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Doping Liquid Argon with Xenon: Enhancing Light Production and Collection Efficiency

Doping Liquid Argon with Xenon: Enhancing Light Production and Collection Efficiency. Carlos Escobar Photon Detection Consortium-August 7, 2018. Motivations for this study History and Background Recent investigations A possible route to a R&D program

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Doping Liquid Argon with Xenon: Enhancing Light Production and Collection Efficiency

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  1. Doping Liquid Argon with Xenon: Enhancing Light Production and Collection Efficiency Carlos Escobar Photon Detection Consortium-August 7, 2018

  2. Motivations for this study History and Background Recent investigations A possible route to a R&D program NB: this is not a comprehensive discussion of the subject; not all the literature is being given credit-literature that goes back to 1972 2 Plan of the presentation

  3. Motivations: The simultaneous read-out of the charge and light signals in LNG’s detectors is an important tool for many experiments ranging from DM to large LAr TPC’s. The light signal provides the much needed t0 for NDK and SN neutrinos and an enhanced light collection would allow for calorimetry and event position reconstruction So far the light signal used (or planned to be used) comes from the VUV scintillation with wavelengths ranging from 78 nm (LNe) to 175 nm(LXe). VUV detection presents many challenges: Use of WLS (long term stability? ) Complicated schemes for collecting the light 3

  4. 3. Recent estimates of Rayleigh scattering length puts it at 55 cm (Grace and Nikkel)- start having pernicious effects especially for extremely large LAr TPC’s (DUNE). This short value for the Rayleigh scattering length if indirectly confirmed by recent results from ArDM and DarkSide-50. 4. Attention has been drawn recently to the possibility that the most commonly used WLS, TPB, might be soluble in LNGs (refs. at the end) 5. Why not shift the light in the bulk volume of the liquid argon? Are there WLS that could de dissolved in LAr? 4 Motivations cont.

  5. Mixing Ar and Xe in the gas phase has a long history going back to the 70’s (laser physics, spectroscopy) see Gendanken, Jortner et al (1972). These works found out very efficient radiationless electronic energy transfer between electronically excited rare gas diatomic molecules and a rare gas atom of a different kind (from ref. above). Does the same happen in LAr doped with Xe? 5 A possible solution: doping LAr with Xe

  6. Let us list right away key points to worry about when discussing Xe doping or any other dopant, for that matter: Long term stability of the doping (is the dopant uniformly spread in the volume? Does it tend to freeze out on the walls? How the wavelength shift affects the fast and slow component of the original LAr light? Is there any effect on the electron lifetime? Any effect on the ionization yield? How accurate is the determination of the final dopant fraction in the bulk volume of LAr? Costs involved in the doping process, not only cost of the dopant itself. And the list goes on….. 5’ 5’

  7. First investigations of Xe doping of LAr Kubota, Doke and collaborators (1976) found a 13% increase in ionization yield for Xe doped LAR as compared to pure Ar for concentrations around 1.6% (by volume)  used this result as evidence for the existence of exciton states in LAr. In 1982 Kubota et al. find that the slow component of the LAr scintillation light shows a decreasing decay time with increasing Xe concentration-next slide 6

  8. Change in decay time of the triplet light-Kubotaet al, NIM 196 (1982), 101. Electrons from Bi 207 7

  9. But then 10 years later Same group But alpha! 7’

  10. Doping Ar with Xe cont. In the early 90’s several groups examined doping LAr with varying concentrations of Xe. Some conclusions (from a review by Arisaka et al. 1. an admixture of 100 ppm Xe was found to produce complete wavelength shifting of the scintillation light from 128 nm to 178 nm [Conti et al. 1996]. 2. Adding Xe to Ar resulted in a progressive increase of scintillation light output, by up to a factor 2, for Xe concentrations up to 1%, in zero electric field, this increase being suppressed by electric fields 1–8 kV/cm [Suzuki et al. 1993]. 3. The addition of only 100 ppm Xe produces considerable changes in scintillation pulse shape, including a small improvement in neutron/gamma pulse shape discrimination for only 300 ppm Xe[Peiffer et al. 2008] suggesting further investigation of pulse shape discrimination at larger Xe fractions. 8

  11. However, a word of caution: recent result by Akimov et al. In a recent article, D. Akimov and colleagues (Journal of Physics: Conf. Series 798 (2017) 012210 doi:10.1088/1742-6596/798/1/012210) claim that We confirm experimentally for the first time that only the slow component of the LAr scintillation light can be wavelength shifted by Xe. The consequence from this fact is that one cannot use Xe-doping as the only one WLS-technology in LAr detectors designed for operation with LXe without losing capability of slow-to-fast component PSD analysis. See next slide 9

  12. Recent result by Akimov et al 10

  13. Xe doping of LAr: recent works TU Munich (Ulrich, Schoenert and various students and postdocs) published in 2014-15 new results obtained with a table-top setup (cubic centimeter volumes) and very intense, pulsed low energy beams (12 keV ). Varying concentrations of Xe, controlling the purity of of the initial LAr with a sophisticated distillation technique. They look at a wide wavelength region from the VUV to the NIR Next slides show some of their results: 11

  14. recent investigations cont. Munich results VUV: shift from 128nm to 174 nm NIR: strong emission at 1,180 nm 12

  15. Recent investigations cont. dependence on Xe concentration: at 10 ppm of Xe the energy transfer from 128 nm to 174 nm is almost complete. Also at 10 ppm the NIR emission is at a maximum 13

  16. Efforts at Fermilab’s PAB In 2016 the Indiana University group of Stuart Mufson and Denver Whittington (now at Syracuse) plus Brian Rebel used the Blanche cryostat with the IU light guide bars as the photon detection system to investigate Xe doping of LAr. They also included NIR photodiodes and I installed a NIR PMT on an observation window to look for the NIR light. Some results: Twice more VUV light was seen at a concentration of 7 ppmv No NIR signals were seen. 14 9

  17. A possible route to a R&D program A two-pronged approach: exploiting the VUV shift (128 174 nm) to improve fabrication and efficiency of the Arapucas for light collection using the NIR light as a viable light signal for LAr TPC’s Doing this in a cryostat having a small TPC (do not expect any changes in the charge production and transport but there was an early indication of a slight increase in charge collection-Suzuki et al 1976 ) 15 10

  18. cont. Exploiting the VUV shift Simplifying and improving the Arapucas Refresher: the Arapuca concept a trap with a dichroic filter as the acceptance window. A WLS is deposited over the dichroic side shifting the VUV light to a λ below the filter cut-off. The trapping effect happens at a 2ndλ shift (2nd WLS that can be deposited either on the glass side of the filter or on the back plane (Vikuiti foil). Currently 2 WLS are being used: pTp does the 1st shift and TPB the 2nd 16 11 11

  19. cont Use VUV filters as the entrance window. No need for 1st WLS! Trapping effect with WLS on the backplane. Huge reduction In price 127nm filter 3US$ per mm^2 172 nm filter 1.7 US$/mm^2 12 12

  20. cont. ADVANTAGES: Simplifies the construction of the Arapuca Reduces the total area covered with WLS Exploits the increase in LY with Xe doping For the internal WLS I propose to use the new engineered WLS being developed by Ponomarenko et al. and already tested in Lxe by Akimov et al. Nanostructured Organosilicon Luminophores (next slide) 18 13

  21. cont. 19

  22. Where and how to do it? Use facilitiesat PAB, there is know how on Xe doping. Good cryogenic infrastructure. My proposal: Use the new cryostat being put together for cold electronics, advantage of having a TPC! Identified already one manufacturer for the VUV filter (eSource Optics) and have already established good communication with them. Will need to establish contact with the NOL WLS developers and engineer it here. Goal: avoid the issues of LArcontamination due to the TPB “emanation”. 20 15

  23. Where and how to do it cont. For the NIR part: SenSl and Hamamatsu have recently developed red –sensitive SiPMs (pde’s around 7-9% at 905nm) and I am already using non-commercial samples from them in PAB at the NIR cryostat. Going from 900 nm to 1,200 nm is a big jump. Possible to do it but there is no time to present it today! 21 16

  24. Resources needed Material: VUV filters of dimensions 50x50 mm US$ 5K Xe and Ar. Visible light SiPMs already available (reused) DAQ available FTE: 0.1 cryo-engineer to work out the Xe doping-only once. 0.25 technician for handling and operation of TallBo Unknown: NOL? 22 17 17

  25. How soon can we start? • As soon as possible! • Thank you! 23

  26. References • Index of refraction, Rayleigh scattering length, and Sellmeier coefficients in solid and liquid argon and xenon Emily Grace, Alistair Butcher, Jocelyn Monroe, James A. NikkelarXiv:1502.04213 Measurement of the attenuation length of argon scintillation light in the ArDMLAr TPC . arXiv:1612.06375 Simulation of argon response and light detection in the DarkSide-50 dual phase TPC arXiv:1707.05630 Stability of tetraphenyl butadiene thin films in liquid xenon P. Sanguino et al Thin Solid Films 600 (2016) 65 B. Jones talk at LIDINE 2017 describes the UTA results on solubility of TPB in LAr. Electronic Energy Transfer Phenomena in Rare Gases.With A. Gedanken, B. Raz and A. Szöke.J. Chem. Phys. 57, 3456 (1972). 24

  27. Refs. • Studies of a three-stage dark matter and neutrino observatory based on multi-ton combinations of liquid xenon and liquid argon detectors, K. Arisaka et al. Astroparticle Physics 36 (2012) 93 • E. Conti et al., Nucl. Instrum. Methods Phys. Res. A382 (1996) 475 • M. Suzuki et al., Nucl. Instrum. Methods Phys. Res. A327 (1993) 67. • P. Peifferet al., J. Instrum. 3 (2008) 08007 • TUM Group: A. Ulrich, A. Neumeir et al. • Intense Vacuum-Ultraviolet and Infrared Scintillation of Liquid Ar-Xe Mixtures Europhys. Lett. 109 12001 (2015) • NOL: Test of SensLSiPM coated with NOL-1 wavelength shifter in liquid xenon, D. Yu. Akimov et al. arXiv:1704.01478 and references therein. 25

  28. Backup slides

  29. Cost Issues Xe is about 1,000 times more expensive than Ar. 10 ppm of Xe is 10^-5 2016 : $11.00/liter Cost of Xe should be 0.01 of Ar. Not considering cryogenic infrastructure for Xe. 27

  30. Conclusions at the recent LIDINE 2017

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