Laboratory Particle-Astrophysics

P. Sokolsky

High Energy Astrophysics Institute, Univ. of Utah.

What is Particle-Astrophysics?

• Key element of Decadal Reviews Astronomy and Astrophysics – multimessenger astronomy

• Messengers - gravitational waves, Radio, IR,Vis.,UV, X-Rays, Gamma-Rays, Cosmic-Rays.

• Using our knowledge of particle interactions to study Astrophysics.

Astroparticle Physics, cont.

• Cosmic Rays - MeV (solar) to 1020 eV.

• Primarily protons and nuclei ( up to Fe), also gamma rays and neutrinos.

• Beyond ~ 1015 eV - energies greater than what is accessible in accelerators.

• Cosmic Rays have been observed with energies at up to ~1020 eV:

• The flux (events per unit area per unit time) follows roughly a power law

~E-3

• Changes of power-law index at “knee” and “ankle”.

Onset of different origins/compositions?

Where does the spectrum stop?

Particle Physics Issues

• Origin – acceleration or decay (top-down/bottom-up).

• Interaction with extragalactic/galactic medium – 2.7 K b.b. radiation, starlight, magnetic fields, remnant neutrino’s, etc.

• Interaction in atmosphere – Extensive Air Shower (EAS) and tertiary emission.

Greisen-Zatsepin-Kuzmin (GZK) Cut-off

(protons)

3×1020 eV

50 Mpc ~Size of local

cluster

•Protons above 6×1019 eV will loose sizable energy – inelastic photoproduction.

•Super-GZK events have been found with no identifiable local sources

Indirect Detection of UHECR

• Low Rate ( 1/km2 centure at 1020 eV) – indirect detection.

• Generate Extensive Air Showers EAS

• Physics of EAS generation– Distribution of particle energies and positions

in shower– Generation of Cherenkov radiation– Generation of Air Fluorescence light

Extensive Air ShowersExtensive Air Showers

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Observation of Cosmic Ray with Fluorescence Technique

• The two detector sites are located 12 km apart

• Geometry of an air shower is determined by triangulation.

• Energy of primary cosmic ray calculated from amount of light collected.

Shower Development – 320 EeV event detected by monocular Fly’s Eye

Fly’s Eye“Big Event”

Typical Stereo HiRes Event:Typical Stereo HiRes Event:July 11, 1999July 11, 1999

Looking South

Layout of AGASA

Highest Energy AGASA Event

The Auger The Auger Hybrid Ground Hybrid Ground

Array/Air Array/Air Fluorescence Fluorescence

DetectorDetector

Future Project

HiRes I and II Monocular Spectrum – Curve is 2-component galactic + extragalactic generic expectation for

unevolved uniform source distribution

Two Complementary Aspects

• UHE Cosmic Rays - opportunity of studying particle physics beyond accelerator energies.

• Use all available laboratory information about UHECR interactions to study astrophysical issues (propagation and source origin and acceleration).

What could particle physicists be missing that is of interest?

• Beam energy too low! (can’t be helped?)

• Wrong kinematic regime (fragmentation region is not studied).

• Wrong target (and beam particle)! p-N (O), up to Fe-N(O) is what occurs in the atmosphere.

• Other than that, Mrs. Lincoln…

Energy

• EAS shower development is MC ( CORSIKA) using hadronic models ( QGS-JET, etc.).

• Provide predictions from cross-sections, multiplicities and inelasticities as function of energy.

• Energy is rapidly degraded to critical energy in air ( ~100 MeV), so that processes that generate the detected particles ( charged particle density at ground, or fluorescence photons ).

Energy, cont.

• The process by which energy is degraded can be studied in the laboratory at the relevant primary energy scale.

• UHECR EAS are superpositions of subshowers.

• SLAC 28.5 GeV electron beam x 1010

particles/bunch ~ > 1020 eV.• Can study how this much energy

manifests at shower maximum.

Relevant Measurable Quantities

• Fluorescence efficiency

• Cherenkov radiation -lateral and angular distribution

• Lateral distribution of secondary charged particles as a function of shower depth.

Methodology

• Treat each beam bunch as “superparticle” and calculate resulting shower as superposition of 28.5 GeV electrons.

• Measure fluorescence, cherenkov, charged particle lateral distribution

• Compare predictions with measurements.

• Validate MC calculations

THICK TARGET SETUP

CORSIKA AIR SHOWERS

THICK TARGET SHOWER DEVELOPMENT

Particle ID

• Photon/hadron identification – Landau Pomeranchuk Migdal (LPM) effect.– Reduces Bethe-Heitler cross-sections above

critical energy for a particular density– Changes shape of gamma ray shower above

few x 1019 eV.– Reality and Details of Effect Conclusively

Confirmed at SLAC by Anthony et al. (1995).

SLAC E-146

• Study 5 to 500 MeV photon production from 8 and 25 GeV electrons thru thin targets.

• 5% precision observation of LPM suppression.

• Confirmation of Migdal approximate formulas (but 6% normalization discrepancy not understood).

Gamma Rays, cont.

• LPM effect modified by Magnetic Brehm on Earth’s Magnetic Field.

• Effective Threshold 1020 eV.

• Azimuthal modulation of shower development.

Hadronic Composition

• Xmax method of measuring UHECR composition.

• Use CORSIKA and models such as QGS-JET and SYBILL to predict distribution of Xmax for p, CNO, Fe nuclei.

• Hadronic models calibrated at accelerator energies – problem with reach to fragmentation region.

• Low energy studies still important – SYBILL (minijet model) HEGRA e-p form factor data modified prediction.

Muon energy loss

• Underground and under-ice experiments must understand TeV muon energy loss in detail.

• Problems with high energy extrapolation of phot-nuclear cross-sections.

• HEGRA ep results make impact.

Comparison of Hadronic Interaction Models

New Detection Techniques

• Radio Detection of UHE EAS– Askaryan effect

• First observation at SLAC FFTB by Saltzberg, et al. SLAC T444

• Search for neutrino interactions in Lunar surface using radio

• Antarctic Ice Experiment - RICE

Impact of SLAC beams

• “This result would not have been possible without the incredible precision and stability of beams at SLAC… The result of this experiment will be hugely important to current efforts to detect ultra-high energy neutrinos. This remarkably small effect went undetected for 40 years…” Saltzberg and Gorham in Interaction Point, 2000.

Conclusion

• Laboratory experiments to support Particle-Astrophysics have played a crucial role.

• Three of them are SLAC experiments– LPM– Askaryan– FLASH – air fluorescence

Conclusion, cont.

• A Center for Laboratory Astrophysics will make doing such experiments much easier.

• Cosmic Ray and other Astrophysicists need accelerator based expertise and clout to be successful.

• By-product is much more direct feedback of UHECR discoveries that may affect particle physics.

• Re-unification of the field