Ultra High Energy Cosmic Rays

Glennys R. FarrarCenter for Cosmology and Particle Physics,

Department of Physics, New York University

1912 Hess discovered cosmic rays – hot air balloon

1927 Cosmic rays seen in cloud chamber

1932 Anderson discovered antimatter (positron); Debate over cosmic rays1937 Discovery of muon

1938 Auger discovered extensive air showers

1946 First air shower experiments; Discovery of pion and kaons1949 Fermi's theory of cosmic rays

1962 First 1020 eV cosmic ray detected 1966 Proposal of GZK cutoff energy for cosmic rays

1991 Fly's Eye detected highest-energy cosmic ray1994 AGASA high-energy event

1995 Pierre Auger Project begun – to be completed 20052002 HiRes and AGASA Debate the GZK cutoff

A Timeline History of High-Energy Cosmic Rays

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An Ultrahigh Energy Shower

First interaction: p + 14N -> thousands of secondary particles, such as: p, n,

Subsequent interactinos: air nucleus -> ~ few hundred particles OR

initiates an electromagnetic cascade,

producing e+- and more ’s

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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- e with a lifetime~ 103 sec.

• Electrons and positrons: e- and e+ .

• Quanta of light: photons or gammas (

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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 ~ 1019 eV.

• 1 MeV = 1 Mega eV = 106 eV• 1 GeV = 1 Giga eV = 109 eV• 1 TeV = 1 Tera eV = 1012 eV

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Some Terminology

• Flux: the amount of something arriving in one unit of area (e.g., 1 m2) 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.

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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 steradian.

• The CR spectrum falls rapidly as energy increases: dN/dE ~E-3

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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 1019 eV would we expect to see per year of full-time data-taking with the NYSCPT if its area is 100 km2?

Hajo Drescher’s Shower Simulations

• 1019 eV proton primary

• Horizontal grid units = 1 km

• Vertical box = 30 km

• Heavy thinning for r < 30 m

• e+, e-, hadrons

Vertical shower, 5:1 aspect ratio

Inclined Shower, 1:1 aspect ratio

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Electromagnetic Component

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Muons

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Hadronic component (neutrons)

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Two Types of Cosmic Ray Detectors

• Ground Shower Array (AGASA, Auger, NYSCPT) – Large area because of low flux (1/ km2 / century > 1020

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

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AGASA Photos

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Greisen Zatsepin Kuzmin Cutoff

• Ultra-high energy protons above ~ 1020 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)

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AGASA Doesn’t See the Predicted GZK Cutoff!

Dotted line: expected spectrum at Earth if sources are uniformly distributedthroughout the Universe andUHECP Energy is degradedas predicted by GZK.

Will HiRes confirm absence of “GZK cutoff”?

If so, what is going on????

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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

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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 km2), for more statistics.– Useful smaller (100 km2), 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.

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New York City: ~10 times the area of AGASA and ~ 350 High Schools

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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?

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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 2003 + AY03-04:– Build, deploy, and operate ~ 100 detectors– First scientific results

• Summer 2004 + AY04-05:– Build, deploy, and operate ~ 1000+ detectors– Major scientific results

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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

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Other Projects and Sources

• CROP (Nebraska) low resolution, large areahttp://www.unl.edu/physics/crop.html

• CHICOS (Los Angeles): low resolution, large area http://www.chicos.caltech.edu/

• NALTA: North American Large Area Time Coincidence Array http://csr.phys.ualberta.ca/nalta/

• NYSCPT: high resolution; large area in Stage IIIhttp://www.physics.nyu.edu/NYSCPT