Transcript CMS Ecal Laser Monitoring System

Harvard ATLAS Group @ CERN LHC
The ATLAS Detector
A general purpose detector designed to study proton-proton collisions at
the CERN Large Hadron Collider (LHC) in Geneva, Switzerland.
These collisions occur at
previously inaccessible
energies:
7 TeV (2010-11)
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.
https://twiki.cern.ch/twiki/bin/view/AtlasPublic/HiggsPublicResults
The Higgs Boson
Phys. Lett. B 726 (2013)
Harvard ATLAS has been active in the analyses
establishing the discovery of the Higgs boson,
focusing on decays to electroweak gauge
bosons.
https://twiki.cern.ch/twiki/bin/view/AtlasPublic/SupersymmetryPublicResults
Searches for Supersymmetry
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).
ATLAS-CONF-2013-049
ATLAS-CONF-2013-030
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
Di-lepton transverse mass
distribution in electron+muon final
state for
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.
Four-lepton invariant mass
for
Further Higgs Searches
Additional Higgs searches are ongoing, now looking for alternative Higgs
production mechanisms and rarer Higgs decays.
ATLAS-CONF-2013-093
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.
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.
(M
/ MR+1 )
i
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pp ® tt ® (bl+n) (bl n)
50 100 150 200 250 300
0.0016
0.0014
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Vector-boson fusion: look for
with two
jets with a rapidity gap (right).
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MR+1 [GeV]
Associated W/Z Higgs
production: look for
with additional leptons (up).
R+2
MadGraph GEN
s=8 TeV
ATLAS-CONF-2013-079
a.u.
ATLAS-CONF-2013-030
Higgs Spin/CP
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)
Faculty
Harvard ATLAS Group
Melissa Franklin, Joao Guimaraes da Costa, John Huth, Masahiro Morii
Postdocs
Pierluigi Catastini, Geraldine Conti, David Lopez Mateos,
Christopher Rogan, Hugh Skottowe
Graduate Students
Phys. Rev. D 82 (2010)
Phys. Lett. B 726 (2013)
Stephen Chan, Brian Clark, Tomo Lazovich, Kevin Mercurio,
William Spearman, Siyuan Sun, Emma Tolley, Tony Tong, Andy Yen
Christopher S. Rogan, on behalf of the Harvard ATLAS Group