Prof. Gritsan's research is focussed on the observation and study of the
new form of matter-energy, such as the Higgs boson.
Together with his colleagues on the CMS experiment on the Large Hadron Collider,
he worked on the Higgs boson discovery
study of its spin-parity quantum numbers
measurement of its production mechanism and deeper understanding of its properties
constraints on the Higgs boson width
comprehensive study of the Higgs boson quantum numbers and anomalous interactions
and taking a number of these measurements to a new level with Run II data from LHC
He worked with a group of experts to develop new methods
(also known as MELA technique and JHU generator)
for the angular and statistical analysis of the decay products and associated particles of the Higgs boson.
Read more about this effort.
All the above measurements point to the property of vacuum, which is filled
with the all-penetrating Higgs field, where the boson is simply its excitation
created in the laboratory
Nobel Prize Physics-2013).
Our past, present, and future depend on the properties
of this field, and we are still to understand all the implications of this grand
discovery and to study in detail this new form of matter-energy never known before.
However, it is likely that the discovered Higgs boson is just a tip of an iceberg
of new states of matter-energy. The undiscovered symmetries of nature which unify
the fundamental forces and particles, the puzzle of dark matter and energy, and
the apparent lack of antimatter in our Universe, all these mysteries point to
something new that could be uncovered at an unprecedented energy scale with the
Large Hadron Collider. Prof. Gritsan's team also pursues both direct searches
for such new states and indirect constraints through precision measurements of the
known states, such as the Higgs boson [1-18] and Z boson
Prior to LHC, direct access to new fundamental particles (such as the Higgs boson
or new states) was beyond the energy reach of operating accelerators.
Gritsan worked with the heavy flavor quarks, such as the "beauty" or b quark,
which were produced in electron-positron annihilations at the BABAR and CLEO
experiments. He was looking for new ways to search for new fundamental particles
that could exist briefly as heavy virtual states in the decays of b quarks.
The Heisenberg uncertainty principle in quantum physics allows such non-trivial
effects, called "penguin" loops, to occur for short instants. On CLEO, he discovered
this process as part of his Ph.D. research. It was the first observation of the
gluonic penguin transition b->s+gluon. On the BABAR experiment, he discovered
a surprisingly large transverse polarization of the vector mesons produced in a penguin decay,
which contradicted all expectations and may become evidence for new particles
and interactions, and took this approach of angular analysis to a new level
Another important aspect of heavy quark decays is that they include the only known
example of Charge-Parity (CP) reversal symmetry violation, which is equivalent
to Time-reversal symmetry violation and which follows from the Cabibbo-Kobayashi-Maskawa
(CKM) quark-mixing model
Nobel Prize Physics-2008).
CP violation is necessary to produce our matter-dominated
Universe and has important cosmological consequences. The Standard Model mechanism
that leads to CP violation is represented graphically by the so-called "Unitarity Triangle."
On the BABAR experiment, Gritsan discovered the B decays to two rho mesons, showing
that an analysis of this system could determine one of the angles alpha of the "Triangle"
precisely by constraining penguin effects
Prof. Gritsan is also an expert on various aspects of high-energy physics detectors,
such as silicon tracking detectors, electromagnetic calorimeters, tracking drift chambers,
triggers. He had been leading the tracking and silicon detector alignment groups at the BARAR
and CMS experiments
An essential element of the LHC program is the alignment of thousands
of silicon detectors that track the particles' paths which must be understood to micron
precision. Prof. Gritsan led the CMS team to successful commissioning of its silicon tracker
alignment at the time of data-taking startup
and was an editor of the very first CMS publication
Further references may be found in