# Synopsis: Deciphering a bump in the spectrum

Measurements at Fermilab hint at a new particle—but not the one they were looking to find.

An important method for searching for new particles is to look for resonances in the energy spectrum of pairs of charged leptons and their antiparticles emitted from high-energy collisions. Such a resonance can be an indication that a particle has decayed into a lepton-antilepton pair. Lepton resonances generally have a cleaner experimental signature and lower background than similar resonances for hadronic final states. This technique has provided evidence of such particles as the $J/\psi$, the $\mathrm{Υ}$, and the $Z$ boson.

In a paper appearing in Physical Review Letters, the CDF (Collider Detector at Fermilab) Collaboration reports searches for resonances in electron-positron pairs created by high-energy proton-antiproton collisions. Their results place significant limits on particles hypothesized in several popular theories that go beyond the standard model, including a prediction for the graviton and various types of $Z\prime$ bosons (new gauge bosons that correspond to additional symmetries). They do find a tantalizing indication of a resonance at around $240\phantom{\rule{0.333em}{0ex}}\text{GeV}/{c}^{2}$: a “bump” or excess of events in that part of the spectrum. The statistical significance is somewhat weak and not strong enough to establish the existence of a particle, but it is strong enough to motivate further searches in this region to confirm or refute the existence of an as yet unknown particle. Although this experiment sees no evidence of the hypothetical particles it searched for, if a new particle is eventually confirmed, theorists will no doubt be scrambling to explain it. – Stanley Brown

### Announcements

More Announcements »

## Subject Areas

Particles and Fields

Mesoscopics

Magnetism

## Related Articles

Astrophysics

### Synopsis: Neutrinos from the North

Using Earth as a neutrino filter, the IceCube neutrino experiment strengthens its claim that it has detected neutrinos from powerful astrophysical accelerators outside our Galaxy. Read More »

Particles and Fields

### Viewpoint: Deciphering Gamma Rays from a Dwarf Galaxy

Are gamma rays from a nearby dwarf galaxy a beacon of dark matter or a false alarm? Read More »

Particles and Fields

### Viewpoint: Elusive Pentaquark Comes into View

A new type of particle containing five quarks has been observed by the LHCb experiment. Read More »