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 eV. Primarily protons and nuclei ( up to Fe), also gamma rays and neutrinos. Beyond ~ eV - energies greater than what is accessible in accelerators.

Cosmic Rays have been observed with energies at up to ~10 20 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) 3×10 20 eV 50 Mpc ~ Size of local cluster Protons above 6×10 19 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/km 2 centure at 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 Showers Zoom on next slide

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: July 11, 1999 RWS Looking South

Layout of AGASA

Highest Energy AGASA Event

The Auger Hybrid Ground Array/Air Fluorescence Detector 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 particles/bunch ~ > 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 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 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