Quark Excitement: Is there anything smaller?
30 May 2012
Mankind has forever sought to determine the most fundamental components of matter. From the atom to the nucleus to the proton and neutron, and finally to the quark, we have asked each step of the way "Is this it or is there something inside?"
ATLAS physicists have just taken another step toward tackling that very question by publishing the results of a search for new kinds of particles decaying into a jet (a spray of hadronic particles) and a photon.
The Physical Review Letters article provides the world's best upper limits to date on the probability of producing such particles, including excited states of quarks.
A recent ATLAS Blog posting explains that, as in the case of atoms, if a particle can be excited then it is necessarily composed of smaller pieces. If the LHC were able to create excited quarks, we should observe them with ATLAS as they emit photons of light and return to being regular quarks.
Although no such excited states were found, the ATLAS study has significantly extended previous results obtained at other colliders. In fact, these measurements rule out the existence of signals ten times fainter and excited quarks 2 TeV more massive than earlier studies.
With the 2012 increase in the LHC energy to 8 TeV, and additional increases in the future, we expect to use these and other techniques to extend the reach of our understanding of matter's most fundamental constituents.
Refer to a new ATLAS Blog article describing our technique and this new result in the search for quark substructure.