CERN Accelerating science

The exclusion limit for Chameleons at CAST are shown with hatched pattern. The KWISP measurement of this work is illustrated in red colour and comparison to other experimental techniques (\cite{gammev,gammevchase,collider,atomin}) is made, assuming a dark energy scale $\Lambda = 2.4 \cdot 10^{-3}$ eV and $n = 1 $. The limit from the previous CAST measurement \cite{castchin} is based on chameleon-to-photon conversion only. In the parameter space of realistic solar models the expected chameleon production maximum, in darker shade, takes place for $B=30$~T and the tachocline length $L_i = 0.05 R_{Sun}$ while the minimum, in lighter shade, is expected for $B=10$~T and the tachocline length $L_i = 0.01 R_{Sun}$.

Calibration graph showing the result of the sine fit. The data points were fitted with the function $I(x) = A \cdot sin(\omega \cdot x+b)+B$\ and the values $A = (133 \pm 4)\cdot 10^2$, $B = -324 \pm 64$, $\omega = 0.02336 \pm 4$, $\varphi = -0.178 \pm 6$ were derived.

Calibration graph. Overlay of the cycles used for calibration. Only the first 532 nm of OPL change are used.

DAQ block schematic.

Expected force at the sensor calculated from the solar chameleon flux assuming $\beta_\gamma = 10^{10.32}$, interaction zone length $L_i = 0.05 \cdot R_{Sun}$ and detector parameters. Solid lines correspond to a dark energy scale $\Lambda = 2.4 \cdot 10^{-3}$~eV, dashed ones to $\Lambda = 1 \cdot 10^{-5}$~eV, and dotted lines to $\Lambda = 0.1$~eV. The interaction zone length is an upper limit according to current Solar models. The flux and consequently the expected force are scaled accordingly for values down to $L_{i} = 0.01 \cdot R_{Sun}$ while the resonance peak is arbitrarily limited to $F = 10^{-2}$~N by the axis scale. The orange band represents 95\% confidence interval centred at the average force value shown by the red dashed line.

The accessible chameleon energy range with the present setup. Only chameleons with masses in the green band between the red and green lines contribute to the radiation pressure on the KWISP sensor.

Schematic layout of the the optical setup (see text).

Background noise spectrum taken in the laboratory with a the $5 x 5 \ \mathrm{mm^2}$, 100 nm thick membrane. The mechanical vibration peaks can be distinguished from background since their frequencies have well defined ratios (see Table \ref{mempeaks}). Integration time was 9 s with an input beam intensity of 5.0 mW (see also text).

A calculation of the chameleon flux at Earth. The interaction region length is taken in its uncertainty interval from 1\% to 5\% of solar radius. For a given pair of energy and field values in the left plot, the corresponding colour in the right plot provides the range of fluxes for various interaction region lengths.

The chopper disk mounted between the vacuum chamber (at right) and the telescope (at left). In the photograph the chameleon beam comes from the left hand side, as indicated by the arrows. The segmented surface of the disk faces downwards and it is illustrated in the framed inset.

Azimuthal coverage of the telescope on 3rd July 2017 during data taking. Picture of the CAST site courtesy of CERN.

Full range single sided amplitude spectrum collected during sun tracking. The acquisition rate was 15258 S/s. The spectrum around the chopper frequency 984 Hz is shown in the inset.