A Forward Calorimeter (FoCal) as upgrade for the ALICE experiment at CERN S. Muhuria , M. Reicherb and T. Tsujic a Variable Energy Cyclotron Centre, Kolkata, India b Department of Physics, Utrecht University, Utrecht, the Netherlands c CNS University of Tokyo, Japan Motivation As an upgrade of the ALICE experiment at the CERN-LHC, we would like to build and install a Forward Electromagnetic Calorimeter (FoCal) to be placed in the pseudorapidity region of 2.5 < η < 4.5, at the position of the existing Photon Multiplicity Detector (PMD). The basic motivation of including the calorimeter in the forward direction is to study outstanding fundamental QCD problems at low Bjorken-x values, such as parton distributions in the nuclei, test of pQCD predictions and to probe high temperature and high density matter in greater detail. A comprehensive measurement of p-p, p-Pb and Pb-Pb collisions at the highest LHC energies will be required. For these measurements, the detector needs to be capable of measuring photons for energies up to at least E ~200 GeV/c. It should allow discrimination of direct photons from neutral pions in a large momentum range and should also provide reasonable jet energy measurements. At present, two possible designs are being considered based on silicon-tungsten calorimetry. We will present physics motivation of this project, measurement items, conceptual detector candidates, and basic performance for the measurements in this poster presentation. 120cm Eta=2.5 Eta=3.0 Eta=4.0 132 tower Conventional Pad+micro-pad readout A tower of the FoCal is a single self-contained detector unit with full depth of the detectors. In order to fully absorb photons of 200 GeV a depth of 25 X0 is needed. The typical longitudinal segmentation will be 24 layers, made of a tungsten absorber and a detection plane of silicon sensors. The transverse size of a tower is driven by availability of silicon wafers in bulk which makes wafers of size either 6.3 cm×6.3 cm or 9.3 cm×9.3 cm. The transverse segmentation inside a tower should provide the required spatial resolution. This can be accomplished by layers with pads of typically 1 cm size, with some high resolution layers before shower maximum. Detector Simulation Detector simulation has been conducted using AliRoot or standalone GEANT4 to verify the detector performance. Basic characteristics such as sampling fraction, linearity, resolution, efficiency for single photon and pi0, sophisticated clustering logic have been checked. Hardware Development Since the channel density is so high, Application Specific Integrated Circuit (ASIC) has been developed. Specifications for the ASIC is summarized as follows. Prototype ASIC for pad readout has been fabricated and test will be done in the future. Development of micro-pad has not been started yet. Candidates are MAPS (Monolithic Active Pixel Sensor) type or HAPS (Hybrid Active Pixel Sensor) with 0.5-1 x 0.5-1 mm2 pads and existing ASICS (HAL25, Beetle, etc). The issues for the latter case are to match the dynamic range (external CMOS attenuator or thinner sensor) and the way to get the signal out. Physics Measurement Accessible pT and parton x by the correlation measurement Pi0 and Jets High rates, large Q2 scale Correlation to shrink x region (due to g+g dominant process) Prompt Photons Low Q2 scale, Small ratio of photon/pi0 Fragmentation contribution Heavy-bosons Large Q2 scale Large pT dileptons p0 (2<y<4) and jets (2<y<4) p0 (2<y<4) and jets (-1<y<1) x2~ 10-4 - 10-3 x2~ 10-3 - 10-2 First segment Second segment Third segment Si micro-pad Tungsten Si pad CPV One of the possible specifications W thickness: 3.5 mm (1X0) wafer size: 9.3cmx9.3cmx0.525mm Si pad size: 1.1x1.1cm2 (64 ch/wafer) Si micro pad : MAPS or < 0.5-1 x 0.5-1 mm2 in preshower stage W+Si pad : 21 -25X0layers 3 or 4 longitudinal segments Summing up raw signal longitudinally in one segment Or readout from individual layers Accessible pT and parton x by prompt photon measurement x1 and x2 x1(left) and x2(middle) vs. photon pT in prompt photon production (photons at eta 3-3.5). Coverage of (x, Q2) with FOCAL Si Pad sensor from Hamamatsu Size: 9.3x9.3 cm2 Thickness: 535mm Pad size: 1.1x1.1 cm2 Number of pads : 64 Cpad = 25pF, Idark =2- 10nA Some examples of RHIC achievement in forward rapidity measurement Pi0 suppression at forward rapidity in d+Au at RHIC Disappearance of away side peak In pi0-pi0 correlation in d+Au at RHIC linearity <1% up to 200GeV Resolution: 18.2%/sqrt(E) + 1.4% Longitudinal shower profile linearity <1% up to 200GeV 150 GeV 70 GeV 30 GeV Resolution: 22%/sqrt(E) + 1.6% Position resolution by micro-pad Pi0 identification Efficiency by pads Pi0 identification Efficiency by micro-pads Efficiency > 50% for E>60 GeV Two gamma clusters start to be merged Efficiency >50% for E<50 GeV 7 1.29 2 0.098 x cellid y cellid 57 12.32 77 22.39 71 16.76 78 16.82 42 12.73 29 4.55 Legend Data count Total energy deposition in MeV Embed 4 gammas with 5mm separation. Cluster reconstructed based on the dynamical fuzzy c-mean Method (d-FCM). 200pF Clow 560pF Chigh 5.6nF 10pF CSA PZ ASIC High side Low side 3mm 4mm 4ch/chip Prototype chip (TSMC 0.5um) Pads readout : Dynamic range: 10fc (1/5MIP) – 200pC (500GeV g) Cross talk < 1%. S/N=10@MIP Trigger capability Dual charge sensitive preamplifier with capacitive division Single preamp+dual shaper Dual transimpedance preamplifier Micro-pad readout: Dynamic range: 2fc – 500fc Z = 1/wC + Zcf/A First prototype high low hspice simulation 2.5usec