arXiv subjects

Michael Schmitt

Publications and source records attributed to Michael Schmitt.

61 records · Page 4Linked to original sources

arXiv2007

Detecting Neutrino Magnetic Moments with Conducting Loops

It is well established that neutrinos have mass, yet it is very difficult to measure those masses directly. Within the standard model of particle physics, neutrinos will have an intrinsic magnetic moment proportional to their mass. We examine the possibility of detecting the magnetic moment using a conducting loop. According to Faraday's Law of Induction, a magnetic dipole passing through a conducting loop induces an electromotive force, or EMF, in the loop. We compute this EMF for neutrinos in several cases, based on a fully covariant formulation of the problem. We discuss prospects for a real experiment, as well as the possibility to test the relativistic formulation of intrinsic magnetic moments.

hep-ex↗

arXiv2004

Apparent Excess in e+e- --> hadrons

We have studied measurements of the cross section for e+e- --> hadrons for center-of-mass energies in the range 20--209 GeV. We find an apparent excess over the predictions of the Standard Model across the whole range amounting to more than 4σ. As an example, we compare the data to predictions for a light scalar down-type quark which fit the excess well.

hep-ex↗

arXiv2003

Invisible Z-Boson Decays at e+e- Colliders

The measurement of the invisible Z-boson decay width at e+e- colliders can be done "indirectly", by subtracting the Z-boson visible partial widths from the Z-boson total width, or "directly", from the process e+e- -> γν\barν. Both procedures are sensitive to different types of new physics and provide information about the couplings of the neutrinos to the Z-boson. At present, measurements at LEP and CHARM II are capable of constraining the left-handed Zνν-coupling, 0.45 <~ g_L <~ 0.5, while the right-handed one is only mildly bounded, |g_R| <= 0.2. We show that measurements at a future e+e- linear collider at different center-of-mass energies, \sqrt{s} = MZ and \sqrt{s}s ~ 170 GeV, would translate into a markedly more precise measurement of the Zνν-couplings. A statistically significant deviation from Standard Model predictions will point toward different new physics mechanisms, depending on whether the discrepancy appears in the direct or the indirect measurement of the invisible Z-width. We discuss some scenarios which illustrate the ability of different invisible Z-boson decay measurements to constrain new physics beyond the Standard Model.

hep-ph↗

arXiv2001

Testing the Standard Model at the Fermilab Tevatron

In this note we study the prospect of high-precision measurements of W boson mass, top quark mass, and forward-backward asymmetry in Z->ee decays and the search for the Higgs boson during Run 2 to challenge the standard model.

hep-ph↗

arXiv1998

Charginos and Neutralinos in the Light of Radiative Corrections: Sealing the Fate of Higgsino Dark Matter

We analyze the LEP constraints from searches for charginos $χ^{\pm}$ and neutralinos $χ_i$, taking into account radiative corrections to the relations between their masses and the underlying Higgs-mixing and gaugino-mass parameters $μ, m_{1/2}$ and the trilinear mass parameter $A_t$. Whilst radiative corrections do not alter the excluded domain in $m_{χ^{\pm}}$ as a function of $m_{χ^{\pm}} - m_χ$, its mapping into the $μ, m_{1/2}$ plane is altered. We update our previous lower limits on the mass of gaugino dark matter and on tan$β$, the ratio of Higgs vacuum expectation values, in the light of the latest LEP data and these radiative corrections. We also discuss the viability of Higgsino dark matter, incorporating co-annihilation effects into the calculation of the Higgsino relic abundance. We find that Higgsino dark matter is viable for only a very limited range of $μ$ and $m_{1/2}$, which will be explored completely by upcoming LEP runs.

hep-ph↗

arXiv1997

Constraints on Neutralino Dark Matter from LEP 2 and Cosmology

A significant lower limit on the mass of the lightest neutralino χcan be obtained by combining the results from sparticle searches at LEP at centre-of-mass energies up to 172 GeV with cosmological considerations, if it is assumed that the χis stable. Exclusion domains from slepton searches close m_χ\sim 0 loopholes that were left open by previous lower-energy LEP searches for charginos and neutralinos, leading to the lower limit $m_χ\ga 17$ GeV. The constraints on supersymmetric parameter space are strengthened significantly if LEP constraints on supersymmetric Higgs bosons are taken into account, and further if the relic neutralino density is required to fall within the range favoured by astrophysics and cosmology. These bounds are considerably strengthened if universality at the GUT scale is assumed for soft supersymmetry-breaking scalar masses, including those of the Higgs bosons. In this case, the Higgs searches play a dramatic role, and we find that m_χ\ga 40 GeV. Furthermore, we find that if tanβ\la 1.7 for μ<0, or tanβ\la 1.4 for μ>0, the cosmological relic density is too large for all values of m_χ.

hep-ph↗

arXiv1996

Supersymmetric Dark Matter in the Light of LEP 1.5

We discuss the lower limit on the mass of the neutralino $χ$ that can be obtained by combining data from $e^+e^-$ annihilation at LEP and elsewhere with astrophysical and theoretical considerations. Loopholes in the purely experimental analysis of ALEPH data from the Z peak and LEP 1.5, which appear when $μ<0$ for certain values of the sneutrino mass $m_{\tildeν}$ and the ratio $\tanβ$ of supersymmetric Higgs vacuum expectation values, may be largely or totally excluded by data from lower-energy $e^+e^-$ data, the hypothesis that most of the cosmological dark matter consists of $χ$ particles, and the assumption that electroweak symmetry breaking is triggered by radiative corrections due to a heavy top quark. The combination of these inputs imposes $m_χ \ge 21.4~\gev$, if soft supersymmetry-breaking masses are assumed to be universal at the grand-unification scale.

hep-ph↗