Searching for New Physics with Jets

1. Searching for New Physics with Jets Mike Shupe, Frederik Ruehr

2. M. Shupe: Summary of Research Achievements 2011 • Physics: (See following slides) Shupe has been the sole or co-editor for 3 of the first 74 physics papers published by the ATLAS experiment, using data accumulated in 2010 and the first half of 2011. These papers report exclusion limits on quark compositeness and the production of new exotic particles, based on the analysis of dijet events in 7 TeV ATLAS collision data. A comprehensive paper describing new results from the full 2011 data set (4.6 fb-1) will be submitted for publication in Spring, 2012. Currently, Shupe is the primary editor on this effort. He will continue editing papers emerging from the ATLAS Exotics Group, focusing next on the 2012 data set, where the LHC is planning to raise the collision energy to 8 TeV. • Service and Upgrade: The array of 35 specialized radiation monitors constructed at Arizona and installed in the ATLAS cavern has continued to take data throughout the 2011 run. This full data set is now in analysis at Arizona, and the rates observed in this array will be compared to results coming from the SLAC based Cavern Backgrounds group. The initial results from SLAC are somewhat puzzling, and the Arizona comparisons should help clear up some of the confusion. These results are needed for the understanding of backgrounds in current running, and for the engineering of ATLAS upgrade detectors.

3. F. Ruehr: Summary of Research Achievements 2011 • Ruehr has been stationed at CERN since 2010, and has been at the center of analysis development in a number of areas. • The multi-jet eta-intercalibration method that he introduced to ATLAS is now one of the standard in-situ techniques used to establish the jet energy scale and its uncertainties. • In mid-2010, Ruehr was appointed to be the Convenor of the ATLAS Jet+X subgroup, which includes both Standard Model physics and the search for new physics – in dijet distributions, in inclusive jet spectra, and in a number of other jet+X channels. • Ruehr has continued to be a leading figure in the analyses of dijet mass and angular distributions for physics beyond the Standard Model.

4. Search for resonances due to excited quarks in the dijet mass spectrum using a 1.0 fb-1 ATLAS data set from 2011. “Search for New Physics in the Dijet Mass Distribution using 1 fb-1 of pp Collision Data at sqrt(s) = 7 TeV collected by the ATLAS Detector'', The ATLAS Collaboration, submitted to Phys. Lett. B (31 August 2011). Accepted for publication. QCD background determined from a smooth fit to the data, then searched for resonances (BumpHunter). Most discrepant region in agreement with QCD (no bumps). Limits set on excited quarks (2.99 TeV), axigluons (3.32 TeV), and color octet scalars (1.92 TeV).

5. Search for quark contact interactions in dijet angular spectra using a 36 pb-1 ATLAS data set from 2010. “Search for New Physics in Dijet Mass and Angular Distributions in pp Collisions at sqrt(s) = 7 TeV Measured with the ATLAS Detector”, The ATLAS Collaboration, New J. Phys. 13 (2011) 053044 (20 Mar 2011) QCD prediction determined PYTHIA with NLOJET++ k-factors. All distributions in agreement with QCD (Bayesian analysis). Exclusion limits at 95% CL are set for quark contact interactions below 6.8 TeV, using new Fc analysis (at right), and 6.6 TeV using traditional c distributions (at left). (Many other limits set in this paper.)

6. ATLAS Limits as of Lepton-Photon 2011: Arrows indicate limits reported by the ATLAS Exotics Group