VECC

1
Calorimetric Options in ALICE
VECC July 14, 2005
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High pT at RHIC dihadrons

• Strong suppression of back-to-back pairs
• apparent path-length dependence

Non-central (20-60)
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Jet quenching at RHIC

• High pT measurements
• suppression of inclusive hadrons at high pT
• direct photons unsuppressed (no color charge)
• near-side dihadron correlations unchanged
• back-to-back dihadron correlations suppressed at
  high pT
• back-to-back dihadron correlations enhanced at
  low pT (momentum balance)
• azimuthal modulation of correlations vis a vis
  reaction plane

• Consistent picture core of reaction volume is
  opaque to jets
• ? surface-biased trigger
• observed jets fragment in vacuum

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Partonic energy loss in hot matter
Multiple soft interactions
(without expansion)
Gluon bremsstrahlung
Opacity expansion (few hard scatters)
(with expansion)
linear dependence of energy loss on gluon
density ?glue measure DE ? color charge density
at early hot, dense phase
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RdAu at high rapidity
Jet Quenching
y increases
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Jets _at_ RHIC summary to date

• jet structure is strongly modified in dense
  matter
• signals are large and statistically robust,
  testable multiple ways
• consistent with partonic energy loss via induced
  gluon radiation
• ? medium is very dense gt 30 times cold nuclear
  matter
• intermediate pT complex phenomena, interplay
  between bulk medium and hard processes ? window
  into partonic equilibration?
• Open issues
• differential measurement of DE (not lower bound)
• shock waves in recoil direction?
• coupling of induced radiation to collective
  flow?
• no direct observation of induced radiation
• no accurate accounting of full jet energy
• dependence on color charge (q/g) and quark mass
  of probe
• .

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Jets in nuclear collisions at the LHC (in one
slide)

• LHC is a new physics regime ? surprises
• higher density ? stronger medium effects?
• Jet cross sections are huge robust statistics
  enable precise, microscopic studies
• Detailed probes of energy loss mechanisms
• Kinematic reach in jet ET is huge from RHIC
  (large quenching effects) to asymptotia (small
  quenching effects?)
• Robust tests of quark mass dependence, color
  charge coupling
• g/Zjet ? fragmentation function
• Hadronization of high energy jets (gt 100 GeV)
• many fragments still have modest pTlt10 GeV/c
• intermediate pT breakdown of factorization?
• coupling of radiation to medium?
• ? new phenomena?

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ALICE PID
Yves Schutz ICPAQGP05
Alice uses all known techniques!
p/K
TPC ITS (dE/dx)
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
EMCAL
1 10
100 p (GeV/c)
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Jet Phase Space
Yves Schutz ICPAQGP05
Jet physics will dominate the LHC heavy-ion
program, ALICE will be the main contender of the
race for jet quenching I. Vitev
Qs
TLQCD
Mini-jets 100/event
100K/year
1/event
Bulk properties
Hard processes Modified by the medium
ALICE Tracking PID
CMSATLAS calorimetry
Jets from Correlations and Leading Particles
Reconstructed Jets
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Why an EMCAL in ALICE?

• CMS and ATLAS have world-class calorimetry with
  very broad kinematic coverage what can ALICE add
  to jet physics in heavy ion collisions at the
  LHC?
• Essential jet measurements modification of
  fragmentation in dense matter response of the
  medium to the jet
• cross sections are huge rate not a primary
  issue
• hermeticity not important in heavy ions
• calorimetry insufficient physics lies in
  detailed changes of fragmentation patterns and
  correlations, including low pT
• Requirements for jet measurements in heavy ions
• precise tracking over very broad kinematic range
  (TPCITS)
• PID over broad kinematic range
• detailed correlations of soft and hard physics
• jet trigger (EMCAL)

ALICEEMCAL bring unique capabilities to LHC
heavy ion program
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EMCAL main jet physics capabilities

• Level 1 trigger for jets, p0/g
• essential for jet ETgt50 GeV
• Improved jet energy resolution
• charged-only jets poor resolution (gt50)
• TPCEMCAL resolution 30
• main effect out-of-cone energy (R0.3 for heavy
  ions)
• also intrinsic resolution missing n, K0L, n
• p0/g discrimination to pT30-40 GeV (cross
  section limit for gjet coincidences in
  acceptance)

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ALICE EMCAL

• Pb-scintillator sampling calorimeter
• -0.7 lt h lt 0.7
• Df 120 degrees
• Energy resolution 15/vE

• 12 super-modules
• 13824 projective towers
• Tower dhxdf0.014x0.014
• It cannot be bigger
• no room
• becomes too heavy

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Tower/module structure shashlik design
Trapezoidal module transverse size varies in
depth from 63x63 to 63x67 mm2 78 layers of 1.6
mm scint/1.6 mm Pb Moliere radius 2 cm
Pb absorber has dimensions of module
Towers defined by smaller optically isolated
scinitillator tiles
Total Pb depth 124 mm 22.1 X0 Comparisons PH
OS 180 mm/8.9 mm 20.2 X0 ATLAS LiqAr/Pb 25
X0 CMS PbWO 25 X0
Module weight 35 kg
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Tower/module construction (contd)
Held together by stainless steel skin
compressional force and friction hold tiles and
absorber in place Shashlik fiber readout 5 mm2
APD Fiber length 35 cm Tower Dh x Df 0.014 x
0.014 Module contains 2x2 or 3x3 towers (TBD)
PHOS APD preamp
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Redesign megatile ? shashlik. Why?
Initial design STAR-type megatile, fibers routed
out ends at h0.7

• Main issue was integration fundamental conflict
  with TOF
• APDs and FEE sit at large h and interfere with
  TOF FEE access
• Shashlik design routes fiber out back of module,
  no conflict
• Additional benefits of shashlik relative to
  megatile design
• shorter fibers saves 0.6-1.0 M
• more uniform distribution of dead area, more
  uniform shower response

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Shashlik Option
Murthy May 2004
Basic tower module 12 x 12 cm Segmentation 1 ,
4 or 16 subgroups
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12 super-modules 13824 projective towers Tower
dhxdf0.014x0.014
ALICE-EMCAL
? super-modules 150 projective towers Tower
dhxdf ??
ALICE-FCAL