1. Simulation study for Forward Calorimeter in LHC-ALICE experiment
Y.Hori, H.Hamagaki, T.Gunji
University of Tokyo, CNS

2. Outline Physics Motivation and Measurement Items
Detector Requirements and its Design
Simulation study of performance
Hardware considerations
Summary and Outlook

3. Physics Motivation Gluon PDF in small-x Gluon saturation
Nuclear dependence of
saturation scale, shadowing

4. Measurement items (x, Q2) map covered by FOCAL Measurement items
Prompt g at h=3~4(5)
p0-jets or dijets
at h=3~4(5) || h=-1~1
Both in p+p,p+Pb collisions
x and pt range of prompt g production (LO level 90% compton)
large-x parton
(quark)
Small-x parton
(gluon)

5. Requirement for the detector
Large dynamic range ( Energy 1 ~ 200GeV)
p0/g separation (two g separation ~ 6mm)　FOCAL z position =4.5m
Fine segmentation
 0.01 particle/cm2 at h~4 in 8.8TeV p+Pb central collisions
Pt (GeV/c) 1 3 7
P(GeV/c)
27.3
81.9
191
2g distance (cm)
4.6
1.5
0.66
p0 kinematics h= 3.5~4
Inclusive g number at FOCAL (z=450) p+Pb 8.8TeV collisions by HIJING
Inclusive g
Pt > 0.5 GeV/c
Pt > 1 GeV/c

6. IP
- 4.5 m
ALICE

7. Conceptual Design of FOCAL Module
Particle
electronics
Silicon Tungsten sampling Calorimeter like PHENIX FOCAL
W is a good absorber
( radiation length X0 = 3.5 mm, Moliere radius = 9 mm)
With Silicon Strip detector for 2 g separation from p0
Fine segment (Si Pad 1cm x 1cm)
X-Y Si Strip
Si Pad + W
Silicon 0.3 mm thickness
2 layers
Strip pitch mm
Si thickness mm
W thickness mm
Pad 1 cm x 1cm
7 layers x 3 segments = 21 layers
total depth 21X0
Charged VETO
Same detector as Si Strip

8. Basic performance and g ID
Linearity up to 200 GeV g < 1%
Sampling fraction ~ 1.4%
detection efficiency > 95%
Energy resolution ~ %
Position resolution ~ 1.5 mm at 10 GeV
Charged hadron/g separation using longitudinal shower profile
p+ rejection g efficiency 90% at 100 GeV

9. 　p0 inv. Mass in HIJING
Two g invariant mass at 3<h<3.5 from HIJING p+Pb event at 8.8 TeV. (Energy and position are smeared according to the resolution.)
S/N ratio

10. p0 reconstruction efficiency
By Invariant mass method using Si Pad detector
Reconstruction efficiency
Reconstruction efficiency with energy
asymmetry cut (<0.8).
Merging Probability [%]
Probability that two g go into neighboring pad.
Probability that two g go into same pad.
p0 up to 70 GeV (pT=7 at h=3) can be measured by invariant
mass method. For the p0 with more than E>70 GeV, we have to
use alternative method.

11. High Energy p02g kinematics
Minimum 2 g distance at FOCAL
- 12mm for 100 GeV p0
- 6mm for 200 GeV p0
2g distance from GeV p0 is constant for energy
asymmetry < 0.8.
Position measurement of 2 g by Si Strip detector and merged
energy measurement by Si Pad detector are useful to identify p0
10 GeV
50,100,200 GeV

12. p0 reconstruction using Si Strip detector
Locate a cluster with large energy deposit in the Si Pad & define search region in the Si Strip
Search for 2 clusters in the Si Strip & obtain distance between the clusters
Applied cut with total energy deposit and 2 clusters distance
Second
cluster
Mask area
First cluster
Strip position (/0.5mm)
200GeV
150GeV
100GeV
70GeV

13. p0 reconstruction using Si Strip detector
Efficiency vs.
position of the strip layer
Efficiency vs. p0 energy for
1mm, 0.5mm strip pitch
200GeVp0
100GeVp0
0.5 mm pitch strip at 6X0
1 mm pitch strip at 6X0
Parameters used in reconstruction algorithm is optimized so that
the contamination is < 1%
50% of the identification efficiency of high energy p0 (>100 GeV)
is achieved using the one strip layer around 5-7X0.

14. R&D of Si Pad detector and Conceptual design of readout electronics
9 inch wafer, 8 x 8 Pad with the size of 1.1 cm x 1.1cm
Heavy alloy
94W-4Ni-2Cu(non-magnetic, density = 17.9g/cm3)
dual amplifier ASIC
charge divide type
requirement - dynamic range 50fC – 500pC
- S/N at MIP = 10
under developed
ADC ALTRO chip
25MHz, 10bit ADC and
digital firmware
We begin to construct prototype
C high
C low

15. Summary and Outlook LHC is suitable place to study small-x physics.
prompt g and jets at forward rapidity are good probe for this
study.
Simulation study was conducted to evaluate the possible detector
design.
In terms of occupancy and p0/g separation, Si - W
Calorimeter with Si Strip is a good choice.
Basics performance was carefully checked.
p0 identification algorithm is developed and the efficiency is
calculated.
Next, we will do full simulation and construct a prototype
Hardware issue - how to realize large dynamic range
⇒　may lead severe cross talk
- how to assemble readout electronics

16. p0 and g yield

17. Prompt g BG

18. Isolation Prompt g Fragment g g from eta g from pi0
Isolation : pT (sum of associated particles in R<0.7) < 0.2*pT(photon)
[R = cone radius defined by sqrt(dh2 + df2)]
Efficiency for isolation cut (0.2):
Prompt g
Fragment g
g from eta
g from pi0
Rejection (efficiency):
pi0 = 50 5 GeV
eta = 20 5 GeV
Efficiency for photons
Prompt = 80% @ 5 GeV
Frag. Photons = 5GeV
S/N w/o isolation = GeV (10 GeV)
S/N with isolation = GeV (10GeV)

19. Simulation Study Longitudinal shower profile Good EM shower profile
Linearity : -1% up to 200 GeV
Dynamic range:
1.2MeV (MIP) - 3 GeV (200GeV g)

20. Si-pad design
9 inch wafer 8x8 pads with 1cm x 1cm