arXiv subjects

A. Liolios

Publications and source records attributed to A. Liolios.

16 recordsLinked to original sources

arXiv2018

Improved Search for Solar Chameleons with a GridPix Detector at CAST

We report on a new search for solar chameleons with the CERN Axion Solar Telescope (CAST). A GridPix detector was used to search for soft X-ray photons in the energy range from 200 eV to 10 keV from converted solar chameleons. No signiffcant excess over the expected background has been observed in the data taken in 2014 and 2015. We set an improved limit on the chameleon photon coupling, $β_γ< 5.7\times10^{10}$ for $1<β_\mathrm{m}<10^6$ at 95% C.L. improving our previous results by a factor two and for the first time reaching sensitivity below the solar luminosity bound for tachocline magnetic fields up to $12.5\,\mathrm{T}$.

hep-ex↗

arXiv2017

New CAST Limit on the Axion-Photon Interaction

During 2003--2015, the CERN Axion Solar Telescope (CAST) has searched for $a\toγ$ conversion in the 9 T magnetic field of a refurbished LHC test magnet that can be directed toward the Sun. In its final phase of solar axion searches (2013--2015), CAST has returned to evacuated magnet pipes, which is optimal for small axion masses. The absence of a significant signal above background provides a world leading limit of $g_{aγ} < 0.66 \times 10^{-10} {\rm GeV}^{-1}$ (95% C.L.) on the axion-photon coupling strength for $m_a \lesssim 0.02$ eV. Compared with the first vacuum phase (2003--2004), the sensitivity was vastly increased with low-background x-ray detectors and a new x-ray telescope. These innovations also serve as pathfinders for a possible next-generation axion helioscope.

hep-ex↗

arXiv2016

Search for chameleons with CAST

In this work we present a search for (solar) chameleons with the CERN Axion Solar Telescope (CAST). This novel experimental technique, in the field of dark energy research, exploits both the chameleon coupling to matter ($β_{\rm m}$) and to photons ($β_γ$) via the Primakoff effect. By reducing the X-ray detection energy threshold used for axions from 1$\,$keV to 400$\,$eV CAST became sensitive to the converted solar chameleon spectrum which peaks around 600$\,$eV. Even though we have not observed any excess above background, we can provide a 95% C.L. limit for the coupling strength of chameleons to photons of $β_γ\!\lesssim\!10^{11}$ for $1<β_{\rm m}<10^6$.

astro-ph.SR↗

arXiv2015

New solar axion search in CAST with $^4$He filling

The CERN Axion Solar Telescope (CAST) searches for $a\toγ$ conversion in the 9 T magnetic field of a refurbished LHC test magnet that can be directed toward the Sun. Two parallel magnet bores can be filled with helium of adjustable pressure to match the X-ray refractive mass $m_γ$ to the axion search mass $m_a$. After the vacuum phase (2003--2004), which is optimal for $m_a\lesssim0.02$ eV, we used $^4$He in 2005--2007 to cover the mass range of 0.02--0.39 eV and $^3$He in 2009--2011 to scan from 0.39--1.17 eV. After improving the detectors and shielding, we returned to $^4$He in 2012 to investigate a narrow $m_a$ range around 0.2 eV ("candidate setting" of our earlier search) and 0.39--0.42 eV, the upper axion mass range reachable with $^4$He, to "cross the axion line" for the KSVZ model. We have improved the limit on the axion-photon coupling to $g_{aγ}< 1.47\times10^{-10} {\rm GeV}^{-1}$ (95% C.L.), depending on the pressure settings. Since 2013, we have returned to vacuum and aim for a significant increase in sensitivity.

hep-ex↗

arXiv2014

CAST solar axion search with 3^He buffer gas: Closing the hot dark matter gap

The CERN Axion Solar Telescope (CAST) has finished its search for solar axions with 3^He buffer gas, covering the search range 0.64 eV < m_a <1.17 eV. This closes the gap to the cosmological hot dark matter limit and actually overlaps with it. From the absence of excess X-rays when the magnet was pointing to the Sun we set a typical upper limit on the axion-photon coupling of g_ag < 3.3 x 10^{-10} GeV^{-1} at 95% CL, with the exact value depending on the pressure setting. Future direct solar axion searches will focus on increasing the sensitivity to smaller values of g_a, for example by the currently discussed next generation helioscope IAXO.

hep-ex↗

arXiv2014

Conceptual Design of the International Axion Observatory (IAXO)

The International Axion Observatory (IAXO) will be a forth generation axion helioscope. As its primary physics goal, IAXO will look for axions or axion-like particles (ALPs) originating in the Sun via the Primakoff conversion of the solar plasma photons. In terms of signal-to-noise ratio, IAXO will be about 4-5 orders of magnitude more sensitive than CAST, currently the most powerful axion helioscope, reaching sensitivity to axion-photon couplings down to a few $\times 10^{-12}$ GeV$^{-1}$ and thus probing a large fraction of the currently unexplored axion and ALP parameter space. IAXO will also be sensitive to solar axions produced by mechanisms mediated by the axion-electron coupling $g_{ae}$ with sensitivity $-$for the first time$-$ to values of $g_{ae}$ not previously excluded by astrophysics. With several other possible physics cases, IAXO has the potential to serve as a multi-purpose facility for generic axion and ALP research in the next decade. In this paper we present the conceptual design of IAXO, which follows the layout of an enhanced axion helioscope, based on a purpose-built 20m-long 8-coils toroidal superconducting magnet. All the eight 60cm-diameter magnet bores are equipped with focusing x-ray optics, able to focus the signal photons into $\sim 0.2$ cm$^2$ spots that are imaged by ultra-low-background Micromegas x-ray detectors. The magnet is built into a structure with elevation and azimuth drives that will allow for solar tracking for $\sim$12 h each day.

physics.ins-det↗

arXiv2013

CAST constraints on the axion-electron coupling

In non-hadronic axion models, which have a tree-level axion-electron interaction, the Sun produces a strong axion flux by bremsstrahlung, Compton scattering, and axio-recombination, the "BCA processes." Based on a new calculation of this flux, including for the first time axio-recombination, we derive limits on the axion-electron Yukawa coupling g_ae and axion-photon interaction strength g_ag using the CAST phase-I data (vacuum phase). For m_a < 10 meV/c2 we find g_ag x g_ae< 8.1 x 10^-23 GeV^-1 at 95% CL. We stress that a next-generation axion helioscope such as the proposed IAXO could push this sensitivity into a range beyond stellar energy-loss limits and test the hypothesis that white-dwarf cooling is dominated by axion emission.

astro-ph.SR↗

arXiv2013

IAXO - The International Axion Observatory

The International Axion Observatory (IAXO) is a next generation axion helioscope aiming at a sensitivity to the axion-photon coupling of a few 10^{-12} GeV^{-1}, i.e. 1-1.5 orders of magnitude beyond sensitivities achieved by the currently most sensitive axion helioscope, the CERN Axion Solar Telescope (CAST). Crucial factors in improving the sensitivity for IAXO are the increase of the magnetic field volume together with the extensive use of x-ray focusing optics and low background detectors, innovations already successfully tested at CAST. Electron-coupled axions invoked to explain the white dwarf cooling, relic axions, and a large variety of more generic axion-like particles (ALPs) along with other novel excitations at the low-energy frontier of elementary particle physics could provide additional physics motivation for IAXO.

physics.ins-det↗

arXiv2012

Results and perspectives of the solar axion search with the CAST experiment

The status of the solar axion search with the CERN Axion Solar Telescope (CAST) will be presented. Recent results obtained by the use of $^3$He as a buffer gas has allowed us to extend our sensitivity to higher axion masses than our previous measurements with $^4$He. With about 1 h of data taking at each of 252 different pressure settings we have scanned the axion mass range 0.39 eV$ \le m_{a} \le $ 0.64 eV. From the absence of an excess of x rays when the magnet was pointing to the Sun we set a typical upper limit on the axion-photon coupling of g$_{aγ} \le 2.3\times 10^{-10}$ GeV$^{-1}$ at 95% C.L., the exact value depending on the pressure setting. CAST published results represent the best experimental limit on the photon couplings to axions and other similar exotic particles dubbed WISPs (Weakly Interacting Slim Particles) in the considered mass range and for the first time the limit enters the region favored by QCD axion models. Preliminary sensitivities for axion masses up to 1.16 eV will also be shown reaching mean upper limits on the axion-photon coupling of g$_{aγ} \le 3.5\times 10^{-10}$ GeV$^{-1}$ at 95% C.L. Expected sensibilities for the extension of the CAST program up to 2014 will be presented. Moreover long term options for a new helioscope experiment will be evoked.

hep-ex↗

arXiv2012

CAST search for sub-eV mass solar axions with 3He buffer gas

The CERN Axion Solar Telescope (CAST) has extended its search for solar axions by using 3He as a buffer gas. At T=1.8 K this allows for larger pressure settings and hence sensitivity to higher axion masses than our previous measurements with 4He. With about 1 h of data taking at each of 252 different pressure settings we have scanned the axion mass range 0.39 eV < m_a < 0.64 eV. From the absence of excess X-rays when the magnet was pointing to the Sun we set a typical upper limit on the axion-photon coupling of g_ag < 2.3 x 10^{-10} GeV^{-1} at 95% CL, the exact value depending on the pressure setting. KSVZ axions are excluded at the upper end of our mass range, the first time ever for any solar axion search. In future we will extend our search to m_a < 1.15 eV, comfortably overlapping with cosmological hot dark matter bounds.

hep-ex↗

arXiv2010

Search for solar axion emission from 7Li and D(p,gamma)3He nuclear decays with the CAST gamma-ray calorimeter

We present the results of a search for a high-energy axion emission signal from 7Li (0.478 MeV) and D(p,gamma)3He (5.5 MeV) nuclear transitions using a low-background gamma-ray calorimeter during Phase I of the CAST experiment. These so-called "hadronic axions" could provide a solution to the long-standing strong-CP problem and can be emitted from the solar core from nuclear M1 transitions. This is the first such search for high-energy pseudoscalar bosons with couplings to nucleons conducted using a helioscope approach. No excess signal above background was found.

hep-ex↗

arXiv2009

Search for 14.4 keV solar axions emitted in the M1-transition of 57Fe nuclei with CAST

We have searched for 14.4 keV solar axions or more general axion-like particles (ALPs), that may be emitted in the M1 nuclear transition of 57Fe, by using the axion-to-photon conversion in the CERN Axion Solar Telescope (CAST) with evacuated magnet bores (Phase I). From the absence of excess of the monoenergetic X-rays when the magnet was pointing to the Sun, we set model-independent constraints on the coupling constants of pseudoscalar particles that couple to two photons and to a nucleon g_{aγ} |-1.19 g_{aN}^{0}+g_{aN}^{3}|<1.36\times 10^{-16} GeV^{-1} for m_{a}<0.03 eV at the 95% confidence level.

hep-ex↗

arXiv2009

Probing eV-scale axions with CAST

We have searched for solar axions or other pseudoscalar particles that couple to two photons by using the CERN Axion Solar Telescope (CAST) setup. Whereas we previously have reported results from CAST with evacuated magnet bores (Phase I), setting limits on lower mass axions, here we report results from CAST where the magnet bores were filled with \hefour gas (Phase II) of variable pressure. The introduction of gas generated a refractive photon mass $m_γ$, thereby achieving the maximum possible conversion rate for those axion masses \ma that match $m_γ$. With 160 different pressure settings we have scanned \ma up to about 0.4 eV, taking approximately 2 h of data for each setting. From the absence of excess X-rays when the magnet was pointing to the Sun, we set a typical upper limit on the axion-photon coupling of $\gag\lesssim 2.17\times 10^{-10} {\rm GeV}^{-1}$ at 95% CL for $\ma \lesssim 0.4$ eV, the exact result depending on the pressure setting. The excluded parameter range covers realistic axion models with a Peccei-Quinn scale in the neighborhood of $f_{\rm a}\sim10^{7}$ GeV. Currently in the second part of CAST Phase II, we are searching for axions with masses up to about 1.2 eV using \hethree as a buffer gas.

hep-ex↗

arXiv2008

Solar axion search with the CAST experiment

The CAST (CERN Axion Solar Telescope) experiment is searching for solar axions by their conversion into photons inside the magnet pipe of an LHC dipole. The analysis of the data recorded during the first phase of the experiment with vacuum in the magnet pipes has resulted in the most restrictive experimental limit on the coupling constant of axions to photons. In the second phase, CAST is operating with a buffer gas inside the magnet pipes in order to extent the sensitivity of the experiment to higher axion masses. We will present the first results on the $^{4}{\rm He}$ data taking as well as the system upgrades that have been operated in the last year in order to adapt the experiment for the $^{3}{\rm He}$ data taking. Expected sensitivities on the coupling constant of axions to photons will be given for the recent $^{3}{\rm He}$ run just started in March 2008.

hep-ex↗

arXiv2008

Search for low Energy solar Axions with CAST

We have started the development of a detector system, sensitive to single photons in the eV energy range, to be suitably coupled to one of the CAST magnet ports. This system should open to CAST a window on possible detection of low energy Axion Like Particles emitted by the sun. Preliminary tests have involved a cooled photomultiplier tube coupled to the CAST magnet via a Galileian telescope and a switched 40 m long optical fiber. This system has reached the limit background level of the detector alone in ideal conditions, and two solar tracking runs have been performed with it at CAST. Such a measurement has never been done before with an axion helioscope. We will present results from these runs and briefly discuss future detector developments.

hep-ex↗

arXiv1999

A Decommissioned LHC Model Magnet as an Axion Telescope

The 8.4 Tesla, 10 m long transverse magnetic field of a twin aperture LHC bending magnet can be utilized as a macroscopic coherent solar axion-to-photon converter. Numerical calculations show that the integrated time of alignment with the Sun would be 33 days per year with the magnet on a tracking table capable of $\pm 5^o$ in the vertical direction and $\pm 40^o$ in the horizontal direction. The existing lower bound on the axion-to-photon coupling constant can be improved by a factor between 50 and 100 in 3 years, i.e., $g_{aγγ} \lesssim 9\cdot 10^{-11} GeV^{-1}$ for axion masses $\lesssim$ 1 eV. This value falls within the existing open axion mass window. The same set-up can simultaneously search for low- and high-energy celestial axions, or axion-like particles, scanning the sky as the Earth rotates and orbits the Sun.

astro-ph↗