Rencontres de Moriond QCD 2012: Direct and indirect searches make the whole picture

Tuesday saw presentations on heavy flavour physics and heavy-ion physics. Among the highlights were an updated scenario for supersymmetry and the latest results on the properties of the quark-gluon plasma.


The green area shows the mass region where supersymmetry (in these graphs, only one specific model is shown) is still allowed. The graph on top is based on results preceding Moriond; the one on the bottom includes new results presented at Moriond. The black and red lines represent the exclusion limits coming from direct searches (CMS data used in this graph) before and after Moriond. The yellow exclusion regions refer to Bs -> μ+μ LHCb results.

The morning’s presentations stressed that, although current theories can naturally explain recent results in heavy flavour physics in a plausible and consistent picture that remains within the Standard Model, new physics contributions have not been excluded. Indeed, if new physics is above LHC reach, flavour phenomena could be the only way to see it.

Nazila Mahmoudi, a CERN theorist, brought together information from direct searches (direct observations of new physics particles, essentially what CMS and ATLAS do) with information from indirect searches (observations of the effects that new particles could have on known phenomena, essentially what LHCb does). As shown in the images, these separate searches are complementary.

The results presented at Moriond are redefining supersymmetry’s allowed area. In the near future, new data expected from both direct and indirect searches, may reveal new physics beyond the Standard Model or allow the HEP community to work out the exclusion regions for a wider variety of new physics and in a more model-independent way.

In the afternoon, presentations focussed on heavy-ion physics. CMS and ATLAS presented their latest results on the properties of the quark-gluon plasma (QGP) using a technique known as “flow measurement”. This technique allows physicists to probe the hydrodynamic properties of the QGP and study the effects of fluctuations in initial conditions. It also provides them with a quantitative estimate of path length dependence of particle energy loss in the QGP medium.

ALICE presented the first published results of their investigations of energy loss by D mesons in the QGP medium. Low energy experiments at RHIC had previously found this energy loss did not depend on the nature (and mass) of the particle, as predicted in theory. However, ALICE results have indicated that it might.

by CERN Bulletin