ALICE FoCal and EIC~ Complementary and similarity on QCD study ~Tatsuya Chujo

TCHoU workshop, March 29, 2024, Tsukuba, JapanForward LHC (FoCal)

FoCal-H
Hadronic Calorimeter

FoCal-E(pad, pixel)

2

Electromagnetic Calorimeter- Forward Calorimeter- LHC ALICE, √sNN = 8.8 TeV, pp, pA- Non-linear QCD evolution, Color

z=7m

glass condensate, initial stages of
Quark Gluon Plasma (QGP)

Main Observables:- Physics in LHC Run 4 (2029-2032)- TDR approved by LHCC onMarch 2024

3.4 < η < 5.8

FoCal (LoI) : CERN-LHCC-2020-009

η = − ln(tan(θ/2))* T. Chujo (FoCal co-project leader, E-pad rep.)

Collision Point (IP2)

••
••
•

π0 (and other neutral mesons)
Isolated (direct) photons
Jets (and di-jets)
Correlations
J/Ψ, UPCEIC eA- Brookhaven National Lab. (BNL, USA)
- Will start operation in 2032
- High luminosity polarized e, p / Ion collider at √s = 28-140 GeV- Luminosity: x100 ~ 1000 higher higher than HERA
- 1st detector: ePIC collaboration
Physics at Electron-Ion Collider (EIC)•Origin of nucleon mass and spin
•3D structure of the nucleon and nucleus•Gluon saturation (Color Glass Condensate)•Hadronization3

What is the Color GlassCondensate (CGC)?

Internal structure of proton and high energy limit
Structure of proton
small xlarge xx = 10−2x = pq,g / p

Mechanism of multipole gluon creations
・Lifetime of parton’s fluctuations: p → Larger, Lifetime → Longer
・Probability of fluctuation generation: x → smaller, Prob. → Larger→ At high energy, increased small fluctuations exponentially !

56Color Glass Condensate (CGC)g →gg

protonK. Watanabe

gluon splitting

∝ Ng

CGC!

nucleusgg →ggluon merge（non-linear effect）∝ Ng2e.g.）Logistic Eq.
dN(t) = κ ((N(t) − N(t)2)
dt⇄ Balitsky-Kovchegov (BK) e.q.

Universality
Saturation

Large xmid-rapidity
Low energy scattering

Small xx≈

2pTs

exp−η

forward rapidity
High energy scattering

7

Color Glass Condensate (CGC)
CGC!
g →gg
gluon splitting∝ Ng

Large xmid-rapidity
Low energy scattering

Small xx≈

2pTs

exp−η

forward rapidityHigh energy scattering

gg →ggluon merge（non-linear effect）∝ Ng2e.g.）Logistic Eq.
dN(t) = κ ((N(t) − N(t)2)
dt⇄ Balitsky-Kovchegov (BK) e.q.

UniversalitySaturation

Where we can see CGC?
2Qs(x)

αs << 1geom

DGLAP• Universal picture of internal structure ofhigh energy hadron (universality)• Log-Log plot !

scalingln Q

ric2

etJIMWLK
BK• Small x and low Q region (but Q >> ΛQCD)→ Essential to explore a wide x-Q2 space• Non-linear QCD evolution

BFKL• Find CGC signal → Gluon densitysaturation
non-perturbative regionln x

αs ~ 18

How we probe gluon density (dipole formalism)

9e+A DISObservables : int. cross section, Structure func. (F2, FL)

qγ∗

x⊥

x⊥

Forward p+AObservables: Inclusive π0, jet, direct γ, γ-jet, di-jet

K. Itakura

e+A DIS & p+A forward observables: same theoretical Framework “ColorDipole (Quadrupole) Formalism”→ NLO cal. is possible→Comparison e+A DIS with forward p+A：Universality of QCD can be tested

10EIC vs. forward LHC
DIS (EIC) eAx≈

2pTsexp−η

- Study of saturation requires to study evolution of observables over large range in x at low Q2- Forward LHC (+RHIC) and EIC are complementary: together they provide a huge lever arm in x
- EIC: Precision control of kinematics + polarization- Forward LHC: Significantly lower x- Observables: isolated γ, jets, open charm, DY, W/Z, hadrons, UPC- Observables in DIS and forward LHC are fundamentally connected via same underlying dipole operator- Multi-messenger program to test QCD universality: does saturation provide a coherent description ofall observables, and is therefore a universal description of the high gluon density regime?

Forward pA
at high energies

11

Key points to understand CGC and QCD• Need a clear CGC signal
2Qs(x)• Hadron measurement →Uncertainty by fragmentation

gealingln Qsc• Explore wide rage of x-Q2 space

ric

2et

• Need to see non-linear evolution of QCD

JIMWLKBK

BFKLsaturation• Theoretically calculable and compare with data (CGC

non-perturbative region

weakly coupled physics) → color dipoleln x• High precision measurements (statistic, systematic)qγ∗（LHC forward pA, EIC eA）

DGLAPom• Need a clean probe (e.g) q + g -> γ+ q

Next generation experiments

αs << 1x⊥x⊥

αs ~ 1

Ultimate question:How is QGP created by HIC?
Unexploredregion(forwardLHC)t = 0 fm/c

O(0.1 fm/c)

O(1 fm/c)
Time

Before collision
Color EM fields E, B
Nucleus

Nucleus(1) Color Glass
Condensate
Collisions(3)quark, gluon
particle
production
Schwingermechanism？

(2) Generationof Color EM
fieldsResearchup to now(4) QGP fluid（local thermalequilibrium）

Glasma (non- equilibrium)↑CGC (front view)(5) Hadron gas
O(10 fm/c)tProper timeτ = const .

x

Mid-rapidity

Forward rapidityη∼0η ∼6η = const .

Hadron gas−x

QGP
GlasmaLooking at “Glasma”
at forward LHC

CGC

CGC+

FoCal/EIC and CGC

15

Saturation signal in FoCal (1)cumulative counts

Expected yields in FoCal (Run-4)
1011

RpPb: forward γ

Projected cumulative yields in FoCal
sNN=8.8 TeV
3.4 < y < 5.5
pp: L =1 pb-1,int
p-Pb: L =100 nb-1 and A=208

1010

int

primary π0
PYTHIA 8 Monash 2013
ppp-Pb910anti-kT jet (R=0.4)
PYTHIA 8 Monash 2013
3.8 < y < 5.1
pp
p-Pb

108

LO Dipole-CGC calculation107

jet p-Pb

106

Rg

jet pp105

4nNNPDF10 208Pb reweighting

π0 p-Pb
104

nNNPDF 90% CL

3γ p-Pb

EIC fit 90% CL

103isolated prompt γ
JETPHOX v1.3.1.4 NLO

FOCAL refit 90% CLπ0 pp

PDF: NNPDF4.0 + nNNPDF3.0

Q2=10 GeV21022FRAG: BFG II
full iso < 2GeV in R=0.4
pp- Large suppression at low pT for isolated γ01010−610203040506070p (GeV/c)
TIsolated γ: qg → qγ ; kT~ Qsat
Ducloué, Lappi, andMäntysaari, Phys. Rev. D97(2018) 054023

γ ppp-Pb

10−510−410−310−210−1

1x- Expected gluon saturation (CGC) in small-x, not yet clear evidence- Excellent probe: isolated photons from quark-gluon Compton scattering

16Saturation signal in FoCal (2)Di-hadron Correlations

Stasto, Wei, Xiao, and Yuan, Phys. Lett. B784 (2018) 301

Forward γ+jet

Forward di-jet•γ+jet: dipole TMD gluon distribution•di-jet: multiple TMD distributions

Dilute-dense LO + Sudakov
probes quadrupole operator- Experimental challenge to see an effect ofCGC in Δφ width?

- Theory: NLO cal. is needed- γ+jet, balanced di-jet at low-x: kT~ Qsat（sensitive to saturation）- changing kT (pT) → exploring non-linear QCD evolution in wide
kinematic coverage of x-Q2 by FoCal17Saturation signal @ EIC eAnd

EIC White Paper, ’12, ’14 (2 ed).

Depletion of di-hadron in e+A as compared to e+p(Domingues et al ‘11; Zheng et al ‘14).

J/ψ, t distribution

Signals of CGC

FoCal technology

・di-hadron correlation (e-A vs. ep), broadening of width・Quasi-elastic coherent J/ψ production (eliminate de-excitation photons~300 MeV)→ZDC is essential !
・shifted t-distribution by CGC

A ZDC design for EIC

FoCal detector(design and current status)

Detector design
E-Pad19E-Pixel

FoCal-E (pad, pixel)
20 layers of W(3.5 mm ≈ 1X0) + silicon sensors:
Two types: Pad (1x1 cm2) and Pixel (30 x 30 μm2)

• Pad: shower profile and total energy• Si PAD sensor• Pixel: position resolution to resolve overlapping showers• CMOS MAPS technology (ALPIDE)

FoCal-H Conventional metal-scintillator design
1 cm

Cu capillary-tubes enclosing BCF scintillating fibers
SiPM readout

30 μm

18 PAD layers + 2 PIXEL layers( = 1 Module, 20 X0)FoCal-E: 22 modules

28

FoCal Japan
Responsibilities:(1) FoCal-E pad, (2)readout and trigger
๏ Univ. of Tsukuba

8 institute, 25 members
๏ Tsukuba Univ. of Tech๏ RIKEN๏ Hiroshima Univ.
๏ Nara Women’s Univ.
๏ Saga Univ.
๏ Nagasaki Inst. of App.
Sciences๏ Kumamoto Univ.

JSPS KAKENHI Grant Number JP20H05638 基盤 (S) (2020-2024, PI 中條)「LHC 超前方光子測定によるグルーオン飽和とQGP生成起源 」

FoCal-Japan: built FoCal-E pad
prototypes and tested

E-pixel

HCal

Uniqueness of FoCal detector
Isolated photon ID

E-pad
PS/SPS test beam in 2022１）High two photon separation power（<~5mm, energy resolution ~3%）
２）Wide energy dynamic rage (from 1 MIP to TeV EM showers）
３）High radiation tolerance（1013 (1MeV neutrons) / cm2）
→FoCal-E pad: mainly developed by FoCal-Japan groupLongitudinal profile (2γ showers)

Trans. profile

21

FoCal-E pad performance
MIP responce

Excellent performance of prototype• Pad MIP single channel distribution and stability• Longitudinal shower profile

22
arXiv:2311.07413

Longitudinal shower profiles

FoCal-E pad performance
Linearity

23
arXiv:2311.07413

Energy resolution

5%Results show expected behavior

EIC-ZDC design

ZDC at around z = +35 m
Aperture: ~ 4 mrad
Available space: 60 x 60 x 200 cm
ePIC-ZDC collaboration in Japan- RIKEN, Tsukuba, Tsukuba Tech,Shinshu, Kobe

- First test beam with Taiwan group at
ELPH, Tohoku Univ. on March 2024.

FoCal technology

24

ePIC ZDC prototype test @ ELPH (2024.03)

25

LYSO crystal with SiPM readout

Hit map of LYSO crystal
calorimeter from online monitoring

26

Summary2Qs(x)αs << 1geom

DGLAP

alingln Q2

scexploring a wide kinematic coverage in x-Q2 is crucialric• To understand QCD and find a clear signal of CGC,

et

• Strong synergies between EIC and LHC forward

JIMWLK
BK

BFKL

saturation
non-perturbative regionln x• Universality test of QCD (color dipole formalism) at
both EIC and forward LHC• FoCal: Common detector technologies at forward
LHC and EIC (ZDC)• We will start FoCal production in Japan from 2024,
and do physics from 2029-2032 (LHC Run-4) andmaybe beyond in ALICE3)

Forward pA
at high energies

DIS (EIC) eA

αs ~ 1