Upgrade of ALICE Electromagnetic Calorimeter to enhance di-jet measurements
Shintaro Kubota for the ALICE collaboration
University of Tsukuba

Introduction
Back-to-back jet produced by hard parton
scatterings (di-jet) is an unique and powerfulprobe to quantify the properties of Quark
Gluon Plasma at LHC. In the ALICE
experiment, the electromagnetic calorimeter(EMCal) provides a crucial role to reconstruct
jets with a good energy resolution, together
with the information by Time Projection
Chamber (TPC).
In order to enhance the capability of back-toback jet identification and yields of jets,
photons, π0 and their correlations, we areconstructing an additional electromagnetic
calorimeter, called DCal (Di-jet Calorimeter) inALICE.

DCal will be placed on the opposite side of
the EMCal in azimuth. DCal has theacceptance of ∆φ=60 and ∆η=1.4 together
with the Photon Spectrometer (PHOS). This
acceptance allows back-to-back hadron-jet,di-jet measurements in ALICE, with R=0.4, up
to pT~150 GeV/c.

Path-length bias: π0+jet measurements
Requiring trigger π0 in DCal, jet in EMCal.
Producing strong geometry bias by hand,i.e. “control” the path length of jet.

DCalEMCal

ALICE simulation

DCalPHOSFig.3 Left: perspective view of the DCal and PHOS.
Right: beam view of EMCal and DCal.

Fig.6 Recoil jet (EMC) vs path length.

Physics with DCal

EMCal

We performed simulations to explore thephysics capabilities by the DCal.
Simulation conditions:•Event generator: qPYTHIA.
•Jet reconstruction: FastJet anti-kT
algorithm R=0.4.

TPCPHOSFig.1 The ALICE detectors.

DCal Collaboration
China•Huazhong Normal UniversityFinland•University of Jyvaskyla
France•LPSC Grenoble, Subatech Nantes, IPHC Strasbourg
Italy•INFN Catania, LNF FrascatiJapan•Hiroshima University, University of Tokyo, University ofTsukuba
Switzerland
•CERN
USA
•Lawrence Berkeley National Laboratory, Wayne State
University, University of Houston, University ofTennessee, Lawrence Livermore National Laboratory
Yale University, Oak Ridge National Laboratory,
Creighton University, Cal Poly San Luis Obispo, Purdue
University

DCal is Pb-Scintillator sampling calorimeterand read out by avalanche photodiode(APD).
Energy resolution is about 10%/√E. DCal
have 6 super module(SM). SM contain 16strip modules, and each strip module consistof 12 towers.

Pb plate & Scintillator

Strip module

Di-jet energy balance(∆∆) in p+pDi-jet energy balance(∆) in p+p and effect ofgap between DCal and PHOS is shown in
Fig.4 and Fig.5.
Fig.7 Trig π0 (DCal) vs path length.

•Recoil jet (Fig.6): Maximizing path length.
•Trigger π0 (Fig.7): Minimizing path length.
•Path length of jet medium, “control”
experiment.
•Efficient trigger of π0 (Level1) is the key,
and it is capable by utilizing existing level1
readout for EMC.

ALICE simulation∆=(ETDCal-ETEMCal)(ETDCal+ETEMCal)/2Fig.4 Di-jet energy balance distribution in p+p andeffect of gap between DCal and PHOS.

Detector DesignTower

Super module

Fig.2 DCal structure

ALICE simulation

Current status & plan
Module production had been started and all
module will ready by the end of 2011.
DCal will be installed in the ALICE
experimental area during the long LHC
shutdown in 2013.

ALICE simulation

Construction in Tsukuba

Shipping module

Cabling SM

Calibration of SM

Fig.5 Dependence of peak width of di-jet energybalance on EMCal threshold ET.

•True di-jet peak ∆~0 with DCal.(Fig.4)•DCal improves ∆ resolution 25%~ 35%.(Fig.5)•Effect by gap between PHOS and DCal issmall.

Fig.5 Module construction