Endeavour’s final flight launches, carrying particle physics payload

On Monday 16 May, Endeavour roared from its seaside launch pad at Cape Canaveral in Florida in its final flight and NASA’s penultimate shuttle launch. Aboard was a revolutionary physics experiment, the Alpha Magnetic Spectrometer, due to be attached to the International Space Station and remain there for rest of the station’s life – at least 10 years.

The 8500-kg Alpha Magnetic Spectrometer, built partially at CERN, home of the Large Hadron Collider in Geneva, is going to study the composition of cosmic rays, charged particles that continually bombard Earth from space. Until now, scientists have been unable to make detailed measurements of these charged particles because they interact with the atmosphere, creating showers of 'secondary particles.'

“This is a very exciting moment for basic science,” said CERN Director General Rolf Heuer in a statement. “We expect interesting complementarities between AMS and the LHC. They look at similar questions from different angles, giving us parallel ways of addressing some of the Universe’s mysteries.”

The spectrometer, also called AMS-02 (AMS-01 was a precursor experiment flown on the shuttle Discovery for 10 days in June 1998), consists of a large magnet that curves the path of any particles entering the detector. From the direction and radius of the curve of the particle’s path, as well as the length of time it takes to pass through the detector, the charge, mass and momentum of the particle can be calculated.

Data to move from NASA to CERN later this year

The detector will produce a data stream of seven gigabits per second, but the 600 computer processors on AMS-02 are able to filter and compress the data to reduce it down by a factor of 3000 into a two Mbit per second transmission to the NASA network of ground stations. This data will also be stored on board the ISS, according to Martin Pohl, one of the principle investigators of AMS and head of physics at the University of Geneva.

All data will first go to two centers based at the Johnson Space Centre in Houston, to be in direct contact with NASA Mission Control: health and status data go to the AMS Payload Operations and Control Center (POCC), which is also the center that operates AMS-02; science data go to the AMS Science Operations  Center (SOC).

Later this year, both centers will move to CERN, with data and commands being transmitted via the Internet, Pohl said, but the Houston POCC and SOC will stay in place as a cold backup in case of trouble. From June 2011, AMS-02 will be operated out of CERN.

The SOC will be the central data repository, where all data are archived and from where they are distributed. It will support local centers as well as on-site analysis, and will contain about 3500 PCs, Pohl said.

All the analysis, though, is still a way off: "We expect event data shortly after installation and commissioning [due to occur in May]. Scientific result require that we first re-align and calibrate the detector. That will take longer, probably several months," Pohl said.

With a better knowledge of the composition of cosmic rays, the AMS-02 team, lead by Nobel laureate Samuel Ting, hope to figure out some mysteries in cosmology, such as the origin of dark matter and the mystery of the missing antimatter.

“From its vantage point in space, AMS will explore such issues as Antimatter, Dark Matter and the origin of Cosmic Rays,” Ting said. “However, its most exciting objective is to probe the unknown because whenever new levels of sensitivities are reached in exploring an unchartered realm, exciting and unimagined discoveries may be expected."

The origin of dark matter

The visible matter in the universe – the Earth, Sun, all the planets and their moons, all the galaxies and any other object including gas or dust – adds up to less than 5% of the total universe. The other 95% is dark matter and dark energy, of which the exact nature is unknown.

“Never in the history of science have we been so aware of our ignorance,” said AMS deputy spokesperson Roberto Battiston. “Today we know that we do not know anything about what makes up 95% of our universe.”

“One of the leading candidates for dark matter is the neutralino,” according to the AMS-02 website. “If neutralinos exist, they could collide with each other producing  excesses of charged or neutral  particles which  can be detected by AMS-02. Anomalous peaks or structures in the energy spectra of  positron, anti-proton, or gamma ray could signal the existence of neutralinos or other dark matter candidates.”

The mystery of the missing antimatter

Every matter particle has an equivalent anti-particle that is identical except that it carries the opposite electric charge. For example, the electron has a positively charged antimatter twin called the positron.

According to current cosmic theories, matter and antimatter would have been created in equal amounts at the Big Bang. But the universe we observe today is made almost entirely from matter. So what happened to all the antimatter? AMS-02 is also going to look for nuclei of antimatter that would signal the existence of large amounts of antimatter elsewhere in the universe.

For more information and updates on AMS-02, see its website or follow @AMS-02 on twitter.