High-energy physics

LLNL scientists are using innovative techniques to find new particles.

Searching for new particles within the Standard Model

The discovery of the Higgs boson particle answered a major question of the Standard Model of particle physics: the mechanism for electroweak symmetry breaking. However, there are still many outstanding questions about the structure of the Standard Model itself, as well as observational phenomena that cannot be explained by the model.

We aim to answer some of these questions by using innovative techniques to find new particles from proton–proton collisions.

Our technique provides clean signals

We focus on finding new physics in events where two protons exchange two photons, which then fuse to produce new fundamental particles.

To find these events, we measure the outgoing protons using detectors 200 meters away from the photon fusion interaction, and then we measure the decay products of the new particle using the Compact Muon Solenoid (CMS) detector.

This signal is much cleaner than the typical events analyzed at the Large Hadron Collider because the protons stay intact and there is not a mess of additional particles from the breakup of the protons.

With the additional information from the proton detectors, the clean signal from the photon fusion event can be deciphered from the much higher cross-section backgrounds where the protons break up.

Featured results

Our results outlined in A.M. Sirunyan, 2018, represent the first observation of proton-tagged gamma–gamma collisions at the electroweak scale. The data demonstrates the excellent performance of the Precision Proton Spectrometer proton-taggers and its potential for high-mass exclusive (proton-tagged) measurements.

Our analysis in V. Khachatryan, 2016, provided the first evidence for gamma–gamma→W⁺W^- production. In the signal region, 13 (2) events are observed over an expected background of 3.9+/-0.6 (0.84+/-0.15) events for 8 (7) TeV. In addition, the most stringent upper limits to date on various anomalous quartic gauge coupling operators were derived from the measured dilepton transverse momentum spectrum.