A Proposed
FOrward CALorimeter Upgrade in PHENIX
Richard Hollis for the PHENIX Collaboration
University of California, Riverside
CAARI 2010
12th August 2010
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Overview
The next decade at RHIC&PHENIXMotivation and Needs
Overview of Current PHENIX DetectorFuture: FOCAL
Event Reconstruction and Expected Impact
Summary
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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 -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
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Onset of Gluon Saturation
Nuclear modification factor: Increasing suppression with
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
BRAHMS: PRL93 (2004) 242303
d+Au collisions
CentralArms
MuonArms
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Theoretical Guidance
Current theoretical description of nuclear pdfs (at small x) is unconstrained How to reduce the
uncertainty?
We can directly access the gluon pdf from direct-
Direct- is a simple measurement as there is no fragmentation function
Access to low-x at high rapidity
EPS09: NPA830 (2010) 599c
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Building detectors to suit physics needs
Need:Forward rapiditiesDirect photonsWell defined energy scale for measurements
Current PHENIX Detector
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The PHENIX Detector
General features
Central region: E-M Calorimeter
• Electron/photon energy measurements
Tracking• Charged particle momenta
Time of Flight• Charged particle identification
Forward region: Muon Tracker
• Muon identification and momentum
Calorimeter• Very forward photons
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The PHENIX Detector
MPC
Muon TrackerMuon identification and momentum
CalorimeterVery forward photons
TriggerBBC and ZDC
E-M CalorimeterElectron/photon energy measurements
TrackingCharged particle momenta
Time of FlightCharged particle identification
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PHENIX Acceptance
Tracking Central region and forward
muon arms
Calorimetry Very limited acceptance
In and
What do we need for the future? and how can we obtain it?
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PHENIX Acceptance
Staged Calorimeter Upgrades
Muon Piston Calorimeter (MPC) 3.1<||<3.9
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EMCMPC MPC
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PHENIX Acceptance
Staged Calorimeter Upgrades
Muon Piston Calorimeter (MPC) 3.1<||<3.9
Forward Calorimeter (FoCal) 1.6<<2.5 d-going side in d+Au
collisions
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EMCMPC MPC
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Finding space in PHENIX
MPC installed ~ 3<||<4
MPC
FoCal: where could it fit?
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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
Silicon-Tungsten sampling calorimeter 21 layers ~21X0
d-side Arm: 1.6<<2.5
Expect good resolution in E and / Active readout
~1.5x1.5cm
Distinct 2-shower 0 up to pT~2 GeV/c (~1.6)
Transverse View
Longitudinal View
6.1cm
Instrumented region
S2
S1
S0
1 “brick”
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FOCAL Technology
Tungsten High density for compactness
Silicon Compact Segmentation is easy/versatile
Can be built in stackable blocks
Read-out: 163 pads per brick 12824 strips per brick
Beam S2
S1
S0
Test-beam setup (CERN 2009)
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FoCal x Coverage
Remember: we need low-x
x coverage: Weak pT dependence
p+p collisions
x versus pT (p+p, 200 GeV)(FoCal Acceptance)
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FoCal x Coverage
Remember: we need low-x
x coverage: Weak pT dependence
Strong dependence
p+p collisions
x versus (p+p, 200 GeV)(FoCal Acceptance)
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FoCal x Coverage
p+p collisions
x versus (p+p, 200 GeV)(FoCal & MPC Acceptance)
Remember: we need low-x
x coverage: Weak pT dependence
Strong dependence FoCal complementary to MPC
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FoCal x Coverage
x for bins (p+p, 200 GeV)(FoCal Acceptance)
Remember: we need low-x
x coverage: Weak pT dependence
Strong dependence FoCal complementary to MPC
Selecting region probes a specific x range
1.6<<2.02.0<<2.5
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FoCal (Expected) Performance
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
d+Au collisions
Note: Simulation of fully-instrumented FOCAL
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What about direct identification?
Important for our measurements in the next decade in Spin d+Au Au+Au
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Identifying 0 and
First: use physics Direct typically are alone Whilst 0 are produced as part
of a hadronic jet Measurement of accompanying
energy can reduce background at minimal expense to
Still, this does not provide full decontamination Need direct 0 identification
Ratio of background/signal(NLO calculation)
p+p collisions
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High energy 0 shower
Origin of all shower particles (red) Shown with effective
resolution of pads
Individual tracks not distinguishable
p+p collisions
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High energy 0 shower
Finer resolution could “see” individual tracks from 0 Up to ~50GeV
Make the whole detector with finer resolution!! Not realistic → what can be
designed?
p+p collisions
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High energy 0 shower
Finer resolution could “see” individual tracks from 0 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 tracks
EM0 EM1 EM2
x y x y x y x y
~2 tow
ers
~70 strips
p+p collisions
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High energy 0 shower
Finer resolution could “see” individual tracks from 0 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 tracksCatch the shower, before it’s too late
Tracks are visiblySeparable
Track showersMerge
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High energy 0 shower
Using a Hough Transform, Transverse/longitudinal
coordinate Find the best track as most
frequently occurring Hough-slope
Use each track vector, full track energy → calculate invariant mass
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High energy 0 reconstruction
Reconstruction of single and 0’s with FOCAL
Observe: good separation of peak and 0 mass peak
Low mass peak from 0’s due to: Large-angle decays One (from 0→) dominating
(asymmetric energy) Only one conversion
Single Particle Simulation
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Understanding the background sources
For each track Found the closest primary
particle Sorted into 4 categories:
0 – is a 0
hit – but not 0, , or dir-Hadron – any
– is an
Full PYTHIA Simulation
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Currently Expected Sensitivity
Lines: nuclear pdf fits based on current data EPS09
Colors represent nuclear pdfs fits with respect to FOCAL uncertainties B lue: within 1 Purple: 2 Cyan: 3
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Summary
PHENIX Forward Calorimeter upgrade (will) provide much extended coverage for a variety of physics topics FoCal complements the existing detectors in terms of additional
phase-space coverage and direct photon identification capabilities at high energies.
Novel design integrates a calorimeter and a tracking device For p+p, d+Au (and Au+Au) collisions