Graduate student Tülin Varol and Prof. Willocq have led an update to the search for contact interactions in the dilepton channel at the LHC. The new results have been submitted to the new Physical Review X online journal and the preprint can be seen at http://arxiv.org/abs/1112.4462. This new search was carried out with about 1 fb-1 of proton-proton collisions data, corresponding to a factor 25 increase in statistics over the previous results. The new search adds the dielectron channel to the dimuon channel and excludes the existence of contact interactions up to scales of about 10 TeV.
Tülin Varol presented those results at CERN on Dec 8 in the context of the “Implications of LHC results for TeV-scale physics” workshop, see her talk in the agenda.
Graduate student Andrew Meade and Professor Ben Brau have made a first measurement of the ratio of production of W and Z bosons in events that also contain a jet. The W and Z are heavy (80-90 times the proton mass!) cousins of the massless photon, and are responsible for the weak nuclear force. Many theories for new physics beyond the standard model include couplings between the W and Z and the new particles. Often, these couplings lead to signatures involving production of W and/or Z particles accompanied by jets. By measuring the ratio of production of W and Z along with a jet, we are able to achieve cancellation of many sources of systematic uncertainties, enabling a precision test of the physics of boson plus jet production, so-called perturbative QCD. We further measure this quantity versus the minimum transverse momentum of the jet, increasing the sensitivity of the comparison with theory. This kind of measurement is also sensitive to deviations in the production rates of either the W or Z, so if we see a discrepancy from prediction, it might be our first hint that there is new physics coupling to the W or Z.
This plot shows the ratio along with several different predictions using different algorithms for comparison. The ratio is plotted versus the minimum jet transverse momentum required.
Graduate student Emily Thompson and Professor Stéphane Willocq performed the first search for contact interactions at the LHC in the dimuon channel using data collected with the ATLAS detector during the 2010 pp collision run. The results of this search have been published in the July 1st edition of Physical Review D Rapid Communications: Phys. Rev. D 84, 011101 (2011), arXiv:1104.4398 [hep-ex]. The limits placed on the compositeness scale Lambda are the most stringent to date.
Emily Thompson earned her PhD in June 2011 and is currently working as a postdoctoral research associate for Columbia University. She continues to work on ATLAS at CERN, focusing on boosted top quarks.
Our group has been leading an effort to measure the ratio of production of W and Z bosons with ATLAS. Our first publication with data acquired in 2010 has been submitted to the arXiv and PLB.
http://arxiv.org/abs/1112.4462. This new search was carried out with about 1 fb-1 of proton-proton collisions data, corresponding to a factor 25 increase in statistics over the previous results. The new search adds the dielectron channel to the dimuon channel and excludes the existence of contact interactions up to scales of about 10 TeV.
