Trinity
A Cherenkov/Fluorescence Telescope
System to detect Cosmogenic
Neutrinos

Nepomuk Otte

School of Physics&Center for Relativistic Astrophysics

ContentScience with ultra-high energy neutrinos
UHE neutrino detection techniques
Tau neutrino interaction in Earth and tau
shower physics
Trinity detector layout
Acceptance and sensitivity dependence ondetector parameters

Nepomuk Otte

2

The Era of Multi-Messenger
Astrophysics

Nepomuk Otte

3Composition & Sources of UHECRFrom R. Engel @ TeVPA2017
Nepomuk Otte

4

Nepomuk Otte

5

Science Motivation:
What is the composition ofUHECR?
●
What are the sources ofUHECR?
●

Nepomuk Otte

6

Astrophysical Neutrinos

F. Halzen @ TeVPA2017
Nepomuk Otte

7

Science Motivation:
●

●

●

●

Nepomuk Otte

What is the composition ofUHECR?
What are the sources ofUHECR?
Extension of IceCube
detected ν flux to 109 GeV?
Test of fundamental
physics

8

Radio Techniques

Nepomuk Otte

9

GRAND

Nepomuk Otte

10

Let there be Light!

Nepomuk Otte

11

Image incamera

Imaging
Atmospheric
CherenkovTechnique

Proven Technique–Angular resolution <0.1°–

Energy resolution 10%–

Excellent backgroundsuppression12

Observations of SNRs with VERITAS

Nepomuk Otte

13

Detector on top of mountain and look into the distance
Earth is approximated as a smooth sphere made of rock

Nepomuk Otte

14

Probability of τ Emergence
Target material:
Rock with ρ = 2.65 g/cm3
Works best for:●>108 GeV●~50 km target
Limiting factors:●
Target to thin: ν does notconvert●Target to thick: τ does notmake it out

Probability if ν conversion and emergence of τ from ground

Nepomuk Otte

15

Tau Shower Fun Facts
Tau emergence angle is ~1°
Tau decay length 49 km x Etau/109 GeV
Tau decay modes
18% electron + neutrinos
65% hadronic (pions + neutrinos)
17% muon + neutrinos → no shower no shower→ no shower A shower develops in 80% of decays

Assume 50% of tau energy go into shower
107-1010 GeV shower develops in~30 radiation length → no shower ~10km

100 TeV tau shower
Nepomuk Otte

16

It is all about Geometry!
Enough light needs toreach the telescope

Maximum decay length set
by requirement of image
containment in camera~10km

Azimuth angle~viewing angle

Elevation fixedby neutrinointeraction
cross section;~1°
Nepomuk Otte

17

Atmospheric Absorption
Haze / aerosol layer up to 1-2 km above ground

Picture taken ~3km above ground on approach to Tucson, AZ
Nepomuk Otte

VERITAS18

Cherenkov Spectrum after Absorption
Shift of spectral peak
for larger distances

Nepomuk Otte

19

Silicon Photomultipliers
Hamamatsu S14520-6050CN

3mmencecs
re w
ou o
Fl indw

v
kone
er ow
hC in dw

Nepomuk OtteNSB20

Radial Cherenkov Intensity
DistributionDistance between
telescope and shower
25 km55km85 km
10 pe/108 GeV/m2

135 km
195 kmTelescope 1 km above ground, shower elevation 1°
Nepomuk Otte

21

The Top View: Fluorescence

Isotropic emission
Emission band: 300 nm – 400 nm
Yield: 6000 photo electrons / GeV
Attenuation length: 9.5 km
For 108 GeV τ:~3 photoelectrons per m2
in 30 km distance
30 km

Nepomuk Otte

22

Trigger Threshold
Detected Night Sky Background:
3.7·106 counts/s/mm2/sr
Assume MACHETE Optics
5° x 60° field of view
0.3° pixel size

10 ns coincidence window
Two neighbor coincidence for telescope trigger1Hz accidental trigger rate

Thresholds of 10 pe, 22 pe, 24 pe, and 155 pe,for 1m2, 5m2, 10m2, and 100 m2 effective mirror area

Nepomuk Otte

23

Trinity: Baseline Configuration
Top view

Side view

10 m2 effective mirror area
2 km

2 km above ground
2° FoV above horizon, 3° FoV below horizon
360° azimuthal acceptance
0.3° minimal reconstructable image length

Nepomuk Otte

24

Sensitivity given per decadeof energy
All neutrino flavor flux
sensitivity
3 years of observation with
20% duty cycle
1 detected tau neutrino
Background free assumption

Nepomuk Otte

25

Trinity: Baseline Configuration
Top view

Side view

10 m2 effective mirror area
2 km

2 km above ground
2° FoV above horizon, 3° FoV below horizon
360° azimuthal acceptance
0.3° minimal reconstructable image length

Nepomuk Otte

26

Minimum Reconstructable
Image Length
Fluorescence
detected events

Cherenkov
detected events

109 GeV neutrinos
Nepomuk Otte

27

Sensitivityof baseline
is solid line

Nepomuk Otte

28

Telescope Location above GroundCan see more distant showers if higher above ground

Nepomuk Otte

29

Not much sensitivity gain if higher than 1 km above ground
Nepomuk Otte

30

Mirror Size
10m2 to 100m2 mirror area, only 13% more acceptance

Nepomuk Otte

31

Nepomuk Otte

32

Field of View Above Horizon
89°

distance to horizon

Acceptance maximal for 2° field of view above horizon.
Biggest impact on detection of distant showers.
Nepomuk Otte

33

Nepomuk Otte

2 km

160 km34

Field of View Above Horizon
89°

distance to horizon

Acceptance maximal for 2° field of view above horizon.
Biggest impact on detection of distant showers.
Nepomuk Otte

35

Sensitivity vs. FoV above Horizon

Nepomuk Otte

36Field of View Below Horizon
10°

Biggest impact for the detection of close showers.
Acceptance maximal for ~3° field of view below horizon.
Nepomuk Otte

37

Sensitivity: FoV below Horizon

Nepomuk Otte

38

Background?!
Cosmic Rays, meteorites, lightning

FoV where tau events are expected is narrow → no shower Veto
Photon arrival time distribution
Stereo imagingMuons

Energy independent low intensity
Negligible spread in arrival time
Stereo imaging

Accidentals

Higher trigger threshold
Stereo imaging

Nepomuk Otte

39

Photon Arrival Time Distribution

Nepomuk Otte

40

Background?!
Cosmic Rays, meteorites, lightning

FoV where tau events are expected is narrow → no shower Veto
Photon arrival time distribution
Stereo imaging

Isolated Muons
Intensity does not depend on energy
Intensity is low (10 m2 mirror)
Negligible spread in arrival time
Stereo imaging

Accidentals
Higher trigger threshold
Stereo imaging
Nepomuk Otte

41

Conclusions
A dedicated air shower
imaging system delivers
competitive sensitivity
Several stations aroundthe world increase
sensitivity
Not expensive
Motivation to startdeveloping a 1 m2
prototype
Nepomuk Otte

42

Detector Design Requirements
360° azimuthal FoV and 5° vertical FoV
10m2 effective mirror area
Minimum 0.3° angular resolution→ no shower >10 pixel per image
Signal sampling speed 100 MS/s
Single photoelectron resolution

Nepomuk Otte

43

MACHETE
A transit imaging atmospheric Cherenkov
telescope to survey half of the very highenergy γ-ray sky
J. Cortina, R. López-Coto, A. Moralejo
Astropart.Phys. 72 (2016) 46-54

Scaled down to 1m2 mirror:
D=1.2 m, f=1.2 m, f/D=1●
Mirror surface: 4.1 m x 7.9 m●
90% containment: 0.42°●
Pixel size: 20 x 20 mm2, 0.3° diameter → no shower
4200 pixel●
Light concentrator: factor 4→ no shower sensor size 9x9mm2 (SiPMs)●

FOV of 5 × 60 sq deg

Costs per station (optics only): ~$500,000
Nepomuk Otte

44

Data Acquisition Requirements

Photon arrival times spread out to ~10 µs→ no shower “slow” 100MS/s DAQ sufficient
NSB: 36mm2 pixel record about→ no shower 4 photon / 1 μs
Single pe signal stretched to 100 ns

Nepomuk Otte

45

Signal Chain
amplifier + shaper
photodetector

100 MS/s, 8 bit FADC

Continuous samplingwith 100 MS/s
Signal processing andtrigger in FPGA
Allows flexible trigger
schemes using timeand amplitude
information

Cost per channel ~$100

Nepomuk Otte

46

Back on the Envelope Cost Estimate
6 Detector stations for 360° FoV:

25,000 pixel * $100/channel (sensor + readout) =$2.5M
Optics ~$4M
Infrastructure ~$500k$7M total + R&D costs ~$500k

Nepomuk Otte47

Next Steps

Nepomuk Otte48

Nepomuk Otte

49

Conclusions
A dedicated Cherenkov/fluorescence instrument can deliver a sensitivity
comparable to ARA/ARIANNA
Both techniques are complementary:

Sensitive to different neutrino flavors → no shower combining results tests physics BSM
View different portions of the sky

Technique is proven and well established in the VHE gamma ray andUHECR communities
Very good angular resolution and energy reconstruction

Open issues need to be addressed with a small prototype
Background photon rates
Cosmic Ray background
Signal extraction and triggering
Advanced methods can significantly improve sensitivity and lower energy threshold

Data analysis: How well can up-going showers separated from down-going ones
Finding optimal site (geometrical acceptance, infrastructure, ...)
Nepomuk Otte

50

Backup

Nepomuk Otte

51

Prototype Site
IOTA site on Kitt Peak, AZ

Nepomuk Otte

52

Askaryan Radio Array (ARA)

Nepomuk Otte

53

ARIANNA

Nepomuk Otte

54

Radio Technique
Pros:
Allows instrumentation of large volumeCheap?
Cons:Prone to radio interference
Large angular resolution of several degrees for inice radio
Energy resolution of >50% for in ice radio
Relatively new experimental technique

What about other detection techniques?
Figure of Merit: cost*sensitivity

Nepomuk Otte55