LSO/LYSO Crystals for Calorimeters in Future HEP Experiments

Liyuan Zhang, Rihua Mao, Fan Yang, Ren-Yuan Zhu

California Institute of Technology April 15, 2013

Talk in the 12th International Conference on Inorganic Scintillators and their Applications, Apr. 15-19. Shanghai

Why LSO/LYSO for HEP? LSO/LYSO is a bright (200 times of PWO), fast (40 ns) and radiation hard

crystal scintillator. The light output loss of 20 to 28 cm long crystals is at a level of 10% after 1 Mrad –ray irradiations, much better than all other crystal scintillators.

The material is widely used in the medical industry. Existing mass production capability would help in crystal cost control.

LSO/LYSO crystals are chosen by the Mu2e and SuperB experiments to

construct electromagnetic calorimeters with total absorption nature. They are also proposed as the active material for sampling calorimeter options for the CMS forward calorimeter upgrade.

References: IEEE Trans. Nucl. Sci. NS-52 (2005) 3133-3140, Nucl. Instrum. Meth. A572 (2007) 218-224, IEEE Trans. Nucl. Sci. NS-54 (2007) 718-724, IEEE Trans. Nucl. Sci. NS-54 (2007) 1319-1326, IEEE Trans. Nucl. Sci. NS-55 (2008) 1759-1766 and IEEE Trans. Nucl. Sci. NS-55 (2008) 2425-2341, N32-4 & N32-5 @ NSS09, Orlando, N38-2 @ NSS10, Knoxville, N29-6 @ NSS11, Valencia.

2 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech April 15, 2013

Twenty Five SuperB Crystals All 25 crystals are characterized in Caltech Crystal Laboratory

The main challenge was to make the LRU within the specification.

3 April 15, 2013 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech

Light Response Non-Uniformity: δ

APD or PMT

4

|δ| < 3% & 4% for 18 X0 (SuperB) & 25X0 (CMS)

D. Graham & C. Seez, CMS Note 1996-002

The measured δ value for SuperB crystals is about 10%, dominated by the tapered geometry, or

optical focusing effect.

Two uniformization methods (side surface blackening and surface

roughening) were tested and it was found that the

surface roughening is more effective.

April 15, 2013 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech

Effect of the Cerium Segregation

It is known that the cerium

concentration along long LYSO crystals is not

uniform, causing non-uniformity up

to 10% at two ends, indicating up to 5% variation in δ is possible because

of the cerium segregation.

10%

seed

5 April 15, 2013 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech

Effect of the Self-Absorption

It is also known that a part of the emission light is absorbed in the crystal: self-absorption. The LAL is a strong function of wavelength with an average of 1.7 m.

6 April 15, 2013 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech

Ray-Tracing Simulation “set-up”

SuperB LYSO crystals

Tyvek paper Silicon oil N=1.52

2 Hamamatsu S8664-55 (2×5×5 mm2)

The simulation package was developed in early eighties, and was used for the L3 BGO and CMS PWO crystals.

7 April 15, 2013 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech

Effects of the cerium distribution and self-absorption are included in the simulation

Polished and Roughened Surfaces

The optical focusing, effect dominates non-uniformity: δ is about 13% for all polished surfaces.

Roughened surface(s) can compensate the optical focusing effect.

The best result is achieved by roughening only one side surface.

April 15, 2013 8 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech

Real Exercise: Roughening SIC-LYSO-L3

The smallest side surface of SIC-LYSO-L3 was roughened to Ra = 0.3 at SIC via a two step process

1st: lapped to Ra = 0.5 by using 11 μm Al2O3 powder for 10 min with 2.5 kg weight 2nd: lapped to Ra = 0.3 by using 6.5 μm SiC powder for 3 min with 1.5 kg weight

Polished SIC-LYSO-L3

Roughened SIC-LYSO-L3

Thanks to SICCAS for roughening this crystal

April 15, 2013 9 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech

Relative Light Output & Uniformity

Ra = 0.3µ uniformizes SIC-L3 to |δ| < 2% All 25 crystals are uniformized to |δ| < 3%

10 April 15, 2013 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech

CMS Forward Calorimeter Upgrade

Pros: low cost and less demanding to radiation hardness of crystals

Cons: not as good as total absorption option

Pros: good energy resolution Cons: high cost and stringent

radiation hardness requirement

11

R.-Y. Zhu, 8/30/2012, forward calorimetry taskforce meeting

April 15, 2013 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech

LYSO Based Shashlik Cell Design

* Based on the simulation of Zhigang Wang, IHEP, Beijing.

LHCb Plan-1 Plan-2

Absorber

Lead (Pb) Lead (Pb) Tungsten (W) Density (g/cm3) 11.4 11.4 19.3

Radiation Length (cm) 0.56 0.56 0.35 Moliere Radius (cm) 1.60 1.60 0.93

dE/dX (MeV/cm) 12.74 12.74 22.1 Thickness (mm) 2 4 2.5 Plates number 66 28 28

Scintillator

BASF-165 Polystyrene (Sc) LYSO LYSO Density (g/cm3) 1.06 7.4 7.4

Light Yield (photons/MeV) 5200 30000 30000 Radiation length (cm) 41.31 1.14 1.14 Moliere Radius (cm) 9.59 2.07 2.07

dE/dX (MeV/cm) 2.05 9.55 9.55 Plate Thickness(mm) 4 2 2

Plates number 67 29 29

WLS Fiber Kurarray Y-11(250) Kurarray Y-11(250) Kurarray Y-11(250)

Diameter (mm) 1.2 1.2 1.2 Number /Cell 16 4 4

Cell Properties

Total Depth (Χ0) 24.22 25.09 25.09 Sampling Fraction (MIPs) 0.25 0.28 0.26

Total Physical Length (cm) 40 17 12.8 Total Sc Length (cm) 26.8 5.8 5.8

Absorber Weight Ratio 0.84 0.75 0.76 Scintillator Weight Ratio 0.16 0.25 0.24 Average Density (g/cm3) 4.47 10.04 13.91

Average Radiation Length (cm) 1.65 0.68 0.51 Average Moliere Radius (cm) 3.6 1.7 1.2 Transverse Dimension (cm) 4.1 1.9 1.4 Sc-depth/Total-depth in X0 0.0268 0.2028 0.2028 WLS Fiber Density (N/cm2) 0.97 1.06 2.07

MIPs Energy Deposition Sc plates (MeV) 54.94 55.39 55.39

Light Yield using MIPs Photon Electrons/GeV 3077 17897 17897

Signal of MIPs Photon Electrons / MIP 169 991 991

Module Properties Energy Resolution (a, %) 8.2 9.0* 9.0*

April 15, 2013 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech 12

Three LYSO Plates with Holes 25 × 25 × 5, 3 and 1.5 mm3

April 15, 2013 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech 13

Two Measurement Setups

1) LYSO plates with

Tyvek wrapping are

readout directly by a

R1306 PMT using a

Cs-137 γ-ray source.

2) LYSO plates with Tyvek

wrapping are readout with

four Y11 WLS fibers of 40

cm long and a R2059 PMT

using a Na-22 γ-ray source

and coincidence.

April 15, 2013 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech 14

PHS of 5 mm LYSO Plate

15

LYSO 25 × 25 × 5 mm3 5 mm plate & 4 x 40 cm Y11 fiber

γ-ray peaks are clearly visible April 15, 2013 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech

PHS of 3 mm LYSO Plate

LYSO 25 × 25 × 3 mm3 3 mm plate & 4 x 40 cm Y11 fiber

γ-ray peaks are clearly visible April 15, 2013 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech 16

PHS of 1.5 mm LYSO Plate

17

Less total absorption events

LYSO 25 × 25 × 1.5 mm3 1/5 mm plate & 4 x 40 cm Y11 fiber

April 15, 2013 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech

PMT Quantum Efficiency

Light Output (LO)

measured in

p.e./MeV are

converted to Light

Yield (LY) in

photons/MeV by

taking out the QE

of the PMT

LY = LO / QE

April 15, 2013 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech 18

Light Collection Efficiencies

* 2009 J. Phys.: Conf. Ser. 160 012047.

Measured light collection efficiencies consist with the LHCb data

Samples 5 mm LYSO 3 mm LYSO 1.5 mm LYSO LHCb cell*

LO1(p.e. /MeV) 3760 3970 4370

LY1 (Photons /MeV) 29,150 30,780 33,880 5,200

LO2 (p.e./MeV) 20.7 24.3 17.9 3.1

LY2 (Photons /MeV) 479 563 414

MIP (p.e./55 MeV) 1,140 1,340 990 169

LO2/LO1 (%) 0.55 0.61 0.41

LO2/LY1 (%) 0.07 0.08 0.05 0.06

LY2/LY1 (%) 1.64 1.83 1.22

April 15, 2013 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech 19

Summary LSO/LYSO crystals with bright, fast scintillation and

excellent radiation hardness is a good candidate material for HEP & NP experiments, especially for those experiments in a severe radiation environment.

The longitudinal non-uniformity issue caused by tapered crystal geometry, self-absorption and cerium segregation can be addressed by roughening one side surface. All 25 SuperB crystals are uniformized to |δ|<3% by roughening the smallest side surface.

LYSO crystal based Shashlik cells are designed. Three LYSO plates of 1.5, 3 and 5 mm thick were measured with direct coupling and through Y11 WLS fibers. The overall light collection efficiency is about 1.5%, which is consistent with the LHCb data measured for the plastic scintillator based Shashlik cells. LYSO-Pb and LYSO-W cells are under construction, and will be tested in beam.

April 15, 2013 20 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech

Shashlik Cells Under Construction

21 April 15, 2013 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech

Rectangular towers consist of 2 mm thick LYSO crystal plates, 4 mm Pb or 2.5 mm W absorbers, and 0.15 mm Tyvek paper layers.

Each tower has 25 X0 length, 1.1 RM transverse dimension and about 25% sampling fraction.

Readout with four Y11 fibers has about 1.5% light collection

efficiency measured by a PMT with air-gap coupling.

The Stochastic term is expected to be 9%.

The total LO is comparable to PWO crystals with PMT

readout. The LO would be higher with Si APD readout.

Cell Design Constraints

Crystal Depth / Total Absorption Depth: < 0.2

Total Cell Depth: ~ 25 X0

Sampling Fraction (MIPs): ~ 25%

Lateral Dimension: ~ 1.1 Rm

WLS Fiber Density: ~ 1/cm2

WLS Fiber distribution: uniform

Thicknesses of absorber and scintillation plates: reasonable for manufacture

April 15, 2013 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech 22

References

1) Irina Machikhiliyan for the LHCb calorimeter group, "The LHCb electromagnetic calorimeter", XIII International Conference on Calorimetry in High Energy Physics (Calor2008).

2) A. Bamberger et al., "The ZEUS forward plug calorimeter with lead-scintillator plates and WLS fiber readout", NIM A450 (2000), p 235-252.

3) C.S. Atoyan et al., "Lead-scintillator electromagnetic calorimeter with wavelength shifting fiber readout", NIM A320 (1992), p144-154.

4) L. labarga and E. Ros, "Mont Carlo study of the light yield, uniformity and energy resolution of electromagnetic calorimeter with a fiber readout system", NIM A249 (1986), p228-234.

April 15, 2013 Talk presented at SCINT2013, Shanghai, by Liyuan Zhang, Caltech 23