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Scientific Report 2007-2009<br />
Particle physics<br />
this effect influences the interaction between any pair of quarks. The three couplings between the<br />
u, c and t quarks with the b are complex numbers that add to zero and that therefore can be<br />
represented as a triangle, called ”Unitarity Triangle”. All the numerous measurements sensitive<br />
to CP violation contribute to determining the apex of such a triangle (see Fig. 2).<br />
The first system where CP violation was observed is the kaon mesons system. While the first<br />
experiments are dated in the ’60s, the latest and more accurate measurements of CP violation were<br />
performed by the NA48/2 experiment [P18]. Similarly the KLOE experiment has recently measured<br />
with unprecedented accuracy the absolute value of the element of the CKM matrix governing<br />
the coupling between the s and u quark, thus yielding the currently most accurate measurement of<br />
the mixing matrix [P19]. Unfortunately the Kaon system suffers from large uncertainties in the understanding<br />
of the impact of strong interactions. In this respect the most sensitive system is constituted<br />
by the B meson. Members of this Department have worked on several aspects of such effects<br />
within BaBar (see [P12, P13, P14]) and CDF [P9]. Fig. 2, realized with a strong effort within this<br />
Department in phenomenological interpretation of a large number of data [T3], shows the combination<br />
of all available measurements. The good agreement between different measurements is a strong<br />
test of the Standard Model and a clear proof of the sensitivity of the data to possible new physics.<br />
Any new particle is extremely likely to alter at least one of the observables that are combined in the<br />
fit. It becomes therefore critical, even in the era of the Energy Frontier, to perform high precision<br />
measurements of the parameters of the ”Unitarity Triangle”. This is the goal of the LHCb experiment<br />
[P7] and is the basis of the proposal of a ultra-high luminosity machine producing B quarks<br />
(SuperB) which is being planned in Frascati, in close liaison with a group in this Department.<br />
Finally the extremely large data sample<br />
collected to perform these precision<br />
measurement has been exploited also to<br />
investigate the spectroscopy of hadrons<br />
(states held together by strong interactions)<br />
with the appearance of new unexpected<br />
states. These states do not seem<br />
to fit with standard mesons and are indeed<br />
good candidates to belong to a new<br />
state of matter made of four quarks or<br />
two quarks and a meson. Such states<br />
are investigated in the low mass range<br />
[P20] and for heavy flavours [P16, P21,<br />
T1].<br />
Figure 4: KLOE results for |V us | 2 , |V us /V ud | 2 , and |V ud | 2 from β<br />
decay measurements, shown as 2σ bands. The ellipse is 1σ contour<br />
from a fit. .<br />
1.2 Astro-Particle Physics<br />
The so-called Astro-Particle Physics is<br />
a field in great expansion. It includes<br />
the studies on neutrino properties, the<br />
sector where the most important discovery of the last decade comes from in the form of the<br />
demonstration of their massive nature. Search for the Dark Matter is the second pillar of this<br />
field. A fundamental role is played by the projects aiming at the detection of gravitational waves<br />
(GW). Our country is particularly blessed by the opportunity of having a superb facility, nearby<br />
located under Gran Sasso mountains for low background, low radioactivity experiments and by<br />
the interferometer built in the plain of Cascina near Pisa for GW search.<br />
<strong>Sapienza</strong> Università di Roma 105 Dipartimento di Fisica