(Some) Optical Requirements for the DS20k veto from G4DS

simulations

Ottawa Collaboration Meeting

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Old design

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AAr Muon and Cosmogenic Veto

Plastic Neutron Veto

AAr Active/Inactive Buffer

UAr Active/Inactive Buffer

30 cm 10 cm 10 cm

Cu Vessel

SiPM

SiPM

SiPMs can also be placed on the outer surface, facing inwards (design in Rome)

New design

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Plastic Neutron Veto

AAr Active Buffer

UAr Active Buffer?

20 cm 70 cm 10 cm

Cu Vessel

SiPM

SiPM

70 cm

AAr Active Buffer

AAr Muon and Cosmogenic Veto

SiPM

TPC

70 cm to maximize gamma containment

Inactive in this simulation

Proposed Readout (1)

Simulate 2.2 MeV gammas uniformly in the PS. Light output in LAr is large (~40 photons per keV) but needs to be converted to be detected. PS light output: 5 photons/keV at ~400 nm

Rely only on direct light (SiPM on both sides). • How to model ESR reflectivity below 200 nm?• Acrylic is opaque to VUV light

SiPM coverage: 400 SiPM on outer cryostat walls, 150+150 on top/bottom caps30x21 = 630 on outer surface, 175+175 on top/bottom capsfor a total of 4.2 m2.

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Optical properties of PS

Emission at 425 nm. Labs(128 nm) ~ 0.001 m Labs(400 nm) ~1.4 m Rindex (128 nm): ~1.6 Rindex(400 nm): ~1.5

Optical properties of LAr

Emission at 128 nm. Labs(128 nm) ~ 100 m Labs(400 nm) ~ 100 m Rindex(128 nm): 1.5 Rindex(400 nm): ~1.22

ESR reflectivity: 99% at 425 nm 0% at 128 nm

SiPM PDE: 40% (QE and fill factor)

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TPC Inactive AAr inside Vessel Active AAr inner Plastic Scintillator

SiPM

Top view, central region

Lateral view of SiPMs

One example

Light produced in PS (400 nm) and tracked. Reflections (99%) at the interface between the outer AAr veto and the LAr filling the protoDUNE cryostat.

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reflections

PS

TPC

Energy spectra in the PS and in the LAr veto

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<— Cross check: sum energy spectrum. Events with less than 2.2 MeV total loose energy in passive materials.

Energy deposited in the PS (keV) Energy deposited in the AAr (keV)

30% of the events deposit >2 MeV in PS

30% of the events deposit >2 MeV in AAr

Light yield

Preliminary average light yield from PS (with SiPM inside AND outside) and AAr The SiPM positioning is not optimized. TPB assumed on SiPM surface, 100% conversion efficiency assumed. 40% PDE binomial fluctuations included.

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0.06 pe/keV 0.19 pe/keV

PE/keVPE/keV

PE spectrum

PE spectrum (left) and cumulative (right, fraction of events below threshold vs threshold in PE)

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The peak corresponds to the full absorption peak in the PS The tail is the gammas that goes in LAr

Full abs in PS: peak at ~ 150 PE

Gammas in LAr

PE Threshold (PE)

Fraction of events below threshold

In principle a threshold at 50 PE would be enough to guarantee ~99.9% efficiency.

AAr 39

Ar spectrum

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BUT the 39Ar spectrum looks like this, with 1% tail above 140 PE (sample the 39Ar beta spectrum and apply LY in AAr from plot above)

PE PE

How much 39Ar? Roughly 130 m3 of AAr correspond to ~180 kHz

==> 1.8 kHz above 140 PE (neglecting the neutron thermalization signal, >~1 ms coincidence window is required)

39Ar in AAr veto

Increasing the PS light output

Again the PE spectrum in the veto, zoom at low PE, dominated by full absorption peak in PS

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5 photons/keV in the PS 7.5 photons/keV in the PS

The peak position scales linearly with the plastic light output and with SiPM coverage. The 39Ar endpoint scales with SiPM coverage

In order to implement a threshold above the 39Ar, we may: - set an higher minimum requirement for the light output of the plastic scintillator - think about a different readout (similar to the previous baseline - but “easier”: higher energy, no 14C issue)

Conclusions

REMINDER: the proposed light readout system described above is based only on direct light from the AAr scintillation and it needs in any case some optimization, to recover the low PE tail of the full absorption peak in the AAr (histogram above).

The total area of SiPM is ~4.2 m2

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All the simulations are very preliminary. Need to cross check the optical parameters of materials and interfaces.

We need to be sensitive to the full absorption peak in the PS, otherwise loose 30% of the events.

Either: - think about an optically isolated PS:

. insensitive to the 39Ar

. not affected by 14C

. more light detectors- increase requirement on light output:

. in principle feasible (up to 10 ph/keV, conservatively assumed in these simulations 5 and 7.5)

full spectrumfull absorption peak in the PSfull absorption peak in AAr

PE

7.5 photons/keV in the PS

OLD SLIDES, no update wrt to ROME CM

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Light detection requirementsThe discussion about the veto efficiency is based on the 100% efficiency in detecting the capture products. Let’s define the optical in-efficiency as the fraction of captures on 10B that are not correctly reconstructed due to poor light collection. How does the SiPM coverage affect the optical inefficiency and how this reflects on the n bg? The implemented light readout system is the following (illustrative). Direct coupling of SiPM to PS can offer more advantages as well as placing them on the outer surface of the PS (facing inwards) should be easier?. Some geometry changes implemented.

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Optical properties of materials and surfaces

Emission at 425 nm. Labs(plastic) ~1.4 m Labs(Ar) ~ 300 m

Rindex (plastic): ~1.5 Rindex(LArgon): ~1.22

ESR (enhanced specular reflector) reflectivity: 99% at 425 nm SiPM PDE: 45% (QE and fill factor)

Light detection requirementsThe energy spectrum (in the PS) of the events we are interested in is highlighted in the plot. The alpha only (and alpha+gamma with escaping gamma) peaks are at about 60 keV. The peak at 540 keV is (alpha + fully contained gamma). The assumed light output is 5 photons per keV (at 425 nm). The outer wall of the cryostat (at that time the geometry was the old, less compact one) is covered with SiPM tiles, uniformly spaced. Sevral iterations for varying coverage.

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5 ph / keV

The simulation consists in:- sampling from the above spectrum one energy

variable

- sample a uniform position in the PS volume

- generating a bunch of photons (n = LY x E)

- record pe channel and time

Octagonal PSOn side onlyMonolithic octagonal PS: 140 cm side, 3.4 m tall, 30 cm m thick.

SiPM on outer surface (9.6x2 + 8x4.8 m2) 17 x 7 on each lateral face, 952 total (2.4 m2), spacing of ~20 cm.Generate light only in the lateral volume. Same coverage for the top/bottom surfaces: additional 477, for a total coverage of 3.6 m2

Optical assumptions: reflector on both surfaces. Is this possible/good idea?

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Optical properties of materials and surfaces

Emission at 425 nm. Labs(plastic) ~1.2 m

Rindex (plastic): ~1.6

ESR (enhanced specular reflector) reflectivity: 99% at 425 nm SiPM PDE: 45% (QE and fill factor)

Full capture spectrum, no (double) corrections

60 keVee for the a only

Number of hits

Using HITS and not charge

5 photons / keV emitted

One test only (total coverage: 3.6 m2)

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Preliminary

Accidentals in PS

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2 channels threshold

3 channels threshold

SiPM DCR of 10-3 Hz/mm2

DCR of 10-3 Hz/mm2 achieved, even if the baseline requirement is 10-1 Hz/mm2

Rate in the TPC is 16 Hz of 39Ar, 40 Hz total?

4E22 C atoms per cm3, 1 ppt 14C, 12 t of plastic scintillator ==> 4.8E17 14C atomsActivity: 3.822E-12 x 4.8E17 = 1.8e6 Bq

4E22 C atoms per cm3, 10-5 ppt 14C, 12 t of plastic scintillator ==> 4.8E12 14C atoms( Borexino: 2.5 10-6 ppt ? TO BE CHECKED )14C Activity: 3.822E-12 x 4.8E12 = 18 Bq

PSD in PS?

Outer LAr Veto

The purpose of the outer detector is to veto cosmogenic events. We need it to be active.

The baseline requirement is the ability to reject events with more than 10 MeV deposited in this volume. Some related questions to be answered are: - how to instrument such a large volume? How many SiPM are required and where to put them.- Is 10 MeV a safe threshold or the pile-up of internal 39Ar (~ 1 MHz!) plus external gammas from the concrete/rocks/HallC/cryostat induce high rate of accidentals?

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Preliminary estimate of the light collection efficiency for light produced in the PS:

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Backup

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Old design, SiPM tiles

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1278 tiles (~20 cm spacing) 576 tiles (~40 cm spacing)

Minimum simulated spacing is ~10 cm, ~4000 tiles (10 m2 active surface)

Backup n yields from Micheal

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Element/Material

Sapphire Acrylic Kapton Si StainlessSteel Teflon Ti SiPM Siliconnitride

238U 1.44E-05 1.22E-06 2.29E-06 2.20E-06 5.34E-07 1.00E-04 2.82E-06 2.24E-06 6.77E-06

232Th 2.21E-05 1.38E-06 3.11E-06 3.45E-06 1.90E-06 1.27E-04 7.33E-06 3.51E-06 1.18E-05

FusedSilica CIC Arlon55NT Arlon85 M50_3140645

M50_3532042

Cu ESR3M Dual3M Arlon55nCu Arlon85nCu

1.23E-06 2.29E-07 2.44E-06 2.17E-06 6.65E-06 4.05E-06 3.18E-08 1.44E-06 1.46E-06 2.40E-06 2.50E-06

1.81E-06 9.88E-07 3.57E-06 3.20E-06 8.59E-06 5.34E-06 3.86E-07 1.60E-06 1.62E-06 3.44E-06 3.65E-06

LocaPon 238U 232Th Uyield Thyield Mass TotalmBq/kg mBq/kg n/decay n/decay [kg] [n/5yr]

NEXO Silicon TPCTop/ 1.1E-01 1.30E-02 2.20E-06 3.45E-06 12 0.5Silicon(PCB) TPCTop/ 1.1E-01 1.30E-02 2.20E-06 3.45E-06 94 4.2

EXO200/ Copper TPCTop/ 1.20E-02 4.00E-03 3.18E-08 3.90E-07 1600 0.5Copper(field Reflector 1.20E-02 4.00E-03 3.18E-08 3.90E-07 280 0.1Copper TPCTop/ 1.20E-02 4.00E-03 3.18E-08 3.90E-07 800 0.2Copper Cryostat 1.20E-02 4.00E-03 3.18E-08 3.90E-07 6300 1.9

DEAPhDp:// Acrylic Reflector 3.70E-03 5.30E-03 1.22E-06 1.38E-06 140 0.3Acrylic TPCTop/ 3.70E-03 5.30E-03 1.22E-06 1.38E-06 400 0.7

Xenon OpPcal Reflector 1.90E+00 6.00E+00 1.22E-06 1.38E-06 4 6.7OpPcal TPCTop/ 1.90E+00 6.00E+00 1.22E-06 1.38E-06 4 6.7

TODO VikuiP Reflector 1.60E+00 9.00E-01 1.44E-06 1.60E-06 1.6 0.9VikuiP Cryostat 1.60E+00 9.00E-01 1.44E-06 1.60E-06 8 4.7

DEAP PlasPc Outside 3.70E-03 5.30E-03 2.61E-06 4.05E-06 15000 73.5Total(TPConly) 27.6

Total 101.1FIXED

Survival probabilities

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SUMMARY DEC 17

YB after TPC tpc + FV after tpc/veto TPC ineff veto ineff comb ineff total n n bg

REFLECTOR

253928 75500 816 2.54E-02 7.55E-03 8.16E-05 1717 0.1401072CRYOS 60990 23838 500 6.10E-03 2.38E-03 5.00E-05 2384 0.1192

0.2593072

AV after TPC tpc + FV after tpc/veto TPC ineff veto ineff comb ineff total n n bg

REFLECTOR

324386 42794 1698 3.24E-02 4.28E-03 1.70E-04 1 0.0001698CRYOS 94704 35563 787 9.47E-03 3.56E-03 7.87E-05 2384 0.1876208SIPM 234150 70277 3464 2.34E-02 7.03E-03 3.46E-04 1820 0.630448

0.8182386

CV after TPC tpc + FV after tpc/veto TPC ineff veto ineff comb ineff total n n bg

REFLECTOR

323382 86592 1243 3.23E-02 8.66E-03 1.24E-04 7.02317196 0.00087298CRYOS 180469 59596 362 1.80E-02 5.96E-03 3.62E-05 6.6439926 0.000240513SIPM 233182 68383 1209 2.33E-02 6.84E-03 1.21E-04 12.944789550.001565025PS 15239 5457 15 1.52E-03 5.46E-04 1.50E-06 73.525725 0.000110289

0.002788806

This columns can change a bit according to how the late time cut in veto is applied and which model for quenching in veto is used

neutron interaction length in plastic

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TPC cuts only

- TPC cuts: single NR’s (PSD cut) in WIMP search ROI (30 to 200 keVNR). Varying FV (from top/bottom/walls)

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0 cm 23.3 t3 cm 21.8 t5 cm 20.8 t 7 cm 19.9 t

9 cm 19 t 11 cm 18.1 t

With the current dimensions:

tau of ~ 6.5 cm 0.1% at 20 cm cut for n from vessel

new design(different from YB because of acrylic reflector)

n from reflector n from vessel

Argon-only veto

A veto based on Argon only will not work, even if capture on 40Ar can be easily tagged (~ 6 MeV) and the Xsection, not shown, at thermal energy is ~1 barn. The reasons: not only argon is a poor moderator (A=40) when the Xsection is large (En > 0.1 MeV), but the deep at En ~ 60 keV makes it transparent for neutrons that reach that energy.

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Radiogenic neutron energy

rangeKinetic energy too small to

induce NR > 20 keVNR

Total XsecCapture Xsec

barn

Adding an active plastic layer

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2.2 MeV g fully contained in 2% of the events

TPC TPC

Imagine a plastic moderator around the copper vessel. If passive, the neutron rejection efficiency is still too small. If active, we need to catch the capture products. When neutrons capture on H, Gd (if loaded) Cu (vessel) the gammas from the capture can be lost -> reduce the size of the inactive volumes (materials around the TPC, LAr itself) -> instrument all the detector volumes (TPC side, but also above and below)

Energy spectrum in the passive LAr buffer regions around the TPC

Possible material candidates exist, eg PMMA (80%) + Naftalene (20%) See NIM 169 (1980) 57-64 (NEW LOW COST ACRYLIC SCINTILLATORS) for all the details (especially optical properties)