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Carlos O. Escobar, Paul Rubinov FERMILAB LIDINE 2017 22-24 SEPTEMBER 2017 Near-Infrared Scintillation of Liquid Argon
Carlos O. Escobar, Paul Rubinov
FERMILAB
LIDINE 2017
22-24 SEPTEMBER 2017
Near-Infrared Scintillation of Liquid Argon
NIR light emission from noble gases has been known since the late 40’s with lines around 1,300 nm.
In condensed noble gases NIR emission was seen in transient optical absorption experiments via electron excitation in late 60’s and early to mid 70’s by various groups. Next slide gives one example for Ar.
Bressi and collaborators pursued for many years the study of NIR emission in both gaseous and liquid states for xenon and argon: clear evidence for NIR emission from gas but much lower LY in liquid.
NIR scintillation from condensed noble gases: history and background
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• example of spectrum obtained in argon:
from Suemoto et al (1977)
• Top: solid
• Middle: liquid
• Bottom: gas
Similar results were
• obtained by Arai and
• co-workers evidence
• for excited neutral rare
• gases molecules (excimers)
• (1.3 eV = 954 nm)
Suemoto et al: Phys. Lett 61A, 131 (1977)
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History and background cont.
Two groups have pursued the investigation of the NIR scintillation in LAr very vigorously in recent years
Novosibirski (Bondar, Buzulutskov et al.) and TU Munich (Ulrich, Schoenert and various students and postdocs).
Both use table-top setups(cubic centimeter volumes)
and very intense, pulsed low energy beams (12 keV electrons Munich and pulsed X-rays between 30 and 40 keV-Bondar et al.)
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Recent Investigations
results from the Munich group indicated NIR emission from LAr: No absolute light yield but spectral information:
Ref: T. Heindl et al. , Europhys. Lett. 91 (2010) 62002
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Summary of the results of the two groups
Munich group
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Results from the two groups cont.
Novosibirski
510+/-90 photons/MeV from 400nm to 1000nm Ref: Buzulutskov et al. JINST 7:P06014,2012
• But, more recently (end of 2014 and beginning of 2015) the Munich group revisited their NIR results in LAr, claiming that impurities had caused the 1st result. Their new line of investigation is mixing small parts of xenon into argon (10 ppm produces the best results: 10,000 NIR photons/MeV at 1,180 nm)
Buzulutskov et al. have
not reconsidered their
results
Recent investigations: coda
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• A vigorous, systematic, experimental program is
• still needed, one that would use larger volumes of LAr with
• 1) rigorous control of purity
• 2 )spectral information
• 3) determination of the time structure of an eventual NIR emission
• 4) determination of the light yield
• 5) “standard” ways of exciting the LAr (radioactive sources; cosmic rays; particle test beams)
Conclusions so far:
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• The standard way of using the light signal in LNG’s TPC’s (for neutrino physics or dark matter exps.) is to detect the VUV light (128nm for LAr). This presents several challenges such as using wavelength shifters to coat surfaces of light guides or photodetectors (stability of coatings, efficiency); adverse effects of Rayleigh scattering (for large volume TPCs) arising from a short Rayleigh scattering length at 128 nm: 55cm (Grace and Nikkel (arXiv:1502.04213 v4) ) which is supported by recent results from the ArDM collaboration at 52 +/- 7 cm (arXiv:1611.02481) and DarkSide-50 at 46 +/- 11 cm.
Going to the NIR avoids Rayleigh scattering, avoids opaqueness of metal surfaces, shadowing by wire meshes and allows for improved charge collection by doping with chemicals such as TMG (an old ICARUS proposal).
Why bother investigating the NIR?
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• Summer 2015: a test using the SCENE cryostat, CPTA SiPMs and a Na22 tagged gamma source.
• Summer 2016: returned to SCENE, still using CPTA SiPMs but this time covered by an IR filter (LP 715nm) and an alpha source (Am241).
• Summer 2017: first use of a dedicated cryostat at Fermilab (PAB).
• Encouraging preliminary results.
NIR in LAr studies at Fermilab
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A new test using SCENE-
summer 2016 Same CPTA’s SiPMs, same read-out electronics but now using an alpha source Am 241, 1C (37,000 dps) Work done with summer intern at Fermilab, Alex Jamieson-Binnie from University of St. Andrews, UK. Next slides are from his final presentation at Fermilab
Experimental Design – Setup
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Experimental Design – Setup
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Experimental Design – Setup
715 nm Filter
• Transmits photons with wavelengths greater than 715 nm
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Analysis uses the triple to double coincidence ratio method
We trigger on double coincidence and look for a triple coincidence, the ratio of triples to doubles give the light yield times the acceptance times the pde of the detector 22
Analysis - Signals
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Analysis – Photon Detection Efficiency
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Analysis – Photon Detection Efficiency
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Analysis – Photon Detection Efficiency
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Analysis – Photon Detection Efficiency
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𝒑𝒅𝒆 = 𝟏% − 𝟐𝟎%
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Analysis – Photon Yield
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Recent tests using a dedicated cryostat at PAB work done with Elizabeth Tilly SULI summer intern
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TttTwo glass chambers (Pyrex), 3 MgF2 observation windows, LN2 cooling
• Inside the cryostat we put two NIR LEDs (850 nm peak ) far from the window where an IR PMT (Hamamatsu R669) is attached with the window covered by the LP filter at 715nm.
New NIR test, cont.
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We operate the PMT at 1,450 V and the signal is read by a digital scope. Trigger threshold is set at a level such that it can still trigger on dim light from the LED (dimming the light by decreasing the voltage on the LED as well as the pulse width). The trigger counts from the scope are sent to a 225 MHz universal counter which counts triggers on a 10 s interval for a couple of hours.
We ran a Kolmogorov-Smirnov test on two data sets: source on vs source off. Null hypothesis is that the two data set come from the same physical process.
Dashed curve: source off
Solid curve: source on
The max. difference
between the two cumulative
distributions is D= 0.9889
corresponding to P=0.000
ruling out the null
hypothesis
Preliminary results
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the two data sets
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Source On: Histogram
Mean: 1006.4
NEED TO DO LIST
• Need to include losses in light transmission through the two glass chambers plus window, through filter and PMT window
• Reflected light “contaminates” source-off data and has to be taken into account for source-on analysis.
• Took data also with source at the level of the PMT (would be source-on position) but source rotated, facing the other way: this should help understanding reflected light issues.
Comments on analysis
• Further analysis: Obtain an estimate of the light yield.
• Use a photodetector with higher sensitivity in the NIR. In the next couple of weeks we will install inside the inner chamber two SenSl new red series SiPMs (5% pde at 900 nm) as well as two Hamamatsu red sensitive MPPCs
• Improve the geometry of the set-up to increase acceptance.
SiPM/MPPC will be next to the Am241 source. Trigger on them and record coincidences with the external IR PMT.
• These are the plans for the very immediate future.
• For the longer term:
• Find a high performance NIR single photon counting detector.
• Select spectral region by a combination of IR filters.
• Design a photodetection system using NIR light!
What next?
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• Thank you!
• We would like to thank Ron Davis, William Miner, Christopher James, Michael Jacobson for their help in assembling the setup, Katherine Cipriano, Frederick Schwartz, and Tyler Funk for their work on the cryogenics and Elizabeth Tilly (summer intern, 2017).
• Fermilab ND for support.
Acknowledgments
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•
• BACKUP SLIDES
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• O2 < 1 ppb
• H2O < 1 ppb
• CO < 1 ppb
• CO2 < 1 ppb
• H2 < 1 ppb
• N2 < 1 ppb
• CH4 < 1 ppb
Liquid argon purity
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Scope trace without amplifier
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Source in LAr
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Inner jar
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