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Anna Phan | USLHC | USA

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ICHEP 2012: Day One

Today was a jam packed day of parallel talks. There were six streams of talks: theory, heavy flavour (b, c, and s quark) physics, top quark measurements, supersymmetry searches, neutrino physics, and jet physics. I split my time between the various streams, starting the day in the heavy flavour physics stream, and moving to the supersymmetry, then the top quark physics and ending the day back in the heavy flavour physics stream. I thought I would (very briefly) highlight one talk in each session…

Firstly, Leptonic and semileptonic B decays with taus at BaBar by Guglielmo De Nardo of The University of Napoli and INFN. While he didn’t present any new results (they were presented earlier at FPCP), they are still worth highlighting, as they are in tension with the Standard Model. So what results did he present? The measurements of various branching ratios of leptonic and semileptonic B decays with taus, and their ratios. Specifically, R(D) = BF(B ->D τ ν) / BF(B -> D l ν) = and R(D(*)) = BF(B ->D(*) τ ν) / BF(B -> D(*) l ν) = 0.332 ± 0.024 ± 0.018 which in combination exceed the Standard Model predicted values by 3.4σ. Since the results had been presented before, instead of going into the analysis in detail, he presented the analysis within the 2HDM type II theory and concluded that that particular theory couldn’t account for the results.

Secondly, Searches for direct pair production of third generation squarks with the ATLAS detector by Martin White of The University of Melbourne. I’m highlighting this result because of personal reasons. I worked on one of the results presented in this talk during my PhD. Below is a nice summary of the supersymmetric top exclusions he presented. I don’t really want to go into detail about the plot, except to say that no supersymmetric tops have been seen by ATLAS in the six analyses summarised within it.

Thirdly, Tevatron and LHC top mass combinations by Frederic Deliot of The Centre d’Etudes de Saclay. I’m highlighting this talk to be fair to all the experiments. I wouldn’t want to select a CDF result in preference to a D0, ATLAS or CMS one for example. The top quark mass is an interesting measurement as it can be used, in combination with the W boson mass, to predict the Standard Model Higgs boson mass. And so the more precise the measurement of the top quark mass is, the more precise the prediction is. Also, now that we have found a Higgs-like particle at 125 GeV, we could see whether the three masses are consistent within the Standard Model or not. The Tevatron combination is m = 173.18 ± 0.56(stat) ± 0.75(syst) GeV and the LHC combination is m = 173.3 ± 0.5 (stat) ± 1.3 (syst) GeV. It is interesting to note that both values are systematically limited (the systematic error is larger than the statistical one) so it won’t be easy to improve the results.

And finally, Direct CP violation in charm at Belle by Byeong Rok Ko of Korea University. In doing this, I apologise to the BaBar, CDF and LHCb presentations on the same topic, but I choose the Belle presentation as it contained the HFAG combination of all the charm CP violation results.

I blogged about the observation of CP violation in the charm meson system by LHCb when the result was released last year. Since then, BaBar, Belle and CDF have all measured the same quantities and the plot above is the combination of all the results. Numerically, the average \(\Delta A_{CP} = (-0.74±0.15)\%\) and is ~4.9σ away from zero. Which means the LHCb result has been confirmed and we need a theoretical explanation and complementary measurements from other decays…

And that’s it for Day One of ICHEP 2012 for me. Until tomorrow everybody!

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