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17th October 2014

Annual Report 2014 P. Pugnat 1, R. Ballou 2, G. Deferne 3, L. Duvillaret 4, M. Finger Jr. 5, M. Finger 5, L. Flekova 6, J. Hosek 6, T. Husek 5, V. Jary 6, R. Jost 7, S. Kunc 8, K. Macuchova 6, K. A. Meissner 9, J. Morville 10, D. Romanini 7, M. Schott 11, A. Siemko 3, M. Slunecka 5, M. Sulc 8, G. Vitrant 4, C. Weinsheimer 11, J. Zicha 6 1 LNCMI, UPR CNRS 3228, UJF – UPS – INSA, BP 166, 38042 Grenoble Cedex-9, France 2 Institut Néel, UPR CNRS 2940, UJF – Grenoble INP, BP166, 38042 Grenoble Cedex-9, France 3 CERN, CH-1211 Geneva-23, Switzerland 4 IMEP-LAHC, UMR CNRS 5130, Minatec – INPG, BP 257, 38016 Grenoble Cedex-1, France 5 Charles University (CUNI), Faculty of Mathematics and Physics, Prague, Czech Republic 6 Czech Technical University (CTU), Prague, Czech Republic 7 LIPhy, UMR CNRS 5588, UJF-Grenoble 1, 38041Grenoble, France 8 Technical University of Liberec (TUL), Czech Republic 9 Institute of Theoretical Physics, University of Warsaw, Poland 10 LASIM, UMR CNRS 5579, Université Claude Bernard Lyon-1, 69622 Villeurbanne, France 11 University of Mainz, Institute of Physics, 55128 Mainz, Germany

Abstract – In 2014, the OSQAR Light Shining through Wall (LSW) experiment has been run very efficiently with both spare LHC dipoles re-commissioned on cryogenic benches at CERN-SM18. To improve the sensitivity, a new 18 W CW laser working at 532 nm and a new CCD detector have been installed, aligned and operated. Preliminary treatments and analysis of data recorded in 2014 provide new exclusion limits for the search of scalar and pseudo-scalar light particle that go much beyond the present reference ones obtained by the ALPS collaboration and slightly improved in 2013 by OSQAR. Final and detailed analyses are ongoing. To further improve the sensitivity of the OSQAR-LSW experiment, the developments and tests of Fabry-Perot cavities have been pursued. For 2015, the OSQAR collaboration will focus on a new proposal for the search of chameleons, a hypothetical scalar particle postulated as a dark energy candidate, which can couple strongly or weakly to matter as a function of the environment. The new required experimental set-up has been successfully tested and validated in 2014.

Outline

1. Introduction .......................................................................................................................................... 2

2. Highlights of 2014 .................................................................................................................................. 2 2.1. Theoretical Developments at the Warsaw University ............................................................................................... 2 2.2. Preparatory phases to increase the optical power of the OSQAR-LSW experiment in Czech Universities & CERN .. 2 2.3. Data analysis in French, German and Czech Institutes .............................................................................................. 4 2.4. OSQAR-LSW experimental run ................................................................................................................................... 4

3. A new proposal from the OSQAR collaboration: The quest of chameleons/SISPs .................................. 6 3.1. Generalities on chameleons ...................................................................................................................................... 6 3.2. Principle of the chameleon/SISPs search in laboratory ............................................................................................. 7 3.3. Integration and validation of the experimental set-up .............................................................................................. 8

4. Objectives for 2015 ............................................................................................................................... 9 4.1. OSQAR-LSW experiment – Next run not before 2016 ............................................................................................... 9 4.2. Run of the OSQAR chameleon experiment in 2015 ................................................................................................. 10

5. Conclusion, Perspectives & Requirements for 2015 ............................................................................. 10 Annex ……………………………………………………………………………………………………………………………………………… 12

1. Introduction

OSQAR aims to explore the low energy frontier of particle and astroparticle physics by combining the simultaneous use of high magnetic fields with laser beams in two distinct experiments. A recent review of the scientific cases concerning Weakly Interacting Sub-eV Particles, i.e. WISPs, can be found in [ 1]. In the first experiment, the photon regeneration effect is looked for as a Light Shining through the Wall (LSW) [ 2],[3], whereas in the second one, the ultra-fine Vacuum Magnetic Birefringence (VMB) predicted by the QED could be measured for the first time [4].

In 2014, OSQAR activities have been focused on the LSW experiment and more precisely on research and development of Fabry-Perot cavities as well as on the run of the experiment. This status report will summarize results obtained in collaborating institutes as well as at CERN within the framework of the OSQAR revised program [5],[6]. It will also propose for 2015 a new OSQAR experimental set-up for the search of particles that can interact strongly with matter such as chameleons [7] or more generally and phenomenologically any Strongly Interacting Sub-eV Particles, i.e. SISPs.

2. Highlights of 2014

2.1. Theoretical Developments at the Warsaw University

Adam Latosinski, Krzysztof A. Meissner and Hermann Nicolai pursue their theoretical investigations beyond the Standard Model without Supersymmetry assuming the spontaneously breakdown of the lepton number symmetry. Axions in the Conformal Standard Model show up at three or more loops in the calculations and it is therefore very difficult to calculate their properties.

2.2. Preparatory phases to increase the optical power of the OSQAR-LSW experiment in Czech Universities and CERN

2.2.1. Development of Fabry-Perot cavities

The design of the optical cavity for the OSQAR experiments has started in 2013 in Czech Institutes. In LSW type experiment one of the important parameter is the photon flux that needs to be maximized to increase the number of photons converted into axions in the magnetic field. Among various possible configurations, the hemispherical cavity design has been chosen as being the optimal one. It is obtained by placing a flat mirror at the location of the beam waist and is known as being very tolerant of angular misalignment of mirrors. Technical challenges are mostly coming from the unusual length of the cavity equal to 19.6 m and of the relative small laser beam size, which should have an overall diameter smaller than 20 mm to fit within the LHC dipole aperture [8].

Fig. 1: Long-Radius hemisherical cavity design.

Severe constraints for the opto-mechanical design of the Fabry-Perot resonator arise from the in-situ integration of both mirrors inside the vacuum chamber fixed to the anticryostat flange of the LHC dipole. Alignments of both these mirrors were designed to enable rough, fine and extra fine real time

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adjustment. Rough alignments allow ±12.5 mm XYZ travel range and ±4° tilt for off-axis position compensation of the laser beam within the magnet aperture. Alignment components are placed outside of the vacuum chamber. The fine alignment of ±3 mm range and ±5° is performed by differential screws. The final and real time adjustment is performed by piezoelectric elements allowing additional 8 μm of translation and 30 arcsec angular tilt. The whole laser resonator system consists of three vacuum parts. The high vacuum chamber of the anticryostat is delimited by the reflective mirrors of the resonator. At rear sides of both mirrors there are two low vacuum sections ensuring reduction of air pressure forces affecting the geometry and position of cavity mirrors. Vacuum chambers are fixed to the optical honeycomb board allowing easy transportation between Czech Institutes and CERN as well as the integration of both parts of the resonator to the LHC dipole (Fig. 2).

Two hemispherical resonators of length long 19.962 m and 0.8 m were designed and built for the 632.8 nm He-Ne laser. The theoretical limit for the finesse deduced from the reflectivity of mirrors reach 259. One of the prototype Fabry-Perot cavity housed inside its vacuum chamber is shown in Fig. 3 during its testing phase prior its integration on LHC magnet at CERN. These tests have allowed checking the adjustability of resonator mirrors, evaluating the cavity finesse and preventing any vacuum leak.

Fig. 2: Design of two vacuum parts holding the mirrors of the resonator – left for spherical mirror, right for planar mirror.

Fig. 3: Completed vacuum chambers of the resonator under laboratory vacuum test.

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The full length Fabry-Perot cavity has been installed and tested for the first time at CERN in 2013 [5]. In 2014, additional tested have been conducted to investigate the problem related to the locking of the Fabry-Perot cavity to the frequency of the laser. Ground vibrations prevent at present the stability of the locking of the cavity for the long experimental run durations and this problem still required full and dedicated considerations.

2.2.2 Locking of the optical cavity and test plan

Usual different approaches have been used with cavities of various lengths to investigate the problem of cavity locking such as the so-called side of fringe lock and top of fringe lock with conventional lock-in technique as well as the Pound-Drever-Hall one [9]. When the distance between mirrors of the cavity increases, the resonant fringe becomes steeper and steeper and conditions regarding seismic stability becomes more and more difficult to achieve. The foresee piezo-elements were not able to provide the required feedback and news ones have been design. To improve the seismic stability heavy concrete blocks have been ordered for the support of mirrors. Also, a dedicated seismic control system similar to the one used for the LIGO and Virgo interferometers [10] is under study. As an additional problem it has been found that the stability of the laser decrease due to the back reflected light within the set-up. This requires the use of a mode-cleaner for the laser stabilization, which will also serve as a protection against the back reflected light. The plan is to test in 2015 a 4 m long cavity at high power using the new piezo-system within a brand new optical laboratory lent by the HiLASE European project [11].

Fig. 4: Simplified experimental set-up with mode-cleaner similar to the one used for LIGO and Virgo, which will be tested in 2015.

2.3. Data analysis in French, German and Czech Institutes

Data analyses for LSW experiment are conducted simultaneously at the CNRS/UJF-Grenoble-1 in France, at the University of Mainz in Germany as well as at the Technical University of Liberec in Czech Republic. They are looking for the optimization of the data analysis from various statistical approaches. Significant progress has been achieved [ 12].

2.4. OSQAR-LSW experimental run

Both new spare LHC dipoles assigned to OSQAR, installed and aligned in 2012 on the dedicated horizontal cryogenic benches B1 and E1 in the SM18 hall have been used for the 2014 OSQAR photon regeneration run after a short re-commissioning period.

Locking part 1 for mode-cleaner

Locking part 2 for the main cavity

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A thermoelectric cooled CCD - Andor iKon-M 934 Series [13] has also been rented and used (Fig. 6). The CCD sensor is composed of a 2D array of 1024 x 1024 square pixels of 13 µm size. The quantum efficiency of the CCD at 532 nm is closed to 90 %, the typical readout noise at 50 kHz is equal to 3.3 e- and the dark current < 0.00047e/Pixel/s at -100°C. The CCD was operated at -95°C as the maximum Peltier cooling efficiency could not be reached. A Verdi V18-series CW laser, i.e. diode-pumped solid-state laser, delivering 18.5 W at 532 nm i.e. 2.33 eV, has been rented from Coherent GmbH (Fig. 5a). The laser beam has been successfully collimated before being aligned within the dipole apertures and the CCD detector located at a distance of 55 m.

To ensure the stability of the alignment during long time integration periods, the position of the laser beam spot has been carefully studied and regularly measured with the CCD before and after each experimental run. For this, the laser beam optical power has been reduced before entering in the aperture of the first dipole with a variable beam splitter attenuator (Fig. 5) as well as before its entrance in the second dipole one using dedicated absorbers. The vacuum was better that 10-5 mbar in both magnet apertures. For each orientation of the linear polarization of the laser beam, namely parallel and perpendicular to the field direction, for scalar and pseudo-scalar light particle search respectively, the total time integration was split in 60 experimental runs of 2 x 5400 s each.

a) b)

Fig. 5: New experimental set-up of the OSQAR-LSW used in 2014; (a) 18 W CW Verdi laser from Coherent at the entrance of the first LHC dipole; (b) variable beam splitter attenuator with its absorber allowing typically a reduction of 10-3 of the beam power during alignment operations and checks.

Fig. 6: The new Peltier-cooled CCD located at the exit of the second LHC dipole.

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Preliminary data analysis has been performed to interpret the LSW experimental runs performed in August and September 2014. It is based on the conservative approach proposed and published in [14]. By considering only about 80 % of data, the new very preliminary exclusion limit obtained and shown in Fig. 7 improves significantly the present reference results obtained by OSQAR [12] and ALPS [ 15] collaborations. The coupling constant limits that can be deduced are about 3∙10-8 GeV-1 for pseudo-scalar and scalar particle search in the massless limit.

All the parameters of the experiment are now carefully checked and the analysis will be completed with all recorded data and improved with the newly method published in [12] before being carefully cross-checked. The final results are planned to be submitted for publication in the second half of 2015.

Fig. 7: Preliminary exclusion limits for the search of new pseudo-scalar particles obtained from the 2014 OSQAR photon regeneration run and corresponding to the analysis of about 80 % of the accumulated data. The same limit has been reached for scalar particles. To highlight the progress achieved, previous OSQAR results are also shown as well as the last result from ALPS.

3. A new proposal from the OSQAR collaboration: The quest of chameleons/SISPs

3.1. Generalities on chameleons

Chameleon Fields, scalar or pseudo-scalar ones, have been introduced in 2004 in the context of cosmology and gravitation to explain dark energy [7]. “The idea is that the mass of the scalar field is not constant in space and time, but rather depends on the environment, in particular, on the local matter density.” In 2007, it has been argued that chameleons may have a different coupling strength to the electromagnetic field than to matter [ 16]. In case of dominant electromagnetic coupling, electromagnetic experiments searching for dark energy may be more efficient than gravitational ones. For examples, it is possible to use laser-based experiment [17],[18], haloscope [ 19] or helioscope [20] and profit from the unique nature of chameleons to look for the “afterglow” of photon-chameleon-photon transitions in a strong magnetic field [21],[22].

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3.2. Principle of the chameleon/SISPs search in laboratory

The electromagnetic couplings between photons and chameleons are analogous to the ones between Axion/Axion-like-particles and photons, namely proportional to the electromagnetic field energy densities E·B and (B2-E2) for pseudo-scalar and scalar particles respectively. These couplings allow photons to oscillate into chameleons and back in the presence of an external magnetic field. As chameleons penetrate the material of the apparatus, such as the walls and windows of a vacuum chamber, their effective mass grows sharply and they reflect. Thus, chameleons with energy less than the effective mass in a material will be completely reflected by that material, allowing them to be trapped inside a “jar” (Fig. 8). Chameleons produced in the jar from photon oscillation will be confined until they are being regenerated in photons, which emerge as an afterglow once the original photon source is turned off [21],[22].

Fig. 8: Principle of the two phase OSQAR afterglow experiment. In phase 1, an absorber is inserted in front of the CCD detector to protect it against the high power laser beam. The dashed line represents the chameleons or SISPs, which are supposed of being strongly interacting with mater. Consequently they are expected to be totally reflected by the windows of the vacuum chamber, trapped and accumulated during the phase 1. In phase 2, the laser is switch-off allowing the detection of a sort of magneto-phosphorescence effect coming from the conversion of chameleons to photons.

The photon to chameleon probability conversion in vacuum permeated by a magnetic field B over a length L is given by [ 23],[24]:

𝒫𝛾↔𝜑 = 4𝜔2𝑔𝛾𝛾2 𝐵2

𝑚𝑒𝑓𝑓4 𝑠𝑖𝑛 (

𝑚𝑒𝑓𝑓2 𝐿

4𝜔) 2 (1)

where ω is the particle energy, meff the effective chameleon mass in the environment and gγγ the di-photon coupling constant of chameleon, which scales with the Planck mass, i.e. gγγ = βγ /MPl. Following the description of GammeV [17], the flux of afterglow photons can be modeled as:

�̇�𝑎𝑓𝑡𝑒𝑟𝑔𝑙𝑜𝑤(𝑡) = 𝜂 𝑃 𝑓𝑒𝑠𝑐 𝑓𝑣𝑜𝑙 𝒫𝛾↔𝜑 2 𝑐

𝜔 𝛤 𝐿𝑡𝑜𝑡𝑎𝑙(1 − 𝑒−𝛤𝛥𝑡)𝑒−𝛤𝑡 (2)

In this expression, η is the detector efficiency, P the power of the laser, fesc and fvol the chameleon escape fraction and the volume fraction respectively, Γ the mean decay rate by chameleon, Ltotal the total length of

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the chameleon chamber (larger than the magnetic length L if no segmentation is used) and ∆t the filling duration.

It should be emphasized that the analysis of CHASE (Chameleon Afterglow Search) type experiments is much more delicate than LSW ones mainly because some parts are model-dependent, and not only those concerning chameleon model parameters, i.e. the potential form, but also those related to the description of experimental conditions such as for example, the interaction of the photon/chameleon wave-function with the surface of the vacuum chamber as a function of its coating [18].

3.3. Integration and validation of the experimental set-up

The afterglow experiment with principle shown in Fig. 8 can be easily integrated within the OSQAR set-up with minimal investments. Regarding to magnetic requirements this experiment is even less demanding than the LSW one as the use of a single LHC dipole providing a magnetic field of 9 T can already allow improving the present reference results obtained by the GammeV-CHASE collaboration [18].

The OSQAR configuration for the quest of chameleon type particles has been tested with two main objectives. The first one was to develop and test dedicated systems allowing risk mitigation in the use of the 18 W laser. A safe running of the experiment for both operators and detector is the highest priority. The second objective was to reach the shortest time delay between switching off the laser generating particles inside the anticryostat of the LHC dipoles and the opening the CCD shutter for the photon detection. As afterglow regenerated photons are expected to decay exponentially with unknown time constant, shortest time improves the experiment sensitivity.

The design of the experiment is schematized in Fig. 9. The key point is the system allowing the fast and safe laser beam dump within a dark chamber for the photon detection. For the phase 1 of the experiment, i.e. the filling of the jar with chameleons (Fig. 8), the valve 1 and the valve 2 are open and the beam is reflected by a mirror to the absorbing brick whereas the valve 3 is close to protect the CCD (Fig. 9). During the phase 2 of the experiment, i.e. the detection of possible afterglow regenerated photons(Fig. 8), the valve 1 and the valve 2 are closed for the darkness required by the photon detection whereas the valve 3 is open (Fig. 9). The status of valves for both phase of the experiment is summarized in Table 1.

Fig. 9: Scheme of the experiment with the laser in the right side, the CCD in the left one, 3 valves, a mirror and the laser beam dump.

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Phase 1: Chameleon filling Phase 2: Photon Detection Valve 1 Open Close Valve 2 Open Close Valve 3 Close Open

Table 1: Both configurations of the experiment corresponding to both phases described in Fig. 8

Fig. 10: A close look to reality: plumbing and leak tightness with light. The picture is taken from the magnet exit during the integration prior to testing. CCD, valve system, mirror and the brick shield of the beam dump can be clearly identified.

Both phases of the experiment (Fig. 8) have been successfully tested with 18.5 W laser beam as well as the operational sequences allowing the transition between them. As already mentioned one of the key points of the experiment is the time delay of the transition between the phase 1 and the phase 2, which has been measured several times and found to be in the range 6-20 s with the use of manual valves. Improvements with automatic valves are under study to detect particles with shorter lifetimes. It can be mentioned that for GammeV [17] the time gap between filling the chamber and observing the afterglow was longer, i.e. in the range 300-1000 s. It can be highlighted that GammeV-CHASE has observed an anomalous orange afterglow effect, which is yet unexplained, i.e. a non-magnetic-phosphorescence effect at a different wavelength than the laser one. This effect prevents actually the observation of possible chameleon afterglow immediately after the laser switch-off, i.e. for t < 120 s [18].

Among other improvements that need to be implemented it can be added that by reducing the distance between windows, chameleons of larger mass can be trapped and probed [18].

4. Objectives for 2015

4.1. OSQAR-LSW experiment – Next run not before 2016

4.1.1. Upgrade phase - Targets for improvements The sensitivity of the OSQAR-LSW experiment can still be improved by:

- Increasing the number of LHC dipoles, which is the most efficient way of improving the OSQAR-LSW sensitivity. Discussions with CERN responsible of the SM18 hall have started about Super-OSQAR (see in Annex the minutes of the meeting of September 1st, 2014),

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- Increasing the number of incoming photons in the first dipole by using one of the Fabry-Perot cavities under test and development as well as a more powerful laser,

- Improving the sensitivity of the detection with dedicated detector development.

To increase the incoming photon flux for the running of the OSQAR-LSW experiment runs in 2016 the following three actions will be pursued in parallel:

i) By locking the new 18 W laser provided by Coherent GmbH to the Fabry-Perot cavity of finesse 250 specially developed by the Czech team, the incoming laser power to generate axion can be in the range of 4-5 kW. ii) The 200 W infrared laser prototype of the HiLASE project [11], is presently considered for use in the OSQAR-LSW experiment. Ongoing discussions are well engaged. iii) A close collaborating effort between OSQAR and ALPS at CERN is still considered as a very interesting option but would require a common recommendation between the CERN-SPSC and the committees in this direction (see in Annex the minutes of the OSQAR-ALPS meeting of September 6th, 2014). The starting point is the preparation of a common OSQAR-ALPs proposal.

More efficient photon detectors with a much lower background are under study. For example, Superconducting Transition Edge sensor coupled to a SQUID readout can allow typically to gain at least 1 order of magnitude in sensitivity but it requires a dilution refrigerator to cool-down the detector down to 30 mK.

4.1.2. Expected results Exclusion limits in the 10-9 GeV-1 range can be reached with the foresee improvements of the OSQAR-LSW experiment within 2-3 years but depend either of the possibility of using more than 2 LHC dipoles at the CERN-SM18 hall or of the result of the development of long length Fabry-Perot cavity [14].

4.2. Run of the OSQAR chameleon experiment in 2015

The GammeV-CHASE experiment searched for afterglow set limits on photon-chameleon couplings much below collider constraints for a wide set of unexplored dark energy models [18]. The new OSQAR experimental set-up for chameleon or SISPs search, which has been validated in 2014 is ready for operation in 2015. As a preliminary estimate from (2), exclusion limits for the di-photon coupling constant gγγ = βγ /MPl ∼ B-1 P-1/4 η-1/4 can be improved by at least a factor of about 3-4 with respect to the present reference result of the GammeV-CHASE collaboration [18] assuming the increase of the magnetic field B from 5 T to 9 T, the laser power P from 3.5 W to 18.5 W, the detector efficient η from 0.29 to 0.87 and the same values for all other parameters.

As an additional motivation supporting the OSQAR-CHASE experimental run concerns the study of the “anomalous” orange afterglow effect observed by the GammeV-CHASE collaboration [25].

5. Conclusion, Perspectives & Requirements for 2015

The OSQAR-LSW has been successfully operated in 2014 with a new 18 W DC laser working at 532 nm and a new Peltier-cooled CCD detector. Long time integration periods have been obtained with the simultaneous use of both spare LHC dipoles each of them providing a magnetic field of 9 T over 14.3 m. The results of the 2014 photon regeneration experimental runs for pseudoscalar/axion and scalar particle search need to be deeply analyzed to settle precisely the new exclusion limits that will become the new reference ones.

Several possibilities are targeted for the OSQAR-LSW experiment to reach incoming optical power in kW range for the OSQAR-LSW experimental run planned in 2016-2017. This will allow further improving exclusion limits for the search of ALPs obtained with this type of experiment.

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For 2015, the experimental run will focus to the chameleon/SISPs search with the new set-up specially developed and successfully tested at CERN. Plan to further improve this set-up with automatic control unit is under study. The request from the collaboration concerns the possibility of using one of the LHC dipoles at 1.9 K committed for OSQAR together with dedicated resources for a minimum experimental run duration of 6 weeks.

Acknowledgements

The OSQAR collaboration would like to thank the CERN-TE teams of the SM18 test hall (MSC-TF, CRG-OD, VSC-LBV) for their valuable technical contributions and efficient devotion for the operation of both LHC dipoles dedicated to OSQAR as well as the management of CERN-TE department for his continuous support.

REFERENCES [1]10th Patras Workshop on Axions, WIMPs and WISPs, 29th June - 4th July 2014, CERN, Geneva Switzerland, http://axion-wimp2014.desy.de/ [2] P. Sikivie, "Detection rates for invisible-axion searches", Phys. Rev. Lett. 51, 1415 (1983); Phys. Rev. D 32, 2988 (1985) [3] K. van Bibber et al., "Proposed experiment to produce and detect light pseudoscalars", Phys. Rev. Lett. 59, 759 (1987) [4] P. Pugnat et al., "OSQAR Proposal", CERN-SPSC-2006-035, SPSC-P-331, 9 November 2006 http://doc.cern.ch//archive/electronic/cern/preprints/spsc/public/spsc-2006-035.pdf [5] P. Pugnat, M. Sulc et al., "OSQAR Annual Report 2013", CERN-SPSC-2013-030, SPSC-SR-125, 17 October 2013 http://cds.cern.ch/record/1611104/files/SPSC-SR-125.pdf [6]P. Pugnat et al., "OSQAR Plan for 2014", CERN-SPSC-2014-012, SPSC-M-784, 26 March 2014 https://cds.cern.ch/record/1690034/files/SPSC-M-784.pdf [7]J. Khoury and A. Weltman, "Chameleon fields: awaiting surprises for tests of gravity in space", Phys. Rev. Lett. 93 171104 (2004) ; J. Khoury and A. Weltman, Phys. Rev. D 69 044026 (2004) [8] P. Pugnat et al., "OSQAR Annual Report 2012", CERN-SPSC-2012-032, SPSC-SR-108, 21 October 2012 https://cds.cern.ch/record/1488899/files/SPSC-SR-108.pdf [9] R. W. P. Drever et al., "Laser phase and frequency stabilization using an optical resonator", Appl. Phys. B, Photophys. Laser Chem. 31, 97–105 (1983) [10] M.G. Beker et al., "Seismic attenuation technology for the Advanced Virgo gravitational wave detector", Physics Procedia 37 1389 – 1397 (2012 ), http://www.sciencedirect.com/science/article/pii/S1875389212018445# [11] http://www.hilase.cz/en/ [12] R. Ballou et al., "Latest Results of the OSQAR Photon Regeneration Experiment for Axion-Like Particle Search", submitted for publication in the Proceedings of 10th Patras-Axion-WIMP-WISP Workshop 2014, DESY-PROC-2014-03, ISSN 1435-8077, ISBN 978-3-935702-90-4, arXiv:1410.2566 [13] http://www.lot-qd.de/files/downloads/andor/en/ccd-detectors/iKon-M_934.pdf [14] P. Pugnat et al., "Search for weakly interacting sub-eV particles with the OSQAR laser-based experiment: results and perspectives", Eur. Phys. J. C 74:3027 (2014), arXiv:1306.0443 [15] K. Ehret et al., "New ALPS results on hidden-sector lightweights", Phys. Lett. B 689 149-155 (2010) [16] P. Brax, C. van de Bruck, and A.-C. Davis, "Compatibility of the Chameleon-Field Model with Fifth-Force Experiments, Cosmology, and PVLAS and CAST Results", Phys. Rev. Lett. 99, 121103 (2007) [17] A. S. Chou et al., "Search for Chameleon Particles Using a Photon-Regeneration Technique", Phys. Rev. Lett. 102 030402 (2009) [18] J. H. Steffen et al., "Laboratory Constraints on Chameleon Dark Energy and Power-Law Fields”, Phys. Rev. Lett. 105 261803 (2010) [19] G. Rybka et al., "Search for chameleon scalar fields with the axion dark matter experiment", Phys. Rev. Lett. 105 051801 (2010) [20] G. Cantatore et al., "Status report of the CAST Experiment, planning and requests for 2013-2014", CERN-SPSC-2013-027, SPSC-SR-123, 14 October 2013, http://cds.cern.ch/record/1610238/files/SPSC-SR-123.pdf [21] M. Ahlers, A. Lindner, A. Ringwald, L. Schrempp, and C. Weniger, "Alpenglow: A signature for chameleons in axion-like particle search experiments", Phys. Rev. D 77, 015018 (2008) [22] H. Gies, D. F. Mota, and D. J. Shaw, "Hidden in the light: Magnetically induced afterglow from trapped chameleon fields", Phys. Rev. D 77, 025016 (2008) [23] G. Raffelt and L. Stodolsky. "Mixing of the photon with low-mass particles", Phys. Rev. D 37, 1237–1249 (1988) [24] A. Upadhye, J. H. Steffen, and A. Weltman, "Constraining chameleon field theories using the GammeV afterglow experiments", Phys. Rev. D 81, 015013 (2010) [25] J.H. Steffen, A. Upadhye, A. Baumbaugh, A.S. Chou, and R. Tomlin, "Anomalous afterglow seen in a chameleon afterglow search", Phys. Rev. D 87, 012003 (2012)

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Annex

OSQAR contributions to International Conferences in 2014

29 June - 4 July 2014, 10th Patras Workshop on Axions, WIMPs and WISPs, CERN, Geneva, Switzerland http://axion-wimp2014.desy.de/e222615/, two contributions, oral and poster

OSQAR Publication List for 2014

P. Pugnat, R. Ballou, M. Schott, T. Husek, M. Sulc, G. Deferne, L. Duvillaret, M. Finger, M. Finger, L. Flekova, J. Hosek, V. Jary, R. Jost, M. Kral, S. Kunc, K. Macuchova, K. A. Meissner, J. Morville, D. Romanini, A. Siemko, M. Slunecka, G. Vitrant, and J. Zicha, “Search for weakly interacting sub-eV particles with the OSQAR laser-based experiment: results and perspectives”, Eur. Phys. J. C 74:3027 (2014), arXiv:1306.0443

J. Hošek, K. Macúchová, Š. Němcová, Š. Kunc , and M. Šulc, “Opto-mechanical design of vacuum laser resonator for the OSQAR experiment”, Proc. SPIE PPR100, Photonics Prague 2014; doi: 10.1117/12.2070226

K. Macúchová, Š. Němcová, J. Hošek, “Differential interferometer for measurement of displacement of laser resonator mirrors”, SPIE- Photonics Prague 2014 Paper No. PPR100-14 – will be issued in proceedings and WoS in 2015.

R. Ballou, G. Deferne, L. Duvillaret, M. Finger, M. Finger, L. Flekova, J. Hosek, T. Husek, V. Jary, R. Jost, M. Kral, S. Kunc, K. Macuchova, K. A. Meissner, J. Morville, P. Pugnat, D. Romanini, M. Schott, A. Siemko, M. Slunecka, M. Sulc, G. Vitrant, C. Weinsheimer, and J. Zicha, “Latest Results of the OSQAR Photon Regeneration Experiment for Axion-Like Particle Search”, submitted for publication in the Proceedings of 10th Patras-Axion-WIMP-WISP Workshop 2014, DESY-PROC-2014-03, ISSN 1435-8077, ISBN 978-3-935702-90-4 arXiv:1410.2566

Attached hereafter two minutes of meetings on the future of OSQAR

Skype-call about OSQAR-ALPS possible future collaboration

September 6th, 2014, 9:30 am

Attendees: A. Lindner (ALPS spokesperson), A. Ringwald (ALPS co-spokesperson), R. Ballou (OSQAR team leader), P. Pugnat (OSQAR spokesperson)

Minutes (extract) Status: Approved

Prior to this meeting the following subjects have been proposed for discussions

- Preparation of a letter to the CERN-DG (?) - Time period is most suitable for a common proposal OSQAR-ALPS knowing that preliminary

proposals are under discussion at CERN for the use of the SM18 hall by the OSQAR experiment : i) 2015-16: short term perspectives for OSQAR with 1+1 dipole & upgrade of the laser power (tbd) ii) 2016-18: Longer term perspective with Super-OSQAR, i.e. 2+2 dipoles (possibly 3+3 ?) & laser power (tbd).

The OSQAR Experiment at CERN is reviewed by the SPSC committee at CERN with as referees aldo.ianni@lngs.infn.it and gavin.salam@cern.ch . The ALPS experiment is reviewed by the DESY PRC committee with as referees ljrosenberg@phys.washington.edu and carena@fnal.gov . It was agreed during the Skype-call that the first objective is to obtain from both committees a recommendation for a common OSQAR-ALPS proposal and both collaborations will contact their committee with this respect. It is too early to present a detailed common proposal for the 2014 annual review of both experiments (16-17 October for ALPS and 21-22 October for OSQAR) but some generalities and trends could be announced. It was agreed that possible directions could be:

1/ 2015-2016: OSQAR-ALPS collaboration at CERN 2/ 2016-2018: Super-OSQAR, with or without ALPS as a function of the progress in the re-installation of Hera superconducting dipoles at DESY 3/ Long-term: ALPS-OSQAR collaboration at DESY.

The present ALPS planning is consistent with the above points 1/ and 3/. The installation at CERN of a part of the ALPS optical setup (including the 35 W laser of 250 k€ with its optics, the cleaning room of at least 3x4 m, …) as well as the development of shorter cavities, could be possible in autumn 2015 as it is expected that within 1 year the whole optical setup for ALPS will be operational. Second half of 2016, all ALPS dipoles are expected to be installed and aligned at DESY. The first run of ALPS-IIc is planned not before the second half of 2017 with the 20 magnet string setup in HERA. This obviously sets the date at which all the optical setup must be back from CERN.

All the above discussions are only based on organizational issues and it was also agreed that the collaboration OSQAR should present to the ALPS collaboration this common proposal if possible during the second half of November 2014 to obtain the agreement from the whole ALPS collaboration.

…

For information, the directorate from DESY will take no decision before having received a recommendation from the DESY PRC committee and this could be the same at CERN from the SPSC. And the loop is closed…

Meeting at CERN-SM18 for the future of OSQAR September 1st, 2014

Attendees - M. Bajko, C. Giloux, P. Pugnat

Minutes - Modifications of test benches configuration are planned at the SM18 test hall for testing magnets of the High Luminosity LHC upgrade. OSQAR program and future were not considered up to now and supposed being ended in 2015 (Email from M. Bajko, 29/08/2014). Thinks are not irreversible and we have started discussions about

i) Short term perspectives of OSQAR, say 2015-16 ii) Longer term perspective with Super-OSQAR, i.e. 2+2 dipoles, possibly in collaboration with ALPS from DESY

Concerning i) and the possibility of using test benches B1 and E1 (Fig. 1) in 2015 and hereafter. The power supply of the bench E1 is planned to be used in parallel with another one to increase the available maximum current for testing purpose. In the present plan, there will be in near future, i.e. post-2015, no power supply for the second OSQAR magnet. Two possibilities have been then discussed. The first one is to introduce a commutation switch allowing the powering of the 2nd OSQAR magnet when both power supplies connected in parallel are not used. This solution seems not possible as it will introduce a too important resistive voltage drop in the circuit. The second possibility that is being studied is to connect both LHC dipoles of OSQAR in series (with the proper polarity) with the power supply of the cluster B.

For ii) and the possibility of building a Super-OSQAR with 2+2 dipoles or more. The solution consisting of simply adding one additional LHC dipole on each test bench B1 and E1 is not the preferred one mostly for space constraint. The former string location in SM18 could be used to connect in series 2+2 dipoles or even 3+3 and this could be combined to a study of fatigue and performance stability of LHC dipoles during long powering runs at ultimate field as well as the occurrence of random quenches. At present a possible time slot for Super-OSQAR is 2016-2018 in parallel with the SC-link test planned in 2016-17 by A. Ballarino. In 2019, a string of quadrupoles for High Luminosity LHC upgrade is planned to be installed and tested at SM18 at the above-mentioned possible location for Super-OSQAR.

E1

B1

Fig.1 SM18 test hall at CERN; benches labeled B1 and E1 are presently used by the OSQAR experiment.