928 research outputs found
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
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)
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
Test Results of a 1.2 kg/s Centrifugal Liquid Helium Pump for the ATLAS Superconducting Toroid Magnet System
The toroid superconducting magnet of ATLAS-LHC experiment at CERN will be indirectly cooled by means of forced flow of liquid helium at about 4.5 K. A centrifugal pump will be used, providing a mass flow of 1.2 kg/s and a differential pressure of 40 kPa (ca. 400 mbar) at about 4300 rpm. Two pumps are foreseen, one for redundancy, in order to feed in parallel the cooling circuits of the Barrel and the two End-Caps toroid magnets. The paper describes the tests carried out at CERN to measure the characteristic curves, i.e. the head versus the mass flow at different rotational speeds, as well as the pump total efficiency. The pump is of the "fullemission" type, i.e. with curved blades and it is equipped with an exchangeable inducer. A dedicated pump test facility has been constructed at CERN, which includes a Coriolis-type liquid helium mass flow meter. This facility is connected to the helium refrigerator used for the tests at CERN of the racetrack magnets of the Barrel and of the End-Cap toroids
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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