Post on 02-Mar-2022
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First results from ALICE
A Large Ion Collider Experiment
ALICE Control Room
waiting for collisions, Monday Nov 23, 16:35
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~ 16:41
The first pp collision event
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ALICE Setup
ALICE characteristics
High charged-particle multiplicity, ~10000 in || < 0.9
all tracked
Large momentum range 0.1 < p < 100 GeV/c
< 10% X0 up to TPC
large PID coverage
photon detectors PHOS, EMCAL, PMD
electron and muon pair trigger at high momenta
quarkonia
good secondary vertex resolution
open charm, beauty
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ALICE completion status 2009
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Time Projection Chamber principle
3-dimensional
track curvature momentum
dE/dx particle identification
I
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TPC Specs
|| < 0.9 (full length tracks)
845 < r < 2466 mm (cf. STAR: 600 to 1892)
drift 2 x 2.5 m, 100 kV, 92 s
dictated by resolution: thin ‘cold gas’ with low diffusion:
Ne/CO2/N2 mixture, 95 m3
high sensitivity to E and T, E/E 10-4, T 0.1 K
event rate for central PbPb 100 – 200 Hz
MWPC’s with pad readout (557,568 channels)
E: 159 samples (= pad rows)
gated to minimize space charge
dE/dx in TPC for Cosmics
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TPC: 87Kr gain map
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dE/dx in TPC for pp collisions
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ALICE PID components
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•match track segments of
upper and lower halfPreliminary:
• pt resolution ~ 6.5% at 10 GeV/c
~ 1% below 1 GeV/c
• design value ~ 4.5% at 10 GeV/c
TPC momentum resolution
Cosmic ray shower in TPC
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TPC laser event
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interleaved with
collisions
ITS: a high-multiplicity pp event
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ITS: Alignment with Cosmic Tracks
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• SPD alignment:
• r ≈12 m
• impact parameter resolution ~56 m
• misalignment < 10 m
close to design values
after
alignment
before
alignment
Improved ITS alignment from pp
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Beam spot (900 GeV pp)
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Online display of beam spot (900 GeV pp)
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V0 detectors (trigger)
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beam halo beam halo
Vertex pointing of TPC
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Beam spot at 2.36 TeV
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ITS: dE/dx
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Transition Radiation Detector
Identification of fast electrons
> 10000
X-ray quanta generated in radiator
conversion in Xenon drift chamber
locally enhanced dE/dx
6 layers in ALICE
misidentifications < 1%
radiator: fibers
TRD Electron Identification
p only ~1 GeV/c, interesting range p > 5 GeV/c
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e± from identified conversions
Checking the material budget
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Resolution
Δrφ ~ 1 … 2 cm
Δr ~ 1 … 5 cm
TRD-TPC track matching
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very preliminary
TOF particle identification
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Track in HMPID
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Muon spectrometer
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Muon trigger efficiency
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‘First physics‘
dNch/d
pt spectra
pt vs Nch
reconstructed K, , …
particle ratios: p/p
HBT
jets
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pp data samples
900 GeV
360 k B on
100 k B = 0
10 k B reversed
2.36 TeV
30 k
_
Rapidity distribution
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Eur.Phys.J.C65:111-125,2010
dNch/d systematics
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Eur.Phys.J.C65:111-125,2010
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• efficiencies for ND, SD, DD from Monte Carlo
• relative abundances of processes from UA5
2.36 TeV data
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• 30k collisions recorded at 2.36 TeV
• final systematic error on dNch/d
under investigation…
preliminary
Nch distribution
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preliminary
pt spectra
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pt vs multiplicity
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• pt in 0.3 < pt < 4 GeV/c and || < 0.8
• TPC multiplicity scale not yet efficiency-corrected
Preliminary
Reconstructed K0s
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online
Reconstructed
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pt GeV/c
Reconstructed 0
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Reconstructed
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- + - p + - + -
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p
-
-
pt = 1.46 GeV/c
decay length 7 cm
p/p Ratio
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_
HBT with pions
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Multiplicity dependence of HBT correlation?
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A first glimpse of jets
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A first glimpse of jets
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Azimuthal jet correlation
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preliminary
Outlook
Detectors are in good shape
Online and offline have profited
from one extra year
still work to do in alignment
looking forward to 3.5+3.5 TeV pp and Pb-Pb
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The End
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Cooling:Temperature Stabilization and Homogeneity
Clearly a challenging item: T 0.1 K
Thermal screens toward TRD and ITS
Readout chamber Al bodies and pad planes: water-cooled
Water cooling of FEE boards (total power 27 kW)
Leakless cooling systems
HV resistive divider rod:
4 x 8 W,
water-cooled
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View into TPC through last ROC opening
ROC pad planes mirrored in central membrane
200 μm planarity of electrodes achieved
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Survey result of ROCs, A-side
1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
0.2
0.1
0
0.1
0.2
A SIDE
SECTOR No
Dev
iatio
n (
mm
)
ziis 0
ziis 1
ziis 2
zo is 0
zo is 1
zo is 2
zo is 3
is
0.3
0.2
0.1
00.
105101520
A S
IDE
Dev
iatio
n (m
m)
yh
xh
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Rays perpendicular
to beam axis
2 x 4 z-planes of 42 rays
Strategic boundary crossings
Effective ray ~1mm
Additional signal from
central electrode
Laser System
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Laser Calibration and
Monitoring System Principle
4 micro mirrors along z, alignment check with CCD at other TPC end
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Commissioning of the ALICE TPCsince Apr 06
72 readout chambers
557,568 channels, 1000 time bins each
4356 front end cards
Pre-commissioning:Gas system: 95 m3
Ne/CO2/N2 (90/10/5), now 2 ppm O2
2 sectors at a time
Full data chain
Cosmic ray tracks
Laser tracks
Noise ~ 0.7 ADC cts
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anode
wire
pad
plane
drift region
88s
L1: 5s
200 Hz
PASA ADCDigital
CircuitRAM
8 CHIPS x
16 CH / CHIP
8 CHIPSx
16 CH / CHIP
CUSTOM IC
(CMOS 0.35m) CUSTOM IC (CMOS 0.25m )
DETECTOR FEC (Front End Card) - 128 CHANNELS
(CLOSE TO THE READOUT PLANE)
570132
PADS
1 MIP = 4.8 fC
S/N = 30 : 1
DYNAMIC = 30 MIP
CSA
SEMI-GAUSS. SHAPER
GAIN = 12 mV / fC
FWHM = 190 ns
10 BIT
< 10 MHz
• BASELINE CORR.
• TAIL CANCELL.
• ZERO SUPPR.
MULTI-EVENT
MEMORY
L2: < 100 s
200 Hz
DDL
(4096 CH / DDL)
Power
consumption:
< 40 mW / channel
gati
ng
gri
dFrontend Electronics: Architecture
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Front-end Card
128 ch
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ALTRO digital tail cancellation
and baseline restoration
Signal of one pad
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Inner readout chamber connected to front end card
FEC in Cu
sandwich
6 cables
per FEC
128 ch/FEC
Calculated space charge effect in the ALICE TPC
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• ALICE geometry
• based on STAR charge density distribution
• 15 kHz collision rate (effect linear with rate)
• event-by-event correction possible
Jim Thomas
STAR
cm
HBT correlations
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ALICE Setup
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ITS
TPC
TRD
TOF
HMPID
PMDMUON
PHOS
EMCAL
Dipole Magnet
L3 Solenoid Magnet
ZDC
ZDC
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PHOS 0
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ITS: track impact parameter resolution (xy)
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