Studies in Charm Physics

University Of Rochester, Rochester NY

Investigators

Abstract

The Standard Model (SM) has been successful at describing all relevant experimental phenomena and, thus, has been generally accepted as the fundamental theory of elementary particle physics. Despite its success, the SM leaves many unanswered questions. These can be classified into two main categories: one for subjects related to possible new physics at unexplored energy scales and the other for physics mostly related to Quantum Chromodynamics (QCD), the fundamental theory of the strong interactions. The SM describes particle physics up to energies of around 100 GeV (Giga electron Volts). It is expected that new particles and new interactions will appear at some higher energy scale, say 1 TeV (Tera electron Volts) . Those new particles and new interactions are presumably needed to solve some inconsistencies within the SM and for the ultimate unification of all interactions. Such physics issues all belong to the first category, and will be addressed by experiments at the LHC, which will start operation in 2008. The second category of unanswered questions includes those requiring QCD. QCD, as the fundamental theory of the strong interactions, is well tested at short distances, but at long distances so-called nonperturbative effects become important and these are not well understood. These effects are very basic to the field of particle physics and include e.g., the structure of hadrons (particles with strong interactions) and the spectrum of hadronic states. Lower energy facilities with high luminosity can address these questions. Among these, the Beijing Electron Positron Collider II (BEPCII), which will operate in the 2 GeV to 4.6 GeV energy range, will be an important contributor. This is because it spans the energy range where both short-distance and long-distance effects can be probed. BES III is a general-purpose detector based at the BEPCII e+e- collider in China. BEPCII has a 100x improvement in its luminosity over its predecessor, There has also recently been a renewal of interest in the subjects of hadron spectroscopy and charm quark physics. This renaissance has been driven in part by experimental reports of charm particle mixing and the discovery of additional narrow-width charm states, plus a plethora of charmonium-like states at the B meson factories. At the same time, a computer intensive technique called lattice Quantum Chromodynamics (QCD) is now coming of age, and we are entering a new era when precise, quantitative predictions from lattice QCD can be tested against experimental measurements. The BES-III experiment at the BEPCII collider in Beijing, which started operation in summer 2008, will accumulate huge data samples relating to these topics. Coupled with currently available results from the (closing) CLEO-c experiment, BES-III will make it possible to study in detail, and with unprecedented high precision, light hadron spectroscopy in the decays of charmonium states and charmed mesons. Many high precision measurements will be accomplished. BES-III analyses are likely to be essential in deciding if recently observed signs of charm mixing are actually due to new physics or not. And precision lattice QCD calculations provide the opportunity to probe the charged Higgs sector in some mass ranges that will be inaccessible to the LHC.