Forward direct photons
withFoCal in ALICE
Tatsuya Chujo
Univ. of Tsukuba
ハドロン散乱ゼロ度測定勉強会Mar 2, 2015
Nagoya University

Outline

1. Physics motivation:

isolated photons at forward rapidity as a signature forsmall-x gluons
2. Detector requirements
3. R&D status and plan
4. Summary
ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal

CGS picture at LHC• Gluon saturation, Color Glass

Condensate (CGC) is afundamental feature of QCD,
expected to be appeared in highenergy.

Low energy

High energy•From the results in d-Au (RHIC)

and p-Pb (LHC) collisions, there
are indications of CGC, but not yet
conclusive.

RHICLHC• Many observables are usedhadrons, which include final stateinteractions.

• A cleaner probe at forward

rapidity is necessary, such as
direct photons
LHC : Larger kinematic reach insaturation region at LHC,compared to RHIC.

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Forward Hadron Production in p-A at LHC
ALICE, arXiv:1308.6726

φ → μ+ + μ-J/ψ → μ+ + μ• RpPb compared to models•••• RpPb at forward rapidity (left) forward/backward ratio (right)

Hadron suppression on forward (proton-going) side at low pT.
J/ψ not described by nPDFs nor by a CGC calculation
Uncertainties on:••

Production mechanism (x sensitivity etc.)
Other nuclear modifications (e.g. energy loss, thermalization in pA?)

• Difficult to obtain conclusive data by hadrons only.
ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal

x-Sensitivity from PYTHIA• Very limited sensitivity withlight hadrons• Much better sensitivity withDrell-Yan and direct photons• Much lower cross section for
Drell-Yan• Not sufficient formeasurement in p-Pb

• Direct photons are optimum
prove for a gluon saturation

ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal

nPDF/DGLAP vs. CGC• Two scenarios forforward γ production
in p+A at LHC:••

Normal nuclear effects
linear evolution,
shadowing
Saturation/CGC running
coupling BK evolution• Strong suppression in direct γ RpA.
• Signals expected at forward η, low-intermediate pT.
ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal

Initial condition and thermalization%Ini(al%condi(on,%CGC,%%early%thermaliza(on%Color%Glass%Collision%
Condensate%(CGC)

“Glasma”

sQGP%produc<on,%thermal%
dynamics%QGP

strongly%coupled%%
Quark%Gluon%Plasma%% Hadron%gas
(sQGP)

t%=%@1%fm%%%%%%%%%%%%%%%%%%t%=%0%fm%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%t=%0.6%fm/c%%%%%%%%%%%%%%%%%%%%t=%20%fm/c%
Time

RHIC/LHC data suggests an early thermalization of QGP(< 0.2 fm), and it is still a big missing link between initialcondition to QGP.
➠ Direct access to initial condition by direct photon
ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal

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Initial conditions of Heavy Ion Collisions

AALLIICCEE,,  SSeepp,,

8t

Understanding of initial condition:→key to understand the QGP properties (e.g. η/s),
early thermalization.
ハドロン散乱ゼロ度測定勉強会, 8名古屋大学 (T. Chujo) ALICE FoCal

η/s, temperaturedependence• IP-Glasma Model (color charge fluctuation)• Higher harmonics ➔ η/s constraints
Minimum η/s at RHIC？

•Temperature dep?
Björn Schenke (BNL) RHIC AGS Users’ Meeting 2013, BNL

C. Gale, S. Jeon, B.Schenke,P.Tribedy, R.Venugopalan, PRL110, 012302 (2013)

ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal

The ALICE Experiment

ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal

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Forward Calorimeter (FoCal) in ALICE•Electromagnetic calorimeterfor γ and π0 measurements,
with Hadron Calorimeter.
• At z ≈ 8m (outside magnet)
3.3 < η < 5.3• Proposed schedule:• mini-FoCal: 2018- (after LS2)
• full FoCal: 2023- (after LS3)
Main challenge: separate γ/π0 at high energy• Need small Molière radius, high-granularity read-out• Si-W calorimeter, granularity ≈ 1mm2
ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal

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FoCal-E Strawman Design• Si/W sandwich calorimeter layer structure:- W absorbers (thickness 1X0)+ Si sensors• Longitudinal segmentation:- 4 segments low granularity (LGL)- 2 segments high granularity (HGL)• LGL segments (PAD)- 4 (or 5) layers of Si/W
- Si-PAD with analog readout- cell size 1 x 1 cm2- 8 x 8 = 64 PADs per layer- signal are longitudinally summed• HGL segments (MAPS)- single layer with W.
- CMOS-pixel (MAPS*).
- pixel size ≈ 25 x 25 μm2- digitally summed in 1mm2 cells*MAPS = Monolithic Active Pixel Sensor
ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal

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Strawman Design
Studied in performance simulations:
24 layers:
W (3.5mm ≈ 1 X0) + Si-sensors (2 types)• low granularity (≈ 1 cm2), Si-pads• high granularity (≈ 1 mm2), obtainedwith pixels (e.g. CMOS-MAPS)

ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal

Detector Performance (simulation)
Energy resolution (FoCal-E)

Pion rejection factor•

Reasonable energy resolution, extremely good two-shower separation
with HG segments (~0.2 mm position resolution at Eγ > 100 GeV)

•Efficient for pion rejection (via shower shape analysis)
ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal

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Performance on RpPb

• Expect significant constraint on direct photon R• Confirm or refine the CGC effect, constrain nPDF

pPb

ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal

Low Granularity Layer (LGL) Prototype, PAD•LGL	  (PAD)	  prototype	  (ORNL):- Si-PAD (Hamamatsu S10938)- cell size 1x1 cm2- longitudinally summed (4 layers), analog
readout = 1 segment- 4 or 5 LGL segments- W layer per Si-PAD	  •Readout	  system:	  – ORNL	  ASICs,	  on	  a	  summing	  board.	  
– RD-­‐51	  SRS	  readout	  system:	  • APV25	  hybrid	  (128	  ch,	  pre-­‐amp,	  shaper)	  • SRS	  Front	  End	  Card	  (FEC)	  and	  ADC.	  
๏ SRS:	  Scalable	  Readout	  System	  (point-­‐to-­‐point	  readout)	  ๏ Responsibility:	  Tsukuba,	  ORNL
APV 25 hybrid (master, slave)
ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal16

High Granularity Layer (HGL) Prototype, MAPS
MAPS prototype• 4x4 cm2 cross section, 28 X0 depth• 24 layers: W absorber + 4 MAPS each
• MIMOSA PHASE 2 chip (IPHC Strasbourg)- 30 μm pixels- 640 μs integration time(needs upgrade – too slow for experiment)• 39 M pixels total• Test with beams at DESY, CERN PS, SPS๏Event Display:measurement (DESY) ofpile-up of two 5.4 GeV
electrons, demonstrates
two-shower separation
Responsibility: Utrecht, NIKHEF, Bergencapabilities
ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal17CERN PS/SPS beam test (2014)✓ Beam time:– PS: Sep. 17 - Oct. 1, 2014
– SPS: Nov. 10-18, 2014
✓ Beam line: PS T9, SPS H8•

Beam energy:– 2 - 10 GeV/c– 30, 50 GeV/c✓ Trigger: 10x10 cm2 & 1x1 cm2 Scinti. +Cherenkov (ON/OFF)✓ Responsibility:– LGL (PAD) :Tsukuba, ORNL– HGL (MAPS) Utrecht, NIKHEF, Bergen
Drawing by Brink, A. van den (Utrecht Univ.)

ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal

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Prototype of “a strawman design”

LGL (PAD), 4 segments
w/ summing board

LGL (PAD) + HGL (MAPS x2)“strawman detector”

ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal

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PS results (show profile)

K. Ito• Longitudinal shower profile:• shower max d (for W) = 19.3 mm (2nd LGL)
• Transverse shower profile:• re-calculate shower center (centroid)• Moliere radius (for W): 9.16 mm• Both longitudinal and transverse shower profiles are
consistent with the expectations.
LGL1

LGL2

LGL3

ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal

LGL420FoCal PAD performance (2014 beam test) W. SatoLinearity

Energy Resolution• Reasonable linearity (except 50 GeV).
• Worse energy resolution in data than simulation due to a noiseproblem, to be improved in 2015 test beam experiment.
ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal

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Plan (2015-)• Preparation for Nov. 2015 PS/SPS beam test.
• Ask the FoCal LoI approval by ALICE in June, thenthe LHCC approval in Nov.
• Under discussion: Mini-FoCal:• FoCal-E prototype (< 10% of acceptance)• to be installed significantly before LS3 (possiblyaround LS2), no modifications to ALICE setup• R&D with RD51:– Tsukuba G. will join RD-51 in 2015 spring officially.
– Communication with Hans M. (RD51) started for
VMM2 (and/or Beatle) readout system for FoCal.
– Need to check that VMM2 SRS system meets ourrequirement for a faster (~ few 100 kHz w/o trig.)
readout. (c.f. APV25 < 200-300 Hz)

ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal

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FoCal on C-side?
• Place detector at end of conical section of C-side beam pipe?
– possible coverage 5.5 < η < 6.5• interesting for low-x physics–very limited space, measurement feasible?
• particle density (Pb–Pb) and background tolerable?

–no overlap with muon arm• Pb–Pb case with QGP physics questionable–possible as extension to FoCal on A-side?

ηmin ≈ 5.5

ηmax ≈ 6.5

ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal23

Idea of Forward Spectrometer in ALICE• Limited physics case–diffraction?
–baryon stopping considered interesting• expected at η = 6-7• no competing theoretical predictions• Would need tracking, magnet, particle ID at large η–very challenging, in particular PID–may need z > 19m

ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal24

Muon Forward Tracker (MFT) Project
MFT: Muon Forward Tracker, proposed in
ALICE (-4.0 < η < -2.5)
Silicon pixel tracker in Muon Spectrometer
Separation of charm/beauty down to very
low pT
Precise ψ(2s) measurement even incentral Pb-Pb
Prompt and non-prompt J/ψ separation
Improve S/B ratio and mass resolution forLow Mass di-muons•••••The MFT project has been approved by theALICE Collaboration to be part of the ALICE
upgrade planned for the LHC LS 2017/2018
Hiroshima G. joined for this project in 2014.
ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal25

Summary• Forward isolated direct photons at LHC are unique signal for lowx gluons and saturation.

• Mini-FoCal installation ~LS2 (2018), and full installation after LS3(2023-).

• MFT upgrade project.
• Schedule on 2015:• LoI submission to ALICE and then to LHCC after the approval.
• Beam test on Nov. 2015
• New readout R&D with CERN RD-51 (VMM2)
ハドロン散乱ゼロ度測定勉強会, 名古屋大学 (T. Chujo) ALICE FoCal