ALICE
March 3, 2008
E. Scapparone
E. Scapparone
12 Maggio, 2010
INSTR08
1
Peculiarita’:
- Ottimizzato per gli ioni pesanti  alte densita’ di tracce ( fino a 8000 per
unita’ di pseudorapidita’);
- Necessita’ di distinguere il tipo di particelle;
- Attenzione all’identificazione dei g;
- non c’e’ necessita’ di “ermeticita’ “, spesso neanche di 4p
 TPC molto lenta, fino a 80 ms di drift
Trigger
- Latenza L0 di ATLAS/CMS/LHCb  2-4 ms. ALICE L0 800 ns
- Fattore di soppressione piccolo (ATLAS/CMS 107 .
ALICE
- Rate (pb-Pb) = 8 barn * 1027 = 8 kHz
- Non basato sulla rivelazione della singola particella ( a parte ECAL)
- Necessaria past-future protection
In teoria L0/L1/L2 + HLT. In pratica L0 + HLT
ALICE: A Large Ion Collider Experiment at CERN-LHC
p-p (L=1031 cm-2 s-1), Pb-Pb (L= 1027 cm-2 s-1)
Size: 16 x 26 meters
Weight: 10,000 tonnes
March 3, 2008
E. Scapparone
INSTR08
5
..also
more
difficult
@ harder…..
RHIC
At RHIC
became
Life in Pb-Pb
interactions
was never easy….
NA49
STAR
March 3, 2008
ALICE simulated central event !
E. Scapparone
INSTR08
6
INSTALLAZIONE
ITS(Inner Tracking System)
Material Budget: ≤ 1% X0 per layer !
SSD
SDD
SPD
Rout=43.6 cm
•
6 layers, three technologies (keep occupancy at a few % for max multiplicity)
•
•
•
SPD: silicon pixels (0.2 m2, two layers, 9.8 M channels)
SDD: silicon drift (1.3 m2, two layers, 133 k channels)
SSD: double-sided silicon strips (4.9 m2, two layers, 2.6 M channels)
March 3, 2008
E. Scapparone
INSTR08
9
ITS
Challenge: track densities at r = 4 cm (1st layer): up to 100 / cm2
SPD (0.2 m2)
Cell size (rf,z) :
50 mm x 425 µm
space resolution(r) : 12 mm
space resolution(z): 100 mm
March 3, 2008
E. Scapparone
6 chips
INSTR08
m
m
SSD (4.9 m2)
cell size (r,z):
95 x 4200 mm2
space resolution (r):
20 mm
space resolution (z);
830 mm
mm
42 40
SDD (1.3 m2)
cell size (r,z):
294 x 150 mm2
space resolution (r, z) : 35 mm
space resolution(z):
23 mm
75 mm
10
Inner Silicon Tracker
Inner Tracking System
~ 10 m2 Si detectors, 6 layers
Pixels, Drift, double sided Strips
Pixels
SPD
Pixels
Drift
SDD
Strips
SSD
March 3, 2008
E. Scapparone
INSTR08
11
alignment with cosmic tracks
after
alignment
before
alignment
TPC
SPD
SSD/SDD
March 3, 2008
E. Scapparone
INSTR08
14
TPC
•
•
Optimized for dN/dη ≈ 8000
• l = 5 m, Ø = 5.6m, 88 m3,
570,000 channels x 500 time bins,
• up to 80 Mbytes/event (after 0
suppression)
Features:
• lightweight: 3% X0 total material for
perpendicular tracks
• novel digital electronics (ALTRO)
• highly integrated, digital shaping; tail
cancellation;0-suppression; Baseline
restoration
• Powerful laser calibration system
Drift gas:Ne (86) / CO2 (9.5) / N2 (4.5)
Bassa diffusione ( necessita 0.1 K
max variazione)
σ(dE/dx) ≈ 5.5 to 6.5 %, depending on
multiplicity (measurements and simulations)
March 3, 2008
E. Scapparone
INSTR08
15
ALICE TPC:
5 years construction
March 3, 2008
E. Scapparone
INSTR08
16
Cosmics recorded in TPC@ALICE
Commissioning with Cosmics and Laser tracks
Spatial resolution and Electronics noise in experiment
according to specifications
March 3, 2008
E. Scapparone
INSTR08
17
TPC performance
g conversion in ALICE
TRD
Transition Radiation Detector (TRD)
March 3, 2008
•
e/p separation in central barrel p>1 GeV/c
•
fast trigger for high momentum particles
(hadrons, electrons)+ tracking
•
540 detectors ~ 760m2
•
18 super modules
•
length: 7m
•
X/X0 ~ 22 %
•
28 m3 Xe/CO2 (85/15)
•
1.2 million channels
E. Scapparone
INSTR08
23
Status:
partially
installed; being commissioned
Average pulse heigth (mV)
TRD - Signal Generation & Processing
March 3, 2008
E. Scapparone
INSTR08
24
TRD Installation
March 3, 2008
E. Scapparone
INSTR08
25
TRD
Electrons
Pions
TOF requirements:
Large array to cover the ALICE barrel (~150 m2)
Time resolution σ < 100 ps
High efficiency, ε > 95%
High segmentation: few thousands of particles per unit of rapidity expected in Pb-Pb
collision at s = 5.5 TeV/nucleon pair
√
ALICE choice: a detector based on MRPC, segmented
in ~157,000 channels, (3.5 x 2.5) cm2 area
March 3, 2008
E. Scapparone
INSTR08
27
TOF
18 Supermodules, each made of 5 modules: 2 external (19 strips),
2 intermediate (19 strips),
1 central (15 strips)
7.4 m
Readout performed by
two VME Crates/Side
2 crates /side
157248 pads, total sensitive
March 3, 2008
Scapparone
area: E.~150
m2
INSTR08
28
Cross section of a double-stack MRPC strip
10 gaps 250 mm
Differential signal to
FEA card
2 rows of 48 readout pads
(3.5 x 2.5 cm2)
Active strip length = 120 cm
March 3, 2008
E. Scapparone
INSTR08
29
Test beam of single strips
Efficiency
ε > 99.9 %
Time resolution( ps)
Gas mixture: C2F4H2(90%) – SF6 (5%) – C4H10(5%)
average ~ 50 ps
Similar results obtained when strips are inserted inside the modules
March 3, 2008
E. Scapparone
INSTR08
30
M = p ((t2 c2 /L2 )-1)1/2
σTOF = 80 ps ;
March 3, 2008
E. Scapparone
B = 0.5 T
INSTR08
31
December 2007 cosmic run
Event display of a muon
crossing the TOF detector
March 3, 2008
E. Scapparone
INSTR08
32
Risoluzione temporale con raggi cosmici
t0
L
t
Risoluzione sul tempo di
volo:
σTOF = 125 ps
Includendo tutti I
contributi
(calibrazione timeslewing non ottimali)
Due misure
indipendenti:
σTOF = σt √2
Risoluzione temporale
sul singolo hit:
σt = 89 ps
p-p
ALICE-TOF
p
K
p
velocity
High Momentum Particle Identifier:
HMPID
•
•
•
•
Proximity Focused RICH
11 m2 active detector area
7 modules
- 0.6< η < 0.6; Δφ = 58 deg
•
CsI Photocathode read by
16100 pads
Threshold momentum =
1.21* (Particle Mass)
•
•
PID optimization for
1 GeV < p < 6 GeV
March 3, 2008
E. Scapparone
INSTR08
35
HMPID
March 3, 2008
E. Scapparone
HMPID
(Sept ’06)
INSTR08
36
Example of a high multiplicity event as seen
by the HMPID
dN/dh=6000
March 3, 2008
E. Scapparone
INSTR08
37
MUON spectrometer set-up
Complex absorber/small
angle shield system (~10 lI)
to minimize background
(90 cm from vertex)
 0.7 T, bending power 3 Tm
 4 MW power, 800 tons
 World’s largest warm dipole
RPC Trigger Chambers
5 stations of high granularity
pad tracking chambers,
over 1 million channels
Trigger pt cut on single m: ~1 GeV/c
March 3, 2008
E. Scapparone
INSTR08
38
ZDC (Zeta Degree Calorimeter)
Misurano l’energia dei nucleoni che non hanno partecipato all’interazione
( spettatori ).
Nspec = Ezdc / EA  Npart = A - Nspec
Protoni e neutroni sono separati dai magneti di LHC  calorimetri distinti.
~ 116 m da ALICE IP
Tungsteno per ZN
e ottone per ZP
- Devono essere:
a) compatti ( poco spazio);
b) resistenti alla radiazione 1 Mrad/day
c) veloci ( 10 ns)
7.2 · 7.2 · 100 cm3 ZN
22.8 · 12 · 150 cm3 ZP
Fibre al quarzo
(effetto Cherenkov)
ZN
Inoltre calorimetro EM a 7 m da IP
Quello che ci interessa non e’ una raffinata misura di energia, ma il conteggio
Dei nucleoni spettatori, ciascuno dei quali ha energia ~ 2.76 TeV
).
s/E ~ 260 % /sqrt(E)+ 10%
s ~ 2760*(260 %/52 + 10%) ~ 2760*15 % ~
420 GeV  piu’ che sufficiente
( 5500 GeV/ coppia di nucleoni
brec(fm)
Centrality measurement in ALICE
Event by event determination of the centrality :
sb ~ 1fm
Zero degree hadronic calorimeters (ZDC) +
electromagnetic calorimeters (ZEM)
EZDC , EZEM
Nspec
Npart
Impact parameter (b)
bgen (fm)
reconstructed
generated
sNpart ~15
Npart
Risoluzione ottenibile  20 Npart
Npart
PHOS
g measurement up to 100 GeV/c  Direct photon from QGP/ Jet quenching p0
17920 PWO crystals
22×22×180 mm3
PHOS resolutions
<s(E)/E> ~ 3% @ 2 GeV
EMCAL
- Trigger per high pT jets, g(p0), elettroni
- Ricostruzionie completa del jet, della sua
composizione e della sua energia
- Separazione g/p0 ad alto pT
-Seperazione elettroni/adroni per studiare
la propagazione dei quark più pesanti
Tecnologia sampling:
77 strati of 1.76mm scint/1.44mm
Pb
ReadOut con fibre WLS + APDs
Geometria proiettiva:
DFDh = 0.0143x0.0143
6.0 x 6.0 x 24.6 cm3 (20. X0)
FORWARD DETECTORS
1) V0
Composto da 2 sottorivelatori (V0A, V0C). 48 scintillatori + fibre WLS + PMT.
- Trigger minimum bias
- Reiezione beam – gas
330 cm
90 cm
- 0.9 m = 2.7 ns
V0C
V0A (z=3.3 m)
Beam gas
V0C (z=-0.9 m)
3.3 m = 11 ns
V0A
2) T0
•
•
•
•
Two arrays of 12 PMTs with
quartz radiators
• T0 Right ( + 0.7 m)
• T0 Left ( - 3.5 m)
Two shoe boxes of fast
electronics inside the magnet (+5
m and –5 m)
Few creates of electronics
outside the magnet
Laser calibration system also
outside the magnet
- Start al TOF ( ~ 50 ps resolution);
- Trigger a L0;
T0L -5 < h < -4.5
T0R 2.9 < h < 3.3
3) FMD (Forward Multiplicity Detector)
charged particle multiplicity information in the pseudorapidity range −3.4 < h <
−1.7 and 1.7 < h < 5.0 ( complementare all’ITS)
51200 strip di silicio disposte in 5 anelli
PMD
Identificatore di g in avanti, 2.3 ≤ η ≤ 3.5
Lepton Acceptance
ATLAS & CMS present a large lepton acceptance |h|<2.4
ALICE combines muonic and electronic channels
- covers the low pT region (quarkonia)
- covers the forward region 2.5<h<4.0
March 3, 2008
E. Scapparone
INSTR08
58
Charged Particle Identification
HADRON-ID
3 s separation
power
All known PID techniques used in ALICE
March 3, 2008
dE/dx (MIP units)
dE/dx (MIP units)
ITS
P(GeV/c)
sdE/dx = 6.8%
at dN/dy=8000
(5.5% for
isolated tracks)
protons TPC
kaons
pions
E. Scapparone
INSTR08
P(GeV/c)
59
Combined PID Performance
Kaon PID (the most difficult case...) (Cp : CK : Cp = 0.75 : 0.15 : 0.1)
Efficiency/Contamination
ITS
TPC
TOF(*)
(120 ps)
p (GeV/c)
p (GeV/c)
Combined PID
ITS & TPC & TOF
(*) very conservative
March 3, 2008
p (GeV/c)
Higher efficiency & Lower
contamination
wrt individual detectors
p (GeV/c)
E. Scapparone
INSTR08
60
Extension of PID to higher momenta
combining the dE/dX of TRD and TPC
Combine TPC and TRD dE/dx capabilities (similar number of samples/track) to get statistical ID
in the relativistic rise region
8<p<10
GeV/c
March 3, 2008
E. Scapparone
INSTR08
61
Nov. 29, 2009
pp
PDG: 1115.7 MeV
pp
PDG: 1115.7 MeV
K0s pp
PDG: 497.6 MeV
f +-
PDG: 1019.5 MeV