Transcript Hollis

Forward Calorimeter Upgrades in PHENIX:
Past and Future
Richard Hollis for the PHENIX Collaboration
University of California, Riverside
Winter Workshop on Nuclear Dynamics
8th January 2010
Overview
 The next decade at RHIC&PHENIX
 Motivation and Needs
 Calorimeter Upgrades
 Past: MPC – currently operational
 Future: FoCal – proposal soon
 Summary
NUCLEARDYNAMICS
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Richard Hollis
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The next decade at PHENIX
 A biased (to Forward Calorimetry) view:




Gluon density at low-x in cold nuclear matter
Proton spin contribution from Gluon Polarization
Measure g-jet production, correlations in Au+Au collisions
Test predictions for the relation between single-transverse spin in
p+p and those in DIS
 For data taking and analysis over the course of the next
decade…
First step: measurements at high h
NUCLEARDYNAMICS
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Onset of Gluon Saturation
d+Au collisions
BRAHMS: PRL93 (2009) 242303
 Nuclear modification factor:
 Increasing suppression with h
 Consistent with the onset of gluon
saturation at small-x in the Au
nucleus.
 Need to study this in more detail by
 identifying particles
 expanding forward coverage
Central
Arms
Muon
Arms
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Proton spin contribution from gluon
polarization
p+p collisions
 Spin contribution from gluon
polarization
xDg
 derived from measured ALL
 currently over a narrow region
of x
 Large uncertainty at low-x
 Need to measure ALL over a
broader region of x
 forward h
 measure direct photons
RHIC
range
0.05 < x < 0.2
NUCLEARDYNAMICS
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Building detectors to suit physics needs
Need:
 Forward rapidities
 Direct photons
 Well defined energy scale for g measurements
NUCLEARDYNAMICS
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PHENIX Acceptance
 Tracking
 Central region and forward
muon arms
mTr
f coverage
2p
mTr
 Calorimetry
0
(F)VTX
 Very limited acceptance
 In f and h
-3
-2
-1
0
1
2
3 h
1
2
3 h
 What do we need for the
future?
0
 and how can we obtain it?
f coverage
2p
EMC
NUCLEARDYNAMICS
-3
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-2
-1
0
PHENIX Acceptance
-3
-2
-1
MPC
0
1
2
EMC
3 h
MPC
0
f coverage
 3.1<|h|<3.9
(F)VTX
0
 Muon Piston Calorimeter
(MPC)
2p
 Staged Calorimeter
Upgrades
mTr
f coverage
2p
mTr
NUCLEARDYNAMICS
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-2
-1
0
1
2
3 h
Muon Piston Calorimeter (MPC)
MPC(N)
 18cm long ~20X0
 2.2x2.2cm transverse
 220 (196) Crystals in N (S)
Counts
 Lead Scintillator (PbW04)
Raw Signal
 South Arm: -3.7<h<-3.1
 North Arm: 3.1<h< 3.9
 Measure p0’s up to 17 GeV
 pT~1.7 GeV/c
 pT>1.7GeV/c – measure single
“clusters”
NUCLEARDYNAMICS
Mixed-event
Background
Yield
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12 < E < 15 GeV
Physics Application
Mid-rapidity p0 Trigger
 Two-particle correlations
 Correlation of central arm p0
and h with MPC p0
 Measure jet modification in
d+Au collisions
Forward Associates
dN
df
Df
NUCLEARDYNAMICS
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Physics Application
Mid-rapidity p0 Trigger
 Two-particle correlations
 Correlation of central arm p0
and h with MPC p0
 Measure jet modification in
d+Au collisions
 Probe low-x (0.006<x<0.1)
 IdA suppression – a
signature of CGC
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Forward Associates
Physics Application
 Calorimeters are versatile
 Measurements using identified
cC and h are underway
3.0<h<4.0
 Preliminary results on
transverse single-spin
asymmetries
• Measurements over a broad
phase space will provide
quantitative tests for models
 How do the calorimeters
contribute to DG – the gluon
contribution to proton spin
 Would like to measure direct gs
NUCLEARDYNAMICS
p+pp0+X at s=62.4 GeV/c2
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PHENIX Acceptance
2p
mTr
f coverage
 Staged Calorimeter
Upgrades
(F)VTX
0
 Muon Piston Calorimeter
(MPC)
-3
 3.1<|h|<3.9
-2
-1
0
1
2
EMC
3 h
MPC
0
f coverage
2p
MPC
 Forward Calorimeter (FoCal)
 1<|h|<3
mTr
NUCLEARDYNAMICS
-3
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-2
-1
0
1
2
3 h
Finding space in PHENIX
MPC
MPC installed ~ 3<|h|<4
FoCal: where could it fit?
NUCLEARDYNAMICS
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Finding space in PHENIX
 Small space in front of
nosecone
 40 cm from vertex
 20 cm deep
 Calorimeter needs to be high
density
 Silicon-Tungsten sampling
calorimeter
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FoCal
Transverse View
 Silicon-Tungsten sampling
calorimeter
 21 layers ~21X0
 Each Arm: 1<|h|<3
Longitudinal View
 Expect good resolution in
E and h/f
6.1cm
 Active readout
~1.5x1.5cm
 Distinct 2-shower p0 up to
pT~3 GeV/c (h~1)
NUCLEARDYNAMICS
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FoCal x Coverage
p+p collisions
x versus pT (p+p, 500 GeV)
(FoCal Acceptance)
NUCLEARDYNAMICS
 x coverage:
 Weak pT dependence
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FoCal x Coverage
p+p collisions
x versus h (p+p, 500 GeV)
(FoCal Acceptance)
NUCLEARDYNAMICS
 x coverage:
 Weak pT dependence
 Strong h dependence
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FoCal x Coverage
p+p collisions
x versus h (p+p, 500 GeV)
(FoCal & MPC Acceptance)
NUCLEARDYNAMICS
 x coverage:
 Weak pT dependence
 Strong h dependence
 FoCal complementary to MPC
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FoCal x Coverage
x for h bins (p+p, 500 GeV)
(FoCal Acceptance)
 x coverage:
 Weak pT dependence
 Strong h dependence
 FoCal complementary to MPC
 Selecting h region probes a
specific x range
NUCLEARDYNAMICS
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FoCal (Expected) Performance
d+Au collisions
 Can one see jets over the
background
 Sufficiently isolated?
 Average background
• Units are measured energy
(~2% of total)
 Single-event background
• ~20 times higher
 30GeV embedded jet
• Visible over the background
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What about direct g identification?
 Important for our measurements in the next decade in
 Spin
 d+Au
 Au+Au
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Identifying p0 and g
p+p collisions
 First: use physics
Ratio of background/signal
(NLO calculation)
 Direct g typically are alone
 Whilst p0 are produced as part
of a hadronic jet
 Measurement of accompanying
energy can reduce background
at minimal expense to g
 Still, this does not provide full
decontamination
 Need direct p0 identification
NUCLEARDYNAMICS
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High energy p0 shower
p+p collisions
 Origin of all shower particles
(red)
 Shown with effective
resolution of pads
 Individual tracks not
distinguishable
NUCLEARDYNAMICS
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High energy p0 shower
p+p collisions
 Finer resolution could “see”
individual tracks from p0
 Up to ~50GeV
 Make the whole detector with finer
resolution!!
 Not realistic → what can be
designed?
NUCLEARDYNAMICS
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Richard Hollis
8th January 2010 ● 25
High energy p0 shower
p+p collisions
 Finer resolution could “see”
individual tracks from p0
 Up to ~50GeV
 Make the whole detector with finer
resolution!!
 Not realistic → what can be
designed?
EM0
EM1
EM2
~2 towers
~70 strips
 Add highly segmented layers of x/y
strips into first segment.
 Measure the development of the
shower at its infancy
 With a resolution to distinguish
individual g tracks
NUCLEARDYNAMICS
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x y
x y
x y
x y
High energy p0 shower
 Finer resolution could “see”
individual tracks from p0
Tracks are visibly
Separable
Track showers
Merge
 Up to ~50GeV
 Make the whole detector with finer
resolution!!
 Not realistic → what can be
designed?
 Add highly segmented layers of x/y
strips into first segment.
 Measure the development of the
shower at its infancy
 With a resolution to distinguish
individual g tracks
NUCLEARDYNAMICS
Catch the shower, before it’s too late
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8th January 2010 ● 27
High energy p0 shower
 Using a Hough Transform,
 Transverse/longitudinal
coordinate
 Find the best track as most
frequently occurring Houghslope
 Use each track vector, full track
energy → calculate invariant
mass
NUCLEARDYNAMICS
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8th January 2010 ● 28
Performance of FoCal Reconstruction
Reconstruction of p0
(p+p 500 GeV minimum bias pythia)
NUCLEARDYNAMICS
Signal reconstruction
(d+Au 200 GeV minimum bias +
embedded pythia g+jet signal)
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Summary
 PHENIX Calorimeter upgrades (will) provide much extended
coverage for a variety of physics topics
 Proven p0 reconstruction in the MPC further our understanding of
forward jet production in d+Au collisions
 FoCal complements the MPC in terms of additional phase-space
coverage and direct photon identification capabilities at high
energies.
 For p+p, d+Au (and Au+Au) collisions
NUCLEARDYNAMICS
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An energy scale for jet suppression
A+A collisions
 h-h correlations exhibit
interesting features … but have
limitations:
 may be subject to surface bias
 may not reveal the jet energy
scale
STAR: PRL103 (2009) 172301
STAR: NPA830 (2009) 685C
 g-h or g-jet could provide
 an energy scale
• (assuming) the g is not [energy]
suppressed
 Reduced surface bias
• as the trigger probe is not
modified
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MPC x Coverage
x versus h (p+p, 500 GeV)
(MPC Acceptance)
NUCLEARDYNAMICS
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8th January 2010 ● 32
d+Au collisions
 Correlation of central arm p0
and h with MPC p0
 Measured associate yields
relative to pp
 Systematic suppression with
centrality
 No appreciable trigger
dependence
 Probe low-x (0.006<x<0.1)
NUCLEARDYNAMICS
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