Forward Calorimeter (FoCal)
Upgrade Project in ALICE
for LHC Run-4
Tatsuya Chujo(Univ. of Tsukuba)

TGSW2021, September 11, 2021 (online)

2/15

How QGP is created?
-100.620Time t (fm/c)

Thermalization: ~0.6 fm/c

©︎ S.Bass

CGC?

(undiscovered yet)collision

Quark Gluon Plazma(QGP)

New research

Hadronization

Freeze-out

On-going researchhigh velocity

Three Open Questions
Q1) What is the origin of QGP? 

Q2) Why QGC rapidly thermalized?

Q3) Does Color Glass Condensate exist?
What is Color Glass Condensate (Gluon Saturation)?

日経サイエンス 2015年8月号

ProtonCGC !

・Predicted by QCD, a universal state of matter can be unveiled at high energy, Undiscovered yet!
・No. of gluons increase → Gluon fusion at some point → Gluon Saturation → Color Glass Condensate

3/15

Early universe vs. high energy heavy ion collisions
Big bang

Little bang
t0+3×10-23 sec. duration

t0+137 ×108 years (now)

CMB

Same？

gaz
hadronhadrongas
QGP

QGP
Color Glass
Condensate？

t0Universe
proton, neutrontime（μs）

QGPT (MeV)

T (MeV)

QGP

Heavy Ion
Collisions
proton, neutrontime（fm/c）

New physics explored by zero degree frontier at high energy
θ=90°

η=0

•To Find CGC…

① Forward→ Zero degrees② Higher energy→ Highest collision energy at LHC

θ=0°

Put detector at very forward region③ Sensitive probe → Photons④ proton < Lead

→ Heavy ion acceleration at LHC

Q ~ pT (Transverse Momentum)（GeV)

LHC
New regime to be explored

Direct measurement of gluon
density by “photons”(penetrating and sensitive probe)

by FoCal

6 times faster to create CGC

by using Lead nucleus

Satisfied all 4 points,

Access to the new regime to detect CGC clearly

for the first time
→ Physics case is compelling

Expected region

for CGC

Higher energy/ more forward

4/15

x≈

2pTsexp−η1. Quantify nuclear modification of the gluon density at small-x• Isolated photons in pp and pPb collisions

2. Explore non-linear QCD evolution

0-π0 and isolated photon-π0 (or jet) correlations
Azimuthalπ•in pp and pPb collisions

3. Investigate the origin of long range flow-like correlations• Azimuthal π0-h correlations using FoCal and central ALICE(and muon arm?) in pp and pPb collisions

4. Explore jet quenching at forward rapidity• Measure high pT neutral pion production in PbPb

Access to an unexplored small-x and low Q2 region:
0- Direct photon, π and jet (+correlations) measurements atvery forward rapidity in pp and p-Pb @ LHC

EPPS16x

R gPb (x, Q 2 = 10 GeV2)

FoCal: Physics goals

R gPb (x, Q 2 = 1 .69 GeV2)

5/15

EPPS16x

Physics Goal: unravel nucleus
structure at small-x
Observables in 3.4 < η < 5.8 @ LHC:••••π0 (and other neutral mesons)
Isolated (direct) photons
Jets (and di-jets)
etc…

6/15

The FoCal project
FoCal-H

FoCal
FoCal-E: high-granularity Si-W sampling
calorimeter for photons and π0
FoCal-H: conventional metal-scintillator
sampling calorimeter for photon isolationand jets

FoCal-E

FoCal LoI has been approved by LHCC
on June 5, 2020
Public Note (LoI) : CERN-LHCC-2020-009- Test beam: 2021 - 2022
- TDR submission : 2022

3.4 < η < 5.8(baseline design @ 7m from IP)

Conceptual design
FoCal-E

20 layers of W(3.5 mm ≈ 1X0) + silicon sensors:
Two types: Pad (LG) and Pixel (HG)

• Pad: shower profile and total energy• Pixel: position resolution to resolve overlapping showers
Separate γ/π0 at high energy
Two photon separation from π0 decay (pT=10 GeV, η=4.5) ~5mm

• Requires small Molière radius and high granularity readout• Si-W calorimeter with effective granularity ≈ 1mm2
FoCal-H

Longitudinal profile (2γ showers)

Trans. profile

Conventional metal-scintillator design
Sampling / tower structure not yet defined
No longitudinal readout required

7/15

8/15

Detector R&D

9/15

CERN PS/SPS (2014)

ELPH (2017)

CERN SPS (2015)

CERN PS/SPS (2018)

CERN SPS (2016)

ELPH (2021.02 & 07)

10/15Full module mini-FoCal at PS, SPS, LHC (2018)
Test beam analysis results
Y. Minato

p+p @ √s = 13 TeV collisions
in ALICE

ΔE/E = 3.6 %@ 150 GeV/c , e- (SPS)(not the final placement)

Module design approaching final geometry
3 PAD sensors, 8x8 pads each• 60 instrumented pad sensor wafers• ~3600 channels• APV25 hybrid + SRS readout• built in Tsukuba• beam tests at CERN
(PS, SPS, ALICE)

Mini-Focal data:
Real pairs Analysis Cuts:

4000

Mixed pairs Distance > 1.5 cm

Energy > 35 GeVentries

APV readout hybrids

π0 peakN. Novitzky

2000

00

0.2

0.4

0.6

Mγ γ [GeV/c]

0.81FoCal-E PAD: main sensor (8x9, p-type, 320um)

11/15

Hamamatsu S16211-0813
p-sub, 320 um, w/ Al,
1 cm2 pad cell size

First time use of p-type for FoCal- 8x9 cells + calibration cells (w/Al),
produced 30, and delivered.

- More rad. hard than n-type.
- Compatible with HGCROC (readout
ASIC for final detector).

front side (w/ Al)back side (Au)
(Tsukuba / RIKEN)

Cosmic test bench for FoCal-E pad

12/15

N. Novitzky• Clear MIP signals seen by the cosmic ray data taking for 8x9 main sensor.
• Plan: will order new design of p-type main sensors (20) and n-type (20) in 2021.

EPICAL-2 test beam at DESY (2019/2020)
Number of pixel hits

13/15

Energy resolution

pixel hits

Two shower separation
50

EPICAL-2 preliminary

Allpix2 simulation

30 GeV e- + 250 GeV e1.2 mm separation

single event

first 6 layers integrated

40302010300 320 340 360

380 400 420

row

0280440column71887 hits

6400

5200

4032002

Detailed response simulations with AllPix2

Cluster counting provide better energy
resolution than hit counting

1400

0200

400600800

1000
columnTwo-shower separation down to0 1 mm should be possible

Digital pixel calorimetry: good energy resolution and excellent spatial resolution

14/15

FoCal test beam experiments in 2021/2022(1) SPS test beam:• H6 beam line, up to ~120 GeV• Sep-Oct. in 2021, and another one in 2022.
FoCal-E• 2 single pad (2021), and 2 pixel layers• 18 single pad (2022), and 2 pixel layers• Use final readout: HGCROC for PAD

FoCal-H
FoCal-E

beam

FoCal-H• 10 x10cm2 area, 60-80cm depth (TBD)(2) Irradiation test @ RIKEN RANS
(3) Beam test @ KEK PF-AR (under construction)

TEST module of FoCal-E pad with HGCROC
To be shipped to CERN for test beam in Sep. 2021

15/15
t0+3×10-23 sec. duration

Summary• Unique capability to access the origin of QGP creation.
0 measurements in forward region at
Isolatedphoton&π•
LHC, for CGC search and determination of nuclear PDF forgluons.

• Silicon-tungsten + PIXEL hybrid detector for EM Calorimeter
part, conventional hadronic calorimeter for hadronic part.

• Endorsed towards Technical Design Report (TDR) by LHCC
in 2020 as a LHC Run-4 upgrade project (2027-).

• Final R&D and evaluations are ongoing.

gazhadronhadrongas
QGP
QGP
Color GlassCondensate？
CGC

FoCal Japanese Institues, partners•

University of Tsukuba:••

Tsukuba University of Technology:••

Yuji Goto, Itaru Nakagawa, Ralf Seidl, Minho Kim, Shima Shimizu,(Kumaoka, JRA D2)

Nagasaki Institute of Applied Science:••

Maya Shimomura, Takashi Hachiya, (B4 student)

RIKEN:••

Toru Sugitate

Nara Women’s University:••

Motoi Inaba

Hiroshima University:••

Tatsuya Chujo, Norbert Novitzky, Yasuo Miake, (new Post-Doc), Takuya
Kumaoka (D2), Yuuki Asatani (M1)

Ken Oyama

Saga University:•Takahito Fusayasu

Cooperative Institutes• Grenoble LPSC: Guernane, Bourrion, Rabi, ...
• Utrecht Univ. / Nikhef: Peitzmann, van Leeuwen(CiC research unit invitation)• KEK Silicon Platform (B) : Tojo, Togawa et al.

List of institutes participating in FoCal (from LoI)

Thank you for yourattentions!

Irradiation test at RIKEN• RIKEN (Wako) RANS, (RIKEN Accelerator
driven compact Neutron Source)• RANS: Proton 7MeV, 100μA, 6 x
1013proton/s, Be target, Neutron 5MeV
max., 1012neutron/s from the target.

• RANS-II: Proton 2.49MeV, 100μA, Litarget, Neutron 0.7MeV max.

• RIKEN/ Tsukuba/ Tsukuba Tech.
• Plan: IV, CV measurements for n-type, ptype sensor with neutron monitor(Kyushu Univ.)

KEK PF-AR
Photon Factory Advance Ring (PF-AR)
New experimental area

- 6.5 GeV and 5 GeV operation- 1.3 μs cycle (single bunch)beam

100 μm φ carbon wireCu
carbon wire to beam halo

- Beam optics committing during the summer shutdown, July-Sep. 2021
- In mid-October, the first beam expected.
- Together with Kyushu Univ, we are going to make beam monitor- We are potentially a main user of this beam line after commissioning.
- Good for FoCal final R&D and calibration etc.

FoCal-E PIXEL
9 ALPIDE chips on a flex cable:
30 x1.5 cm2(developed for pCT application)

Full module: 2 x 3 “strings”

MIMOSA pixel calorimeter→FoCal design: 15-chip flex cables

Flex cable design is progressing(Bergen, Utrecht / Nikhef, LTU, Kharkov)

EPICAL: (sm)all-pixel E-cal prototype

Timeline• Next important step:Entering the engineering phase towards testbeam(s) 2021/22 and TDR• Production estimated to fit well into 24 months• Plus half a year of "learning curve"(not adjusted for Covid-19 changes)

FoCal-H
Plan for test beam (2021)- HCal prototype based on Cu capillary tubes- Fibers and tube samples acquired
Performance/resolution simulations (on-going)- Optimize performance, e.g. optimal ratio of activepassive material, granularity.
- large run time in had. shower simulation, but solutions
being worked out
Choice of readout (SiPM/APD)- SiPM being explored: more cost-effective and HGCROC
compatible version exists(Copenhagen)(Similar approach suggested and being tested by
IDEA collaboration in Oct 2020, e.g. see talk)

Energy resolution for charged pions

FoCal-E integration
Module:18 PAD layers + 2 PIXEL layers
16 cm

8 cm

45 cm

Readout, power, cooling are connected on one side

FoCal-E: 22 modules

Key ingredients for isolated photon measurement
π0 reconstruction efficiency

Isolation energy distribution

Direct γ/all cluster ratio

Cut at 2 GeV

Main ingredients for direct photon identification

0 reconstruction efficiency: measure backgroundπ•• Isolation cut (EmCal + HCal)• Rejection of decays by invariant mass reconstruction

Improvement in signal fraction by factor ~10 to ~0.1-0.6

Expected performance and impact on nPDF
1 + rel unc

R. Khalek et al.,arXiv:1904.00018
1.4p-Pb, s = 8.8 TeV
4.75 < η < 5.25
lab
ALICE simulation

1.2

10.8

L = 50 nb-1

INCnlo based
Eff. err.=0.05
Decay err.=0.05

10200.6030p (GeV)T• Systematic uncertainty ~20% at ~4 GeV• Below ~6 GeV, uncertainty rises due toremaining background• Significant improvement (up to factor 2)

on EPPS16 gluon PDF• Similar improvement as from open charm• Test factorization/universality• Below 4 GeV: challenging regime• Also measure direct photons bystatistical subtraction

Recent nuclear PDFs: nNNPDF from DIS
and minimal theoretical assumptions• No constraints for x < 10-2 from DIS• FOCAL provides significant constraints•

over a broad range: ~10-5 - 10-2
Outperforming the EIC for x < 10-3