Ultra High Energy Cosmic Rays Glennys R. Farrar Center for Cosmology and Particle Physics, Department of Physics, New York University

Hess discovered cosmic rays – hot air balloon Cosmic rays seen in cloud chamber Anderson discovered antimatter (positron); Debate over cosmic rays Discovery of muon Auger discovered extensive air showers First air shower experiments; Discovery of pion and kaons Fermi's theory of cosmic rays First eV cosmic ray detected Proposal of GZK cutoff energy for cosmic rays Fly's Eye detected highest-energy cosmic ray AGASA high-energy event Pierre Auger Project begun – to be completed HiRes and AGASA Debate the GZK cutoff A Timeline History of High-Energy Cosmic Rays

8/12/02G. R. Farrar, NYU3 An Ultrahigh Energy Shower First interaction: p + 14 N -> thousands of secondary particles, such as:  p +, p -, p 0, K +-0, L, S, p, n,... Subsequent interactinos:  p +- + air nucleus -> ~ few hundred particles OR  p +- -> m +- n m  p 0 -> g g  g initiates an electromagnetic cascade, producing e +- and more g ’s

8/12/02G. R. Farrar, NYU4 Some Types of Cosmic Particles Atomic nuclei: protons and neutrons. E.g., 12 C is composed of 6 p and 6 n. Protons: the hydrogen atom is 1 p and 1 e - Neutrons: decay into a proton via the reaction n -> p e - n e with a lifetime t ~ 10 3 sec. Electrons and positrons: e - and e +. Quanta of light: photons or gammas ( g)

8/12/02G. R. Farrar, NYU5 Cosmic Ray Energies A standard unit for elementary particle energies is the “electron Volt” – eV. 1 eV is the kinetic energy of 1 electron moved through a potential of 1 Volt. Ultra-high energy cosmic particles have energies greater than ~ eV. 1 MeV = 1 Mega eV = 10 6 eV 1 GeV = 1 Giga eV = 10 9 eV 1 TeV = 1 Tera eV = eV

8/12/02G. R. Farrar, NYU6 Some Terminology Flux: the amount of something arriving in one unit of area (e.g., 1 m 2 ) in one unit of time (e.g., 1 sec). Spectrum: A plot showing the amount of something, as a function of energy. In the next slide, the “something” is the number of particles in one bin of energy.

8/12/02G. R. Farrar, NYU7 Cosmic Ray Energy Spectrum In this spectrum, the Log of the flux in one unit of angle (sr) is plotted versus the Log of the energy. A sphere has 4 p steradian. The CR spectrum falls rapidly as energy increases: dN/dE ~E -3

8/12/02G. R. Farrar, NYU8 Problems 1.From the graphed spectrum, find a more exact value of the exponent p, in the expression flux ~ E -p. (Hint: take the Log of this formula). 2.Approximately how many events of energy above eV would we expect to see per year of full-time data-taking with the NYSCPT if its area is 100 km 2 ?

Hajo Drescher’s Shower Simulations eV proton primary Horizontal grid units = 1 km Vertical box = 30 km Heavy thinning for r < 30 m e +, e -, g, m, hadrons

Vertical shower, 5:1 aspect ratio

Inclined Shower, 1:1 aspect ratio

8/12/02G. R. Farrar, NYU12 Electromagnetic Component

8/12/02G. R. Farrar, NYU13 Muons

8/12/02G. R. Farrar, NYU14 Hadronic component (neutrons)

8/12/02G. R. Farrar, NYU15 Two Types of Cosmic Ray Detectors Ground Shower Array (AGASA, Auger, NYSCPT) –Large area because of low flux (1/ km 2 / century > eV) –Collects data day and night, any weather –Measures direction by arrival times across array –Relies on modeling of shower to infer energy and primary type Air Fluorescence (HiRes, Auger) –10% duty cycle (clear, moonless nights…) –Difficult to calibrate –Insensitive to atmospheric shower modeling

AGASA AUGER 2005

8/12/02G. R. Farrar, NYU17 AGASA Photos

8/12/02G. R. Farrar, NYU18 Greisen Zatsepin Kuzmin Cutoff Ultra-high energy protons above ~ electron Volts (~10 Joules!) Collide with low energy Cosmic Microwave Background photons (400 / cm 3 ) p +  p +  Pion takes energy from the initial proton => energy of a UHE proton degrades in ~ 100 Million light years (nearby in cosmic terms! – visible universe is about 10 billion light years across)

8/12/02G. R. Farrar, NYU19 AGASA Doesn’t See the Predicted GZK Cutoff! Dotted line: expected spectrum at Earth if sources are uniformly distributed throughout the Universe and UHECP Energy is degraded as predicted by GZK. Will HiRes confirm absence of “GZK cutoff”? If so, what is going on????

8/12/02G. R. Farrar, NYU20 Important Science Goals of a UHECP Telescope Good energy resolution (~ 10 % ?) –AGASA, HiRes, Auger ~ 30 % –Structure in energy spectrum will elucidate source. Good angular resolution (0.1 degree ?) –Identify sources –Determine the magnetic field in our galactic halo and between (only possible with good energy resolution) Detailed information on shower structure (e.g., arrival time) –Validate model of atmospheric shower –Improve determination of primary energy and type

8/12/02G. R. Farrar, NYU21 Cutting Edge UHE Cosmic Particle Telescope in New York City What design? –Ground Array (no need for expensive Air Fluorescence because Auger will cross calibrate techniques). –For better resolution : closer spacing than AGASA, much closer than Auger -- being simulated now. How large an area? –Best large (1000 km 2 ), for more statistics. –Useful smaller (100 km 2 ), because of high resolution and detailed shower information. –Can start “small” and improve. “Flash ADC” and high resolution => NYSCPT will be a premier Air Shower Array, even with just 100 detectors.

8/12/02G. R. Farrar, NYU22 New York City: ~10 times the area of AGASA and ~ 350 High Schools

8/12/02G. R. Farrar, NYU23 A Plan Deployment staged over three years. –Stage I: Core group of HS teachers and students (“masters”) collaborate with physicists to build and use prototype detectors and develop curriculum. (NYSCPT Summer Institute, Aug. 9-23, 2002). –Stage II: Second group of teachers (~ 10 per master teacher?) will be engaged; including most public, private and parochial high schools –Stage III: Include remaining schools; deploy additional non- school-based detectors (roofs of homes, libraries, apartment buildings). Expand to middle schools? Beyond city limits?

8/12/02G. R. Farrar, NYU24 Timetable Summer 2002: –10 HS teachers with 18 students –2 week Institute: build prototype detectors, work on initial curriculum ideas AY 02-03: –Operate 10 detector systems; initial science analyses. –Complete simulations and finalize the design. –Investigate issues with non-school detectors. –Refine and extend curriculum materials. Summer AY03-04: –Build, deploy, and operate ~ 100 detectors –First scientific results Summer AY04-05: –Build, deploy, and operate ~ detectors –Major scientific results

8/12/02G. R. Farrar, NYU25 Serious Contributors to the Effort so far: Scientists: –Faculty: Glennys Farrar (NYU), Reshmi Mukherjee (Barnard), Stefan Westerhoff (Columbia) –“Expert Consultants”: M. Teshima (AGASA), P. Sokolsky and L. Weincke (HiRes), Brian Fick (Auger), D. Hanna (STACEE) –Postdoc: Hajo Drescher (NYU -- simulation) –Grad students: Britt Reichborn-Kjennerud, Doug Bramel, Segev Benzi, Andy O’Neill –Undergrad: Dietrech Washington Educators: Wesley Pitts (CUNY Gateway to Learning) Supported by National Science Foundation, NYU, Columbia, Wolfram Research

8/12/02G. R. Farrar, NYU26 Other Projects and Sources CROP (Nebraska) low resolution, large area CHICOS (Los Angeles): low resolution, large area NALTA: North American Large Area Time Coincidence Array NYSCPT: high resolution; large area in Stage III