Result

Collision events in the figure above are arranged according to degree of momentum imbalance: balanced events pile up on the left while unbalanced events are put on the right. One of the supersymmetric models that CMS ruled out is shown in yellow: if this model were true, the physicists would have observed twice as many unbalanced events (See figure 2 in the paper for details). Editor’s note: This is the first CMS Result written by Jim Pivarski, a CMS collaborator….

In the telephone game a message is garbled by changes in how it is repeated. Today’s article describes how we defeat a similar subatomic process using the world’s largest collection of top quarks. When I was young, a bunch of us would play the telephone game. In this game, a person would whisper a message to someone. That person would whisper it to someone else and, after a series of whispers, we’d compare what was the last person heard to…

In the insert figure, the measured top quark mass is shown at the bottom of the curve. In the larger image, the blue points show the data from the most recent measurement and the red lines show how well the data fit with a prediction of the signal and background combined. The black line shows the predicted background only. The top quark is the heaviest currently known elementary particle, with a mass nearly equal to that of a gold atom….

Particle collisions that look like this are used to search for leptoquarks. This figure is specifically for (electron + up/down quark) type collisions. Leptoquarks are theoretical particles. While there are theories that suggest these particles are real, we live in a world full of leptons (the electron is the most familiar example) and quarks (which are generally found in the nucleus of an atom.) We don’t understand why there are two types of particles (quarks and leptons) and we have…

Sand fairies redux

The top figure shows the normal production and decay processes of top quarks. In the bottom figure, the magenta section shows a FCNC process. This type of event is forbidden in the Standard Model and, if it were observed, would require rewriting of the books. In an earlier article, I compared the search for something that the Standard Model deems impossible to searching for tiny fairies in the sand on a beach. I also promised that this wouldn’t be the…

Some of the Feynman diagrams that contribute to the decay of a D0 (a meson composed of a charm quark and up anti-quark) to a pair of muons. The loops (square or triangle) in the diagrams are an indication that the processes they represent are suppressed. This decay has no processes without loops in the Standard Model. But new physics can have processes without loops and these can dominate over the Standard Model contribution, so this decay becomes an interesting…

The search for the Higgs boson is like a jigsaw puzzle. Just as no single piece reveals the whole picture, no single analysis will find the Higgs boson. Without all pieces, the picture is incomplete. In the 1960s, a bevy of physicists pieced together our current understanding of the electromagnetic and weak forces. The first task was to show how those forces were two facets of an underlying single force, called the electroweak force. The second task they accomplished showed…

The plot shows four different measured cross sections (points) compared to the hashed lines, which are the theoretical expectation. The top three are control samples that are in excellent agreement with theory. The lower most point is the presented measurement that is also in excellent agreement with Standard Model expectation. Physicists test the Standard Model to see if the pieces in place, or those they think might be missing, can tell them anything new. One important test is to measure…

One theoretical speculation about why gravity is so much weaker than the other known forces postulates the existence of additional dimensions beyond the familiar three. If this idea is true, then the LHC might be able to create microscopic black holes. If observed, they would have a major impact on our understanding of the laws of physics. According to the laws of physics as we currently understand them, it is impossible to make microscopic black holes at the LHC. There…

The W’ boson is a hypothetical, much more massive, cousin of the W boson. This article describes a new search for it. In the late 1960s, theorists were able to mathematically show that the electromagnetic and weak nuclear forces were actually two facets of a single common force, now called the electroweak force. This new theory postulated two new particles called the W and Z bosons. The theory was vindicated in 1983 with the discovery of both of them by…