Friday, May 25, 2012 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

BaBar: 3.4-sigma excess in tau-nu decays of B

This is just a simple link with a comment. The BaBar collaboration located at SLAC just published a preprint

Evidence for an excess of \(B \to D({}^*) \tau \nu\) decays
in which it announced the measurement of the ratio of branching ratios of decays of mesons\[

{\mathcal R}(D({}^*)) = \frac{B(B\to D({}^*)\tau^- \bar \nu_\tau)}{B(B\to D({}^*)\ell^-\bar\nu_\ell)}

\] in 426 inverse femtobarns of their data where \(\ell=e\) or \(\mu\). You may see that they measure the decays of the \(B\)-mesons to \(D\)-mesons or their antiparticles which also include a charged lepton and the corresponding neutrino in the final state.

They want to know how many of these decays choose the \(\tau\) lepton and its neutrino from the choice of three possible generations.

Their results are\[

{\mathcal R} (D) &= 0.440\pm 0.058\pm 0.042\\
{\mathcal R} (D^*) &= 0.332\pm 0.024\pm 0.018

\] which correspond to excesses by 2.0 and 2.7 standard deviations, respectively. When combined, the excess over the Standard Model predictions stands at 3.4 standard deviations. It's surely not a proof of new physics but it's intriguing.

Note that in August 2011, I mentioned a smaller excess, 1.8 sigma in the same ratio of branching ratios (PDF). It seems that the excess has grown stronger as you would expect if it were a sign of a real new thing.

The authors claim that the excess isn't compatible with the explanation involving an intermediate charged Higgs boson from a 2-Higgs model, type II 2HDM. It is not clear to me whether this may be interpreted as a disagreement with the MSSM in general as well.

The reason for the disagreement is that they may quantify the required \(\tan\beta/m_{H^+}\) that produces the excess (see Figure 2). When they do so, they get incompatible results from the decays with a \(D\) meson – \(0.45/\GeV\) or so – and from those including a \(D^*\) meson – \(0.75/\GeV\) or so (the error is of order \(0.05/\GeV\) in both cases).

Note that the BaBar's competitors at LHCb have announced some results on B decays that are compatible with the Standard Model as well as a new 3-sigma hint of new source of CP-violation that would go beyond the Standard Model.

In this experimental search for anomaly in meson decays, the signs of new physics start to emerge but it may still be too early to say that they're something else than fluke or human errors.

Old Town Square isn't a zoo

This is what happened to the 600-year-old Prague Astronomical Clock yesterday. A foreign chimp apparently wanted to impress those pretty attractive babes.

He broke and stole a piece of the stone, too. Police caught him but the media didn't tell us about his nationality. I kind of agree with many of the commenters that instead of terrorizing our citizens for minor traffic violations, they should pay a few cops as snipers who guard similar historical places 24 hours a day.

Update: He was a young American. He told the Czech cops that the reason why he climbed there was that there was no table saying "Don't Climb at the Astronomical Clock" around. ;-) TRF strongly advises U.S. readers not to climb at the Prague Astronomical Clock.

Add to Digg this Add to reddit

snail feedback (0) :