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Scientific Report 2007-2009<br />
Particle physics<br />
P11. Heavy Flavor and Spectroscopy with the CDF experiment<br />
The Tevatron collider at Fermilab provides protonantiproton<br />
collisions at √ s = 1.96 TeV. The integrated<br />
luminosity collected until the end of 2009 was about 6<br />
fb −1 corresponding to approximately 3 · 10 10 b-quarks<br />
produced in the acceptance of the CDF detector. The b-<br />
quarks hadronize in all sort of b-mesons and b-baryons,<br />
in contrast to e + e − machines operating at the Y(4S)<br />
which can only study B + and B d mesons, allowing thus<br />
the discovery and detailed spectroscopy of previously unseen<br />
b-baryons or other exotic states and the search for<br />
rare decays of the Bs 0 meson. Moreover the sophisticated<br />
trigger capability of the CDF detector allowed for<br />
the first time the online selection of events characterized<br />
by the presence of charged particles that do not point<br />
back to the primary collision point, a clear signature of<br />
the long lifetime of b-hadrons. The latter option has<br />
been made possible by the development of the Silicon<br />
Vertex Trigger (SVT), a custom hardware processor for<br />
fast pattern reconstruction and track fitting in the silicon<br />
vertex detectors (< 20 µs) at the trigger level. The CDF<br />
group in Roma gave important contributions to the SVT<br />
deployment and operation. The sample collected by the<br />
SVT allowed the observation of several hadronic decay<br />
modes of the Bs 0 meson, like Bs 0 → ϕϕ that has been discovered<br />
by a team from Roma. Subsequently a detailed<br />
investigation of the polarization amplitudes in this channel<br />
has been performed in order to check the calculations<br />
made in the QCDf and pQCD theoretical frameworks.<br />
Other two body decay modes of the Bs 0 meson have been<br />
Candidates per 20 MeV/c<br />
2<br />
1000<br />
800<br />
600<br />
400<br />
200<br />
-1<br />
CDF Run II Preliminary L =1 fb<br />
int<br />
0<br />
B → K + π -<br />
0<br />
B → K - π +<br />
0 0 + -<br />
Bs/Bs<br />
→ K K<br />
0 0<br />
+ -<br />
B /B → π π<br />
0<br />
0 + -<br />
B → K - s π + +Bs<br />
→ K π<br />
0 - 0<br />
Λ → pπ + Λ → pπ +<br />
b<br />
b<br />
0 - 0 +<br />
Λb<br />
→ pK + Λb<br />
→ pK<br />
Combinatorial backg.<br />
Three-body B decays<br />
0<br />
5 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8<br />
2<br />
Invariant ππ-mass[GeV/c<br />
]<br />
Figure 1: Invariant mass of two body B 0 d and B 0 s candidates<br />
showing the overlapping mass distribution of the four<br />
identified decay modes.<br />
observed for the first time [1]. The Bs 0 → K + K − and<br />
Bs 0 → K − π + signals, shown in Figure 1, have to be disentangled<br />
from the overlapping two body modes of the<br />
B d meson by a multidimensional fit to the mass, kinematics<br />
and specific ionization of the two tracks. The first<br />
measurement of direct CP violation in the B s system has<br />
been performed using the Bs 0 → K − π + decay.<br />
The rare decay mode Bs<br />
0 → µ + µ − has a very suppressed<br />
Branching Ratio (BR) in the Standard Model<br />
due to helicity suppression. However, in many theories<br />
beyond the Standard Model this suppression is lifted and<br />
BR larger by factors as large as 100 are predicted. The<br />
CDF collaboration published[2] the most stringent upper<br />
limit on the Bs 0 → µ + µ − BR (< 4.3 · 10 −8 @95%C.L.),<br />
severely constraining models of new physics.<br />
The large yield of B-meson and the excellent momentum<br />
resolution provided by the central drift chamber<br />
and silicon detectors has allowed CDF to study<br />
in detail the resonance structure of the rare decay<br />
B + → J/ψϕK + [3]. In particular evidence for a near<br />
threshold resonant structure in the J/ψϕ mass spectrum<br />
has been shown, Figure 2. The significance of<br />
the peak is 3.8σ and its mass and width have been<br />
measured M = 4143.0 ± 2.9(stat.) ± 1.2(syst.) MeV,<br />
Γ = 11.7 +8.3<br />
−5.0 (stat.) ± 3.7(syst.) MeV. Awaiting further<br />
confirmation speculations about this new exotic state include<br />
a DsD ∗ s ∗ molecule or a 4 quark [cs][¯c¯s].<br />
2<br />
Candidates/10 MeV/c<br />
CDF II Preliminary, 2.7 fb<br />
9<br />
8<br />
7<br />
6<br />
5<br />
4<br />
3<br />
2<br />
1<br />
0<br />
1 1.1 1.2 1.3 1.4 1.5<br />
2<br />
∆M (GeV/c )<br />
Figure 2: Invariant mass of J/ψϕ system (minus J/ψ mass)<br />
in B + → J/ψϕK + decays showing the Y(4140) resonance<br />
over a phase space background.<br />
CDF has discovered in the last three years several<br />
new b-baryons. In particular the Σ ± b<br />
(with [uud] and<br />
[ddb] quark content respectively) have been discovered<br />
in the SVT samples by looking for their decay to<br />
Λ b π. Additionally Ξ b ([dsb]) and Ω b ([ssb]) have been<br />
identified respectively in the channel Ξ b → J/ψΞ − , with<br />
Ξ − → Λπ − and Ω b → J/ψΩ − with Ω − → Λk − [4].<br />
References<br />
1. T. Aaltonen et al., Phys. Rev. Lett. 103, 031801 (2009).<br />
2. T. Aaltonen et al., Phys. Rev. Lett. 100, 101802 (2008).<br />
3. T. Aaltonen et al., Phys. Rev. Lett. 102, 242002 (2009).<br />
4. T. Aaltonen et al., Phys. Rev. Lett. 99, 052002 (2007).<br />
Authors<br />
S. De Cecco 1 , C. Dionisi, S. Giagu, M. Iori, C. Luci, P.<br />
Mastrandrea 1 , M. Rescigno 1 , L. Zanello<br />
http://www.roma1.infn.it/exp/cdf/<br />
-1<br />
<strong>Sapienza</strong> Università di Roma 118 Dipartimento di Fisica