High-Energy Collisions with ALICE at the LHC
2. The Alice Experiment
Graduate Days of the Graduate School of Fundamental Physics Heidelberg, 5. - 9. October 2009
1 High Energy Collisions with Alice: The Alice Experiment 2.1 Overview: Experimental Methods
2 High Energy Collisions with Alice: The Alice Experiment Momentum Measument in Magnetic Fields
centripetal force Lorentz force Useful pocket formula: v p in GeV, q = ze mv 2 FqvB= = pzBr0,3 r F r = pmvqBr= = B field in Tesla Deflection radius in m
1 m in a 1 Tesla field deflects a 1 GeV particle by 17°
Fixed Target: Collider: Typical resolution: B p = (~ 1%) (~ 1%) p [GeV/c] p B Multiple scattering Uncertainty in the measurement of the B parallel to beam axis (dominant at deflection angle Measurement of pT low pT) (dominant at large pT)
3 High Energy Collisions with Alice: The Alice Experiment Particle Identification via dE/dx (I)
Bethe-Bloch formula:
dE Z 11 2mc222 T Kz22 ln e max = 22 dx A 22 I
2 22 12 x in g/cm KNrmc= 4 Ae e = 0,307 MeVg cm
me : Masse des Elektrons
re : klassischer Elektronenradius = 2,82 fm
N A :Avogadro-Zahl : Geschwindigkeit des Teilchens ( =1/ 1-2 ) z: Ladung des einfallenden Teilchens Z: Ladungszahl des Mediums A: Massenzahl des Mediums
Tmax : Maximale in einem Stoß auf ein Elektron übertragbare Energie 222 2mce Tmmax = 2 :Masse des einfallenden Teilchens mm 12+ ee+ mm I : Mittlere Anregungsenergie des Mediums : Dichte-Korrektur (transversale Ausdehnung des e.m. Feldes)
4 High Energy Collisions with Alice: The Alice Experiment Particle Identification via dE/dx (II)
x = thickness in g/cm2 = distance z density , i.e. dE/dz = dE/dx Minimum at = 3 – 4, i.e., at 0,96 c „minimum ionizing particles“ (Mips) dE/dx fall-off: ~ 1/2 Rise at relativistic energies dE 1 dE 22 ~ ~ln dx 2 dx Due to increase of the transverse component of the E field with Lorentz Rise for solids less strong than for gases
Typical values for (dE/dx)min 1 – 2 MeV g-1 cm2
5 High Energy Collisions with Alice: The Alice Experiment SpecificSpecific EnergyEnergy LossLoss dE/dxdE/dx
proton/pion separation up to p = 1.1 GeV/c
6 High Energy Collisions with Alice: The Alice Experiment Time of Flight
Mass from p and ToF t: p s m = , = c t
Non-relativistic: 111ct = = pm ms
Relativistic:
2 11 ct = 1 pm s
Distance to TOF detector ~ 5 m (c = 30 cm/ns) Relativity works: the curves are not straight lines in this plot 7 High Energy Collisions with Alice: The Alice Experiment erenkov Radiation
Durchquert ein geladenes Teilchen Radiator-Material (z.B. Plexiglas) mit v > c/n (= Lichtgeschw. im Medium) c t n ein Medium, dann bildet das Licht der geladenes angeregten Atome eine Wellenfront Teilchen unter festem Winkel zur Teilchenbahn vc= ct c t 1 cos = n = vcnLicht = / ct n Anzahl abgestrahlter Photonen pro Abgestrahlte Photonen überwiegend Wegstrecke und Wellenlängenintervall: im blauen Frequenzbereich:
22 d2Nz 1 dN d12 N = 1,() nn= 222 d 2 ddxn ddx Bsp.: Teilchen (z = 1) mit = 1 in Wasser (n = 1,33): dEx / d= 400 eV/cm klein gegenüber gesamtem E-Verlust!
8 High Energy Collisions with Alice: The Alice Experiment Calorimeters
Energie E Szintillator elektromagnetischer Schauer: Absorber
Anzahl Schauer- teilchen:
NEtot Wellenlängen- schieber
Sampling-Kalorimeter
Energieauflösung: 2 Typen: N 11 E tot = Homogene Kalorimeter ENtot NEtot (z.B. Bleiglas) Gute homogene Kalorimeter erreichen Sampling-Kalorimeter 6% E E E /GeV
9 High Energy Collisions with Alice: The Alice Experiment Large Hadron Collider LHC at CERN
Alice ALICE Collaboration
Spain/Cuba Romania Japan Brazil South Africa Korea USA Italy China India Croatia Armenia Ukraine Mexico JINR
Russia France
Netherlands Hungary UK Greece Germany Sweden Poland Finland > 1000 Members Norway CERN Slovak Rep. Denmark Czech Rep. ~ 100 Institutes ~ 30 Countries 150 MCHF
11 High Energy Collisions with Alice: The Alice Experiment ALICE at LHC 1000 scientists, 30 nations
TRD
ITS TPC
ITS: measures secondary vertex, open heavy-flavor, c and b TPC: tracks and identifies charged particles, (e,μ), , K, p TRD: identifies electrons above 1 GeV, fast trigger (6μs) 12 High Energy Collisions with Alice: The Alice Experiment p+p collision in ALICE (simulation)
13 High Energy Collisions with Alice: The Alice Experiment ALICE
14 High Energy Collisions with Alice: The Alice Experiment ALICE Detectors: Pseudorapidity Coverage
15 High Energy Collisions with Alice: The Alice Experiment Particle Identification in ALICE
‘stable’ hadrons (, K, p): 100 MeV < p < 5 GeV (few 10 GeV) - dE/dx in silicon (ITS) and gas (TPC) + time-of-flight (TOF) + Cherenkov (RICH) 0 + - decay topologies (KS , K , K , , , D) 0 - KS and decays below 10 GeV (secondary vertex reconstruction) leptons (e, μ), photons, , 0 - electrons TRD: p > 1 GeV, muons: p > 5 GeV, 0 in PHOS: 1 < p < 80 GeV 16 High Energy Collisions with Alice: The Alice Experiment Invariant Mass
17 High Energy Collisions with Alice: The Alice Experiment Pointing Resolution
18 High Energy Collisions with Alice: The Alice Experiment s
ALICE in 2004
19 High Energy Collisions with Alice: The Alice Experiment 2.2 Inner Tracking System (ITS)
20 High Energy Collisions with Alice: The Alice Experiment Inner Tracking System (ITS)
6 layers silicon 2 pixel detectors (SPD) 2 drift detectors (SDD) 2 strip detector (SSD) Reconstruction of primary vertex ( < 100 μm ) Secondary vertex, e.g., for heavy-quark measurements
SSD SPD
SDD
21 High Energy Collisions with Alice: The Alice Experiment 3 x 2 Layers Silicon Technology
Strips Inner Tracking System SSD ~ 10 m2 Si detectors, 6 layers double sided Strips, Drift, Pixels
Pixels SPD Drift SDD
22 High Energy Collisions with Alice: The Alice Experiment ITS - Sliding the SSD/SDD over the SPD
TPC
SPD
SSD/SDD
23 High Energy Collisions with Alice: The Alice Experiment 2.3 Time Projection Chamber (TPC)
24 High Energy Collisions with Alice: The Alice Experiment ALICE TPC: The world’s largest Time Projection Chamber
Radius: 85 cm – 247 cm Length: 2 2.5 m ~ 90 m3 gas: E Ne/CO2 (90/10) E Drift field: E = 400 V/cm Drift length: 2 2.5 m Drift time: 88 μs (500 bins) MWPC readout #channels: 560,000 Max. trigger rate: 200 Hz 180 space points/track: (x,y,z < 500 μm) Nominal B field: 0.5 T particle ID down to p ~ 100 MeV/c Can handle up 15000 T (cf. ATLAS: 2 T, CMS: 4 T) tracks
25 High Energy Collisions with Alice: The Alice Experiment 26 High Energy Collisions with Alice: The Alice Experiment TPC Installation Position Monitor (January 2007)
27 < 100 m horizontal, < 100 m vertical in 2 days 27 High Energy
28 High Energy Collisions with Alice: The Alice Experiment TPC commissioning
TPC installed in ALICE, running continuously May-October 2008, and since Aug 2009 60 million events (cosmics, krypton, and laser) recorded
transverse momentum resolution, B=0.5 T
resolution at 10 GeV: measured 6.5% design 4.5%
performance at design, TPC ready for collisions
29 High Energy Collisions with Alice: The Alice Experiment TPC commissioning
TPC installed in ALICE, running continuously May-October 2008, and since Aug 2009 60 million events (cosmics, krypton, and laser) recorded
particle identification via dE/dx
resolution: measured <5% design 5.5%
performance at design, TPC ready for collisions
30 High Energy Collisions with Alice: The Alice Experiment Electronic Noise and Drift Velocity
Rel. arrival time Entries x 100ns
average noise = 700 electrons required drift velocity close to theoretical limit uniformity: 0.3‰ measured: 1‰, consistent with T = 0.3 K vertical variation
drift time map with laser (before optimization of cooling)
31 High Energy Collisions with Alice: The Alice Experiment Temperature homogeneity
Requirement: < 0.1 K
Achieved by actively stabilizing 50 cooling loops using information from 500 temperature sensors (36 inside entries gas volume).
Further improvements down to 80 mK in progress.
32 High Energy Collisions with Alice: The Alice Experiment 2.4 Transition Radiation Detector (TRD)
33 High Energy Collisions with Alice: The Alice Experiment Transition Radiation Detector
electron identification and trigger quarkonia e+e– charm and beauty
540 chambers /18 supermodules total area: 694 m2 (3 tennis courts) gas volume: 25.8 m3 (Xe-CO2) resolution (r): 400 μm read-out channels: 1.2x106 (30 million pixels) power dissipation: 70 kW
chamber production finished 7 supermodules in 2009 completion 2010
90% funded by Germany: GSI, Univ. DA, HD,FRA,MS, FH Cologne, Worms
34 High Energy Collisions with Alice: The Alice Experiment Transition Radiation
Charged particles emit transition radiation when cross boundaries of media with different
Small probability many boundaries
Here: Lorentz factor > 1000 only electrons emit TR identify electrons !
35 High Energy Collisions with Alice: The Alice Experiment TRD Signal Generation
Charged particles induce a signal in the detector Only electrons produce transition radiation Electron ID, misidentified pions 1 % or less
36 High Energy Collisions with Alice: The Alice Experiment TRD Signal Processing
PASA TRAP • 2 custom designed ASICS - pre-amplifier/shaper (PASA) - ADC/tracklet-processor (TRAP): contain 275k CPUs to process 65 MBytes of raw data
• tracking and trigger decision Multi Chip Module (MCM) within 6.5μs
• selection of high momentum electrons
• 70kW cooling power required
37 High Energy Collisions with Alice: The Alice Experiment First supermodule assembly Heidelberg
Chip modules with TRD cooling elements supermodule
6th layer finished Installation of 2nd layer getting ready for transport to CERN, shipped in Sep 2006
38 High Energy Collisions with Alice: The Alice Experiment First TRD supermodule in ALICE Oct 2006
39 High Energy Collisions with Alice: The Alice Experiment TRD in the ALICE Cavern
TOF TRD
40 High Energy Collisions with Alice: The Alice Experiment 2.5 Calorimeters and more
41 High Energy Collisions with Alice: The Alice Experiment Photon Spectrometer
Status: 3/5 constructed 1 module installed & commissioned 2 more modules to be constructed complete by 2010 crystal
2 ~ 8 m PbW04 crystals, r ~ 5m
18 k channels, 20X0 APD R/O high42 resolution & granularity Electromagnetic Jet Calorimeter
• construction start April 2008 • approved & funded Dec 2008 • US, Italy, France, Finland • approx. 20% to be installed by May • complete early 2010
44 m2 Pb-Scint sampling calo,
20 X0, 13 k FEE APD R/O ||<0.7 = 110o r = 4.4 m
43 Nov 2007: OctEMCAL 2008 Split J. supportSchukraft Forward Detectors
FMD (Forward Multiplicity Detector) V0A detector: 3 planes Si-pad, -3.4 < < -1.7 , 1.7 < < 5.0 T0 2-arrays 12 quartz Cherenkov counters 30ps res. Start for TOF detector V0 2 scintillator arrays, 32 tiles V0A: 1.7 < < 5.0, V0C: -3.7 < < -1.7 wave length shifting fibers Minimum bias trigger in p+p and A+A ZDC (Zero Degree Calorimeter) 2-neutron, 2-proton calorimeters, 116m from IP PMD (Photon Multiplicity Detector) 2.3 < <3.5
44 High Energy Collisions with Alice: The Alice Experiment Trigger and Data Acquisition
LTU LTU HMPI MUON CTP D
Trigger
Trigger: three level architecture L0, L1, L2 Continuous online operation Data from March to September 2008 (24/7): Acquisition - up to 500 (1200) MB/s transfer - raw data rate of 2.5 PBytes / year
45 High Energy Collisions with Alice: The Alice Experiment ALICE: First Physics Topics
Claus Jorgensen p spectrum Pseudorapidity T of charged density dN/d tracks
CDF: CDF: Phys. Rev. Phys. Rev. Lett. D41, 2330 (1990) 51, 1819 (1988)
Multiplicity Mean pT vs distribution multiplicity
UA5: CDF: Z. Phys Phys. Rev. 43, 357 (1989) D65,072005(2002) Only a few ten thousand events are necessary for these analyses
46 High Energy Collisions with Alice: The Alice Experiment Extra Slides Particle Identification in ALICE
5 ‘stable’ particle species: e, μ, , K, p Instable particles through decay products Forward Rapidity muon: p > 5 GeV/c Central Barrel • velocity & momentum mass of e, μ, , K, p e,μ, photons, 0 • invariant mass quarkonia, e.g. J/, • e in TRD: p > 1 GeV/c 0 + - • decay topology K , K , K , , D • 0 in PHOS: 1 < p < 80 GeV/c • excellent particle ID up to ~ 50 to 60 GeV/c
48 High Energy Collisions with Alice: The Alice Experiment TRD commissioning
4 supermodules installed in ALICE, cosmic ray data taking in 2008 50 000 horizontal tracks acquired (TRD L1 trigger commissioned and used) Reconstruction and first iteration for calibration parameters (gain, drift velocity) completed
cosmic event triggered by TRD L1
uniformity better than 10%
49 High Energy Collisions with Alice: The Alice Experiment Circulating Protons in LHC
ITS tracks on 12.9.2008 Circulating beam 2: 7 reconstructed tracks, common stray particle causing an vertex interaction in the ITS
50 High Energy Collisions with Alice: The Alice Experiment