download report - Sapienza

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