U NIVERSIDADE T ÉCNICA DE L ISBOA
I NSTITUTO S UPERIOR T ÉCNICO
Prompt and displaced muon production
in Indium-Indium collisions
as measured by the NA60 experiment
André David Tinoco Mendes
(Licenciado)
Dissertação submetida para a obtenção do Grau de Doutor em Física
Orientador
Co-Orientador
Doutor João Carlos Carvalho de Sá Seixas
Doutor Carlos Manuel de Assunção Lopes Lourenço
Júri
Presidente
Vogais
Reitor da Universidade Técnica de Lisboa
Doutor Jorge Venceslau Comprido Dias de Deus
Doutor Louis Kluberg
Doutor João Carlos Carvalho de Sá Seixas
Doutor Carlos Manuel de Assunção Lopes Lourenço
Doutor Gaspar Pereira Morais Barreira
Fevereiro de 2006
Instituto Superior Técnico
Universidade Técnica de Lisboa
The NA60 Experiment
European Organization for Particle Physics
Cover figure On the left side, a measurement comparable to previous experiments: dimuon
mass. We have data (black squares), Drell-Yan (red up triangles) normalised to NA3 and NA50
measurements (1.0), open charm muon pairs (blue down triangles) normalised to a world average of
charm production cross-sections (1.0) and the sum of the last two (green circles). The best description
of this distribution in the intermediate mass region (χ2 /ndf=1.8 for 1.2 < Mµµ < 2.7 GeV/c2 ) comes
from fixing the Drell-Yan yield to our expectation (allowing for a ±10% variation to account for normalisation errors) and letting the open charm contribution free. We see that the while the high mass
region is properly described, the open charm yield would seem to be enhanced by a factor 3.77 ± 0.22
with respect to the world average. On the right side, a measurement unique to NA60: weighted
muon offsets with respect to the identified interaction vertex (∆). For events in the intermediate
mass region (1.2 < Mµµ < 2.7 GeV/c2 ) we now leave a prompt (red up triangles) contribution and
an open charm (blue down triangles) contribution simultaneously free, with a resulting fit χ2 /ndf
of 0.9. The prompt yield is found to be 1.91 ± 0.11 higher than the expected Drell-Yan contribution
which described the mass spectrum, while open charm is at the same level of p-A dimuon measurements by NA50, namely roughly two times higher than the world average. These results show that
a prompt source of dimuons other than Drell-Yan is responsible for the dimuon intermediate mass
region excess seen by NA60, NA50 and NA38.
U NIVERSIDADE T ÉCNICA DE L ISBOA
I NSTITUTO S UPERIOR T ÉCNICO
Prompt and displaced muon production
in Indium-Indium collisions
as measured by the NA60 experiment
André David Tinoco Mendes
(Licenciado)
Dissertação submetida para a obtenção do Grau de Doutor em Física
Orientador
Co-Orientador
Doutor João Carlos Carvalho de Sá Seixas
Doutor Carlos Manuel de Assunção Lopes Lourenço
Júri
Presidente
Vogais
Reitor da Universidade Técnica de Lisboa
Doutor Jorge Venceslau Comprido Dias de Deus
Doutor Louis Kluberg
Doutor João Carlos Carvalho de Sá Seixas
Doutor Carlos Manuel de Assunção Lopes Lourenço
Doutor Gaspar Pereira Morais Barreira
Fevereiro de 2006