This forum is a place to share information on the public project, help steer where it goes, interact with
the physicists involved, and help improve it.
We are asking for your help
At the heart of the AEgIS experiment lies the detection of annihilations of antiprotons with nuclei, which
produce nuclear fragments, protons, and high energy pions. The process is poorly studied,
but we need to understand it very well.
For this reason, we are taking data on antiproton annihilations either directly in photographic film
or in very thin foils of different materials directly in front of it. Each annihilation
produces a starburst-like pattern in the photographic film, formed by the particles produced
by the annihilation or as a side product of the annihilation.
For each annihilation, we are asking you to
help us count the annihilation products as imaged in the film, identify each of them (are the produced
tracks barely visible, well visible or really dark lines?), and give an estimate of where
the annihilation took place (the annihilation point itself may not be visible if the annihilation takes place
in a foil, rather than in the film). You'll be able to scan through the fim like with a microscope,
changing the focus into deeper and deeper parts of the film.
We'll then tabulate the types of annihilation products, their numbers and perhaps even
their energy (if they come to rest in the photographic film), and use that information to
compare with (and improve!) simulations of the annihilation process.
This new site is geared towards high school students and their (physics) teachers. It contains
introductory material into the physics and gives a detailed explanation of what we hope to
learn through your help. If you are interested in participating as a high school class, please
get in touch with us
This is our first attempt to ask for public help in analyzing photographic images of
antiproton annihilations, which has received much attention. This site is now closed for
further analysis, but still contains a good overview of what we are trying to achieve.
Crowd sourcing particle physics data analysis...
Hi everybody, and first of all, thank you for your interest! As an avid follower of galaxyzoo and
related crowdcrafting and public science projects, I have been thinking about how to open high energy physics
research to public involvement in a similar manner. With the AEgIS experiment,
we may have a first possibility, but I am sure that we will find more.
built around the attempt to measure the gravitational interaction between matter
and antimatter using antihydrogen atoms. Specifically, the AEgIS experiment will
form a horizontal pulsed beam of antihydrogen atoms. These will follow a
parabolic trajectory, dropping for a small amount of time (about 2ms), and will
then hit a surface made of matter, where they annihilate. The tiny vertical shift
caused by gravity (20 micrometers if antimatter behaves as matter does) needs to
be detected to about 1 micrometer, and the dropping time to 10 microseconds. To
measure the drop, or rather the impact point of each atom with the "wall"
(actually a thin foil), we intend to place photographic emulsion plates behind
it which will detect the fragments flying off in all directions that result from
the annihilation of an antihydrogen nucleus with a nucleus of the wall. Only a
handful of fragments are produced in each annihilation, and finding the few that
fly through the emulsion is tricky: some may fly straight through, but some may
fly off at a shallow angle, and not be detected in the immediate vicinity of the
annihilation point, and in any case, we can't see the annihilation vertex itself,
since that happens in the wall. We thus rely on finding and tagging individual
tracks, and associating them to annihilation points. Once we have those points,
we can associate flight times to each of them by matching them with other,
external detectors and see how much a given atom has dropped in a given amount of
In the future, each of the emulsion plates should have an area of about 10x10 cm^2, and we will change plates about
once a week once the experiment is running. If we are lucky, we should see about 1000 annihilations
in that period of time, which we want to tag unambiguously, but perhaps 100's of thousands of tracks
that go straight through, produced
by antiprotons annihilating far away from this detector, and we need to tag those as well. Some of
those particles will also strike a nucleus in the wall and can lead to fragments that look like
annihilations (but aren't). By characterizing annihilations (caused by antiprotons or antihydrogen
atoms), as well as these background processes, we expect to be able to get a clean(er) data sample.
However, annihilation-induced fragmentation depends on the material of the wall, and very little
data are available to help us fine-tune our algorithms.
For this reason, we have taken (last days of 2012) and are continuing to take data on the annihilation
of antiprotons with different foil materials. These are the data you are looking at right now. We are
trying to determine our antiproton annihilation tagging efficiencies, our background rates, and the
annihilation process itself, as well as trying to optimize our detection scheme. One important element
is the presence of protons, or better yet, a heavy nuclear fragment, stemming from the break-up of
the nucleus that the antiproton annihilated with. Because these are probably slow and heavy, these
should generate dark (in the case of protons) or very dark (in the case of fragments) tracks in the
emulsion, that are very different from the very light tracks (pions) stemming from the annihilation
between an antiproton and a proton or a neutron of the nucleus. We hope to count the numbers of each
type of annihilation product, possibly their energy, and furthermore try to find out whether they all
come from the same annihilation (by tagging the intersection point they .
Our plans (status August 2014) are thus the following:
- in a first step, carry out tests of the track tagging (this means finding
tracks, and determining their end points). We also want to
measure of the identity of the particle leaving the track, by tagging it as weakly visible (pions or
other "minimum ionizing particles", well visible (protons) or very pronounced (nuclear fragments),
which provides us with richer
possibilities to understand the annihilation process on different nuclei. Here, we will need help
from you for
suggestions what should be improved, and if you are a programmer, perhaps help in implementing the
- a second step, in which tracks are tied together into "vertices", common origins of tracks, which
may or may not be visible (in case the annihilation took place before the photographic film).
That's new in the user interface, and will need some testing.
- once we have the vertices, and know the identity of the fragments coming from them, we can start
writing papers on the annihilation and fragmentation processes of antiprotons on Al, Ti, Fe, Cu,
Ag, Au, Pb (we tried to cover a large range of nuclei, from very light ones to very heavy ones).
We can also use the vertices to see how parallel the foil was to the emulsion in order to better
understand how well we can reconstruct vertices via this technique.
The longer term step, that of detecting antihydrogen annihilations with this method, and measuring
their gravitational interaction, will happen once we understand how to make a beam of antihydrogen,
something we are working on right now. In the mean time, however, we're also spending a small amount of our antiproton time
on taking the data that you will be looking at.
Our goal in this beta release is to understand our systematic errors using the data we have, work on the
user interface, and generally try to get the machinery working so that we'll be ready once more data
come in. As involving the public in our analysis is something completely new for us, please bear
with us as we stumble, make embarrassing mistakes, and slowly get to the point where you have as
much fun as we do.
Copyright 2014 - AEgIS Collaboration - CERN