The National Science FoundationThe Kavli Foundation APS April 2008 Meeting - St. Louis, Missouri...

The National Science Foundation The Kavli FoundationAPS April 2008 Meeting - St. Louis, Missouri

Results from Cosmic-Ray Experiments

Vasiliki PavlidouKavli Institute for Cosmological Physics,

The University of Chicago


Outline

• Ultra-high--energy cosmic-rays: issues and detection

techniques

• A hybrid experiment: the Pierre Auger Observatory

• Recent results from cosmic ray experiments:

GZK flux suppression; anisotropies at the highest energies

• Sources of UHE neutrinos and expected fluxes

• Neutrino detection techniques for UHE Cosmic-Ray

Experiments

• Current neutrino limits from Auger and HiRes

• Outlook


UHECRs: the questions

• Highest energy particles (> 1018 eV)– Spectrum?– Protons, heavier

nuclei, photons? – Top-down or bottom-

up?– Local or cosmological?– Sources?

S. Swordy


Detecting UHECRs

Credit: Cosmus team (http://astro.uchicago.edu/cosmus)

Detection techniques:• detect fluorescent emittion generated by shower (Fly’s Eye, HiRes: Sokolsky Panofsky Prize talk, session E2)• detect shower footprint on ground(AGASA)


The Pierre Auger Observatory of Ultra-high Energy Cosmic Rays:

a hybrid experiment

~400 scientists from ~70 Institutions and 17 countries

Currently:•1550 tanks taking data •24 fluorescence telescopes in 4 stations overlooking array

AIM: 1600 tanks, 3,000km2


Advantages of the hybrid technique

• Good statistics (100% duty cycle for SD)

• Straight-forward aperture and exposure determination for SD

• Model-independent energy calibration for FD calibration of SD using hybrid events

• Accurate geometry reconstruction for hybrid events (arrival direction determination <0.2 degrees) calibration of SD (arrival direction accuracy typically < 1 degree).


Recent CR results and implications for neutrinos and astrophysics


I. The CR spectrum at the highest energies

• CR flux above 1019.6 eV suppressed! (HiRes, Auger)

• But what does this mean? 2.69

5.1

2.81

4.2


QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Interpretation of CR flux suppression• Possible interpretations:

– cosmological suppression due to energy losses on CMB (GZK cutoff)

– accelerators running out of steam (cutoff in source spectrum)

• How to tell: – Measure spectra of individual nearby sources

(difficult!)– if suppression cosmological: highest energy (super-

GZK) events only sample local universe (highly anisotropic) sky distribution of super-GZK events might look anisotropic

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

E. Armengaudsims by A. Kravtsov


II. The UHECR Sky is anisotropic

Cen A

AGN

Patrick Younk talk - session T8, Monday @ 3:30

Pierre Auger Collaboration 2007, Science, 318, 939Pierre Auger Collaboration 2008, APh, 29, 188


Implications for Charged Particle Astrophysics

• Flux suppression at highest energies is cosmological

• Sources are extragalactic, and extend to cosmological distances

• The highest-energy cosmic-ray sky is anisotropic, but nature of sources is still unclear

• Intergalactic B-field small cosmic rays good messengers for mapping the nearby universe

• Astrophysics!– UHECR source identification, study– Timely concurrent operation with gamma-ray, neutrino, and

low-energy photon observatories– UHECR astronomy possible: time to build a bigger telescope!

Auger North


Auger North

• Planned location in Colorado, US• Full-sky coverage• Optimized for operation in energies where arrival

directions are anisotropic• Sufficient exposure

(~ 7 x South) to:– Detect individual

sources– Calculate fluxes,

spectra– Answer fundamental

questions about nature’smost powerful accelerators, their physics, and their energy sources

– Map the Galactic/intergalactic magnetic field! B. Siffert


Implications for Neutrino Astrophysics

• GZK cutoff observed cosmogenic neutrinos guaranteed!High Energy Proton sees

Cosmic Microwave Background as High Energy

Gamma Rays!

p+cmb + p + 0

n + +

n p + e- + e

+ + +

+ e+ + e +

GZK, Photopion, orGZK, Photopion, orCosmogenic NeutrinosCosmogenic Neutrinos


GZK neutrinos guaranteed but…

• … flux and spectrum are model dependent

• conversely: if we measure cosmogenic neutrino flux, we can constrain source models

Allard et al ‘06


Other potential sources of UHE neutrinos

• Astrophysical: Interactions of accelerated hadrons within possible sources (GRBs, AGN)

• Exotic: Topological defects, superheavy dark matter

L. Cazonfluxes from Protheroe 1999 review, arXiv:astro-ph/9809144


Neutrino detection in cosmic ray air shower experiments

• Two Detection Channels:– Down-going neutrinos (all flavors) interacting in

the atmosphere– Up-going tau neutrinos interacting in Earth crust -

> Earth skimming neutrinos

Lint () ~ 500 km (for >95 degrees: Earth opaque) LEloss ( ~ 10 km (for e: much smaller)

Ldecay () ~ 50 km (for : much larger)


Down-going neutrinos

Young neutrino shower

Old hadronic shower


Earth-skimming neutrinos


Auger (and HiRes) neutrino limits

Pierre Auger Collaboration 2008, PRL submitted, arXiv:0712.1909(HiRes limits from: K. Martens for the HiRes Collaboration 2007, arXiv: 0707.4417)


Outlook

• UHE CR results: flux suppression, anisotropies at highest energies

• Charged particle astronomy possible; with increased statistics: source identification, measurement of flux, spectra

• GZK cutoff observed: CR sources extragalactic, cosmological

• Implications for neutrino astrophysics: cosmogenic neutrino flux guaranteed, flux associated with UHECR sources plausible

• UHECR experiments capable of discriminating neutrino-like events

• Current limits at ~10x GZK flux

• Detection of cosmogenic neutrinos, neutrinos from UHECR sources in <10yr in most optimistic models (meaningful constraints guaranteed within same time)

The National Science FoundationThe Kavli Foundation APS April 2008 Meeting - St. Louis, Missouri...

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