APRIM 2011-- Chiang Mai July 28, 2011 Heliospheric Physics with IceTop Paul Evenson University of Delaware Department of Physics and Astronomy

APRIM 2011-- Chiang Mai July 28, 2011

Heliospheric Physics with

IceTop

Paul EvensonUniversity of

DelawareDepartment of

Physics and Astronomy

Chiang Mai, July 28, 20112

IceCube: A New View of the Universe from the South Pole


IceCube Collaboration


Cosmic Neutrinos

• IceCube is a particle “telescope” that peers through the earth to open a new window onto the universe. It will observe violent astrophysical sources such as supernovae, gamma ray bursts, and cataclysmic phenomena involving black holes and neutron stars.

• IceCube will also search for dark matter, and could reveal new physical processes associated with the origin of the highest energy particles in nature.

• This “new window” on the universe will open via neutrinos, not light.

• It is likely that the processes that produce these particles are scaled up versions of processes that occur in the solar system


Ice Cube Concept

• Trillions of neutrinos stream through your body every second, but none may leave a trace in your lifetime.

• IceCube uses a large volume (one cubic kilometer) of ice at the South Pole to detect rare neutrino interactions.

• Most often these interactions generate an energetic muon.

• In the ultra-transparent ice, the muon radiates blue light that is detected by the optical sensors that comprise IceCube

• Muons follow the arrival direction of the original neutrino

• By measuring the arrival time and amount of light at each sensor the arrival direction of the neutrino is determined


Ice Cube Operation


Hot Water Drilling



IceTop Detectors

• Blocks of clear ice produced in tanks at the Pole

• Cherenkov radiation measured by standard IceCube photon detectors

• Two tanks separated by 10 meters form a station

2 m

0.9 m

Diffusely reflecting liner


Installing the Detector “Tanks”


Fill Tanks with Water then Just Let Them Freeze


Removing Dissolved Air Produces Perfectly Clear Ice

• Dual degassing units are seen under 75 cm of ice

• DOMs are frozen into the ice


PY03:4

PY04:12PY05:16

PY06:18

PY07:18

PY08:12

IIceCube Layout

100 m

Grid north

South Pole

Large showers with E ~ 100-1000 PeV will clarify transition from galactic to

extra-galactic cosmic rays.

Showers triggering 4 stations give ~300 TeV threshold for EAS array

Small showers (2-10 TeV) associated with the dominant muon background in the deep detector are detected as 2-tank coincidences at a station.


“Showers” from Low Energy (1 - 10 GeV) Primary Particles

• Particles with energy as low as 1 GeV produce secondaries that survive to the surface

• Rarely does a single detector see more than one secondary from a primary

• Large detectors can have high enough counting rates to make statistically significant measurements of the primary flux

• Conventional detectors count muons or neutrons


The First Extraterrestrial Event Detected by IceCube

Dec 14, 2006 photograph of auroras near Madison, WI

Dec 13, 2006 X3-Class Solar Flare (SOHO)

IceTop and Spaceship Earth Observations of the Solar Flare

http://www.spaceweather.com/images2006/13dec06/eit_narrow.gif


Why IceTop Works as a GeV Particle Spectrometer

• Neutron monitors are comparatively insensitive to the particle spectrum

• IceTop detectors are thick (90 g/cm2) so the Cherenkov light output is a function of both the species and energy of incoming particles

• Individual waveform recording, and extensive onboard processing, allow the return of pulse height spectra with ten second time resolution even at the kilohertz counting rate inherent to the detector


Secondary Particle Spectra

• At the South Pole, spectra of secondary particles “remember” a lot of information about the primary spectrum.


Response Functions

• Analog information from IceTop yields multiple response functions simultaneously


Solar Particle Spectrum Published in Ap J Letters

• Excess count rate as a function of pre-event counting rate.

• Each point represents one discriminator in one DOM.

• By using the response function for each DOM we fit a power law (in momentum) to the data assuming that the composition is the same as galactic cosmic rays

• The lines show one sigma (systematic) errors


IceTop and PAMELA

Credit: M. Casolino


Neutron Monitors and IceTop

• Good agreement (with understanding of viewing direction)

• IceTop determines a precise spectrum

• Anisotropy comes entirely from the monitor network

• Here we see the failure of the “separability” assumption in one particular analysis of neutron monitor data alone


Neutron Monitors and IceTop

• Cherenkov and neutron monitor response functions are similar but have significant differences


• South Pole station has a 3-NM64 and detectors with no lead shielding.

• These “Polar Bares” responds to lower particle energy on average.

ENERGY SPECTRUM: POLAR BARE METHOD


• “Polar Bares” responds to lower energy particles.

• Bare to NM64 ratio provides information on the particle spectrum.

• This event shows a dispersive onset as the faster particles arrive first.

• Spectrum softens to ~P – 5 (where P is rigidity), which is fairly typical for GLE.

• Dip around 06:55 UT may be related to the change in propagation conditions indicated by our transport model

• Element composition is a source of systematic error in the spectral index

ENERGY SPECTRUM: POLAR BARE METHOD


Element Composition and Spectrum from IceTop and the Neutron Monitor

• Simulated loci of count rate ratios, varying spectral index (horizontal) and helium fraction (vertical).

• Statistical errors (+/- one sigma) are shown by line thickness.– 20 January 2005

spectrum – “Galactic” composition

• IceTop (black, blue) lines converge in the “interesting” region

• Bare/NM64 (red) line crosses at the proper (i.e. simulation input) values


Conclusions

• IceTop is a powerful new tool in the study of energetic solar particles

• Now we just hope that the sun has not quit on us

Documents

APRIM 2011-- Chiang Mai July 28, 2011 Heliospheric Physics with IceTop Paul Evenson University of Delaware Department of Physics and Astronomy