Annual Report 2017 P. Pugnat 1, R. Ballou 2, G. Deferne 3, J. Hosek 4, S. Kunc 5, K. A. Meissner 6, M. Schott 7*, A. Siemko 3, M.

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1 4 th October 2017 Annual Report 2017 P. Pugnat 1, R. Ballou 2, G. Deferne 3, J. Hosek 4, S. Kunc 5, K. A. Meissner 6, M. Schott 7*, A. Siemko 3, M. Sulc 5 1 LNCMI, UPR CNRS 3228, UJF UPS INSA, BP 166, Grenoble Cedex-9, France 2 Institut Néel, UPR CNRS 2940, UJF Grenoble INP, BP166, Grenoble Cedex-9, France 3 CERN, CH-1211 Geneva-23, Switzerland 4 Czech Technical University (CTU), Prague, Czech Republic 5 Technical University of Liberec (TUL), Czech Republic 6 Institute of Theoretical Physics, University of Warsaw, Poland 7 University of Mainz, Institute of Physics, Mainz, Germany * Involved in OSQAR-LSW and OSQAR-VMB but not in OSQAR-CHASE CERN-SPSC / SPSC-SR /10/2017 Abstract In 2017, the OSQAR-CHASE experiment dedicated to the search of chameleon particles has been run with one spare LHC dipoles installed and re-commissioned on its dedicated cryogenic bench at CERN- SM18. High vacuum condition has been reached within the magnet aperture using cryo-pumping. A 18 W CW laser working at 532 nm and a state-of-the art CCD detector have been installed, aligned and operated searching for a phosphorescent signal of the vacuum permeated by the magnetic field coming from Chameleons. The analysis of the data is ongoing. In parallel, a new analysis of the OSQAR-LSW data recorded during the 2014 experimental run is being pursued. It is based on the cross-correlation method and will allow further improvement of the present reference exclusion limits obtained by OSQAR-LSW for scalar and pseudoscalar sub-ev axion like particle search. Additional gains in the sensitivity of OSQAR-LSW can be obtained by using more than 2 LHC dipoles and by developing dedicated Fabry-Perot cavities. A new French- German proposal has been submitted in 2017 to the ANR-DFG funding agencies to support these developments. Concerning OSQAR-VMB, the first phase is coming to an end. The next one requires the development of a long Fabry-Perot cavity and a revision of the optical detection scheme. An extended European initiative is being prepared within the scope of the Physic Beyond Collider (PBC) working group to measure the vacuum magnetic birefringence at CERN. Outline 1. Introduction Activities related to OSQAR-CHASE Reminder The 2017 experimental run Experimental set-up Data recorded Preliminary data analysis Activities related to OSQAR-LSW Activities related to OSQAR-VMB Perspectives OSQAR-CHASE OSQAR-LSW OSQAR-VMB Conclusion, Perspectives & Requirements... 8 Annex...9 References.9

2 1. Introduction OSQAR explore the low energy frontier of particle/astroparticle physics by combining the simultaneous use of high transverse magnetic fields with laser beams in three distinct experiments. OSQAR-VMB aims to measure the ultra-fine Vacuum Magnetic Birefringence [1] predicted by the QED [2]. OSQAR-LSW is looking for the photon regeneration effect [3] as a Light Shining through the Wall (LSW) [4],[5],[6]. The third experiment, OSQAR-CHASE, is looking for hypothetical particles called Chameleons [7],[8],[9] whose mass depends on the local matter density [ 10]. This status report will summarize results obtained in 2017 for the above three OSQAR experiments as well as short and long term perspectives. 2. Activities related to OSQAR-CHASE 2.1. Reminder OSQAR-CHASE described in [7],[8],[9] is following the pioneering work of the GammeV collaboration [11],[12],[13],[14]. The electromagnetic couplings between photons and chameleons are assumed to be same as the ones between Axion/Axion-like-particles (ALPs) and photons, namely proportional to the Lorentz invariants of electromagnetic fields E B and (B 2 -E 2 ) for pseudoscalar and scalar particles, respectively. These couplings allow photons oscillating into chameleons and back in the presence of a transverse magnetic field. When chameleons attempt to penetrate materials, such as the walls and windows, their effective mass grows sharply and they reflect. Chameleons with energy less than the effective mass in the material will be completely reflected at the material surface, allowing them to be trapped inside a vacuum chamber. These Chameleons produced from photon oscillation will be confined until they are being regenerated into photons, which emerge as an exponential time decay afterglow signal once the original photon source is turned off [16]. The OSQAR-CHASE main objective [7],[8],[9] is to improve by a factor of about 3-4 the present exclusion limits settled by GammeV-CHASE [11],[13]. In addition it was planned to probe the fragmentation of Chameleons The 2017 experimental run Experimental set-up OSQAR-CHASE requires a single LHC dipole connected to its cryogenic feedbox and power converter at CERN-SM18 [7],[8],[9]. Dipole apertures have been equipped with anticryostats [15] used as vacuum pipes. The selected aperture has been closed by two BK7 windows with antireflexion coating clamped at each extremity. Improvements with respect to the 2016 OSQAR-CHASE set-up have been introduced such as the replacement of all elastomer seals by metallic ones to reduce the outgassing. Cleaning followed by a thorough leak detection have been performed prior to connect two turbomolecular pumping groups across the selected anticryostat, one at each extremity, i.e. at the laser beam entrance and at the exit. Both sides have also been equipped with valves and compact vacuum gauges from Pfeiffer (PKR 251, FPM sealed, DN25 ISO-KF). These gauges are full range type with two sensors in one housing, i.e. Pirani and hot cathode gauges of Bayard-Alpert type for pressure measurements down to 10-3 mbar and mbar, respectively. To reach ultra-high vacuum condition (UHV) within the selected LHC dipole aperture, the powering of the anticryostat has not been switched-on to profit from the cryopumping effect and was cooldown at a much slower speed than the superconducting dipole. Stable conditions in temperature and pressure have been reached after about 280 h (Fig. 1) with the temperature of the long anticryostats reaching -170 C. 2

3 The pressure measured at the level of the turbomolecular pumps and near the gauges were equal to mbar and mbar, respectively. Fig. 1: Temperature evolutions from the 5 July until the 11 August of the long anticryostat (in blue), the short one (in green) and the interconnection part (in orange). The temperature of the anticryostat part within the magnetic field during the OSQAR-CHASE run was around -170 C. The same Verdi V18-series CW laser as the one used for the 2014 OSQAR-LSW and 2016 OSQAR- CHASE experimental runs has been rented from Coherent GmbH, i.e. a diode-pumped solid-state laser delivering 18.5 W at 532 nm (2.33 ev). The laser beam has been properly collimated prior to its alignment within the dipole aperture (Fig.2) and the CCD detector located 19.3 m away at the magnet exit. A 1 week delay in the laser delivery has shorten the duration of the experimental run. Fig. 2: The 18 W Verdi laser at the magnet entrance with optical elements to reduce the optical power during the alignment phase as well as to rotate the linear polarization of light. For the photon detection the same thermoelectric cooled USB CCD Camera (Andor ikon-du934p- BV Back-Illuminate) as the one used for the 2016 run [8] has been rented. The CCD sensor is composed of a 2D array of 1024 x 1024 square pixels of 13 µm size. The quantum efficiency (QE) of the CCD at 550 nm is 3

4 95 %, the typical readout noise at 50 khz is equal to 2.9 e-/pixel and the dark current < e-/pixel/s at -100 C. To focalize the photon regenerated bean from Chameleons a lens with a focal length of 0.1 m was inserted in front of the CCD. No second detector (PMT or CCD) has been inserted in the laser side. A 532 ± 5 nm band-pass filter has been used for selective detection around the laser wavelength. The possibility of Chameleon fragmentation is then probed without the filter relaying on the CCD sensitivity in the close IR (QE = 15 % at 1000 nm). A second filter of larger band-pass ( nm) has also been used. Fig. 3: The CCD connected to the dark chamber at the magnet exit with the second pumping group on the left side Data recorded The OSQAR-CHASE experimental run started July 6 th to end August 11 st, The summary of most experimental runs performed is given in Table 1. Chameleon runs have been performed with valves of the pumping groups and vacuum gauge closed. The charging and discharging time periods have been varied from ¼ h up to about 12.5 h and the time exposure of the CCD adapted to exponential decays (Table 1). Data acquisition have been repeated with the dipole magnetic field settled to 8.76 T and without magnetic field as well as with and without filter and for both linear polarization of the laser beam, i.e. parallel and perpendicular to the magnetic field. Number of sub-runs Charging time [s] Exposure times for the photon regeneration [s] Comments 5 x x 1000 Scalar, pseudoscalar & background x 1000 Scalar investigation 2 x , 10, 20, 50, 100, 250, 500, 1000 Scalar & background , 10, 20, 50, 100, 250, 500, 1000 Investigations with filters Table 1: Various time frame configurations of the 2017 OSQAR-CHASE run. Scalar and pseudoscalar Chameleons have been probed with linear polarization perpendicular and parallel to the magnetic field, respectively. The background has been characterized from CCD data recording without magnetic field. 4

5 Preliminary data analysis For the experimental runs, the CCD has been used with binning 16x16 pixels. In this configuration the readout noise and dark current measured at -90 C were 3.1 e-/superpixel and lower than e- /pixel/s, respectively. For the overall detection system (including QE of CCD chip, Fresnel reflections on the camera input window, two focusing lens, output window from anticryostat and sensitivity of A/D conversion) the same sensitivity as for the 2016 run [8] and equal to (0.65 ± 0.03) ADU/photon can be considered at the laser frequency. To define the region of interest (ROI) on the CCD [8],[9] dedicated measurements have been performed using a diffuse light source placed on the central axis of the anticryostat at the magnet entrance (Fig. 4) from which a threshold at 15 % of the maximum has been defined. The ROI contains 1047 super pixels over a total of 64 2, i.e superpixels. a) b) Fig.4: Definition of the region of interest (ROI) in the CCD sensitive area of 13 x 13 mm 2. a) Diffused light recorded on the CCD. b) Binary mask of the region of interest set at 15% threshold of the maximum. Quantitative analysis of the recorded data is currently being performed in a similar way than for the 2016 run [8]. All data were corrected from cosmic contamination. A preliminary analysis of the cumulated counts on the 64 x 64 binned super pixels of 16 x 16 for different afterglow exposure times has been conducted by the French team. The average count per superpixels has been plot as a function of the exposure time for the whole CCD, within the ROI previously defined and outside the ROI for two sub-runs with exposure time up to 14 x 1000 s. Whereas the exponential decay afterglow signal observed in 2016 is still visible (Fig. 5a), it disappears once the difference between data taken with and without magnetic field is performed (Fig. 5b & 5c). In Fig. 5d, the data corresponding to scalar Chameleon with short exposition time is also shown after subtraction of the background obtained without magnetic field. As a first and unambiguous conclusion, no afterglow signal coming from Chameleons has been detected. The exclusion limits that can draw from these null results are in progress. Detailed investigations with narrow band-pass (10 nm) and larger band-pass ( nm) filters show that the short time exponential decay signal (Fig. 5a) also visible for pseudoscalar Chameleon search is due to thermal photons coming most probably from the charging phase with the 18.5 W laser bean, which has heated optical components, and not from fragmentation of Chameleons since it is observed with and without magnetic field. 5

6 a) b) c) d) Fig.5: Preliminary results of the OSQAR-CHASE 2017 experimental run. a) Data for scalar Chameleon search recorded with the magnetic field. b) after substraction of the background determined without magnetic field. c) Data for pseudoscalar Chameleon search recorded with the magnetic field after subtraction of the background. d) Data for scalar Chameleon search with short exposure time after subtraction of the background. No afterglow signal is visible and the exclusion limits will be deduced from the quantitative analysis. The errors bars represent the standard deviations. 3. Activities related to OSQAR-LSW The limits of di-photon coupling constant at 95 % confidence level in the nearly massless limit deduced from OSQAR LSW are equal to GeV -1 and GeV -1 for pseudoscalar and scalar particle search, respectively [3]. These limits constitute the present reference results for LSW type experiment. Other statistical analysis methods are being applied to these data to improve the sensitivity and therefore the above exclusion limits. The Czech team is developing a cross-correlation method which is very similar to the Wiener matched filtering technics used to analyze Virgo and Ligo data for example. Preliminary results is shown in Fig.6 for pseudoscalar search and can be further improved. 6

7 Fig.6: Preliminary results obtained from the new analysis of the OSQAR-LSW 2014 data based on the crosscorrelation method. 4. Activities related to OSQAR-VMB Most of the OSQAR-VMB activities were conducted by the Czech team within the scope of the PhD of S. Kunc [16]. A new high sensitive birefringence measurement method based on the electro-optic modulator has been analytically calculated and experimentally tested with the Cotton-Mouton effect measured for the nitrogen gas. One of the main results of this work concerns the measurement of the linear dependence of the of N 2 gas as a function of its pressure with a slope equal to ( ± ) TT 22 aattmm 11. This result obtained from a single path within the transverse magnetic field produced by one spare LHC dipole is in good agreement with reference values published in the literature. Various sources of noise have been discussed, and the sensitivity of the experimental setup has been presented. Optical cavities and their implementation have been proposed and modeled leading to a new solution for the VMB measurement. 5. Perspectives 5.1. OSQAR-CHASE Focus will be given to the data analysis of the 2017 experimental run. None additional requirements with the spare LHC dipole in cold condition are planned at present OSQAR-LSW Short term perspectives for OSQAR-LSW will focus on the development of a 20 m long Fabry-Perot cavity to increase the number of incoming photons in the first LHC dipole. A proposal has been submitted to the French-German ANR-DFG funding agencies (cf. Annex) and the planning is given in Table 2. Year Quarter Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Infrastructure at CERN Cavity developments Integration, LHC magnet Experimental LSW Run Data analysis Table 2: Overview of work-plan for the first phase of the proposed project. Contributions of the German/French partner are marked green/blue. Common activities are marked in grey. 7

8 The ANR-DFG proposal will require the access to the CERN-SM18 hall in 2018 to further characterize the vibration spectra and perform in-situ dedicated tests of the cavity. For the long term perspectives and as an ultimate objective it is worth mentioning that there are at CERN 30 spare 9 T/14.3 m long LHC dipoles. Even if 10 of them can be reserved for the LHC in case of serious problems, dipoles could be used for a LSW experiment of unprecedented sensitivity. Indeed with a magnetic length for the overall experiment equal to 20 x 14.3 x 9 = 2574 T m, the APS-II proposal can be surpassed by a factor of 5.5 assuming similar experimental set-ups. Such a possibility is being discussed at CERN within the newly appointed Physics Beyond Collider (PBC) working group [17] OSQAR-VMB Progress in OSQAR-VMB is dependent of the result of 20 m long Fabry-Perot cavity development even if the VMB requirements are different from the LSW ones, which focuses principally on the optimization of the optical power in the magnetic field. For the long term perspective, a European initiative for the VMB measurement is being discussed within the framework of the CERN/PBC working group. The objective is to profit from the 26 year worldwide efforts to review them and propose a new optical scheme to possibly implement it at CERN within one spare LHC dipole. 6. Conclusion, Perspectives & Requirements OSQAR-CHASE has been operated in 2017 with the 18 W DC laser working at 532 nm and state of the art Peltier-cooled CCD detector. Vacuum conditions within the LHC dipole aperture were better than the previous 2016 run and data recorded with and without magnetic fields allows a precise subtraction of the background. The data analysis is in progress. New analysis of the 2014 OSQAR-LSW data is ongoing. Preliminary results are promising and will allow further improving the exclusion limits for the search of scalar and pseudoscalar ALPs. Among various possibilities to improve OSQAR-LSW, the one focusing on the development of 20 m long Fabry- Perot cavity to increase the incoming optical power up to the kw range is targeted. A proposal has been submitted to the French-German funding agencies for this purpose. Within the scope of this proposal, the access to the OSQAR test bench at SM18 is needed during 2018 for the development of the long Fabry- Perot cavity. The new OSQAR-LSW run with two spare LHC dipoles in cold condition is planned for 3 months during the second half of For OSQAR-VMB, an initiative within the Physics beyond collider working group is being studied to extend the collaboration possibly toward a meta-collaboration. 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, V. Baglin for its valuable advice on vacuum science and technologies as well as the management of the CERN-TE department for his continuous support. 8

9 Annex International Conferences - New data analysis for OSQAR LSW, Štěpán Kunc, Presentation to the 13 th PATRAS Workoshop on Axions, WIMPs and WISPs, May 15-19, 2017, Thessaloniki (Greece) - Dark Matter search with light shining through wall experiments, Rafik Ballou, invited talk to 13 th Rencontres du Vietnam: Exploring the Dark Universe, July 23-29, 2017, Quy Nhon, (Vietnam), Proposal submitted to the ANR-DFG funding agencies Joint Project Proposal, ANR DFG 2017 NLE, 24 months, re-submitted in March 2017: R. Ballou (CNRS IN, Grenoble), Matthias Schott (University of Mainz), P. Pugnat (CNRS LNCMI, Grenoble), Search for Axion Like Particles with a LHC Dipole based Laser Cavity (AxCaL). Answer expected in October Project summary - This project aims at searching ultra-light particles, predicted in many extensions of the Standard Model of particle physics, by using state-of-the-art superconducting magnets at the CERN combined with advanced optical techniques to be developed. Axions, and more generally pseudoscalar or scalar axion-like particles, will be searched by the method of light-shining-through-a-wall using two dipole magnets of the Large Hadron Collider, providing a magnetic field strength of 9.5 T over a length of 14.3 m. One of the main improvements proposed here, compared to the previous experiments conducted with LHC magnets, is the implementation of an optical cavity in the first magnet, which leads to a sensitivity gain by a factor of 6 compared to the currently most sensitive model independent limits for axion-like particles with masses 1 mev. The required developments build the basis for a future measurement of the vacuum magnetic birefringence effect. Initially anticipated to 36 months this is decreased to 24 months because of constraints on the availability of the LHC dipoles at the SM18 hall at CERN. Upgrade of cryogenics and installations of a string of insertion magnets are scheduled for that will forbid any data-taking runs within the frame of the present project in the third year. This will not impact the light-shining-through-a-wall experimental runs, however, the dedicated searches of axion-like particles via vacuum magnetic-birefringence studies have to be postponed. This task indeed was targeted in the final stage of the project and as a preliminary step towards the extremely challenging objective to reach the conditions for the measurement of the vacuum magnetic-birefringence associated with the virtual electron-positron pairs predicted within Quantum Electrodynamics. We anticipate instead, by means of the experimental setup for the light-shining-througha-wall, to extend our search of ultra-light particles to massive photons and the mini-charged particles of the hidden sectors. References [1] P. Pugnat et al., Czech J. Phys. 55, A389 (2005) [2] H. Euler and B. Kockel, Naturwiss. 23, 246 (1935); W. Heisenberg and H. Euler, Z. Phys. 98, 714 (1936). [3] R. Ballou, et al. (OSQAR collaboration), New Exclusion Limits for the Search of Scalar and Pseudoscalar Axion-Like Particles from Light Shining Through a Wall, Phys. Rev. D 92, (2015); [4] P. Sikivie, "Detection rates for invisible-axion searches", Phys. Rev. Lett. 51, 1415 (1983); Phys. Rev. D 32, 2988 (1985) [5] A. A. Ansel'm, Sov. J. Nucl. Phys. 42, 936 (1985) [6] K. van Bibber et al., "Proposed experiment to produce and detect light pseudoscalars", Phys. Rev. Lett. 59, 759 (1987) [7] P. Pugnat et al., "OSQAR-CHASE Proposal, CERN-SPSC , SPSC-P-331-ADD-1, 16 March [8] P. Pugnat et al., "OSQAR Annual Report 2016, CERN-SPSC / SPSC-SR-196, 7 October

10 [9] P. Pugnat et al., "OSQAR Addendum for the 2017 run, CERN-SPSC / SPSC-P-331-ADD-1-ADD-1, 4 April [10] J. Khoury and A. Weltman, "Chameleon fields: awaiting surprises for tests of gravity in space", Phys. Rev. Lett (2004) ; J. Khoury and A. Weltman, Phys. Rev. D (2004) [11] A. S. Chou et al., "Search for Chameleon Particles Using a Photon-Regeneration Technique", Phys. Rev. Lett (2009) [12] A. Upadhye, J. H. Steffen, and A. Weltman, "Constraining chameleon field theories using the GammeV afterglow experiments", Phys. Rev. D 81, (2010) [13] J. H. Steffen et al., "Laboratory Constraints on Chameleon Dark Energy and Power-Law Fields", Phys. Rev. Lett (2010) [14] A. Upadhye, J. H. Steffen, and A. S. Chou, "Designing dark energy afterglow experiments", Phys. Rev. D 86, (2012) [15] O. Dunkel, P. Legrand and P. Sievers, A Warm Bore Anticryostat for Series Magnetic Measurements of LHC Superconducting Dipole and Short Straight Section Magnets, CERN-LHC-Project-Report-685, (2004); [16] S. Kunc, "Study of the Magnetically Induced QED Birefringence of the Vacuum in experiment OSQAR, PhD submitted to the Technical University of Liberec, 2017 [17] P. Pugnat, Main highlights of the HIMAFUN workshop, PBC Technology Working Group Meeting, 22 September 2017, 10