1,846 research outputs found
Hard production of a Z boson plus heavy flavor jets at LHC and the intrinsic charm content of a proton
The cross section of associated production of a Z boson with heavy flavor
jets in collisions is calculated using the SHERPA Monte Carlo generator
and the analytical combined QCD approach based on kt-factorization at small x
and conventional collinear QCD at large x. A satisfactory description of the
ATLAS and CMS data on the spectra of Z bosons and c-jets in the whole
rapidity, y, region is shown. Searching for the intrinsic charm (IC)
contribution in these processes, which could be visible at large y > 1.5, we
study observables very sensitive to non-zero IC contributions and less affected
by theoretical QCD scale uncertainties. One of such observables is the
so-called double ratio: the ratio of the differential cross section of Z + c
production in the central region of |y| < 1.5 and in the forward region 1.5 <
|y| < 2.5, divided by the same ratio for Z + b production. These observables
could be more promising for the search of IC at LHC as compared to the
observables considered earlier.Comment: 18 pages, 7 figure
The first measurement of temperature standard deviation along the line-of-sight in galaxy clusters
Clusters of galaxies are mainly formed by merging of smaller structures,
according to the standard cosmological scenario. If the mass of a substructure
is >10% of that of a galaxy cluster, the temperature distribution of the
intracluster medium (ICM) in a merging cluster becomes inhomogeneous. Various
methods have been used to derive the two-dimensional projected temperature
distribution of the ICM. However, methods for studying temperature distribution
along the line-of-sight through the cluster were absent. In this paper, we
present the first measurement of the temperature standard deviation along the
line-of-sight, using as a reference case the multifrequency SZ measurements of
the Bullet Cluster. We find that the value of the temperature standard
deviation is high and equals to (10.6+/-3.8) keV in the Bullet Cluster. This
result shows that the temperature distribution in the Bullet Cluster is
strongly inhomogeneous along the line-of-sight and provides a new method for
studying galaxy clusters in depth.Comment: 5 pages, 1 figure, published in MNRAS Letter
Can electron distribution functions be derived through the Sunyaev-Zel'dovich effect?
Measurements of the Sunyaev-Zel'dovich (hereafter SZ) effect distortion of
the cosmic microwave background provide methods to derive the gas pressure and
temperature of galaxy clusters. Here we study the ability of SZ effect
observations to derive the electron distribution function (DF) in massive
galaxy clusters.
Our calculations of the SZ effect include relativistic corrections considered
within the framework of the Wright formalism and use a decomposition technique
of electron DFs into Fourier series. Using multi-frequency measurements of the
SZ effect, we find the solution of a linear system of equations that is used to
derive the Fourier coefficients; we further analyze different frequency samples
to decrease uncertainties in Fourier coefficient estimations.
We propose a method to derive DFs of electrons using SZ multi-frequency
observations of massive galaxy clusters. We found that the best frequency
sample to derive an electron DF includes high frequencies =375, 600, 700,
857 GHz. We show that it is possible to distinguish a Juttner DF from a
Maxwell-Bolzman DF as well as from a Juttner DF with the second electron
population by means of SZ observations for the best frequency sample if the
precision of SZ intensity measurements is less than 0.1%. We demonstrate by
means of 3D hydrodynamic numerical simulations of a hot merging galaxy cluster
that the morphologies of SZ intensity maps are different for frequencies
=375, 600, 700, 857 GHz. We stress that measurements of SZ intensities at
these frequencies are a promising tool for studying electron distribution
functions in galaxy clusters.Comment: 11 pages, 12 figures, published in Astronomy and Astrophysic
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