exotic nuclei structure and reaction noyaux exotiques ... - IPN - IN2P3

First p-p p collisions in the ALICE muon spectrometer
IPNO Participation: L. Bimbot, B. Boyer, V. Chambert, S. Drouet, B. Espagnon, C. Hadjidakis, I. Hrivnacova,
B.Y. Ky, G. Lalu, V. Lafage, Y. Le Bornec, M. Lopez-Noriega, M. Malek, G. Noël, S. Rousseau,
C. Suire, D. Tapia-Takaki, N. Willis and SEP technicians.
Collaboration : INFN Cagliari, IRFU/SPhN, PNPI Gatchina, SINP Kolkata, SUBATECH Nantes, VECC
Kolkata.
La période 2008-2009 restera, pour le LHC, celle d'un incident important suivi du retentissant succès des
premières collisions proton-proton. Après l’installation des détecteurs et le début de la mise en service en
2007, la phase de tests s’est poursuivie en 2008 avec des prises de données en rayonnement cosmique
jusqu’à la première tentative de démarrage du LHC qui se solda par un échec. Les tests en cosmique se
sont donc poursuivis début 2009 jusqu’à la fin de l’année où le LHC a pu délivrer ses premiers faisceaux de
protons accélérés à 450 GeV puis très rapidement à 1,18 TeV. Ces premières données ont permis à ALICE
de faire la première publication des expériences LHC. Elles ont surtout validé le bon fonctionnement de
l’ensemble du détecteur.
The IPNO ALICE team is involved in the ALICE
project since its early dates. With the first p-p collisions
delivered by the LHC, the year 2009 has
seen the outcome of years of efforts building one
of the most complex detectors ever made [1,2].
The years 2008-2009 were devoted to the commissioning
of the muon spectrometer and to the first
data taking in cosmic runs, preparing for the first
LHC beam.
Commissioning phase and cosmic runs.
As presented in the previous activity report, the
first tracking station of the muon spectrometer,
built by IPN Orsay, was successfully commissioned
in 2007 [3]. Thus, only station 1 participated
in the first ALICE cosmic run of December 2007.
Triggers were delivered by a scintillator array located
on the top of the L3 magnet (~90 Hz) to all
subsystems ready in the global ALICE data acquisition.
Very good results were obtained with station
1 in terms of readout electronic and data acquisition
software [4,5]. In addition, the first clusters
were observed. After this first success, cosmic
runs continued with stations 1 and 2 in February
2008 with a dedicated single muon trigger delivered
by the RPC chambers of the muon spectrometer.
In September 2008, the LHC circulated both
beams rather quickly, but stopped only nine days
latter due to an electrical link failure causing a major
liquid helium leak. The LHC suffered of important
damages requiring a full year to repair it.
Therefore ALICE continued the cosmic runs until
the end of 2009. During these cosmic tests, we
were able to check and to improve the performances
(noise, pedestal stability, gain, data taking
efficiency …) of all the tracking and trigger stations
of the muon spectrometer. The first muon tracks
hitting all the stations were observed during this
period (Fig 1).
The detector readout system called CROCUS, in-
tegrated in the global ALICE software framework
(Data AcQuisition, Off/On-line and Experiment
Control System) exhibited a very good stability.
Fig 1 : First reconstructed muon track with dipole
magnet on (cosmic run).
First p-p collisions with the ALICE forward
muon spectrometer !
On November 23rd 2009, the LHC successfully
delivered the first p-p collisions to ALICE at SPS
injection energy, thus a centre of mass energy of
s = 900 GeV. A few hundred of minimum bias
triggers were collected by the ALICE subsystems
robust enough to cope with the unstable beam
conditions, i.e. the silicon tracker or ITS (Inner
Tracking System). These data provided such clear
physics results that ALICE was able to submit the
first LHC paper on November 28th. This paper was
accepted for publication on December 1st [6] !
This demonstrates clearly that the ALICE detector
was in perfect working order, that the analysis procedures
are ready and efficient, and finally, that
the reactivity of the ALICE collaboration was at its
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