ALICE the experiment

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ALICEthe experiment
G. Paic
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An experiment is..

• A physics goal
• A experimental setup detectors
• A way to record and analyze (DAQ)
• Software for simulation analysis

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ALICE Physics goals

• Global observables
• Multiplicities, ? distributions
• Degrees of freedom as a function of T
• hadron ratios and spectra, dilepton continuum,
  direct photons
• Early state manifestation of collective effects
• elliptic flow
• Energy loss of partons in quark gluon plasma
• jet quenching, high pt spectra, open charm and
  open beauty
• Study deconfinement
• charmonium and bottonium spectroscopy
• Baryon number propagation
• Pbar/p
• Study chiral symmetry restoration
• neutral to charged ratios, resonance decays

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ALICE Physics goals

• Detect fluctuation phenomena - critical behavior
• event-by-event particle composition, spectra
• Measure the geometry of the emitting source
• HBT, impact parameter via zero-degree energy
  flow
• Study pp collisions in the new energy domain
• Search for Centauro events,

NEEDS

• Large acceptance
• Good tracking capabilities

• Wide momentum coverage
• P.I.D. of hadrons and leptons

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The community is used to difficulties!
A compendium of tracking, PID andother detector
techniques
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SPS Pb ions since 1995 _at_ 158 Gev/nucleon
NA49 experiment A Pb-Pb event
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RHIC Started last year
A central Au-Au event _at_ 130 GeV/nucleon CM energy
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Status of ALICE

• Most detectors have produced TDRs, approved by
  the LHCC
• The Transition Radiation Detector TDR has been
  submitted on October 3rd
• The TOF TDR addendum will be submitted March 2002
• The Trigger/DAQ and Offline TP are in progress
• The RD is finishing (for example, the frontend
  in .25 mm radtol technology for the three
  detectors of the Inner Tracking System is
  working, prototypes of all detectors, from
  silicon to crystals, from muon trigger chambers
  to TOF, are under test and prove to meet the
  performance requirements)
• Major detectors systems are now in the
  production phase TPC, ITS, HMPID, MUON ARM,
  PHOS.
• The Physics Performance Report is in preparation,
  using the full OO ALICE software chain
• The DAQ Data Challenges are progressing towards
  ALICE performance

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ALICE LAYOUT
Inner Tracking System (ITS) 6 Si Layers (pixels,
drift, strips) Vertex reconstruction,
dE/dx -0.9lt?lt0.9
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ALICE LAYOUT
TPC Tracking, dE/dx -0.9lt?lt0.9
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ALICE LAYOUT
TRD Identification of electrons (pgt1
GeV/c) -0.9lt?lt0.9
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ALICE LAYOUT
TOF PID (K,p,?) -0.9lt?lt0.9
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ALICE LAYOUT

• HMPID High Momentum Particle Identification (?,
  K, p)
• RICH
• Hard Probes

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ALICE LAYOUT

• PHOS ? identification
• PbWO4 crystals
• phtons and neutral mesons
• ?-jet tagging

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ALICE LAYOUT

• PMD Photon Multiplicity Detector
• Preshower detector with fine granularity
• E-by-E fluctuaction, DCC, flow (S. Raniwalas
  talk)

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ALICE LAYOUT

• MUON arm
• Dimuons and vector mesons
• 2.4 lt? lt 4
• P. Crochets talk

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ALICE ACCEPTANCE
Y.Foka, Chia
h
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ITS tracking
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TRD TOF
0
PHOS
HMPID
TPC
-1
ITS multiplicity
-2
0
100
1
2
3
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pt
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ALICE simulations
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Physics Performace studies simulation tools
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A Central Pb-Pb event
2 degree slice
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DAQ challenges
1 Encyclopedia Britannica/s
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Tracking

• dN/d?max8000 tracking in the central
  barrel is a great challenge !
• Requirements (TPCITS)
• Good efficiency (gt 90 ) for pT gt 0.1 GeV/c
• Momentum resolution (dp/p) 1?2 at low momenta
  and few at 5 GeV/s
• Good vertexing capabilities V0, charm
• Particle identification (dE/dx, kinks)

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Tracking solutions

• Tracking finding and fitting Kalman filtering
• Track seeding outer TPC (lower track density)
• Tracks prolonged to ITS
• In ITS Kalman vertex constraint (?z100 ?m)
• From ITS back propagation to TRD

Needs
Primary vertex position measurement
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Vertex determination
Zv is estimated starting from a correlation
between the first 2 ITS layers (PIXEL) in a
narrow azimuthal (??) window
R
Layer 2
R2
Layer 1
R1
Zv
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Vertex determination/2
zv
Zv resolution (?m)
Pb-Pb ? ?z ? 5?10 ?m ?x ?Y ? 25 ?m p-p ?
?z ? 200 ?m No dependence on B
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0.5 mrad
pT 1
Central Pb-Pb -- B0.4 T
all pT
pTgt 5 GeV/c B(T)
0.2 0.5 0.2
0.5 ?p/p TPC () 2.4 1.2
8.5 5.8 ?p/p TPCITS () 1.6
0.7 3.4 1.4
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-primary vertex - secondary vertices gt
for Hyperons gt for Charm and Beauty
- dE/dx for particle identification (_at_low
momenta) - improve TPC momentum resolution -
stand-alone tracking for low-Pt particles
Tracking eff. In TPC
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Particle Identification

• p, K, p identified in large acceptance (2p 1.8
  units h) via a combination of dE/dx in Si and TPC
  and TOF from 100 MeV to 2 (p/K) - 3.5 (K/p)
  GeV/c
• Electrons identified from 100 MeV/c to 100 GeV/c
  (with varying efficiency) combining SiTPCTOF
  with a dedicated TRD
• In small acceptance HMPID extends PID to 5 GeV
• Photons measured with high resolution in PHOS,
  counting in PMD and EM energy flow in EMCAL

p/K
TPC ITS (dE/dx)
All PID strategies implemented in ALICE
K/p
e /p
p/K
e /p
TOF
K/p
p/K
HMPID (RICH)
K/p
0 1 2
3 4
5 p (GeV/c)
TRD e /p
PHOS g /p0
1 10
100 p (GeV/c)
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Particle Identification /2
TPC
ITS
TOF
HMPID
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HMPID

• PID range
• 1 lt p lt 3 GeV/c p K
• 2 lt p lt 5 GeV/c p

Radiator 15 mm C6F14 n1.3 _at_ 170 nm

• Photon detector
• MWPC with CH4 at
• atmospheric pressure
• (4 mm sensitive gap)
• analogue pad readout

Photon converter Reflective layer of CsI (QE
23 _at_ 170 nm)
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HMPID proto in STAR
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TPC
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TPC/2
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(No Transcript)
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ToF test results
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PHOS
Physics Thermal radiation High pt physics
Tagged jets Detector Dimensions h ? ?0.12, ? ?
100? (1?8 m2) at radius R ? 4.6 m PbWO4
crystals, X0 0.89 cm, lint 19.5 cm, Moliere
radius 2.0 cm Granularity 2.2?2.2 cm2 (Dh ? Dj
? 0.005 ? 0.005), length 18 cm p0 identified
from 3 to gt 50 GeV/c Energy resolution 2 above
3 GeV/c Starting pre-production
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Secondary vertex (Hyperons K0)
Algorithms for secondary vertex finding with ITS
have been implemented in AliRoot
K0? ??-
ITS
?-
p
K-
?
????p
?-
Pythia p-p event ????p
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TRD
main aims high pt (gt 1 GeV) electron
identification trigger on high pt (gt3 GeV)
electrons and jets physics heavy quarks (c,
b), quarkonia (J/Psi, Y), jets
detector fiber radiator to induce
TR (g gt 2000) large (800 m2), high
granularity (gt 1M ch.) drift detectors online
trigger electronics to select stiff tracks
(measure sagitta)
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TRD in ALICE
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DCCs
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Forward detectors
V0 1.6 lt h lt 3.9 Interaction trigger,
centrality trigger and beam-gas rejection. Two
arrays of 72 scintillator tiles readout via fibers
Forward detectors
PMD
T0L
FMD Measure Multiplicity and h dist. over 1.6 lt h
lt 3, -5.4 lt h lt -1.6 Silicon pad detector disks
(slow readout) with 12k analog channels (occ.gt1)
T0R 2.6 lt h lt 3.3 T0 for the
TOF ( 50 ps time res.) Two arrays of 12 quartz
counters. Also backup to V0
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Castor

• Tungsten/Quartz fiber calorimeter
• Segmented longitudinally
• 17 m from IP 5.6 lt h lt 7.2
• Baryon dense region

• Measure Eem/Ehad and longitudinal evolution of
  cascade

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(No Transcript)
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ALICE computing
ALICE computing same order of magnitude as
ATLAS or CMS ALICE offline status Major
decisions already taken (DAQ, Off-line) Move to
C completed (TDRs produced with the new
framework) Adoption of the ROOT framework
Physics performance and computing in a single
team Aggressive Data Challenge program ALICE
Physics Performance Report Evaluation of
acceptance, efficiency, resolution for
signals Step1 Simulation of 10,000 central
Pb-Pb events Step2 Signal Superposition
Reconstruction 100,000 events Step3 Event
Analysis Analysis Object Data 1 TB x
nsignals 200 TB total Started November 2001
with test production of 1000 PbPb events
Distributed production in several ALICE sites
using GRID tools
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Dimuon Spectrometer

• Study the production of the J/Y, Y', U, U' and
  U'' versus the centrality of the reaction
• Resolution of 70 MeV on the J/Y and 100 MeV on
  the U
• overall performance improved with updated
  detector design

Plot of 1-month Pb run result, showing the good
separation of the various resonances, allowing a
systematic study of Debye screening
The absorber design is being revised to try to
overcome a major cost overrun
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Secondary vertices and hard probes hadronic charm
Secondary vertex finding capabilities PID can
be exploited to detect processes as D0?K-? and
D ?K- ? ? (and chg. conjugates)

• gt 100 charm pairs / central event
• D0?K-? has been studied
• 0.55 D0?K-? accepted/event
• Mass 1.864 GeV/c2 c?124 ?m
• Large uncertainties indirect measurements at
  SPS (excess A-A w.r.t. p-p)
• Also important for J/? normalisation

() Alice PPR preliminary
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D0?K-?

• Full ITS simulation
• Parametrization of TOF and TPC (for sake of
  statistics)
• Signal (Pythia) and background (parametrized
  Hijing) treated separately

• Cuts
• M(K?) M(D0)lt1?18 MeV
• pTgt800 MeV/c
• cos ?lt0.5
• Distlt200 ?m
• d0? ? d0K lt -4104 (?m)2
• cos?plt0.98

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D0?K-?
107 central Pb-Pb events
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? ? - channel

• ?M 94.5 MeV/c2 at the ?
• Separation of ?, ?, ?
• Total efficiency 75
• Expected statistics (significance 1 yr)
• J/? 310
• ? 12
• ? 39
• ? 19
• ? 12

P. Crochet
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ee- channel

• TRD
• -0.9lt?lt0.9
• 1.2 M number of channels
• El. id. for pgt1 GeV/c
• El. Trigger (L1) for pgt3 GeV/c

? efficiency
? rejection gt50 _at_dN/dy8000
Electron efficiency
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ee- channel
TPCTRD ? J/? and ? ? , ? and ? separation
with B0.4 T
B0.2 T
B0.4 T
High ee- yield from b and c quarks 240106
evts/yr from c 540 103 evts/yr from b
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ee- channel J/? from b
c? 300?400 ?m for D and B mesons B(D) ? e X
The d0 of the electron can be measured with the
ITS
d0 lt cut ? resonances d0 gt cut ? D,B mesons

• M spectrum for d0gtcut
• B?J/? signal singled out
• Measurement of bottom cross section

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Jets via leading particle in TPC

• Find the leading particle
• If leading particle has a ptmaxgt 4 GeV use it as
  a seed for jet.
• Particles with ptgt 2 GeV are associated to the
  jet if ?R?(??2??2) lt 0.7
• Calculate sum of momentum vectors.
• Mark all used particles.
• Repeat until no more seeds are found.

2-Jet in pp
A.Morsch
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Jets /2
Single 100 GeV Jets DR0.7
100 GeV Jets in central PbPb
Underlying Event
TRD jet trigger
First studies give 1Hz trigger rate for central
PbPb collisions and pt jet gt 100 GeV/c
real jets triggers 0.7/s false triggers
0.3/s
Y.Foka, A. Morsch
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Summary/II

• ALICE has started the production phase
• The simulations are in full swing for the PPR
• The diversity of the experiment covers a large
  part of the possible signals

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The ALICE Collaboration
937 members (63 from CERN MS) 77
Institutions 28 Countries
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D0?K-?

• Yield and significance
• 8100 / 107 Pb-Pb central events
• S/B5.3 S/?B10.9 _at_dN/dy8000
• S/Bgt21 S/?Bgt22 _at_dN/dy4000

() Alice PPR preliminary
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Jet Rates in Central ALICE (?lt.9)
pp L 1030cm-2s-1
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WHY HEAVY IONS AT THE LHC? /1
Central collisions SPS RHIC LHC
s1/2(GeV) 17 200 5500
dNch/dy 500 650 3-8 x103
e (GeV/fm3) 2.5 3.5 15-40
Vf(fm3) 103 7x103 2x104
tQGP (fm/c) lt1 1.5-4.0 4-10
t0 (fm/c) 1 0.5 lt0.2

1. ?LHCgt ?RHICgt ?SPS
2. VfLHCgt VfRHICgt VfSPS
3. tLHC gt tRHIC gt tSPS