39 research outputs found
Extra generations and discrepancies of electroweak precision data
It is shown that additional chiral generations are not excluded by the latest
electroweak precision data if one assumes that there is no mixing with the
known three generations. In the case of ``heavy extra generations'', when all
four new particles are heavier than boson, quality of the fit for the one
new generation is as good as for zero new generations (Standard Model). In the
case of neutral leptons with masses around 50 GeV (``partially heavy extra
generations'') the minimum of is between one and two extra
generations.Comment: 10 pages, TeX. An additional reference and P.P.S. about heavy higgs
are adde
Two-Loop Gluon-Condensate Contributions To Heavy-Quark Current Correlators: Exact Results And Approximations
The coefficient functions of the gluon condensate , in the correlators
of heavy-quark vector, axial, scalar and pseudoscalar currents, are obtained
analytically, to two loops, for all values of . In the limiting
cases , , and , comparisons are made with previous
partial results. Approximation methods, based on these limiting cases, are
critically assessed, with a view to three-loop work. High accuracy is achieved
using a few moments as input. A {\em single} moment, combined with only the
{\em leading} threshold and asymptotic behaviours, gives the two-loop
corrections to better than 1% in the next 10 moments. A two-loop fit to vector
data yields GeV.Comment: 9 page
On the search for muonic photons in neutrino experiments
Conserved muonic number may turn out to be a conserved muonic charge, coupled
to muonic photons, gamma_mu. Muons and muonic neutrinos would emit gamma_mu's,
which might be discovered by analysing the data from the past and future high
energy neutrino experiments (like CHARM II, CCFR, CHORUS, NOMAD, etc.). There
are two sources of gamma_mu's in these experiments: 1) internal bremsstrahlung
in pion and kaon decays into mu and nu_mu, which provide neutrino beams; 2)
external bremsstrahlung of muons in the shielding of the neutrino beam. In both
cases the gamma_mu's would pass freely through the shielding and produce narrow
muonic pairs in the neutrino detectors. These pairs could be distinguished from
the trident events nu_mu + Z -> nu_mu + mu^+ + mu^- + Z by their kinematical
properties: small p_t of the muon pair, small invariant mass, etc. All the
above processes are quantitatively analysed in this paper.Comment: 12 pages, latex, 14 figures, LaTEX, PS file and figures in EPS format
available at http://marwww.in2p3.fr/leptop/mugamma/mugamma.htm
TESLA: Potentials of and Options in Stoponium Searches
In some supersymmetric extensions of the Standard Model fairly light
superpartner of t-quark is predicted, which may form bound states - stoponiums.
We estimate potentials of TESLA linear collider in search for stoponium,
considering the basic e+e- option and the gamma-gamma option (Photon Linear
Collider - PLC).
It is found that PLC could be the best machine for discovery of these new
narrow strong resonances. It can produce thousands stoponiums per 100 fb
integrated luminosity in the high energy peak. In the case of scenarios when
stoponium decays mainly into gluons the signal/background ratio is about 1/4.
The channel S->hh into two lightest Higgs bosons could be also seen with high
significance. Thus, several weeks run is sufficient for the stoponium
discovery, if its mass is approximately known (e.g. from observation of direct
stops production at LHC). Then, in MSSM scenarios with dominant S->hh decay PLC
shows excellent possibilities to discover bound state of stops, practically
immediately after beginning of operating.
The e+e- option also has some prospects to observe stoponium but only in the
case of scenarios with dominant decay into two lightest Higgs bosons, with tens
of events per 100 . Interesting possibility appears in the case when
the resonance is seated on 0.1% width luminosity peak - one could resolve the
stoponium exited states.Comment: Standard LaTeX, 15 pages, 2 figures, uses elsart.cls. Talk at the
International Workshop on High Energy Photon Colliders (GG2000, DESY,
Hamburg, June 14-17, 2000), to be published in Nucl. Instr. and Meth. A.
Numbers for e+e- production are change
Effects of genuine dimension-six Higgs operators
We systematically discuss the consequences of genuine dimension-six Higgs
operators. These operators are not subject to stringent constraints from
electroweak precision data. However, they can modify the couplings of the Higgs
boson to electroweak gauge bosons and, in particular, the Higgs
self-interactions. We study the sensitivity to which those couplings can be
probed at future \ee linear colliders in the sub-TeV and in the multi-TeV
range. We find that for GeV with a luminosity of 1 ab the
anomalous and couplings may be probed to about the 0.01 level, and
the anomalous coupling to about the 0.1 level.Comment: 21 pages, 17 figures; typos corrected and references adde
Two Photon Radiation in W and Z Boson Production at the Tevatron Collider
We present a calculation of two photon radiation in W and Z boson production
in hadronic collisions, based on the complete matrix elements for the processes
q\bar q'\to\ell^\pm\nu\gamma\gamma and q\bar q\to\ell^+\ell^-\gamma\gamma,
including finite charged lepton masses. In order to achieve stable numerical
results over the full phase space, multiconfiguration Monte Carlo techniques
are used to map the peaks in the differential cross section. Numerical results
are presented for the Fermilab Tevatron.Comment: Revtex, 28 pages, 3 figure
Consequences of the extra SM families on the Higgs boson production at Tevatron and LHC
The latest electroweak precission data allow the existence of additional
chiral generations in the standard model. We study the influence of extra
generations on the production of SM Higgs boson at hadron colliders. Due to the
enhancement of the gluon fusion channel, the ``golden mode'' becomes more
promising even at upgraded Tevatron. Furthermore, the formation of the fourth
family quarkonia with the subsequent decay introduces
additional tool for the investigation of the Higgs boson properties.Comment: 12 pages, 6 figures, 2 table
Examining the Higgs boson potential at lepton and hadron colliders: a comparative analysis
We investigate inclusive Standard Model Higgs boson pair production at lepton
and hadron colliders for Higgs boson masses in the range 120 GeV < m_H < 200
GeV. For m_H < 140 GeV we find that hadron colliders have a very limited
capability to determine the Higgs boson self-coupling, \lambda, due to an
overwhelming background. We also find that, in this mass range, supersymmetric
Higgs boson pairs may be observable at the LHC, but a measurement of the self
coupling will not be possible. For m_H > 140 GeV we examine ZHH and HH nu
bar-nu production at a future e+e- linear collider with center of mass energy
in the range of sqrt{s}=0.5 - 1 TeV, and find that this is likely to be equally
difficult. Combining our results with those of previous literature, which has
demonstrated the capability of hadron and lepton machines to determine \lambda
in either the high or the low mass regions, we establish a very strong
complementarity of these machines.Comment: Revtex, 25 pages, 2 tables, 10 figure
Determining the Higgs Boson Self Coupling at Hadron Colliders
Inclusive Standard Model Higgs boson pair production at hadron colliders has
the capability to determine the Higgs boson self-coupling, lambda. We present a
detailed analysis of the gg\to HH\to (W^+W^-)(W^+W^-)\to
(jjl^\pm\nu)(jj{l'}^\pm\nu) and gg\to HH\to (W^+W^-)(W^+W^-)\to
(jjl^\pm\nu)({l'}^\pm\nu {l''}^\mp\nu) (l, {l'}, {l''}=e, \mu) signal channels,
and the relevant background processes, for the CERN Large Hadron Collider, and
a future Very Large Hadron Collider operating at a center-of-mass energy of 200
TeV. We also derive quantitative sensitivity limits for lambda. We find that it
should be possible at the LHC with design luminosity to establish that the
Standard Model Higgs boson has a non-zero self-coupling and that lambda /
lambda_{SM} can be restricted to a range of 0-3.8 at 95% confidence level (CL)
if its mass is between 150 and 200 GeV. At a 200 TeV collider with an
integrated luminosity of 300 fb^{-1}, lambda can be determined with an accuracy
of 8 - 25% at 95% CL in the same mass range.Comment: 28 pages, Revtex3, 9 figures, 3 table
Single Top Quark at Future Hadron Colliders. Complete Signal and Background Study
We perform a detail theoretical study including decays and jet fragmentation
of all the important modes of the single top quark production and all basic
background processes at the upgraded Tevatron and LHC colliders. Special
attention was paid to the complete tree level calculation of the QCD fake
background which was not considered in the previous studies. Analysis of the
various kinematical distributions for the signal and backgrounds allowed to
work out a set of cuts for an efficient background suppression and extraction
of the signal. It was shown that the signal to background ratio after optimized
cuts could reach about 0.4 at the Tevatron and 1 at the LHC. The remaining
after cuts rate of the signal at the LHC for the signature is
expected to be about 6.1 pb and will be enough to study the single top physics
even during the LHC operation at a low luminosity.Comment: 15 pages, LaTex, 7 figure