1. Harvard ATLAS Group @ CERN LHC
A general purpose detector designed to study proton-proton collisions at the CERN Large Hadron Collider (LHC) in Geneva, Switzerland.
The ATLAS Detector
These collisions occur at previously inaccessible energies:
7 TeV ( )
8 TeV (2012)
Layers of varying detector technology are used to measure the properties (charge, mass, momentum, type) of particles.
The Harvard ATLAS Group has participated in the construction, commissioning, calibration and operation of ATLAS, particularly for the muon spectrometer.
This information is used to analyze collision events, reconstructing intermediate particle states like Higgs bosons, top quarks or new particles associated with beyond the Standard Model (BSM) physics.
The Higgs Boson
Searches for Supersymmetry
Phys. Lett. B 726 (2013)
Harvard ATLAS is also working on searches for BSM physics, including a variety of analyses looking for evidence of superpartners of the SM gauge bosons (charginos and neutralinos).
Harvard ATLAS has been active in the analyses establishing the discovery of the Higgs boson, focusing on decays to electroweak gauge bosons.
ATLAS-CONF
ATLAS-CONF
The most sensitive searches look for W and Z bosons decaying to leptons, identifying Higgs boson decays through kinematic variables sensitive to the Higgs mass
Final states with two opposite sign leptons are queried for the presence of events with chargino pair-production, with each chargino decaying to a W boson and weakly interacting neutralino. The neutralino would escape detection, resulting in a signature of imbalanced momentum.
Di-lepton transverse mass distribution in electron+muon final state for
Four-lepton invariant mass
for
ATLAS-CONF
Higgs bosons can also be used as a probe of new physics. A search for chargino and neutralino associated production looks for Higgs coming from sparticle decays, followed by a decay to b-quarks.
Further Higgs Searches
Additional Higgs searches are ongoing, now looking for alternative Higgs production mechanisms and rarer Higgs decays.
Event Reconstruction Techniques
Many interesting processes contain one or more weakly interacting particles in the final state which escape detection. Without the ability to directly measure their momenta, these events are under-constrained and their kinematics (masses, decay angles) cannot be fully measured. Recursive Rest-frame Reconstruction is a new technique for systematically determining a basis of kinematic variables in these events.
ATLAS-CONF
Associated W/Z Higgs production: look for
with additional leptons (up).
Vector-boson fusion: look for
with two jets with a rapidity gap (right).
ATLAS-CONF
Higgs Spin/CP
Harvard ATLAS Group
Faculty
Melissa Franklin, Joao Guimaraes da Costa, John Huth, Masahiro Morii
The spin and quantum numbers of the Higgs are being measured in several final states. For
lepton decay angles
are used to test
possibilities using
likelihood ratios (q)
Postdocs
Pierluigi Catastini, Geraldine Conti, David Lopez Mateos, Christopher Rogan, Hugh Skottowe
Graduate Students
Stephen Chan, Brian Clark, Tomo Lazovich, Kevin Mercurio, William Spearman, Siyuan Sun, Emma Tolley, Tony Tong, Andy Yen
Phys. Rev. D 82 (2010)
Phys. Lett. B 726 (2013)
Christopher S. Rogan, on behalf of the Harvard ATLAS Group