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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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