717 research outputs found
Self-Organising Networks for Classification: developing Applications to Science Analysis for Astroparticle Physics
Physics analysis in astroparticle experiments requires the capability of
recognizing new phenomena; in order to establish what is new, it is important
to develop tools for automatic classification, able to compare the final result
with data from different detectors. A typical example is the problem of Gamma
Ray Burst detection, classification, and possible association to known sources:
for this task physicists will need in the next years tools to associate data
from optical databases, from satellite experiments (EGRET, GLAST), and from
Cherenkov telescopes (MAGIC, HESS, CANGAROO, VERITAS)
Measurements of vacuum magnetic birefringence using permanent dipole magnets: the PVLAS experiment
The PVLAS collaboration is presently assembling a new apparatus (at the INFN
section of Ferrara, Italy) to detect vacuum magnetic birefringence (VMB). VMB
is related to the structure of the QED vacuum and is predicted by the
Euler-Heisenberg-Weisskopf effective Lagrangian. It can be detected by
measuring the ellipticity acquired by a linearly polarised light beam
propagating through a strong magnetic field. Using the very same optical
technique it is also possible to search for hypothetical low-mass particles
interacting with two photons, such as axion-like (ALP) or millicharged
particles (MCP). Here we report results of a scaled-down test setup and
describe the new PVLAS apparatus. This latter one is in construction and is
based on a high-sensitivity ellipsometer with a high-finesse Fabry-Perot cavity
() and two 0.8 m long 2.5 T rotating permanent dipole magnets.
Measurements with the test setup have improved by a factor 2 the previous upper
bound on the parameter , which determines the strength of the nonlinear
terms in the QED Lagrangian: T
95% c.l. Furthermore, new laboratory limits have been put on the inverse
coupling constant of ALPs to two photons and confirmation of previous limits on
the fractional charge of millicharged particles is given
The PVLAS experiment: measuring vacuum magnetic birefringence and dichroism with a birefringent Fabry-Perot cavity
Vacuum magnetic birefringence was predicted long time ago and is still
lacking a direct experimental confirmation. Several experimental efforts are
striving to reach this goal, and the sequence of results promises a success in
the next few years. This measurement generally is accompanied by the search for
hypothetical light particles that couple to two photons. The PVLAS experiment
employs a sensitive polarimeter based on a high finesse Fabry-Perot cavity. In
this paper we report on the latest experimental results of this experiment. The
data are analysed taking into account the intrinsic birefringence of the
dielectric mirrors of the cavity. Besides the limit on the vacuum magnetic
birefringence, the measurements also allow the model-independent exclusion of
new regions in the parameter space of axion-like and milli-charged particles.
In particular, these last limits hold also for all types of neutrinos,
resulting in a laboratory limit on their charge
New PVLAS model independent limit for the axion coupling to for axion masses above 1meV
During 2014 the PVLAS experiment has started data taking with a new apparatus
installed at the INFN Section of Ferrara, Italy. The main target of the
experiment is the observation of magnetic birefringence of vacuum. According to
QED, the ellipticity generated by the magnetic birefringence of vacuum in the
experimental apparatus is expected to be . No ellipticity signal is present so far with a noise floor
after 210 hours of data taking.
The resulting ellipticity limit provides the best model independent upper limit
on the coupling of axions to for axion masses above eV
First results from the new PVLAS apparatus: a new limit on vacuum magnetic birefringence
Several groups are carrying out experiments to observe and measure vacuum
magnetic birefringence, predicted by Quantum Electrodynamics (QED). We have
started running the new PVLAS apparatus installed in Ferrara, Italy, and have
measured a noise floor value for the unitary field magnetic birefringence of
vacuum T (the error
represents a 1 deviation). This measurement is compatible with zero and
hence represents a new limit on vacuum magnetic birefringence deriving from non
linear electrodynamics. This result reduces to a factor 50 the gap to be
overcome to measure for the first time the value of predicted by QED:
~T. These birefringence measurements also yield improved
model-independent bounds on the coupling constant of axion-like particles to
two photons, for masses greater than 1 meV, along with a factor two improvement
of the fractional charge limit on millicharged particles (fermions and
scalars), including neutrinos
Measurement of the Cotton Mouton effect of water vapour
In this paper we report on a measurement of the Cotton Mouton effect of water
vapour. Measurement performed at room temperature ( K) with a wavelength
of 1064 nm gave the value for the
unit magnetic birefringence (1 T magnetic field and atmospheric pressure)
Experimental observation of optical rotation generated in vacuum by a magnetic field
We report the experimental observation of a light polarization rotation in
vacuum in the presence of a transverse magnetic field. Assuming that data
distribution is Gaussian, the average measured rotation is (3.9+/-0.5)e-12
rad/pass, at 5 T with 44000 passes through a 1m long magnet, with lambda = 1064
nm. The relevance of this result in terms of the existence of a light, neutral,
spin-zero particle is discussed.Comment: 11 pages, 4 figures, submitted to Physical Review Letters Comment to
version 2: minor changes to abstract and final discussion. Added 2 references
Comment to version 3: corrected minor typographical errors, eliminated the
distinction between scalar and pseudoscalar in the particle interpretation of
the resul
Towards a direct measurement of vacuum magnetic birefringence: PVLAS achievements
Nonlinear effects in vacuum have been predicted but never observed yet
directly. The PVLAS collaboration has long been working on an apparatus aimed
at detecting such effects by measuring vacuum magnetic birefringence.
Unfortunately the sensitivity has been affected by unaccounted noise and
systematics since the beginning. A new small prototype ellipsometer has been
designed and characterized at the Department of Physics of the University of
Ferrara, Italy entirely mounted on a single seismically isolated optical bench.
With a finesse F = 414000 and a cavity length L = 0.5 m we have reached the
predicted sensitivity of psi = 2x10^-8 1/sqrt(Hz) given the laser power at the
output of the ellipsomenter of P = 24 mW. This record result demonstrates the
feasibility of reaching such sensitivities and opens the way to designing a
dedicated apparatus for a first detection of vacuum magnetic birefringence
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