Many members of the ATLAS Experiment Collaboration have been at the European Physical Society's HEP 2011 conference in Grenoble, France, this week, revealing the results of 35 new and exciting physics analyses for the very first time.
The results are based on painstaking examinations of a large amount of data collected by the ATLAS Experiment as it combed the gleanings from high-speed proton collisions at the Large Hadron Collider at CERN in Geneva, Switzerland. This data amounted to one inverse femtobarn, which equates to around 70 million million collisions. Even more data will be taken during the coming months.
The new results build on extensive measurements already made by ATLAS to study physics processes related to the Standard Model of particle physics - physicists' current best theory describing fundamental particles and how they interact. ATLAS results presented at EPS narrow down the mass range where the much talked-about Higgs boson - the final missing piece of the Standard Model - could possibly be hiding. This is just the tip of the iceberg in the quest for new physics, though, and ATLAS is simultaneously exploring many possible scenarios, all of which were presented at the conference. Such topics include supersymmetry, extra dimensions of space, particles more fundamental than quarks, particles of new forces, and much more.
ATLAS physicists blogged live from HEP 2011, which gathered over 700 physicists and dozens of journalists from around the world.
Worldwide news coverage of EPS HEP 2011.
Homing in on the Higgs boson. This figure shows the expected and observed sensitivity of the search for the Higgs that arises from combining the results of searches in all decay modes studied to date. The black undulating dashed line shows ATLAS' predicted sensitivity to the Higgs boson in the mass range 100-600 GeV, based on simulations. The green and yellow bands correspond to the uncertainty in these predictions. The solid black line shows ATLAS' limit on Higgs production based on actual data collected. The plot shows that, with one inverse femtobarn of data collected, ATLAS can exclude with 95 per cent confidence the existence of a Higgs wherever the solid line dips below the horizontal dashed line, i.e. 155-190 GeV and 295 and 450 GeV. In some other regions, there are small excesses above expectations.
Scouring data for dijet resonances as evidence of new particles. The black dots show the number of observed dijets (two collimated highly-energetic clusters of particles called 'jets') in actual data, in a mass range of 700-4000 GeV. The red line shows theoretically predicted values for how many dijet events are expected in this mass range. The blocky red line at the bottom of the plot shows how much the observed data differed from the predictions. A value of more than 3 in this region might be considered a first hint of the presence of a new particle. ATLAS saw the largest 'excess' of this sort between the two vertical blue lines (1160-1350 GeV), but it is not striking enough to suggest the presence of a new particle.
|Non-Higgs New Physics Searches:
Mass reach of ATLAS searches for new phenomena (not including SM/BSM Higgs). Only a representative selection of the available results is shown. Top: all searches, middle: SUSY only, bottom: other than SUSY.
Example Event Displays
|Candidate ZZ to 4 muons:
Display of an event candidate with two Z bosons decaying to two muons each. Muons (their tracks shown here as red lines) are able to pass relatively unhindered through every layer of the ATLAS detector.
Event display showing a rare 'monojet' of high-energy particles being thrust from the collision point at around the 10 o'clock angle (when you look at the dot in the centre, you are looking directly down the beam). The 'lego plot' on the right shows the position and amount of energy of everything in the collision event.
|Single Top Quark Candidate:
An event candidate of production of a single top quark, rather than the usual top-antitop pair production. A top quark can decay to an electron (red line), two jets (shown in blue and yellow), and several other particles that are not detected (the 'missing energy' that these other particles represent is clumped together into one vector, shown in pink).