The Askaryan Radio Array (ARA) Detecting Neutrinos in Antarctica
Jonathan Davies
1 Unanswered questions in Astro-Particle Physics What are the sources of the highest energy cosmic rays?
Can we use cosmogenic neutrinos to learn about astrophysical objects?
Is there new particle physics at ultra high energies and distances of propagation?
2 The GZK Effect and why we think there are UHEN At energies above ~1019.5eV cosmic rays will interact with CMB photons producing neutrinos
Process is known as the GZK effect
Auger and HiRes measurements of UHE cosmic rays consistent with GZK cut-off
Guaranteed GZK neutrino flux, but how large? The Pierre Auger Collaboration (2010): Phys. Lett. B 685 (4–5): 239–246. HiRes 3 Collaboration, Astropart. Phys. 32 (2009) 53. Why High Energy Neutrinos? For Astronomers: UHEN as cosmic messengers Ne uThetrin Prettyos: Th Picturese only k nown messengerInfrareds X-Ray What extra information can we obtain Argument usingat P neutrinoseV ene rgies and above instead of photons? !"#$#%&'(#&$')*#+,'-.'/,01'!"#$% !$&'()*#&+%&+%,-%.%µ/"01% 2")34$&(+'% 2")34,5'6)3$78(,&1%5)"**1$1'%26% 78Radio9#1:'5%&$%;<=%!$&)155%"*%"::% Optical Neutrinos? 1+1$4#15 >&($)15%1?*1+'%*&%@A%B%%%%C1D%E Crab Nebula in visible (green), !"#$%&'&%('%)*"+,-)." radio (red) and X-ray (blue) /&'01%(%&*'%+ FG%>*('6%&9%*H1%H#4H15*%1+1$46% 21-+#"3'0-+($4."* !$&)15515%"+'%!"$*#):15% Neutrino small cross-section means For Particle Physicists: *H$&(4H&(*%*H1%(+#01$51%!"#$%!"&' they can penetrate further in space I1D 8< The1D%+1 300(*$#+& %'TeV1*1) *&(CoM)$5 Neutrino Beam Argument and at higher energies than photons and cosmic rays C&%49)3)%$,,'J1D%+1(*$#+&% '1*1)*#&+K%5,&74%':#3'$",';<=' %,9$37%#':(9> Neutrinos point back to sources, unlike cosmic rays
4 P. Gorham For Astrophysicists: !!"#$%!&'()*+ !,-$.!/%0-1$(0'*%2!$%3!&-401'%*2!5678!9-+:)'8!;1--(- !7
The Particle Argument
From P. Gorham R. Nichol, UCL -- VLVνT 2009, Athens 5
Tuesday, 13 October 2009 ANRV391-NS59-15 ARI 16 September 2009 15:36
Cosmic Ray Flux 105
10 2
10–1
10–4
2 10–7 1/m year
Knee
–1 10–10 sr s Gev) 2 10–13 Flux (m 2 10–16 1/km year Flux measured over 10 decades in energy Ankle 10–19 LEAP Proton Non-thermal power law spectrum 10–22 AKENO KASCADE Auger SD by University College London on 04/03/13. For personal use only. Auger hybrid 10–25 AGASA 1020eV HiRes-I monocular Cosmic ray, hence neutrino flux very 2 Annu. Rev. Nucl. Part. Sci. 2009.59:319-345. Downloaded from www.annualreviews.org HiRes-II monocular 1/km century low (1/km2 century) 10–28
109 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 Energy (eV) Need very large detectors ~100km2 FigureJ. 1 J. Beatty and S. Westerhoff, Ann. Rev. Nucl. Part. Sci. 59, 319 (2009) 5 Overview of the cosmic ray spectrum. Approximate energies of the breaks in the spectrum commonly referred to as the knee and the ankle are indicated by arrows. Data are from LEAP (4), Proton (5), AKENO (6), KASCADE (7), Auger surface detector (SD) (8), Auger hybrid (9), AGASA (10), HiRes-I monocular (11), and HiRes-II monocular (11). Scaling of LEAP proton-only data to the all-particle spectrum follows (12).
www.annualreviews.org The Highest-Energy Cosmic Rays 321 • Radio Neutrino Detection – Askaryan Effect Optical Cherenkov techniques (example IceCube) prohibitively expensive to scale up we need a technique that can be used in large detectors…
e± or γ L ≈ 10m
Rmoliere ≈ 10cm
Gurgen Askaryan predicted coherent radio emission from neutrino induced cascades
20% negative charge excess develops: • Compton scattering ɣ + e-(rest) ⇒ ɣ + e- Coherent radio emission – ⇒ • Positron annihilation e+ + e-(rest) ɣ need an abundant radio
transparent medium Excess travels with v > c / n • Cherenkov emission • Coherent for λ > R 6 Introducing the Askaryan Radio Array (ARA)
Detect radio emission from Achieve O(10km3) detection Use timing and neutrino induced particle volume per station using polarisation information for cascades in Antarctic ice array of antenna clusters neutrino reconstruction
Coherent radio emission (Askaryan Radiation)
Neutrino interaction RF Antennae Charge excess Incoherent optical Cherenkov
Bed Rock 7 ARA 37 Layout
Single Station Measurement systems: - 16 antennae, 150-800MHz (8 h. pol, 8 v. pol) - 4 holes ~20m spacing - DAQ electronics, computer
Calibration systems: - 2 holes ~40m distance - 4 calibration antennae 37 Stations (2 h. pol, 2 v. pol) 200m below the surface Each station can act as a stand alone ~200km2 coverage neutrino detector 8 ARA Sub-Station – The Antennae
Surface antenna
9 V. pol H. pol ARA Sub-Station – Signal Chain NotchFilters RF Over FiberOver RF Low Noise Amplifiers LowNoise
10 ARA Sub-Station – DAQ
• 150-850 MHz bandwidth
• 3.2 GSa/s sampling (4x Nyquist)
• Low power consumption
• Autonomous data taking
NotchFilters RF Over FiberOver RF Low Noise Amplifiers LowNoise
11 Acquisition Data Electronicsand Computer UCL's Efforts
• DAQ development and testing – Online DAQ software for event read out and system monitoring – Testing and characterisation of digitisers and DAQ hardware
• Part of deployment and commissioning team • Analysis software development – Offline software to form basis of prototype and future station analysis • Timing calibration for radio waveform digitisers – Custom ASICs (IRS2) sampling at 3.2GS/s 12 Event Reconstruction
• In situ calibration sources are used to mimic neutrino signal • Reconstruction using timing differences between signal at antennae
Pulser Δt signal
Apply calibrations
13 ARA's Sensitivity to GZK Neutrinos
Prototype station has operated for 2 years
First 3 stations installed this past (austral) summer
Full ARA array improves sensitivity in peak flux region by 2 orders of magnitude
ARA could make the first measurements of GZK neutrinos
14 Thanks for listening
15 Finding a neutrino signal Each station records ~100million events / year Need very strong Theory predicts ~1 events / year background rejection
Is there co-incident power in antennae? Trigger
Thermal noise rejected by event Is it thermal noise? reconstruction and coherence
Is it Anthropogenic? Identify human noise sources
Neutrino candidate How many unknown unknowns are there?
16 Deep Antennae – Why and How Ray traces 200m 0
Receiver 1 Transmitter Depth [km] 2
3 0 1 2 3 4 Distance [km]
Index of refraction varies with depth, leading to shadowing in the ice
Burying the antennae greatly improves Hot water drill melts ice and volumetric acceptance pumps out waste water to produce 200m deep dry 17 holes