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A recent experimental paper measures a difference between the top quark and anti-top quark masses:

Fermilab-Pub-11-062-E, CDF Collaboration, Measurement of the mass difference between $t$ and $\bar{t}$ quarks

We present a direct measurement of the mass difference between $t$ and $\bar{t}$ quarks using $t\bar{t}$ candidate events in the lepton+jets channel, collected with the CDF II detector at Fermilab's 1.96 TeV Tevatron $p\bar{p}$ Collider. We make an event by event estimate of the mass difference to construct templates for top quark pair signal events and background events. The resulting mass difference distribution of data is compared to templates of signals and background using a maximum likelihood fit. From a sample corresponding to an integrated luminosity of 1/5.6 fb, we measure a mass difference, $\mathrm{M}_{t} - > \mathrm{M}_{\bar{t}}$ $= -3.3 \pm > 1.4(\textrm{stat}) \pm 1.0(\textrm{syst})$, approximately two standard deviations away from the CPT hypothesis of zero mass difference. This is the most precise measurement of a mass difference between $t$ and its $\bar{t}$ partner to date.

http://arxiv.org/abs/1103.2782

This seems to pile on to the recent evidence showing differences between the masses of the neutrinos and anti-neutrinos. But unlike neutrinos, quarks can't be Majorana spinors. So what theoretical explanations for this are possible?

Carl Brannen
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2 Answers2

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There is one simple, obvious, and almost certainly correct theoretical explanation: two-sigma effects show up all the time and, like most of them, this one is not real.

Matt Reece
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I suppose it will be a painful wait for the 5 sigma. Well, quarks are confined, so maybe it's OK for them to exhibit genuine CPT violation, whereas the neutral particles need renaming according to the mirror picture. But on the other hand, the quark braids have neutral strands, and if we mix (say for the proton) the uud, udu and duu sets, then there are enough neutral strands for component Majorana states.