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Quarks are gregarious particles, but only within limits. Protons, neutrons, and other baryons are made up of three quarks, while unstable particles called mesons are composed of a quark-antiquark pair. (An antiquark is the antimatter partner to a quark.) Nothing with more than three quarks in a single particle has been found in nature, at least under ordinary circumstances.

Since 2008, however, researchers at CERN in Europe and at Belle in Japan found hints of a four-quark particle. Those hints were confirmed today by physicists at the LHCb experiment at CERN. To discover and characterize the particle, researchers sifted through 25,000 decays of mesons resulting from more than 180 trillion collisions at the Large Hadron Collider. This object they studied, known affectionately as Z(4430)^-, has provided the first unambiguous measurement of a four-quark particle; earlier experiments also provided hints about another candidate, the Z_c(3900)⁺.

With that much data, physicists were able to determine the composition of the Z(4430)^-: it consists of a charm quark, a charm anti-quark, a down quark, and an up antiquark. The "4430" part of the name indicates its mass: 4,430 million electron-volts, which a little more than four times the mass of a proton (938 million electron volts). The combination of quarks gives the Z(4430)^- a negative electric charge, hence the "-" in the label. The particle is highly unstable, so none of them are expected to be seen in nature.

Los Alamos National Lab

As recent disclosures have reminded us, security is not a simple matter. Most will tell you that the weak link in the chain is us: we simply don't use good security habits. But we're only one part of a number of issues. Although passwords are weaker than they should be, a strong password used on a weak system won't be much help. There is still a lot of necessary work being done to ensure that communication between parties is strongly encrypted.

One option that has received waves of attention over the last ten years is quantum key distribution (QKD). Despite its promise of absolute security, QKD has many practical difficulties that have limited it to niche applications. Now, in a nice bit of work, researchers have shown how to implement QKD for handheld devices.

A quick recap of QKD

Light has a property called polarization, which is measured with respect to a reference frame. So, for instance, horizontally polarized light has its electric field aligned with the ground, while vertically polarized light has its electric field aligned perpendicular to the ground. In between, we can have diagonal and anti-diagonal polarized light.

After twelve-and-a-half years, the curtain fell on Windows XP yesterday: the aged operating system transitioned out of extended support and into a long, dark, unsupported and unpatched twilight. Bespoke patches will still be made for those customers willing to pay enough money—mainly governments and large corporations with significant Windows XP installed bases—but for most of the world, XP is now officially a dead operating system.

Windows XP wasn't the only thing to be shuffled into unsupported purgatory yesterday, though. Also included in the group of applications to be dumped down the memory hole is the browser that everyone loves to hate: Internet Explorer 6.

For all its terribleness now, IE6 accomplished a pretty stunning set of achievements. It's the browser that definitively killed Netscape Navigator and ended the first great "Web Browser War." At its height, IE6 was the browser of choice for ninety percent of the Web's users. Its crushing market dominance also ensured that businesses used it internally as well as externally, developing ActiveX-based Web applications for it and further perpetuating Microsoft's ecosystem lock-in.