Search for Rare Particle Decay Comes Up Short

Aug 01, 2006 feature
BaBar detector image
BaBar detector image. Credit: Berkeley Lab

Based on work performed at a large particle detector known as the BaBaR experiment, scientists announced recently that they do not see evidence to support theoretical predictions that an extremely rare particle decay — the decay of the neutral “B” particle into a negative “tau” particle and its antiparticle, the positive tau — occurs often enough to be measured.

The search was initiated based on additions to the “Standard Model,” the broad physics theory that describes fundamental particles, how they interact, and how they bind together to form composite particles. The B particle, for example, is a member of a class of composite particles known as “mesons,” which consist of one quark — the “building block” of all other particles — and one antiquark. The tau, a fundamental, non-composite particle, can be thought of as a very heavy electron.

The original Standard Model allows the B meson to decay into the tau pair, but at a rate so low as to be extremely difficult to measure. However, recent proposed extensions to the model predict that the decay should occur at a measurable rate, perhaps through the addition of unknown forces or particles. Enter the BaBaR experiment.

Located at the Stanford Linear Accelerator Center (SLAC) near Stanford University, BaBaR was built, ultimately, to determine why matter dominates the present-day universe, with very little antimatter leftover from the Big Bang. The detector is positioned around one section of a very large particle accelerator, where a beam of electrons and a beam of anti-electrons — i.e. positrons — are directed in opposite circular paths at nearly the speed of light by a large ring of very powerful magnets.

The collisions produce B and anti-B mesons, which in turn decay into a shower of other particles. These particles pass into the BABAR detector, which records their trajectories, energies, and electric charge. From this data, scientists in the BABAR collaboration (about 600 physicists from more than 70 institutions worldwide) can work backward to determine how the B mesons decay.

“Our results show, at the 90 percent confidence level, that this decay occurs so infrequently as to be undetectable by BaBar. Our result is important because of what we did not find, since this places limits of possible new physics beyond the Standard Model,” said the experiment’s spokesperson, SLAC physicist David MacFarlane, to PhysOrg.com.

BaBar physicists analyzed the collisions by calculating the “branching ratio” for this particular decay. In essence, the size of this number tells them how often the decay occurs versus other possible decay paths for the B meson. The branching ratio for the neutral B-to-tau/anti-tau decay was determined to be — at the largest — 0.0041.

This research was published in the June 23, 2006, online edition of Physical Review Letters.

On the Net: www.slac.stanford.edu/BFROOT/

By Laura Mgrdichian, Copyright 2006 PhysOrg.com

Explore further: Soft, energy-efficient robotic wings

Related Stories

Theory of the strong interaction verified

4 hours ago

The fact that the neutron is slightly more massive than the proton is the reason why atomic nuclei have exactly those properties that make our world and ultimately our existence possible. Eighty years after ...

Recreating the heart of a star on Earth

Mar 24, 2015

By recreating the extreme conditions similar to those found half-way into the Sun in a thin metal foil, Oxford University researchers have captured crucial information about how electrons and ions interact in a unique state ...

Getting a critical edge on plutonium identification

Mar 24, 2015

A collaboration between NIST scientists and colleagues at Los Alamos National Laboratory (LANL) has resulted in a new kind of sensor that can be used to investigate the telltale isotopic composition of plutonium ...

LHCb's new analysis confirms old puzzle

Mar 23, 2015

Today, at the 50th Moriond Electroweak conference (link) (La Thuile, Italy), LHCb physicists presented their latest analysis of the rare B → K*μμ decay. The new results show deviations from Standard Mode ...

Explainer: What are fundamental particles?

Mar 20, 2015

It is often claimed that the Ancient Greeks were the first to identify objects that have no size, yet are able to build up the world around us through their interactions. And as we are able to observe th ...

Researchers study fluctuations in solar radiation

Mar 18, 2015

The Sun is the Earth's principal source of energy and climate driver. Yet sometimes it sends more light to the Earth than other times. Astronomers working with Natalie Krivova at the Max Planck Institute ...

Recommended for you

Soft, energy-efficient robotic wings

16 hours ago

Dielectric elastomers are novel materials for making actuators or motors with soft and lightweight properties that can undergo large active deformations with high-energy conversion efficiencies. This has ...

Super sensitive measurement of magnetic fields

Mar 30, 2015

There are electrical signals in the nervous system, the brain and throughout the human body and there are tiny magnetic fields associated with these signals that could be important for medical science. Researchers ...

New idea for Dyson sphere proposed

Mar 30, 2015

(Phys.org)—A pair of Turkish space scientists with Bogazici University has proposed that researchers looking for the existence of Dyson spheres might be looking at the wrong objects. İbrahim Semiz and ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.