran}$) between the sterile neutrino ($ν_{s}$) and the muon neutrino ($ν_μ$) could be effectively searched for via the Primakoff effect, in the process of $ν_μ Z \to ν_{s}Z$ conversion in the external Coulomb field of a nucleus $Z$, with the subsequent $ν_{s}\to ν_μ + γ$ decay. From the recent results of the NOMAD neutrino detector at CERN a model-independent constraint of $μ_{tran} < (10^{-6} - 10^{-9}) μ_{B}$ is obtained depending on the value of $ν_{s}$ mass. For the $m_{s}\sim O(1) GeV$ region these bounds are comparable with the present experimental ones on $ν_μ$ and $ν_{e}$ diagonal magnetic moments and are more sensitive than those on $ν_τ$ magnetic moment. From the same analysis the constraint on $ν_τ(ν_{s})\to ν_μ +γ+ γ$ decay lifetime $τ> 2\times10^{13} sec/m_ν^{7}(MeV)$ is obtained. The limit is valid for neutrino masses up to $m_ν\sim O(1)GeV$.

hep-ph↗

arXiv1999

New Physics Discovery Potential in Future Experiments

We propose a method to estimate the probability of new physics discovery in future high energy physics experiments. Physics simulation gives both the average numbers of background and of signal events. We find that the proper definition of the significance for , >> 1 is S_{12} = sqrt( + ) - sqrt( ) in comparison with often used significances S_1 = /sqrt( ) and S_2 = /sqrt( + ). We propose a method for taking into account the systematical errors related to nonexact knowledge of background and signal cross sections. An account of such systematics is very essential in the search for supersymmetry at LHC. We also propose a method for estimation of exclusion limits on new physics in future experiments.

physics.data-an↗

arXiv1998

Gaugino pair production at LHC (CMS)

hep-ph↗

arXiv1998

On Observability of Signal over Background

Several statistics used by physicists to declare the signal observability over the background are compared. It is shown that the frequentist method of testing a precise hypothesis allows one to estimate the power value of criteria with specified level of significance for the considered statistics by Monte Carlo calculations. The application of this approach for the analysis of discovery potential of experiments is discussed.

physics.data-an↗

arXiv1998

Towards the Observation of Signal over Background in Future Experiments

We propose a method to estimate the probability of new physics discovery in future high energy physics experiments. Physics simulation gives both the average numbers $ $ of background and $ $ of signal events. We find that the proper definition of the significance for $ , \gg 1$ is $S_{12} = \sqrt{ + } - \sqrt{ }$ in comparison with often used significances $S_1 = /\sqrt{ }$ and $S_2 = /\sqrt{ + }$. We also propose a method for taking into account the systematical errors related to nonexact knowledge of background and signal cross sections. An account of such systematics is very essential in the search for supersymmetry at LHC.

physics.data-an↗

arXiv1998

The search for charged sleptons and flavour lepton number violation at LHC (CMS)

We study a possibility to detect charged sleptons and flavour lepton number violation at LHC (CMS). We investigate the production and decays of right- and left-handed sleptons separately. We have found that for luminosity L = 10**5 1/pb it would be possible to detect right-handed sleptons with a mass up to 325 GeV and left-handed ones with a mass up to 350 GeV. We also investigate a possibility to look for flavour lepton number violation in slepton decays due to the mixing of different slepton generations. We find that for the maximal (smu_R - se_R) mixing it is possible to detect such effect for sleptons with a mass up to 250 GeV.

hep-ph↗

arXiv1998

Exotic muon decays and the KARMEN anomaly

An anomaly in time distribution of neutrinos from the ISIS pulsed beam stop source observed by the KARMEN collaboration is discussed. We show that the anomaly can be interpreted as a superposition of two exponentials, both having time constants consistent with the $μ^{+}$ lifetime of 2.2 $μs$. % and, therefore, It is assumed that they both originate from muon decays at rest. One of them describes the time distribution of the prompt neutrino events, while the other describes the time distribution of events from delayed decays of slowly moving ($β\simeq 0.02$) particles in the KARMEN calorimeter. We propose here that these particles are produced in exotic decays of positive muons $μ^{+}\to e^{+} + X$, resulting in the second exponential time distribution shifted by the time of flight with respect to the time distribution of neutrino events. This model gives an aceptable fit to the KARMEN data if $X$ has a mass of 103.9 MeV. The possible decay modes of this new massive neutral particle are discussed. This hypothesis can be experimentally tested in the near future by studying the low energy part of the $e^{+}$ spectrum in the $μ^{+}$ decays.

hep-ph↗

arXiv1998

Phenomenology of $SU(3) \otimes SU(2) \otimes U(1)$ supersymmetric model with Dirac neutrino masses

We consider supersymmetric extension of standard electroweak model with Dirac neutrino masses. In such model for significant region of the parameters right-handed tau sneutrino is the lightest superparticle and right-handed charged tau slepton is the next to lightest superparticle. Due to the smallness of the neutrino masses the right-handed tau slepton is long-lived particle that changes the standard signatures used in the search for supersymmetry at supercolliders. The most striking signatures of such scenario is the existence of highly ionizing tracks and excess of multilepton events that is similar to the phenomenology of gauge-mediated supersymmetry breaking models

hep-ph↗

arXiv1998

On search for a new light gauge boson from $π^{0}(η)\toγ+ X$ decays in neutrino experiments

It is shown that a new light gauge boson $X$ which might be produced in the decays of pseudoscalar mesons $π^{0}(η)\toγ+ X$ could be effectively searched for in neutrino experiments via the Primakoff effect, in the process of $X + Z\to π^{0}(η) + Z$ conversion in the external Coulomb field of a nucleus. An estimate of the $X\to π^{0}$ conversion rate for the NOMAD neutrino detector at CERN is given.

hep-ph↗

arXiv1998

The search for sleptons and flavour lepton number violation at LHC (CMS)

We study a possibility to detect sleptons and flavour lepton number violation at LHC (CMS). We investigate the production and decays of right- and left-handed sleptons separately. We have found that for L = 10**5 1/pb it would be possible to discover right-handed sleptons with a mass up to 350 GeV and left-handed ones with a mass up to 350 GeV. We also investigate a possibility to look for flavour lepton number violation in slepton decays due to the mixing of different generations sleptons. We find that for the maximal (smu_R - se_R) mixing it is possible to detect such effect for sleptons with a mass up to 250 GeV.

hep-ph↗

arXiv1997

Update of the electromagnetic effective coupling constant $α(M^2_Z)$

We recalculate the hadronic contribution to the effective electromagnetic coupling constant $α(M^2_Z)$ using quasi-analytical approximations for the cross-section of $e^{+}e^{-} \to hadrons$ proposed earlier by one of the authors(N.V.K.,Mod.Phys.Lett.A9(1994)2825). We find that $α^{-1}(M^2_Z) = 128.98 \pm 0.06$.

hep-ph↗

arXiv1997

The Higgs boson mass bound in MSSM broken at high scale

We study the dependence of the Higgs boson mass on the supersymmetry breaking scale in the minimal supersymmetric extension of the standard Weinberg-Salam model. In particular, we find that for supersymmetry breaking scale $10^8$ GeV $\leq M_s \leq 10^{16}$ GeV and for $m^{pole}_{top} = 175 \pm 5 $ GeV the Higgs boson mass is 120 GeV $ \leq m_h \leq 160 $ GeV

hep-ph↗

arXiv1997

Supersymmetric SU(5) model with large supersymmetry breaking scale

Taking into account uncertainties related with the initial coupling constants and threshold corrections at low and high scales we find that in standard supersymmetric SU(5) model the supersymmetry breaking scale could be up to $10^8$ GeV. In the extensions of the standard supersymmetric SU(5) model the supersymmetry breaking scale could be up to $O(10^{12})$ GeV. In standard SU(5) supersymmetric model it is possible to increase the GUT scale up to $5 \cdot 10^{17}$ GeV provided that the masses of chiral superoctets and supertriplets are $m_{3,8} \sim O(10^{13})$ GeV. For SU(5) supersymmetric model with $10^6$ GeV $\leq M_{SUSY} \leq 10^8$ GeV the Higgs boson mass is predicted to be 120 GeV $\leq m_h \leq $ 150 GeV.

hep-ph↗

arXiv1997

Influence of $SU(2) \otimes U(1)$ singlet scalars on Higgs boson signal at LHC

We investigate a model of $SU(2) \otimes U(1)$ singlet scalars coupled to Standard Model. We point out that for the case of maximal mixing between singlet scalars and standard Higgs boson the Higgs boson production cross section is smaller than the standard Higgs boson production by factor $\frac{1}{N+1}$, where N is the number of singlet scalar scalars. For the case of big mixing Higgs boson could be nonobservable at LHC. However, there is also a possibility for the observation of scalar singlets at LHC. As a quasirealistic example we discuss a supersymmetric $SU(2) \otimes U(1)$ electroweak model with an additional gauge singlet chiral superfield.

hep-ph↗

arXiv1997

The search for new physics by the measurement of the 4-jet cross section at LHC and FNAL

We investigate the possibility to look for new physics by the measurement of the 4-jet cross section at LHC and FNAL. In particular, we consider the model with scalar colour octet and the supersymmetric model with R-parity violation. In both models pair produced new particles decay into 2 jets thus leading to 4-jet events. Therefore, the measurement of the distributions of 4-jet differential cross section on the invariant dijet masses allows to look for new physics. The main background comes from standard QCD 4-jet events. We find that at LHC it would be possible to discover scalar colour particles with masses up to 900 Gev and for FNAL the corresponding bound is 175 Gev.

hep-ph↗