Transcript Document

a
FOrward CALorimeter
Overview
Richard Seto
Winter Workshop on Nuclear Dynamics
Feb 7, 2009
1
NSAC milestones – Physics Goals
Year
#
MileStone
FOCAL
2012
DM8
Determine gluon densities at low x in cold nuclei via p+ Au or d + Au collisions.
Required
for direct
photon
pA physics – nuclear gluon pdf
2013
HP12
G
2014
DM10
(new)
-Jet AuAu
2015
HP13
(new)
transverse
spin
phenomena
Utilize polarized proton collisions at center of mass energies of 200 and 500 GeV,
in combination with global QCD analyses, to determine if gluons have
appreciable polarization over any range of momentum fraction between 1 and
30% of the momentum of a polarized proton.
Low-x
Direct 
Measure jet and photon production and their correlations in A≈200 ion+ion
collisions at energies from medium RHIC energies to the highest achievable
energies at LHC.
DM10 captures efforts to measure jet correlations over a span of energies at
RHIC and a new program using the CERN Large Hadron Collider and its ALICE,
ATLAS and CMS detectors.
Marginal
without
FOCAL
Test unique QCD predictions for relation between single-transverse spin
phenomena in p-p scattering and those observed in deep-inelastic lepton
scattering
New Milestone HP13 reflects the intense activity and theoretical breakthroughs of
recent years in understanding the parton distribution functions accessed in spin
asymmetries for hard-scattering reactions involving a transversely polarized
proton. This leads to new experimental opportunities to test all our concepts for
analyzing hard scattering with perturbative QCD.
Required
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Nuclear Gluon PDF’s : DM8
Look for saturation
effects at low x
Saturation at
x  Measure initial state of
low x
Heavy Ion Collision
measure gluon PDF’s in
pA physics – nuclear gluon pdf
nuclei! (DM8)
xG(x)
x1 
pT 
x2 
pT 
s
s

(e
(e
 e Jet )

 e Jet )

direct 
jets –x resolution
forward η(low-x)
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Longitudinal Spin G, g(x) : HP12
0
LL
A
What is the gluon contribution to the proton spin. Is it at low-x?
Phenix and STAR have put constraints on G

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Longitudinal Spin G, g(x) : HP12
DSSV finds
 g(x) very small at medium x
(even compared to GRSV or DNS)
 best fit has a node at x ~ 0.1
 huge uncertainties at small x
Current data is sensitive to G for
xgluon= 0.020.3
small-x
0.001· x · 0.05
RHIC
range
x
0.05· x · 0.2
EXTEND MEASUREMENTS TO LOW x!
Forward
Measure x
direct 
jets –x resolution
forward η(low-x)
0 0
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Major new Thrust
Transverse Spin Phenomena: HP13
Sivers




use -jet to measure
Sivers
Use 0 in jet to
measure Collins
determination of the
process dependence of
the Sivers effect in
+jet events
So what does Sivers
tell us about orbital
angular momentum?
direct  -jet
0
forward η(low-x)
large η coverage
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Correlations with jets in heavy Ion
collisions: DM10
for example
“jet”


?
Study the medium via
long range correlations
with jets
are these correlations
from a response by the
medium?
leading
EM shower
EM - shower
large η coverage
Jet correlations in AuAu
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To meet these goals we must have a
detector that measures:





direct  and electromagnetic showers
jet angles to obtain x2
0 s
forward  to reach low-x
has large  coverage
now what do we build?
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Schematic of PHENIX
central magnet
MPC 3<||<4

Central Arms





||<0.3
Tracking
PbSc/PbGl(EMC)
PID
VTX to come

calorimetry
Muon arms





1.1<||<2.4
magnet
tracking
-ID
FVTX to come
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Perfect space for FOCAL! (but tight!)
40 cm from Vertex
FOCAL
14 EM bricks
14 HAD bricks
HAD behind EM
20 cm of space
nosecone
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FOCAL Requirements








Ability to measure photons and π0’s to 30 GeV
Energy resolution < 25%/E
Compact (20 cm depth)
Ability to identify EM/hadronic activity
Jet angular measurement
High granularity ~ similar to central arms
small mollier radius ~1.4 cm
large acceptance – rapidity coverage x2 ~ 0.001
Densest calorimeter -> Si W
We wanted large  coverage
what sort of coverage if we put a detector where the nosecones are?
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2
FOCAL a large acceptance calorimeter
MPC
tracking
tracking
Muon tracking
EMC
MPC
f coverage
EMC
FOCAL
Muon tracking
FOCAL
0
VTX & FVTX
-3
-2
-1
0
What’s missing?
1
2
3 rapidity
FORward CALorimetery
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reach in x2 for g(x) and GA(x)
s~Q
2
EMC+VTX
EMC+VTX+FOCAL
EMC+VTX+FOCAL+MPC
log(x2)
X2  10-3
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FOCAL Design
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Overall Detector – stack the bricks
“brick”
supertower
85 cm
Note this
ledge may not be
in the final design
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Design Tungsten-Silicon
Pads: 21 layers
535 m silicon
16 cells: 15.5mmx15.5mm


Pads
Silicon
Design
X and Y Strips: 4 layers

x-y high resolution strip planes

segments=
128 strips: 6.2cmx0.5mm
γ/π0 Discriminator=EM0
EM1
EM2
Supertower
Particle
Direction
6cm
4 planes of x-y “strips”
(8 physical planes)
Silicon “pads”
4 mm W 16
Vital statistics

~17 cm in length
22 X0 ~ 0.9

Strips – read out by SVX-4
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EM0= /0, EM1, EM2 segments
8 layer *128 strips=1024 strips/super-tower
1024 strips/super-tower*160 super-towers/side = 163,840 strips/side
163840 strips/side (1detector/128 strips) = 1280 Strip Detectors/side
163,840 strips /(128 channels/chip)= 1280 chips/side
Pads – read out by ADC– 3 longitudinal readouts

160 supertowers/side*21 detectors/supertower=
 3360 Si pad detectors/side


3360 detector*16channels/detector= 53760 pads/side
readout channels (pads)


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160 supe-rtowers/side *16 pads/tower*3 towers =7680 readouts/side
Bricks

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2x4 supertowers: 4
2x6 supertowers: 6
2x7 supertowers: 4
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Detection – how it works
Some detector performance
examples
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Status of simulations

Stand alone done w/ GEANT3/G4 to study

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Full PISA
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jet resolution (G3/PISA)
2 track 0 (G3/PISA)
Several levels

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/0 separation, single track 0 (G4)
EM shower energy/angle resolutions (G4)
Statistical errors, backgrounds, resolutions folded into Pythia level
calculations
Full PISA simulation using old configuration
Transverse spin physics – task force formed – simulations in
progress (early step is to put models etc into simulations)
*PISA – PHENIX Geant3 simulation
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It’s a tracking device
EM0
EM1
EM2
A 10 GeV photon “track”
Pixel-like tracking:
3 layers + vertex
Each “hit” is the
center of gravity
of the cluster in
the segment
vertex
Iterative pattern
recognition
algorithm uses a
parameterization
of the shower
shape for energy
sharing among
clusters in a
segment and among
tracks in the
calorimeter.
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Energy Resolution (Geant4)
New Geometry
Excludes Strips
no sampling fraction correction
0.00+0.20/√E
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adequate: we wanted ~ 0.25/√E
/0 identification: pp 2 track 0 pT<5 GeV
E=6-10 GeV
pt=1.-1.5
y=1-1.5
pt=0.5-1.0
y=1.5-2.0
pt=2.-2.5
y=1-1.5
pt=1.5-2.0
y=1.5-2.0
pt=4.-4.5
y=1-1.5
pt=0.5-1.0
y=2-2.5
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/0 identification:
Single track /0

50 GeV pi0
for pt>5 GeV




showers overlap
use x/y + vertex to
get opening angle
Energy from
Calorimeter
Energy Asymmetry –
assume 50-50 split
as a first algorithm
4-x, 2x
X-view
Y-view
4-y, 3y
invariant mass
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10 GeV
~1.65 (Geant4-pp events)
Assumed 0 region
0
Assumed  region

/0 identification: single track /0
tested at various energies and angles, so far at pp multiplicities
Fake  reconstruction: 20%
Real 0 reconstruction: 50-60%
Real  reconstruction: ~ 60%
Fake 0 reconstruction ~ 5%
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Longitudinal Spin G, g(x) : HP12
ALL
GSC, Response +
Background
150/pb, P=0.7
RHIC
region
FOCAL Direct Gamma ALL
next step: use -jet to constrain x
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Selecting x with rapidity cuts 0 0
0
LL
A
log(x2)
GSC
DSSV
(2nd 0)



Longitudinal Spin Goal
Use 0 as a stand in for jets and do a correlation
require 1st 0 pT>2.5 GeV, =1-3 (into focal)
Choose 2nd 0 to be opposite side in f and  to go to low x2
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“Direct” Constraint of G(x) in Nuclei:DM8
Valence
Gluon
Sea
GPb ( x)
G p ( x)
Eskola et al, JHEP0807:102,2008 hep-ph/0802.0139
q

Compton
g
q
Annihilation
q
•G(x) in nuclei almost unconstrained at low x
•Proposal: Measure -jet in d+Au collisions to extract G(x) in nuclei
q

g
unknown
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Resolutions

EM shower



energy – 20%/E
angular – 6mr
xgluon 
Jet angular resolution

pT 
s
(e

 eJet )
60 mr @ pt=20 GeV
jet angular
resolution
x2~ resolution 15%
pT
x2 / x2
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Expected Error for GA(x)/Gp(x) :DM8
pT jet>4 GeV, ptgamma>2
d+Au: Ldt = 0.45 pb -1 x 0.25 eff
p+p: Ldt = 240 pb-1 x 0.25 eff
G(x)Au/G(x)p
Current uncertainty
Log(x2)
•Possibility for a dramatic improvement in understanding of G(x) in nuclei
•Impact is widespread
•Errors are statistical only
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Studying the medium through jet “tomography” DM10
leading
particle
hadrons
leading particle
suppressed
q
hadrons
q
q
q
hadrons
leading
particle
hadrons
leading particle
suppressed
trig
assoc
pT >2.5 GeV/c, pT
> 20 MeV/c,
Au+Au 0-30%
“jet”
jet
ridge
E. Wenger (PHOBOS), QM2008
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Jet correlation studies with the FoCal

Need




higher-pT triggers,
Extended  reach
large 
How:



DM10
trigger on high-energy  in FoCal
study associated particles in central and muon arms
What:



Extended  reach and  range (~6)
Study particle composition of correlated particles using
central/muon arm PID detectors including photons
Heavy-quark studies via leptons in central/muon arms
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Strategy:

Parameterize background by studying average energy
deposited in the detector (E) and its fluctuations (RMS)
Study efficiency and contamination for set values of Nσ
 Emeas  E 
N  

RMS


2
/0 trigger eff, AuAu b=3.2 fm
=[1.,1.5] Ecut> ~15 GeV
/0 trigger eff

E
ERMS
background
assuming
pp high pt
rates
S:B~10:1
high pT em shower
embedded in
hijing
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Conclusion

We want to address the following NSAC milestones





These goals can addressed by calorimeter which




measure G at low-x to see if the gluon contributes to the proton
spin
measure the nuclear gluon pdf’s
to study the effects of transverse spin and its connection to the
orbital angular momentum of the constituents of the proton
Study long range correlations between jets and secondary particles
as a means to understand the medium created in heavy ion
collisions at RHIC
can identify and measure s and 0
can measure the jet angular resolution and together with the
information from the  can lead to a reasonable measurement of x2
has large rapidity coverage and can probe x2  10-3
We now have a have design

Prototype in April
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