The next figure shows the average scattering length
is shown as a function of depth. Note that the effective scattering length,
L_eff, is (approximately) the average length to isotropize the direction
of all but 1/e of the photons. This important parameter for diffusion
calculations is related to the geometric scattering length by L_eff=L_geo/(1-<cos(angle)>).
The wavelength of light used for this study was 532nm (the wavelength of
light from a frequency doubled YAG). On the left side of the
same figure, the horizontal projection of the OM locations for the various
strings are shown. The OMs in the yellow and green color bands are
in the best ice for our purpose.
Here is the RA-Dec plot of atm nu events for B10 data . There are ~300 events in the sample
|The zenith angle distribution is shown next. Horizontal events have cos(zenith)=0, and upward vertical events have cos(zenith)= -1. Note that AMANDA has very little sensitivity to neutrino oscillations due to its relatively large energy threshold, although we have included such effects in the predicted flux.|
|This figure shows the space angle resolution and the deduced point spread function. The angular resolution and absolute pointing were checked by using events that struck both the SPASE air shower array and AMANDA-B10 array. The point spread function is fit well by a function composed of the sum of two gaussians. The tail is partially due to high energy muons that are not well reconstructed.||
This is the effective area of the detector for muons that have energies of 1, 10, and 100 TeV. This shows that AMANDA B10 reaches an effective area of 10,000 m2 for 1 TeV muons.
This figure provides the average muon flux limit as a function of declination. The solid black line includes the impact of systematic uncertainty in the calculations (as illustrated by the various symbols in the legend), and represents the final result of the B10 analysis using data from 1997.
This figure compares the B10 muon flux limits as a function of declination (based on only 1 year of data collected during 1997, which corresponds to less than 1/3 of a year of live time due to delays associated with commissioning) with limits presented by MACRO and Super Kamiokanda collaborations. The solid red line is the same as the solid black line of the left figure. The dashed curves correspond azimuthal variation in the flux limits due to the bin-to-bin statistical variation for the same declination band.
The next figure shows the neutrino flux limits from the 1997 data analysis
and compares to a representative set of models (selected to illustrate
the variety of spectral shapes). Also, the expected sensitivity of
AMANDA-II and IceCube are shown.
The AMANDA-B10 result is true for declinations greater than +40 degrees and includes the impact of systematic uncertainty. The expected sensitivity for AMANDA-II is shown assuming that the complete data on tape is analyzed.
|AMANDA-II Point Search:
The figure below shows the neutrino sky as seen by AMANDA-II using data
from just the first year of operation (Feb -Oct of 2000). The point source
analysis is still in progress so we remain "blind" to the true azimuthal
(or right ascension, RA) distribution of events to insure that human expectation
does not bias the analysis. So the events times are ignored, which
effectively scrambles the right ascension of the event.
A total of 1129 events are shown in the figure of equatorial coordinates. The RA coordinates are scrambled. Compared to the previous sky map from AMANDA-B10, the coverage near the horizon (declination = 0 degrees) is markedly improved. The angular resolution of AMANDA-II is much improved so the angular dimensions of a search bin are likely to be reduced to 6x6 square degrees.
Gamma Ray Bursts (or GRBs) are the most spectacular and powerful explosions
in the sky. Their duration lasts from milliseconds to hundreds of seconds,
and they tend to cluster into two distinct populations. They are
also extremely distant, with redshifts exceeding Z=1, although most of
what is known about distances is deduced from the longer duration GRBs.
We search for correlation between the GRB event time and location provided
by gamma ray satellites. Unfortunately, one of the most powerful
detectors (called BATSE on the Compton Gamma Ray Observatory) ceased operation
in May of 2000. AMANDA-B10 has reported limits for GRBs that were
observed in 1997.
Simulation of GRB explosion which shows strong jet features (dark) and predicts strong relativistic flows. High energy neutrino production may occur along the barrel of the jets.
The most sensitive mode to search for diffuse flux of HE neutrinos uses
the muon signals.
The current (July 2002) limits are shown in the next figure for AMANDA-B10
and Baikal. Note that the AMANDA limits are not yet published and should
be considered preliminary. Systematic studies have not yet been fully
completed. AMANDA-II and IceCube are also shown. The curve
labeled (down) utilizes the EHE analysis to search for neutrino-induced
muons in the downgoing direction (from above the local horizon of the detector).
The sensitivity of AMANDA of AMANDA-II is sufficient to search for sources
below the "evolved" Waxman-Bahcall limit of ~5x10-8 GeV/cm2/s/sr.
The main background to the upgoing muon flux is atmospheric neutrinos generated by cosmic ray collisions. At high energy energies, direct production by charm decay becomes important, although the predicted fluxes have large uncertainty. As the neutrino energies increase beyond 10^7 GeV, most of the signal comes from above or very near the horizon and therefore prompt MUONs become a significant background. The importance of the background depends on the magnitude of the flux and detector energy and angular resolution. From the figure, the minimum flux levels of AMANDA-II are not impacted by charm contributions for the most of the current models of charm production in the atmosphere.
Figure: Diffuse flux limits on the sum of all neutrino flavors as derived from AMANDA-B10 using muons (lower blue) and cascades (lower red). These limits were derived assuming neutrinos oscillate so the flux of all flavors is equal.
Like with accelerator physics, most of the interest neutrino astrophysics is at the extreme energy frontier, which we label "extreme high energy" or EHE. Perhaps the most reliable flux predictions (after atmospheric neutrinos) involve the GZK mechanism. Neutrinos are produced by the inevitable collisions between cosmic rays and the cosmic microwave background. Although the physics required by GZK mechanism is straightforward, the GZK mechanism is still in doubt because one of its predictions has not yet been confirmed. The GZK mechanism predicts are rather strong upper limit on the energy of the cosmic ray, but this upper limit has not yet been clearly identified.
Perhaps the most intriguing aspect of neutrino physics at extreme energies is the potential to study fundamental theories of particle physics. For example, Jonathan Feng (UCI) and his colleagues predict that extremely energetic neutrinos create micro-black holes as the collide with nuclei of atoms in the earth, if certain models of strong gravity are correct.
Experimentally, neutrinos at EHE energies are difficult to detect. As
the neutrino energies increase to 1 PeV (1015 eV), the earth
becomes opaque except near the horizon. We have developed a new technique
to search for "downgoing" nearly horizontal muons. They can be distinguished
from the blizzard of downgoing muons from cosmic ray collisions because
the energies are much higher than muons generated by cosmic ray collisions.
The effective detection area for muons at these energies is very large,
typically 0.2 km2 for AMANDA-B10! We show preliminary results from
our study of AMANDA-B10 data from 1997.
|This limit was derived using only 3 months of data from 1997 (the remaining
data was not suitable for this technique). The horizontal extent
of the black experimental limit indicates the energy interval that contains
~90% of the detected events if you assume a differential energy spectrum
proportional to E-2. For E-2, the maximum
energy is about 1018 eV, but since few EHE models predict E-2,
the horizontal extent of the red line indicates the complete interval of
sensitivity that was studied. It indicates that the lower energy
threshold with this technique is about 1 PeV. The maximum energy is a consequence
of limitations in the muon propagation programs (now corrected), not a
limitation with AMANDA.
The effective detection area of AMANDA-II is even larger than B10.
This graphic (from Joakim Edsjo) shows the capture of dark matter WIMPs by the sun, but a similar picture applies to capture of the WIMPs by the core of the earth. The annihilations of WIMPs in the core produce muon neutrinos, and they can be observed by AMANDA if they interact near the detector.
Figure shows the AMANDA-B10 limit (solid black line) deduced by searching for high energy neutrinos from the center of the earth. Other experimental limits are shown for comparison. For this science, all experimental techniques are limited by irreducible background from atmospheric neutrinos. The green dots represent SUSY models that are already excluded by direct search techniques.
We are just beginning to search for WIMPs from the sun. It is relatively
difficult for AMANDA because the sun remains near the horizon where most
of the residual background events appear to come from. Therefore,
we expect the first substantial result from AMANDA-II due to its superior
background rejection near the horizon.
The extremely low ambient photon flux in deep ice provides the opportunity
to monitor the galaxy for supernova explosions. Supernova events
are expected to generate neutrinos at low energies (< 20 MeV), nominally
too low of an energy to trigger AMANDA electronics. However, a nearby
supernova blast would generate so many neutrinos that enough of them would
interact within 10m of each AMANDA OM and produce Cherenkov light.
The extra photons could contribute the average "noise" rate from each OM.
By summing the signals from each OM, a statistically significant signature
of a supernova can be obtained. We have installed special electronics
to read out and sum the "noise" rates from each OM.
|AMANDA-B10 can monitor about 68% of the stars in our galaxy, and AMANDA-II
can reach 95% of the stars in our galaxy.
The AMANDA collaboration is working with SNEWS (supernova early warning system) members to provide timing information to help pinpoint the position of the supernova by triangulation.