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Anna Phan | USLHC | USA

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ICHEP 2012: Day Three

Today was another day of parallel talks. There was again six streams of talks where again the topics in each stream varied throughout the day. I would have loved to spend the day in the Higgs stream, listening to the new ATLAS, CMS, CDF and D0 results, however, I spent the day in the heavy flavour physics stream. This was because my talk was scheduled in this stream.


Today, on behalf of the LHCb collaboration, I presented measurements of \(B_s^0\) meson lifetimes. And because I can, I’ll summarise the results I presented for you all. *winks*

First off, I need to give you a bit of background regarding the \(B_s^0\) meson. As the \(B_s^0\) meson is neutral, it can transform, via the box Feynman diagrams on the left to its antimatter partner, the \(\overline{B}_s^0\) meson, and back again. If we look at and manipulate the equations governing the mixing and decay of the \(B_s^0-\overline{B}_s^0\) meson system we find that there are two \(B_s^0\) mass eigenstates, \(B_{s,H}^0\) and \(B_{s,L}^0\), with two different lifetimes, \(\tau_H = 1 / \Gamma_H\) and \(\tau_L = \Gamma_l\) with \(\Delta\Gamma_s = \Gamma_L – \Gamma_H\) and \(\Gamma_s = (\Gamma_L+\Gamma_H)/2\).

We can measure \(\Delta\Gamma_s\) and \(\Gamma_s\) through the analysis of the decay \(B_s^0 \to J/\psi \phi\) and access \(\tau_H\) and \(\tau_L\) from the measurement of the \(B_s^0\) lifetime in \(B_s^0 \to J/\psi f_0(980)\) and \(B_s^0 \to K^+K^-\) decays:

\(\Gamma_s = 0.6580 \pm 0.0054 \pm 0.0066\, {\rm ps}^{−1}\)
\(\Delta\Gamma_s = 0.116 \pm 0.018 \pm 0.006 \,{\rm ps}^{−1}\)
\(\tau_H \simeq \tau_{J/\psi f_0} = 1.700 \pm 0.040 \pm 0.026 \,{\rm ps}\)
\(\tau_L \simeq \tau_{KK} = 1.468 \pm 0.046 \pm 0.006 \,{\rm ps}\)

These results can all be shown as a function of \(\Delta\Gamma_s\) and \(\Gamma_s\) like below. You can see that all the results are fairly consistent, and the experimental combination overlaps all three individual experimental results. It is also consistent with the theoretical prediction of \(\Delta\Gamma_s\).

The measurement of \(B_s^0\) lifetimes and the information they provide regarding \(\Delta\Gamma_s\) is interesting as the value of \(\Delta\Gamma_s\) can be affected by physics beyond the Standard Model…

And that’s it for Day Three of ICHEP 2012 for me. Until Monday everybody!

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