The ALICE Forward Multiplicity Detector from Design to Installation
Overview Matter and the Quark Gluon Plasma Heavy Ion Collisions and ALICE The Forward Multiplicity Detector: Motivation, sensors, electronics, tests Offline data analysis: Geometry, simulation, reconstruction analysis 2
Matter 0.1m 10-8m 10-10m 10-14m 10-15m force mediators (bosons) (fermions) leptons quarks Standard model describes this by matter particles (fermions) and force particles (bosons): photons: electromagnetic gluons: strong force Z and W bosons: weak force } 3
4 Forces Gravity Apple falls, moon in orbit, 1/r2 behaviour Electro-magnetism Light bulb, 1/r2 behaviour, +/charge, γ Heavier elements, Weak nuclear force e- mr/r behaviour, Z0 and W± Quarks in nucleons, nucleons in nuclei, Strong nuclear force gluons, colour gluons and quarks 4
QCD and Confinement Quantum Chromo Dynamics (QCD) theory of strong nuclear force. Quarks and gluons have colour! Quark-quark-potential V(r) a/r+b r a/r r qualitative difference between the q-q and the Coulomb potentials If you try to separate two quarks, you will just get two new ones Quarks are confined to the nucleons difficult theory tough to measure 5
Quark Gluon Plasma (QGP) Confinement:... if you compress the hadronic matter Colour cannot be probed directly, but... the q-q potential is screened and the hadrons dissolve quark gluon plasma the quarks (and gluons) are confined in white objects (hadrons) 6
Where to find QGP early universe quark gluon plasma T temperature TC RHIC LHC SPS AGS hadron gas SIS Nuclear Matter 940 MeV baryon chemical potential crab nebula neutron stars µb 7
Overview Matter and the Quark Gluon Plasma Heavy Ion Collisions and ALICE The Forward Multiplicity Detector: Motivation, sensors, electronics, tests Offline data analysis: Geometry, simulation, reconstruction analysis 8
Colliding Heavy Ions Before collision: ~99.999994% speed of light, Lorentz contracted pancakes QCD interactions, quark-matter creation, high density & temperature Phase transition? Re-combine to hadrons (confined), re-scattering Kinetic freeze-out, final state particles Measurable particles 9
Large Hadron Collider LHC will collide : Pb-Pb at s NN = 5.4 TeV s = 14 TeV p-p at 10
A Large Ion Collider Experiment (ALICE) EMCAL ITS T0, V0 beam TRD TPC MUON PMD HMPID beam TOF PHOS FMD 11
Detecting Particles Barrel detectors (ITS, TPC, TRD, TOF, HMPID): measure path of particles and identify particles. MUON: Direct di-lepton measurements. PHOS: Direct photon measurements. T0, V0: provide trigger information. FMD: Particle multiplicity, event plane, and flow (simulation of central collision) 12
Overview Matter and the Quark Gluon Plasma Heavy Ion Collisions and ALICE The Forward Multiplicity Detector: Motivation, sensors, electronics, tests Offline data analysis: Geometry, simulation, reconstruction analysis 13
Forward Multiplicity Detector Interaction point FMD2 FMD3 FMD1 14
Why the FMD? (1) FMD measures number of charged particles at low angles - or high = log tan /2 Region not covered by other ALICE detectors. Charged particle multiplicity Baseline measurement (how much is there) 1st order model discriminator Used to select events 15
Why the FMD? (2) Determine event-plane ªR Used in jet-analysis study medium effects. Q: How strongly does the QCD matter effect the produced particles? A: (RHIC) Quite a bit! 16
Why the FMD? (3) Measure azimuthal asymmetry v2 at small angles Fourier decomposition of dmch/d' with ' relative to ªR 3 E 2 [ d N 1 d N = 1 2 v n cos n R 3 2 p dp dy dp n=1 v n = cos n[ R ] Q: QCD matter have colour? A: (RHIC) yes! Q: is a phase reached? A: (RHIC) yes Q: do we understand it? A: No! 17 ]
What is the FMD? 3 sub-detector: FMD1, 2, & 3 2 types of rings: inner and outer Made of silicon sensors Inners: 20 azimuthal sectors, 512 radial strips Outers: 40 azimuthal sectors, 256 radial strips Total of 51,200 channels 18
Front-End Electronics Sensor+hybrid (module) Digitiser card (FMDD) Trigger (L0) ALTRO & I2C buses Trigger & timing Ethernet Read-out Controller (RCU) & Detector Control System Card (DCSC) DAQ link 19
Data Path in the FMD Sensor register charged particles VA1 amplifies and serialises analogue signal 3 ALTRO digitises analogue signal RCU fetch data from ALTRO and pass it to DAQ. 20
Sensors Manufactured by Hamamatsu Cut from 6 320μm thick wafers Pitch: Inners: ~250μm Outers: ~500μm Low leakage current High stability < 1 dead channels 21
Hybrid Cards Glued & bonded to sensor Designed and manufactured by IDEAS Hybrid card holds VA13 pre-amplifiers To/from FMDD VA13 Bonds VA13: Time-tested VIKING family Low noise, high gain Radiation tolerant 128 input channels, serialised into 1 output channel Adjustable peaking time Calibration pulser calibrate signal size. 22
Module Performance All modules tested in laboratory with IDEAS test system. Estimates of best signal-to-noise ratio: Inners: 59:1 to 65:1 Outers: 56:1 to 61:1 Test beam results from ASTRID using IDEAS test system: Inners: 57:1 to 63:1 Outers: ~ 35:1 23
Digitiser Cards (FMDD) Designed at NBI (based on TPC FEC) Re-use TPC custom ADC - the ALTRO chip Main components: 3 ALTRO ADCs 1 Board Controller (BC) 4 5 channel monitors Connections to hybrids Bus connection 24
What does the FMDD do? ALTRO: Parallel Analogue-todigital converter Multi-event buffer Signal processing BC: Govern communication Monitor Temperatures, voltages, currents Trigger handling Control VA1 - incl. 3 read-out, bias, pulser calibration RCU monitors state turns off card in case of problems. 25
FMDD Board Controller Implemented as Firmware in FPGA Developed at NBI based on TPC BC, but completely re-written Allow control of all aspects of R/O, etc. Remotely reprogrammable 26
Read-out Controller Unit TPC design RCU chip: Trigger handling RCU chip Control of FMDD (on back) Monitor FMDD Embedded Read-out ALTROs computer Push data to DAQ DCSC computer: Detector control Provide control of system RCU to Ctrl. Sys. card Provide status info on RCU & FMDD Trigger & timing Data link Ethernet link 27
Data Acquisition Signal from sensor, digitised by ALTRO, readout and sent to DAQ by RCU. DAQ collects sub-event data write to permanent store Special programs analyse online data for pedestals and gains. Provide monitor channels 28
Detector Control System Control & monitor FEE, power supplies, cooling. FEE control/monitor based on TPC but revamped for FMD. Re-use custom software as much as possible Robust design of configuration DB 29
Test beam results Full system test at ASTRID 630MeV e- beam c.f. Carsten Søgaard 30
Overview Matter and the Quark Gluon Plasma Heavy Ion Collisions and ALICE The Forward Multiplicity Detector: Motivation, sensors, electronics, tests Offline data analysis: Geometry, simulation, reconstruction analysis 31
Offline software Geometric description Simulation of events Reconstruction of events Analysis 32
Reconstruction Process raw data recorded by DAQ needed. For each strip, do Pedestal subtraction (pedestals from special DAQ program) Gain matching (gain from special DAQ pulser program) Path length correction Rough multiplicity estimate But that is not enough! 33
Sharing Particles traverse >1 strip signal shared over 2 (or, less often, more) strips Merge signals into single strip... but still more to come 34
# Particle Cuts Fit Landau to distribution Define cuts based on probability Compare to simulation input 35
Background Correction Large contribution from external material In some places up to 300% Crucial for proper charged particle multiplicity c.f. Hans Hjersing Dalsgaard 36
Charged Particle Multiplicity Density Data processing Pedestal Gain Path length Sharing # of particle cuts Background Final charged particle multiplicity c.f. Hans Hjersing Dalsgaard 37
Event Plane and v2 Use ' segments to determine event plane ªR Determine event plane resolution Rk Determine v2 6% flow input 38
Conclusions & outlook Well tested detector Good performance High s/n Efficiency > 99.5% < 1 dead channels Stable FMD2+3 installed FMD3 fully commissioned. Offline software ready Need better understanding of background & cuts FMD1 installed in a few days FDR2 will see operational FMD2+3 Ready for first beam this summer 39