The Di-jet calorimeter arm (DCal) is currently being integrated within ALICE. DCal has the same structure as the existing ALICE EMCal, a large lead-scintillator sampling electromagnetic calorimeter with avalanche photo-diode readout. The DCal and EMCal are situated back-to-back in azimuth, with the EMCal subtending 110 degrees and the DCal subtending 60 degrees, and with both detectors covering |η| < 0.7. EMCal consists of a contiguous set of 10 EMCal super modules, while DCal uses 6 super modules of the EMCal design and is used in conjunction with 3 super modules of the existing PHOS electromagnetic calorimeter. Together they provide good acceptance for di-jets with radii R ≤ 0.4,making possible di-jet measurements exceeding transverse momenta pT ~ 150 GeV/c in the upcoming run, when LHC restarts.
The DCal will extend significantly the jet quenching measurements enabled by the EMCal in ALICE, by providing large acceptance for back-to-back correlation measurements of jets and hadrons. The current ALICE detector has already demonstrated good capabilities for inclusive jet measurements, utilizing ITS and TPC together with EMCal; however, experience with jet quenching measurements has shown that the combination of inclusive and correlation measurements is a much more powerful probe of jet quenching than inclusive measurements alone. Addition of the DCal in ALICE makes hadron-jet and jet-jet correlation measurements possible at high statistics over a very broad kinematic range, expanding ALICE physics capabilities significantly.
Figure 1. DCal and PHOS new support beams and support cradle are assembled and ready for installation inside L3
One of the most significant measurements enabled by the DCal is the correlation of a jet recoiling back-to-back from a triggered high pT neutral pion. This measurement exploits the phenomenology of jet quenching to provide a unique geometric bias, maximizing the path length of the recoiling jet in the hot medium. Moreover, the DCal and EMCal will measure the correlation of fully reconstructed jet pairs with large cone radius (R ~ 0.4), enabling the study of energy balance between recoiling jet pairs. The DCal extension will also play a key role in extending the kinematic reach for the heavy-flavor decay electrons and photons. DCal enhances ALICE triggering capabilities and enables qualitatively new correlation measurements at high momentum.
Figure 2. DCal and PHOS supermodules insertion test was performed above ground at POINT 2
With all of the hardware fabricated and tested the installation in the cavern had just started and will continue throughout 2013 and early 2014. The planning is to install the C-side super-modules before the end of 2013 and the A-side will be inserted in February 2014 after the PHOS modules are ready for installation.