John Ellison

Research

John Ellison is an experimental particle physicist. He has worked on silicon detectors, measurements of the elctroweak trilinear gauge boson couplings, measurements of CP vioation in the B_s system, and searches for new particles inlcuding heavy Majorana neutrinos.

Ellison was one of the early leaders in the DØ Silicon Microstrip Tracker (SMT). He was co-leader of the project in the early R&D and construction phase, and made major contributions to the tracker conceptual design, silicon sensor design, fabrication and testing, and module assembly. These charged particle detectors have the capability of selecting events containing B-hadron decays by precisely measuring secondary vertices which, due to the B lifetime of 1.5 psec, are significantly detached from the primary proton-antiproton interaction vertex. This capability is crucial for the DØ top quark and B physics programs as well as for the search for the Higgs boson. The SMT was installed in 2001 and was operated very succesfully until the end of the Tevatron data-taking in 2011. For more information about the SMT and the DØ detector see arXiv:physics/1005.0801.

Ellison led measurements of electroweak boson pair production at the Tevatron. These processes are particularly interesting since they probe the non-Abelian gauge boson trilinear couplings of the Standard Model (i.e. the WWγ and WWZ couplings). They are also sensitive to deviations from the tree-level Standard Model couplings, which may arise due to compositeness of the W and Z bosons, SUSY radiative loop corrections, or other non-SM phenomena. For a review see arXiv:hep-ph/9804322. Ellison also made many contributions to measurements of other properties of the W and Z bosons while DØ Run 1 Physics Analysis Convener.

Other work on DØ has been on the measurement of CP violation parameters in the B_s-meson system, using B_s --> J/ψ φ decays. CP violation in the B_d system has been well examined by the B-factories, but the B_s system was not accessible. We utilized the abundant production of B_s mesons at the Tevatron and made the first direct measurement of the CP-violation phase φ_s.

On CMS at the Large Hadron Collider Ellison is working on the simulation and conceptual design of the upgarde tracker, which is planned to be installed in CMS beginning with a new pixel detector in 2017 (phase 1 upgrade), and eventually leading to a replacement of the whole tracking system (phase 2). The upgrade is needed to cope with the high luminsity expected as the LHC accelerator is upgraded. The tracking and b-tagging efficiencies will be significantly degraded at high luminosity due to the large occupancy and, for the inner layers, radiation damage. The upgraded detector will incorporate an extra layer and smaller inner radius, and the phase 2 tracker will add the capability of a level-1 track trigger.

Ellison is leading searches for heavy Majorana neutrinos at CMS. Heavy Majorana neutrinos are predicted in several beyon-the-SM models and their existence could explain the masses of the SM light neutrinos via the see saw mechanism. Heavy Majorana neutrinos can lead to interesting lepton-number violating processes resulting in same-sign dilepton events, a signature that has relatively low SM backgrounds. We have set the first limits on the heavy Majorana neutrino mixing parameters for masses above 100 GeV.

Selected Publications

CMS Collaboration, "Search for heavy Majorana neutrinos in μ^± μ^± + jets and e^± e^± + jets events in pp collisions at √ s = 7 TeV ,"
Phys. Lett. B (2012), in press, arXiv.org:1207.6079.

DØ Collaboration, "Measurement of the B_s⁰ Mixing Parameters from the Flavor-Tagged Decay B_s⁰ → J / Ψ φ ,"
Phys. Rev. Lett. 101, 241801 (2008), arXiv.org:0802.2255.

DØ Collaboration, "Lifetime Difference and CP-Violating Phase in the B_s⁰ System,"
Phys. Rev. Lett. 98, 121801 (2007), arXiv.org:hep-ex/0701012.

DØ Collaboration, "Direct Limits on the B_s⁰ Oscillation Frequency,"
Phys. Rev. Lett. 97, 021802 (2006), arXiv.org:hep-ex/0603029.

DØ Collaboration, "Measurement of the Lifetime Difference in the B_s System,"
Phys. Rev. Lett. 95, 171801 (2005), arXiv.org:hep-ex/0507084.

DØ Collaboration, "A Measurement of the Ratio of Inclusive Cross Sections p p → Zb / p p → Zj at √ s = 1.96 TeV,"
Phys. Rev. Lett. 94, 161801 (2005), arXiv.org:hep-ex/0410078.

DØ Collaboration, "A Search for Wbb and WH Production in p p Collisions at √ s = 1.96 TeV,"
Phys. Rev. Lett. 94, 091802 (2005), arXiv.org:hep-ex/0410062.

DØ Collaboration, "A precision measurement of the mass of the top quark,"
Nature 429, 638 (2004), arXiv.org:hep-ex/0406031.

DØ Collaboration, "Improved W Boson Mass Measurement with the DØ Detector,"
Phys. Rev. D 66, 012001 (2002), arXiv.org:hep-ex/0204014.

DØ Collaboration, "Studies of WW and WZ Production and Limits on Anomalous WWgamma and WWZ Couplings,"
Phys. Rev. D 60 072002 (1999), arXiv.org:hep-ex/9905005.

Report of the Working Group on Precision Measurements, Proceedings of Physics at Run II: QCD and Weak Boson Physics Workshop, Batavia, Illinois, 4-6 March 1999, FERMILAB-CONF-01-282-E.

J. Ellison and J. Wudka, "Study of Trilinear Gauge Boson Couplings at the Tevatron Collider,"
Annual Review of Nuclear and Particle Science 48, 33 (1998), arXiv.org:hep-ex/9804322.

DØ Collaboration, "Limits on Anomalous WW γ and WWZ Couplings,"
Phys. Rev. D (Rapid Communications) 58, 031102 (1998), arXiv.org:hep-ex/9803017.

DØ Collaboration, "Studies of Gauge Boson Pair Production and Trilinear Couplings,"
Phys. Rev. D 56, 6742 (1997), arXiv.org:hep-ex/9704004.

DØ Collaboration, "Limits on Anomalous WW γ Couplings from p p → W γ + X Events at √ s = 1.8 TeV,"
Phys. Rev. Lett. 78, 3634 (1997), arXiv.org:hep-ex/9612002.