# Presentation: 004099

## Ultra-High Energy Cosmic Radiation

- and what it teaches us about astro- and fundamental physics

- Günter Sigl
- GReCO, Institut d’Astrophysique de Paris, CNRS
- _[http://](http://www.iap.fr/users/sigl/homepage.html)__[www.iap.fr](http://www.iap.fr/users/sigl/homepage.html)__[/](http://www.iap.fr/users/sigl/homepage.html)__[users](http://www.iap.fr/users/sigl/homepage.html)__[/](http://www.iap.fr/users/sigl/homepage.html)__[sigl](http://www.iap.fr/users/sigl/homepage.html)__[/](http://www.iap.fr/users/sigl/homepage.html)__[homepage.html](http://www.iap.fr/users/sigl/homepage.html)_

- General facts and the experimental situation
- Acceleration (“bottom-up” scenario)
- Cosmic magnetic fields and their role in cosmic ray physics
- New interactions and new particles

## Further reading:

- short review: Science **291 **(2001) 73
- long review: Physics Reports **327** (2000) 109
- review collection: Lecture Notes in Physics **576** (2001) (eds.: M.Lemoine, G.Sigl)

## The cosmic ray spectrum stretches over some 12 orders of magnitude in energy

- The cosmic ray spectrum stretches over some 12 orders of magnitude in energy
-  and some 30 orders of magnitude in differential flux:

## The structure of the spectrum and scenarios of its origin

**The structure of the spectrum and scenarios of its origin**

**knee**

**ankle**

**toe ?**

## Atmospheric Showers and their Detection

- Ground array measures lateral distribution
- Primary energy proportional to density 600m from shower core

- Fly’s Eye technique measures
- fluorescence emission
- The shower maximum is given by
-     Xmax ~ X0 + X1 log Ep
- where X0 depends on primary type
- for given energy Ep

**Atmospheric Showers and their Detection**

## A Tension between the Newest Fluorescence Data (HiRes)

**and Ground Array Results?**
**Or: Is there a Cut-Off after all?**

## Next-Generation Ultra-High Energy Cosmic Ray Experiments

| Experiments | starting date | acceptance
in km2sr | angular
resolution | energy
resolution |
| --- | --- | --- | --- | --- |
| High – Res
Fly’s Eye | since 1999 | 350-1000 | few degrees | ~40% mono
~10% stereo |
| Telescope Array | maybe with Auger North | 1700-5000 | ~1o ? | ~20% ? |
| Auger ground | full size in about 2004 | >7000 | < 2o | ~15% |
| Auger hybrid | ~2004 | >700 | ~0.25o | ~8% |
| EUSO/OWL
space-based | >2010 | ~105 ? | ~1o ? | <30% ? |
| radio detection | ??? | >1000 ? | few degrees ? | ??? |

**Next-Generation Ultra-High Energy Cosmic Ray Experiments**

- compare to AGASA acceptance ~ 230 km2sr

## The southern Auger site is under

**The southern Auger site is under**
**construction.**

## The Ultra-High Energy Cosmic Ray Mystery consists of

**(at least) Three Interrelated Challenges**

**1.) electromagnetically or strongly interacting particles above**
**     ****10****20**** eV loose energy within less than about 50 Mpc.**

**2.) in most conventional scenarios exceptionally powerful**
**     ****acceleration sources within that distance are needed.    **

**3.) The observed distribution seems to be very isotropic**
**     ****(except for a possible interesting small scale clustering)  **

## The Greisen-Zatsepin-Kuzmin (GZK) effect

- Nucleons can produce pions on the cosmic microwave background

- nucleon

- 

- sources must be in cosmological backyard
- Only Lorentz symmetry breaking at Г>1011
- could avoid this conclusion.

## First Order Fermi Shock

**First Order Fermi Shock**
**Acceleration**

- The ball hit by the racket in
- random directions:
- leads to spectrum E-q, *q *≥ 2.
- As for man-made accelerators the
- maximal energy is limited by the
- gyroradius staying below the shock
- size,

*u**1*

*u**2*

## A possible acceleration site associated with shocks in hot spots of active galaxies

**A possible acceleration site associated with shocks in hot spots of active galaxies**

## Arrival Directions of Cosmic Rays above 4x1019 eV

- Akeno 20 km2, 17/02/1990 – 31/07/2001, zenith angle < 45o

- Red squares : events above 1020 eV, green circles : events of (4 – 10)x1019 eV

- Shaded circles = clustering within 2.5o.

- Chance probability of clustering from isotropic distribution is < 1%.

## HiRes sees no significant anisotropy above 1018 eV

**HiRes sees no significant anisotropy above 10****18**** eV**

## Cosmic Magnetic Fields and their Role in Cosmic Ray Physics

- Cosmic rays above ~1019 eV are probably extragalactic and
- may be deflected mostly by extragalactic fields *B*XG rather
- than by galactic fields.
- However, very little is known about about *B*XG:
- It could be as small as 10-20 G (primordial seeds, Biermann
- battery) or up to fractions of micro Gauss if concentrated
- in the local Supercluster (equipartition with plasma).

## Deflection and Angular Resolution

**Deflection and Angular Resolution**

## Strong fields in our Supergalactic Neighbourhood: Numerical simulations

- A source at 3.4 Mpc distance injecting protons with spectrum E-2.4 up to 1022 eV
- A uniform Kolmogorov magnetic field of strength 0.3 micro Gauss and largest
- turbulent eddy size of 1 Mpc.

- Isola, Lemoine, Sigl

- Conclusions:
-      1.) Isotropy inconsistent with only one source.
-      2.) Strong fields produce interesting lensing (clustering) effects.

- 105 trajectories,
- 251 images between
- 20 and 300 EeV,
- 2.5o angular resolution

## Supergalactic Neighbourhood and Magnetic Fields are strongly structured

- baryon density-cut
- through 50Mpc3 box

## How many sources in a strongly structured and magnitezed environment?

**How many sources in a strongly structured and magnitezed environment?**

- Assume source density follows baryon density, field is stochastic and uniform
- with a Kolmogorov spectrum up to largest eddy scale of 1 Mpc.

- Current (AGASA) data can be fit with 10-100 sources if observer is surrounded
- by fields ≥ 0.1 micro Gauss:

- Isola, Sigl, astro-ph/0203273, Miniati, Ensslin, Sigl, in preparation

- Diamonds=simulations; statistical and total (including cosmic variance) error bars
- Histogram=AGASA data.

- power spectrum

- auto-correlation function

- CL=17%

- CL=63%

## Ultra-High Energy Cosmic Rays and the Connection to

******-ray and Neutrino Astrophysics**

- accelerated protons interact:

- => energy fluences in -rays and
-     neutrinos are comparable due to
-     isospin symmetry.

- The neutrino spectrum is unmodified,
- whereas -rays pile up below the pair
- production threshold on the CMB at a
- few 1014 eV.

- The Universe acts as a calorimeter for
- the total injected electromagnetic
- energy above the pair threshold. This
- constrains the neutrino fluxes.

## The total injected electromagnetic energy is constrained by the diffuse -ray

- flux measured by EGRET in the MeV – 100 GeV regime

## New Particles and New Interactions

| Farrar, Biermann | radio-load quasars | ~1% |
| --- | --- | --- |
| Virmani et al. | radio-load quasars | ~0.1% |
| Tinyakov, Tkachev | BL-Lac objects | ~10-5 |
| G.S. et al. | radio-load quasars | ~10% |

- If this is confirmed, one can only think of 3 possibilities:

- 1.) Neutrino primaries
-      but Standard Model interaction probability in atmosphere is ~10-5.

-  resonant (Z0) secondary production on massive relic neutrinos:
-     needs extreme parameters and huge neutrino fluxes.

- 2.) New heavy neutral (SUSY) hadron X0: *m(X**0**) > m**N** *increases GZK threshold.
-      but basically ruled out by constraints from accelerator experiments.

- 3.) New weakly interacting light (keV-MeV) neutral particle
-      electromagnetic coupling small enough to avoid GZK effect; hadronic coupling
-      large enough to allow normal air showers: very tough to do.

- In all cases: more potential sources, BUT charged primary to be accelerated to
- even higher energies.

-  strong interactions above ~1TeV: only moderate neutrino fluxes required.

**New Particles and New Interactions**

## Probes of Neutrino Interactions beyond the Standard Model

- Note: For primary energies around 1020 eV:

- Center of mass energies for collisions with relic backgrounds
-      ~100 MeV – 100 GeV ―> physics well understood

- Center of mass energies for collisions with nucleons in the atmosphere
-      ~100 TeV – 1 PeV ―> probes physics beyond reach of accelerators

- This increase is not sufficient
- to explain the highest energy
- cosmic rays, but can be probed
- with deeply penetrating showers.

## However, the neutrino flux from pion-production of extra-galactic trans-GZK

**However, the neutrino flux from pion-production of extra-galactic trans-GZK**
** ****cosmic rays allows to put limits on ****the neutrino-nucleon cross section:**

- Future experiments will either close the window down to the Standard Model
- cross section, discover higher cross sections, or find sources beyond the
- cosmogenic flux. How to disentangle new sources and new cross sections?

## Earth-skimming τ-neutrinos

- Air-shower probability per τ-neutrino at 1020 eV for 1018 eV (1)
- and 1019 eV (2) threshold energy for space-based detection.

- Kusenko, Weiler, PRL 88 (2002) 121104

- Comparison of earth-skimming and horizontal shower rates allows to
- measure the neutrino-nucleon cross section in the 100 TeV range.

## Future neutrino flux sensitivities

**Future neutrino flux sensitivities**

- Kalashev, Kuzmin, Semikoz, Sigl, hep-ph/0205050

## Ultra-High Energy Neutrino Detection: Traditional and New Ideas

- Mostly uses the charged-current reactions:

- 1.) detect Cherenkov radiation from muons in deep sea or ice
-      AMANDA, ANTARES, BAIKAL, NESTOR
-      aims at 1 km3 for E> 100 GeV to 1 TeV

- 2.) horizontal air showers for electron and τ-neutrinos
-      PIERRE AUGER, MOUNT
-      for E> 1018 eV, increased efficiency for τ-neutrinos if surrounded by
-      mountains on 100 km scale which is decay length of produced taus.

- 3.) detection of inclined showers from space for E>1020 eV
-      EUSO, OWL

- 4.) acoustic detection in water: hydrophonic arrays

- 5.) detection of radio emission from negative charge excess of showers
-      produced in air, water, ice, or in skimming rock.
-      RICE (in South-pole ice), GLUE (radio-telescope observing the moons rim)

- 6.) Earth-skimming events in ground arrays or fluorescence detectors.

## Conclusions

- 1.) The origin of very high energy cosmic rays is one of the fundamental
-      unsolved questions of astroparticle physics.
-      This is especially true at the highest energies, but even the origin of
-      Galactic cosmic rays is not resolved beyond doubt.

- 2.) Pion-production establishes a very important link between the physics
-      of high energy cosmic rays on the one hand, and -ray and neutrino
-      astrophysics on the other hand. All three of these fields should be
-      considered together.

- 4.) At energies above ~1018 eV, the center-of mass energies are above
-      a TeV and thus beyond the reach of accelerator experiments. Especially
-      in the neutrino sector, where Standard Model cross sections are small,
-      this probes potentially new physics beyond the electroweak scale.

- 3.) Acceleration and sky distribution of cosmic rays are strongly linked to the
-      in part poorly known strength and distribution of cosmic magnetic fields.

- 5.) The coming 3-5 years promise an about 100-fold increase of ultra-high
-      energy cosmic ray data due to experiments that are under either
-      construction or in the proposal stage.

- 6.) Many new ideas on a modest cost scale, especially for ultra-high energy
-      neutrino detection, are currently under discussion.