8,222 research outputs found
New technique to measure the cavity defects of Fabry-Perot interferometers
(Abridged):
We define and test a new technique to accurately measure the cavity defects
of air-spaced FPIs, including distortions due to the spectral tuning process
typical of astronomical observations. We further develop a correction technique
to maintain the shape of the cavity as constant as possible during the spectral
scan. These are necessary steps to optimize the spectral transmission profile
of a two-dimensional spectrograph using one or more FPIs.
We devise a generalization of the techniques developed for the so-called
phase-shifting interferometry to the case of FPIs. The technique is applicable
to any FPI that can be tuned via changing the cavity spacing (-axis), and
can be used for any etalon regardless of the coating' reflectivity. The major
strength of our method is the ability to fully characterize the cavity during a
spectral scan, allowing for the determination of scan-dependent modifications
of the plates. As a test, we have applied this technique to three 50 mm
diameter interferometers, with cavity gaps ranging between 600 micron and 3 mm,
coated for use in the visible range.
We obtain accurate and reliable measures of the cavity defects of air-spaced
FPIs, and of their evolution during the entire spectral scan. Our main, and
unexpected, result is that the relative tilt between the two FPI plates varies
significantly during the spectral scan, and can dominate the cavity defects; in
particular, we observe that the tilt component at the extremes of the scan is
sensibly larger than at the center of the scan. Exploiting the capability of
the electronic controllers to set the reference plane at any given spectral
step, we develop a correction technique that allows the minimization of the
tilt during a complete spectral scan. The correction remains highly stable over
long periods, well beyond the typical duration of astronomical observations.Comment: 15 pages, 20+ figures, accepted for publication in A&A. Two
additional movies are available in the online version of the pape
Charmed Hadrons from Coalescence plus Fragmentation in relativistic nucleus-nucleus collisions at RHIC and LHC
In a coalescence plus fragmentation approach we calculate the heavy
baryon/meson ratio and the spectra of charmed hadrons ,
and in a wide range of transverse momentum from low up
to about 10 GeV and discuss their ratios from RHIC to LHC energies without any
change of the coalescence parameters. We have included the contribution from
decays of heavy hadron resonances and also the one due to fragmentation of
heavy quarks which do not undergo the coalescence process. The coalescence
process is tuned to have all charm quarks hadronizing in the
limit and at finite charm quarks not undergoing coalescence are
hadronized by independent fragmentation. The dependence of the
baryon/meson ratios are found to be sensitive to the masses of coalescing
quarks, in particular the can reach values of about at \mbox{GeV}, or larger, similarly to the light
baryon/meson ratio like and , however a marked difference is
a quite weak dependence with respect to the light case, such that a
larger value at intermediate implies a relatively large value also for
the integrated yields. A comparison with other coalescence model and with the
prediction of thermal model is discussed.Comment: 13 pages, 9 figures. Fig. 5 updated and some minor changes in the
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Propagation of heavy baryons in heavy-ion collisions
The drag and diffusion coefficients of heavy baryons ( and
) in the hadronic phase created in the latter stage of the heavy-ion
collisions at RHIC and LHC energies have been evaluated recently. In this work
we compute some experimental observables, such as the nuclear suppression
factor and the elliptic flow of heavy baryons at RHIC and LHC
energies, highlighting the role of the hadronic phase contribution to these
observables, which are going to be measured at Run 3 of LHC. For the time
evolution of the heavy quarks in the QGP and heavy baryons in the hadronic
phase we use the Langevin dynamics. For the hadronization of the heavy quarks
to heavy baryons we employ Peterson fragmentation functions. We observe a
strong suppression of both the and . We find that the
hadronic medium has a sizable impact on the heavy-baryon elliptic flow whereas
the impact of hadronic medium rescattering is almost unnoticeable on the
nuclear suppression factor. We evaluate the ratio at RHIC and
LHC. We find that ratio remain unaffected due to the hadronic
phase rescattering which enable it as a nobel probe of QGP phase dynamics along
with its hadronization.Comment: 22 pages, 15 figure
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