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Search for Wisps Gains Momentum CERN Courier September 2018 Dark matter Got radiation? Knirck/MPIS Search for See what you’ve been missing WISPs gains momentum Despite tremendous efforts, the search for the constituents of dark matter has so far been unsuccessful. Interest is therefore growing in new experiments that probe dark-matter candidates such as axions and other very weakly interacting sub-eV particles. PhotoPPhoPhotPhhhohotoottooc coccourtesyourteuurturrtertrtetesysyyo ooffEf E EUEUROfusion.URROfROfuROOfuOffufussiosionsiioniioonon..W WWeWebsite:ebsbsitbsitssiitite:e:w: wwww.euro-fusion.orgwwwww.ew.wweuro-urro-oo-fusfufusiusiusussiioon.oonon.nn.n.ono.o. orrgg Photo courtesy of EUROfusion. Website: www.euro-fusion.org Understanding the nature of dark matter is one of the most press- which is broken spontaneously in the vacuum. Such extensions ing problems in physics. This strangely nonreactive material is contain an additional scalar field with a potential shaped like a Imaging in radiation environments just got easier estimated, from astronomical observations, to make up 85% of all Mexican hat – similar to the Higgs potential in the SM (figure 1). matter in the universe. The known particles of the Standard Model This leads to spontaneous breaking of symmetry at a scale cor- (SM) of particle physics, on the other hand, account for a paltry 15%. responding to the radius of the trough of the hat: excitations in the With superior capabilities for operating in radiation environments, the MegaRAD cameras provide Physicists have proposed many dark-matter candidates. Two in direction along the trough correspond to a light Nambu–Goldstone excellent image quality well beyond dose limitations of conventional cameras, and are well suited particular stand out because they arise in extensions of the SM that (NG) boson, while the excitation in the radial direction perpen- solve other fundamental puzzles, and because there are a variety dicular to the trough corresponds to a heavy particle with a mass for radiation hardened imaging applications of experimental opportunities to search for them. The first is the determined by the symmetry-breaking scale. The strengths of the neutralino, which is the lightest supersymmetric partner of the SM interactions between such light bosons and regular SM particles neutral bosons. The second is the axion, postulated 40 years ago to are inversely proportional to the symmetry-breaking energy scale solve the strong CP problem in quantum chromodynamics (QCD). and are therefore very weak. Being light, very weakly interacting While the neutralino belongs to the category of weakly interacting and cold due to their non-thermal production history, these parti- massive particles (WIMPs), the axion is the prime example of a cles qualify as natural WISP cold dark-matter candidates. very weakly interacting sub-eV particle (WISP). Neutralinos as WIMPs have dominated the search for cold dark Primordial production matter since the mid-1980s, when it was realised that massive In fact, WISP dark matter is inevitably produced in the early uni- particles with a cross section of the order of the weak interaction verse. When the temperature in the primordial plasma drops below KiloRAD PTZ radiation MegaRAD3 produce color MegaRAD1 produce would result in precisely the right density to explain dark matter. the symmetry-breaking scale, the boson fields are frozen at a ran- or monochrome video up to monochrome video up to resistant camera with 3 x 106 rads total dose 1 x 106 rads total dose Pan/Tilt/Zoom There have been tremendous efforts to hunt for WIMPs both at dom initial value in each causally-connected region. Later, they hadron colliders, especially now at CERN’s Large Hadron Col- relax towards the minimum of their potential at zero fields and lider (LHC), and in large underground detectors, such as CDMS, oscillate around it. Since there is no significant damping of these In the United States: International: CRESST, DARKSIDE, LUX, PandaX and XENON. However, up field oscillations via decays or interactions, the bosons behave as a For customer service, call 1-800-888-8761 For customer service, call [01) 315-451-9410 to now, no WIMP has been observed (CERN Courier July/August very cold dark-matter fluid. If symmetry breaking occurs after the To fax an order, use 1-315-451-9421 To fax an order, use [01) 315-451-9410 2018 p9). likely inflationary-expansion epoch of the universe (corresponding Email: sales.cidtec@thermofi sher.com Email: sales.cidtec@thermofi sher.com Very light bosons as WISPs are a firm prediction of models that to a post-inflationary symmetry-breaking scenario), WISP dark solve problems of the SM by the postulation of a new symmetry matter would also be produced by the decay of topological defects from the realignment of patches of the universe with random initial Find out more at thermofi sher.com/cidtec Image above: test setup of the MADMAX experiment with conditions. A huge region in parameter space spanned by WISP sapphire plates to allow the detection of axion–photon conversion. masses and their symmetry-breaking scales can give rise to the For Research Use Only. Not for use in diagnostic procedures. © 2018 Thermo Fisher Scientifi c Inc. All rights reserved. All trademarks are the property of Thermo Fisher Scientifi c and its subsidiaries unless otherwise specifi ed 25 CCSep18_Axions_v5.indd 25 20/08/2018 16:45 CERNCOURIER www. V OLUME 5 8 N UMBER 7 S EPTEMBER 2 0 1 8 CERN Courier September 2018 HIGH VOLTAGE Dark matter Fig. 1. The potential of a complex AMPLIFIERS unbroken symmetry V scalar field in primordial plasma in the very early universe (left) Employing unique and proprietary circuitry to takes the form of a Sombrero produce a closed-loop amplifier system which features exceptional DC stability and excellent (right) once the temperature wideband performance characteristics. drops below the symmetry- breaking scale. The energy-breaking scale • Voltage Range to ±50 kV corresponds to the radius of the • Slew Rates to 1500 V / μs valley from the centre, while the axion represents oscillations • Current to 10 A around one of the minima, which • Bandwidth to 3 MHz arise due to QCD gluon-field fluctuations. Fig. 2. Left: diagram showing γ +1-716-438-7555 Trek was acquired a axion–photon coupling via by Advanced Energy [email protected] axion–pion oscillation. Right: via Industries, Inc. a π0 the Primakoff effect, a virtual www.trekinc.com in early 2018. High voltage accelerator assembly for ion-source photon can be borrowed from a ø 560 x L 450 mm static magnetic field (denoted by the cross) to induce photons to convert into axions or vice versa, as first suggested by P Sikivie. Cryogenic WafPro#1-CERN 9/21/13 3:06 PM Page 1 observed dark-matter distribution. axion-like particles (ALPs), which are very similar to axions but The axion is a particularly well-motivated example of a WISP. It do not solve the CP problem of QCD, or lightweight, weakly inter- Problems was proposed to explain the results of searches for a static electric acting, so-called hidden photons, for example. String theory sug- dipole moment of the neutron, which would constitute a CP-violating gests a plenitude of ALPs, which could have couplings to photons, wanted! effect of QCD. The size of this CP-violation, parameterised by the leptons or light quarks. angle θ, is predicted to have an arbitrary value between –π and π, Due to their tiny masses, WISPs might also be produced inside yet experiments show its absolute value to be less than 10–10. If θ stars or alter the propagation of photons in the universe. Observa- Cryogenic Wafer is replaced by a dynamical field,θ (x), as proposed by Peccei and tions of stellar evolutions hint at such signals: red giants, helium- Quinn in 1977, QCD dynamics ensures that the low-energy effective burning stars and white dwarfs seem to be experiencing unseen Probe Stations potential of the axion field has an absolute minimum atθ = 0. There- energy losses exceeding those expected from neutrino emission. FRIALIT®-DEGUSSIT® fore, in vacuum, the CP violating effects due to the θ angle in QCD Intriguingly, these anomalies can be explained in a unified manner disappear – providing an elegant solution to the strong CP problem. by the existence of a sub-keV-mass axion or ALP with a coupling HigH Performance The axion is the inevitable particle excitation of θ(x), and its mass is both to electrons and photons. Additionally, observations suggest ceramics determined by the unknown breaking scale of the global symmetry. that the propagation of TeV photons in the universe suffers less Lattice-QCD calculations performed last year precisely deter- than expected from interactions with the extragalactic background mined the temperature and corresponding time after the Big Bang light. This, in turn, could be explained by the conversion of photons Expert for accelerator parts made when axion cold dark-matter could have formed as a function of into ALPs and back in astrophysical magnetic fields, interestingly of high performance ceramics the axion mass. It was found that, in the post-inflationary symme- with about the same axion–photon coupling strength as indicated Applications include nano science, materials and try breaking scenario, the axion mass has to exceed 28 μeV; other- by the observed stellar anomalies. Both effects have been known spintronics wise, the predicted amount of dark matter overshoots the observed for almost 10 years. They are scientifically disputed, but a WISP www.friatec.com 3.2 K - 675 K; high vacuum or UHV amount. Taking into account the additional production of axion explanation has not yet been excluded. Up to 8 probes, DC to 67 GHz, plus fiber optics dark-matter from the decay of topological defects, an axion with a mass between 30 μeV and Experimental landscape Zoom optics with camera and monitor 10 meV may account for all of Most experiments searching for WISPs exploit their possible mix- Cooling options: liquid helium, liquid nitrogen or the dark matter in the universe.
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