2,866 research outputs found
An analytical program for fermion pair production in e+e- annihilation
We describe how to use {\tt ZFITTER}, a program based on a semi-analytical approach to fermion pair production in e^+ e^- annihilation and Bhabha scattering. A flexible treatment of complete {\cal O}(\alpha) QED corrections, also including higher orders, allows for three calculational {\bf chains} with different realistic sets of restrictions in the photon phase space. {\tt ZFITTER} consists of several {\bf branches} with varying assumptions on the underlying hard scattering process. One includes complete {\cal O}(\alpha) weak loop corrections with a resummation of leading higher-order terms. Alternatively, an ansatz inspired from S-matrix theory, or several model-independent effective Born cross sections may be convoluted. The program calculates cross sections, forward-backward asymmetries, and for \tau~pair production also the final-state polarization. Various {\bf interfaces} allow fits to be performed with different sets of free parameters
Solar neutrinos: global analysis with day and night spectra from SNO
We perform global analysis of the solar neutrino data including the day and
night spectra of events at SNO. In the context of two active neutrino mixing,
the best fit of the data is provided by the LMA MSW solution with Delta m^2 =
6.15 10^{-5} eV^2, tan^2\theta = 0.41, f_B = 1.05, where f_B is the boron
neutrino flux in units of the corresponding flux in the Standard Solar Model
(SSM). At 3 sigma level we find the following upper bounds: tan^2\theta < 0.84
and Delta m^2 < 3.6 10^{-4} eV^2. From 1 sigma-interval we expect the day-night
asymmetries of the charged current and electron scattering events to be:
A_{DN}^{CC} = 3.9 +3.6-2.9 and A_{DN}^{ES} = 2.1 +2.1-1.4. The only other
solution which appears at 3 sigma-level is the VAC solution with Delta m^2 =
4.5 10^{-10} eV^2, tan^2\theta = 2.1 and f_B=0.75. The best fit point in the
LOW region, with Delta m^2 = 0.93 10^{-7} eV^2 and tan^2\theta = 0.64, is
accepted at 99.95% (3.5 sigma) C.L. . The least chi^2 point from the SMA
solution region, with Delta m^2 = 4.6 10^{-6} eV^2 and tan^2\theta = 5 10^{-4},
could be accepted at 5.5 sigma-level only. In the three neutrino context the
influence of theta_{13} is studied. We find that with increase of theta_{13}
the LMA best fit point shifts to larger Delta m^2, mixing angle is practically
unchanged, and the quality of the fit becomes worse. The fits of LOW and SMA
slightly improve. Predictions for KamLAND experiment (total rates, spectrum
distortion) have been calculated.Comment: Typos corrected, reference adde
The MSW effect and Matter Effects in Neutrino Oscillations
The MSW (Mikheyev-Smirnov-Wolfenstein) effect is the adiabatic or partially
adiabatic neutrino flavor conversion in medium with varying density. The main
notions related to the effect, its dynamics and physical picture are reviewed.
The large mixing MSW effect is realized inside the Sun providing the solution
of the solar neutrino problem. The small mixing MSW effect driven by the 1-3
mixing can be realized for the supernova (SN) neutrinos. Inside the collapsing
stars new elements of the MSW dynamics may show up: the non-oscillatory
transition, non-adiabatic conversion, time dependent adiabaticity violation
induced by shock waves. Effects of the resonance enhancement and the parametric
enhancement of oscillations can be realized for the atmospheric and accelerator
neutrinos in the Earth. Precise results for neutrino oscillations in the low
density medium with arbitrary density profile are presented and the attenuation
effect is described. The area of applications is the solar and SN neutrinos
inside the Earth, and the results are crucial for the neutrino oscillation
tomography.Comment: 18 pages, latex, 6 figures, talk given at the Nobel Symposium 129,
``Neutrino Physics'', Haga Slott, August 19 - 24, 200
Cosmology and New Physics
A comparison of the standard models in particle physics and in cosmology
demonstrates that they are not compatible, though both are well established.
Basics of modern cosmology are briefly reviewed. It is argued that the
measurements of the main cosmological parameters are achieved through many
independent physical phenomena and this minimizes possible interpretation
errors. It is shown that astronomy demands new physics beyond the frameworks of
the (minimal) standard model in particle physics. More revolutionary
modifications of the basic principles of the theory are also discussed.Comment: 37 pages, 5 figures; lectures presented at 9th International Moscow
School of Physics (34th ITEP Winter School
Neutral Particles in Light of the Majorana-Ahluwalia Ideas
The first part of this article (Sections I and II) presents oneself an
overview of theory and phenomenology of truly neutral particles based on the
papers of Majorana, Racah, Furry, McLennan and Case. The recent development of
the construct, undertaken by Ahluwalia [{\it Mod. Phys. Lett. A}{\bf 9} (1994)
439; {\it Acta Phys. Polon. B}{\bf 25} (1994) 1267; Preprints LANL
LA-UR-94-1252, LA-UR-94-3118], could be relevant for explanation of the present
experimental situation in neutrino physics and astrophysics.
In Section III the new fundamental wave equations for self/anti-self
conjugate type-II spinors, proposed by Ahluwalia, are re-casted to covariant
form. The connection with the Foldy-Nigam-Bargmann-Wightman- Wigner (FNBWW)
type quantum field theory is found. The possible applications to the problem of
neutrino oscillations are discussed.Comment: REVTEX file. 21pp. No figure
Four--Neutrino Oscillation Solutions of the Solar Neutrino Problem
We present an analysis of the neutrino oscillation solutions of the solar
neutrino problem in the framework of four-neutrino mixing where a sterile
neutrino is added to the three standard ones. We perform a fit to the full data
set corresponding to the 825-day Super-Kamiokande data sample as well as to
Chlorine, GALLEX and SAGE and Kamiokande experiments. In our analysis we use
all measured total event rates as well as all Super-Kamiokande data on the
zenith angle dependence and the recoil electron energy spectrum. We consider
both transitions via the Mikheyev-Smirnov-Wolfenstein (MSW) mechanism as well
as oscillations in vacuum (just-so) and find the allowed solutions for
different values of the additional mixing angles. This framework permits
transitions into active or sterile neutrinos controlled by the additional
parameter . We discuss the
maximum allowed values of this additional mixing parameter for the different
solutions.Comment: 28 pages Latex file using RevTeX. 8 postscript figures included
(bitmapped for compression). Detailed explanation of criterion 3 and lower
two graphs of Fig. 8. Misprints corrected in table II.A full version of the
paper can be found at http://ific.uv.es/~penya/papers/four
Measurement of K^0_e3 form factors
The semileptonic decay of the neutral K meson, KL -> pi e nu (Ke3), was used
to study the strangeness-changing weak interaction of hadrons. A sample of 5.6
million reconstructed events recorded by the NA48 experiment was used to
measure the Dalitz plot density. Admitting all possible Lorentz-covariant
couplings, the form factors for vector (f_+(q^2)), scalar (f_S) and tensor
(f_T) interactions were measured. The linear slope of the vector form factor
lambda_+ = 0.0284+-0.0007+-0.0013 and values for the ratios |f_S/f_+(0)| =
0.015^{+0.007}_{-0.010}+-0.012 and |f_T/f_+(0)| = 0.05^{+0.03}_{-0.04}+-0.03
were obtained. The values for f_S and f_T are consistent with zero. Assuming
only Vector-Axial vector couplings, lambda_+ = 0.0288+-0.0004+-0.0011 and a
good fit consistent with pure V-A couplings were obtained. Alternatively, a fit
to a dipole form factor yields a pole mass of M = 859+-18 MeV, consistent with
the K^*(892) mass.Comment: 16 pages, 7 figures. submitted to Phys. Lett.
Measurement of the cross-section and charge asymmetry of bosons produced in proton-proton collisions at TeV with the ATLAS detector
This paper presents measurements of the and cross-sections and the associated charge asymmetry as a
function of the absolute pseudorapidity of the decay muon. The data were
collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with
the ATLAS experiment at the LHC and correspond to a total integrated luminosity
of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements
varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the
1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured
with an uncertainty between 0.002 and 0.003. The results are compared with
predictions based on next-to-next-to-leading-order calculations with various
parton distribution functions and have the sensitivity to discriminate between
them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables,
submitted to EPJC. All figures including auxiliary figures are available at
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13
Search for squarks and gluinos in events with isolated leptons, jets and missing transverse momentum at s√=8 TeV with the ATLAS detector
The results of a search for supersymmetry in final states containing at least one isolated lepton (electron or muon), jets and large missing transverse momentum with the ATLAS detector at the Large Hadron Collider are reported. The search is based on proton-proton collision data at a centre-of-mass energy s√=8 TeV collected in 2012, corresponding to an integrated luminosity of 20 fb−1. No significant excess above the Standard Model expectation is observed. Limits are set on supersymmetric particle masses for various supersymmetric models. Depending on the model, the search excludes gluino masses up to 1.32 TeV and squark masses up to 840 GeV. Limits are also set on the parameters of a minimal universal extra dimension model, excluding a compactification radius of 1/R c = 950 GeV for a cut-off scale times radius (ΛR c) of approximately 30
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