Particle playground smaller particles
Particles that fly even a few millimeters before decaying would leave unusual signatures: kinked or offset tracks, or jets that emerge gradually instead of all at once.
Like an onion, each detector contains layers of subsystems-trackers that trace charged particles, calorimeters that measure particle energies, and chambers that detect penetrating and particularly handy particles called muons-all arrayed around a central point where the accelerator's proton beams collide. Long-lived particles also emerge in "dark sector" theories that envision undetectable particles that interact with ordinary matter only through "porthole" particles, such as a dark photon that every so often would replace an ordinary photon in a particle interaction.ĬMS and ATLAS, however, were designed to detect particles that decay instantaneously. For example, a scheme called supersymmetry posits that every standard model particle has a heavier superpartner, some of which could be long-lived. "Almost all the frameworks for beyond-the-standard-model physics predict the existence of long-lived particles," she says. That idea is more than a shot in the dark, says Giovanna Cottin, a theorist at National Taiwan University in Taipei.
#Particle playground smaller particles zip
Long-lived particles, however, would zip through part or all of the detector before decaying. That's how CMS and its rival detector, A Toroidal LHC Apparatus (ATLAS), spotted the Higgs, which in a trillionth of a nanosecond can decay into, among other things, a pair of photons or two "jets" of lighter particles. "We haven't found any new physics with the assumptions we started with, so maybe we need to change the assumptions," says Juliette Alimena, a physicist at Ohio State University in Columbus who works with the Compact Muon Solenoid (CMS), one of the two main particle detectors fed by the LHC.įor decades, physicists have relied on a simple strategy to look for new particles: Smash together protons or electrons at ever-higher energies to produce heavy new particles and watch them decay instantly into lighter, familiar particles within the huge, barrel-shaped detectors. But the LHC has yet to blast out anything beyond the standard model. In 2012, experimenters at the $5 billion LHC discovered the Higgs boson, the last particle predicted by the standard model of particles and forces, and the key to explaining how fundamental particles get their masses. They argue the LHC's next run should emphasize such searches, and some are calling for new detectors that could sniff out the fugitive particles.
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Next week, they will gather at the LHC's home, CERN, the European particle physics laboratory near Geneva, Switzerland, to discuss how to capture them. Are new particles materializing right under physicists' noses and going unnoticed? The world's great atom smasher, the Large Hadron Collider (LHC), could be making long-lived particles that slip through its detectors, some researchers say.