1,809 research outputs found
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
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
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)
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