Design of a New Electromagnetic Calorimeter for the sPHENIX Experiment at RHIC Craig Woody Brookhaven National Lab For the PHENIX Collaboration CALOR 2014 Giessen, Germany April 10, 2014

Outline C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 2 Overview of sPHENIX and its evolution to ePHENIX Requirements for the sPHENIX/ePHENIX calorimeter systems Design studies for the EMCAL (HCAL to follow in next talk by E.Kistenev) RHIC and sPHENIX/ePHENIX long range plan

The sPHENIX Experiment C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 3 Major upgrade to the PHENIX Experiment at RHIC Primary purpose is to measure jets in heavy ion collisions Measure total energy using calorimetry (including hadron) Good solid angle coverage (|  |< 1,  =2  ) Provide a basis for a future Day 1 detector (ePHENIX) for eRHIC (Brookhaven’s version of the Electron Ion Collider) Study nucleon structure and QCD in nuclei over a broad range of x and Q 2 using deep inelastic polarized ep and eA collisions

Why Measure Jets at RHIC ? C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 4 RHIC allows studying the QGP near T c High flexibility - Can study over a wide energy range - A+B (U+U), pp,dA, ep, eA… Complimentary to LHC RHIC A great deal of interesting physics is taking place near T c Measuring full jets provided a means to carry out a detailed study of parton energy loss in the dense QGP medium

Measuring Jets at RHIC C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 5 RHIC can produce over 50 billion Au+Au events per year sPHENIX can record 20 billion events without selective triggers Real jets dominate for p T > 20 GeV Rates for jets are high Event rates per year 10 7 jets p T > 20 GeV 10 6 jets p T > 30 GeV 80% are dijet events 10 4 direct  events with p T > 20 GeV

Detector Requirements Detector Requirements C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 6 Technology Choices: EMCAL → 1) Tungsten Scintillating Fiber 2) Lead Scintillator Shashlik (~ ALICE EMCAL) HCAL → Iron Scintillating Tile with WLS Fiber Readout → SiPMs Large solid angle coverage (± 1.1 in , 2  in  ) Moderate energy resolution EMCAL ~ %/√E for HI collision (need ~ 12%/√E for ep/eA collisions) HCAL ~ 75 %/√E (single particle), ~100 %/√E (jet) Compact (for EMCAL  small R M, short X 0 ) Physically small (dense) – occupies minimal space High segmentation for heavy ion collisions Hermetic Projective (approximately) Readout works in a magnetic field Low cost (very recent → )

The Current PHENIX Detector C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 7

Solenoid Magnet HCAL EMCAL VTX C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 8 The sPHENIX Detector

The BaBar Solenoid Magnet The BaBar Solenoid Magnet C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 9 Ownership officially transferred to BNL Being prepared for shipping Dimensions: R inner = 140 cm R outer – 173 cm L = 385 cm Field 1.5 Tesla (Nominal) Homogeneous in center Higher field at ends  Better forward tracking

C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 10 Calorimeter Options Calorimeter Options Compact EMCAL Thin section of HCAL inside magnet Lower density EMCAL Both sections of HCAL outside magnet Smaller Moliere radius better for HI collisions Thin HCAL section can be used for e/h separation Smaller overall HCAL  lower cost Larger Moliere radius worse for HI collions EMCAL can be Pb/Sc design  lower cost Overall HCAL larger  Higher cost

eRHIC: An Electron Ion Collider at Brookhaven C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 11 Electron beam accelerated with 1.33 GeV Energy Recovery Linac (ERL) and circulated in two Fixed Field Alternating Gradient transport rings inside RHIC tunnel colliding with existing proton and ion beams: 12 passes: 15.9 GeV, full luminosity16 passes: 21.2 GeV, reduced luminosity Single collision of each electron bunch allows for large beam disruption per pass giving high luminosity and high electron polarization Energy: Electron: 6.6–21.2 GeV Proton: 25–250 GeV Ions: 10–100 GeV √s: up to 145 GeV Polarization: Electrons: 80% Protons and 3 He: 70% Luminosity: >10 33 cm -2 s -1 FFAG Recirculating Electron Rings (uses permanent magnets)

C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 12 The ePHENIX Detector

Crystal C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 13

Original Concept: Optical Accordion C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 14 Accordion design similar to ATLAS Liquid Argon Calorimeter Want to be projective in both r-  and  Accordion prevents channeling and allows readout on the front or back of the absorber stack Can make projective in r-  by tapering thickness of tungsten plates Can make projective in  by fanning out fibers Oscillations must be kept small because of minimum bending radius of fibers and plates Readout Towers Plates Fibers Particle

Problems with Accordion Tungsten plates undergo “spring back” during cooling Difficult to control shape to better than ~ 0.5 mm with current process Difficult to make “high frequency” accordion because must have minimum bending radius for fibers and plates Plastic mold made to same desired shape as accordion plates Accordion is actually more desirable since it keeps the shower more compact in the transverse dimension Not giving up on the accordion, but we decided to build the first prototype with flat tilted plates (similar to HCAL) Tilted flat plates and accordion strive to accomplish the same thing: Improve longitudinal sampling and prevent channeling C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 15

EMCAL Tilted Plate Configuration C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 16 A.Kiselev (BNL) 2 mm W + 1 mm fiber 1 mm W + 1 mm fiber Energy Resolution vs Tilt Angle Monte Carlo Simulation (Flat plates - No Accordion)

EMCAL Prototype Assembly Epoxy is applied to 2 tungsten plates Twelve sandwiches are glued together to form a module Fibers are assembled into frames Plates and fiber layer are glued together under vacuum to form a “sandwich” Finished W-SciFi sandwich Sandwich is cured under weight and vacuum 2 x 0.5 mm flat W plates, 1 mm fibers, rear spacer for tapering C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 17

Correcting for Attenuation Length along the Fiber Compact calorimeter results in short fibers (~ 10 cm) Strong enhancement in light output near readout end of fiber due to cladding light Paint ends of fibers black to absorb cladding light Improves uniformity at the expense of reducing light output C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 18

Absorber Stack C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 19 Stack of 7 tower modules (not yet glued) Readout has 7x7 optically separated towers X 0 ~ 7 mm R M ~ 2 cm Readout end of module is potted with white reflecting epoxy. Other end is covered with 3M ESR reflector Looking through absorber stackReadout end of absorber stack

Towers are formed by Segmenting Readout End with Light Collecting Cavities Plastic collector box is made by 3D printing Cavities are coated with a white diffusing reflector SiPMs can be mounted to the top or sides of the cavities Height kept small to minimize radial space C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 20

Light Collection Cavities Seven rows of seven cavities mounted to a frame and readout boards are connected at the back Many prototypes were tested to determine the placement of the SiPM in order to optimize light collection efficiency and uniformity Assumed one SiPM per cavity to minimize cost C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 21

Light Collection Efficiency and Uniformity SiPM entered on dome Average efficiency = 4.6% Max/Min ratio = ° from center Average efficiency = 4.7% Max/Min ratio = ° from center Average efficiency = 4.2% Max/Min ratio = 1.6 Area ratio (3x3 mm 2 SiPM to 25x27 mm 2 cavity) = 1.3% C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 22

SiPMs and Readout Electronics C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 23 Readout Preamp (voltage amplifier) Temperature sensor (thermistor) Individual bias voltage adjustment Feedback circuit to adjust bias voltage for temperature stabilization S.Boose SiPMs High gain (~10 6 ) High noise (~ few MHz/mm 2 at ~ 1 p.e. level) Sensitive to temperature and voltage G ~ (V op -V br ), V br varies with T (~50 mV/°C  dG/dT ~ 10% /°C) Limited dynamic range due to finite number of pixels Hamamatsu S P) 3x3 mm K 25  m pixels

SiPM Readout Electronics C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 24 Common readout system used for EMCAL and HCAL Preamp (voltage amplifier) Temperature sensor (thermistor) Feedback circuit to adjust bias voltage for temperature stabilization and control Setup for testing SiPMs Bias control Temperature stabilization Linearity measurements 12 bit Compensation of gain variation with temperature of a Hamamatsu S P S.Boose

Final Light Collection Module C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 25

Final Assembly C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 26

Final Assembly C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 27

C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 28 Fermilab Beam Test Test of combined EMCAL and HCAL prototypes at Fermilab in Feb 2014 (sPHENIX 2/5-2/25, STAR 2/26-3/18)

C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 29 Fermilab Beam Test

C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 30 MIP Peak 120 GeV protons Minimum ionizing peaks correspond to ~ 30 MeV per tower

C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 31 Calibration of Towers with MIPs Plates perpendicular to beam (90°) 120 GeV protons Minimum ionizing peaks correspond to ~ 30 MeV per tower

C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 32 Measurement of Light Output Light yield ~ 100 p.e. on PMT Energy deposit = 29 MeV - total energy deposit from mip traversing perpendicular (12 layers) of one tower of absorber stack  3.5 p.e./MeV  3500 p.e./GeV Assume 90% light collection  3900 p.e./GeV in calorimeter Light collection efficiency of 4.7% from cavities  ~ 180 p.e./GeV with SiPM (assuming PDE SiPM  QE PMT )  ~ 7% contribution to energy  resolution from photon statistics PMT coupled directly onto one tower module of absorber stack (12 layers) Beam (120 GeV p) traverses tower perpendicular to plates (E dep = 29 MeV) Light yield measured in three positions across tower module

C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 33 Tower Readout with SiPMs MIPs in single towers Test with 3 central rows of towers with 2 SiPM readout 2 SiPMs 1 SiPM x2 Horizontal scan with MIPs

C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 34 Transverse Position Dependence 8 GeV electrons 8 x 5 mm slats Single Tower 3x3 Tower Sum ~ 5%

C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 35 Longitudinal Position Dependence  y = 23 mm 5 different calorimeter positions along fiber direction 120 GeV protons

RHIC Long Range Plan C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 36 (B.Mueller, Jan 2014)

Summary C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 37 sPHENIX will be a new experiment at RHIC designed to measure jets using calorimetry that will enable a detailed study of the QGP near the critical temperature The primary candidate for the EMCAL for sPHENIX is a compact W-SciFi design sPHENIX will provide a basis for a Day 1 detector for eRHIC We hope that sPHENIX can begin data taking ~ 2021

Backup Slides C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 38

LED Calibration System Splitter fixture for testing uniformity and efficiency of 1x7 splitters 1x7 splitter for distribution of calibration light to light collection cells LED Pulser PIN diode for monitoring LED 1:7 split1:8 split SiPM C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 39

C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 40 LED Pulser Calibration All channels working and giving reasonable signals 7x7 Tower Array

Kinematic Coverage for EIC Physics C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 41 Polarized e-p Collisions Electrons on Heavy Ions

EIC Particle Production Rates C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 42 L = cm -1 s x 250 GeV

A New Dedicated Detector for eRHIC C.Woody, CALOR 2014, Giessen, Germany, 4/10/14 43 (x≈5×10 -3,Q 2 =10 (GeV/c) 2 ) J. Huang (BNL) e -, 10 GeV/c DIS e - IP Detailed material map based on NIM papers p, 250 GeV/c SIDIS Event