PPD CMS Physics

CMS Physics
22 Feb 2011

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CMS Physics

Members of the PPD CMS group have interests in several areas of physics

High-energy electrons and photons

An important topic is the search for heavy resonances (generically called Z' and W') whose existence are predicted by a variety of theoretical models. RAL physicists are involved in preparations and analyses for these searches in channels where high-energy electrons are produced. RAL physicists have contributed to the publication of the most stringent limits set for these heavy resonances

The above figures show a dielectron invariant mass distribution (left) and the limit on the ratio of cross sections as a function of invariant mass

Quantum Black Holes

Exotic theories that postulate the existence of extra spatial dimensions, predict that microscopic black holes might be produced at the LHC. If we detect them, it would be a huge advance of our understanding of gravity. We take advantage of the distinct decay signatures of quantum black holes to search for these events and set limits on their production cross sections.

The above figures show the electon-muon invariant mass distribution (left) and the limit on the cross section for different numbers of extra dimentions n.

Long-lived particles

Most of the exotic particles that the LHC is searching for (Z', black holes etc) are predicted to decay almost immediately to other particles, which we observe in our detector. A few, such as the mysterious 'dark matter' particle may have very long lifetimes. We search for particles that fly part way through our detector before decaying to electrons dor muons.

The above figures show the distribution of transverse impact parameter significance |d₀|/σ_d for events in the signal region (|ΔΦ| < π/2) for dielectons (left) and dimuons (right)

Exotic boosted Z's

We look for massive exotic particles that decay to boosted Z bosons. The RAL group develops techniques to identify adjacent electron pairs in the detector from boosted Z decays that are no longer isolated.

The above figure shows the predicted and observed transverse momentum spectra of reconstructed Z boson candidates passing selection criteria

Exotic Higgs physics

With the discovery of the standard model Higgs there is further incentive to look at models which predict additional Higgs states. Specifically the NMSSM where we consider the case of a light Higgs that is highly boosted. We look at decay of the Higgs to two b-quarks. As the light Higgs is typically boosted, two overlapping b-jets are produced. At RAL we look at techniques to identify events with overlapping jets.

Top physics

With the largest number of top events being available at the LHC, we are able participate in precision measurements of spin correlation variables

The above figure shows the normalized differential cross section from data (points).

NeXT

We work closely with the NExT institute, further enhancing our connection between theorists and experimentalists.

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