A new Si recoil tracking detector for the R3B experiment at GSI

Nick AshwoodThe University of Birmingham

Outline Motivation

Suppression of spectroscopic factors Quasi-free scattering

Current work GSI and current experimental set-up

Future plans Upgrade for FAIR and R3B New detectors

The new Si tracking detector The R3BRoot simulation package Design considerations Physics simulations Mechanical design and electronics

Further work

Shell structure

Modification of shell structure Unlike atomic shell

structure, the nuclear shell model is under a potential of it’s own making. Choice of potential

alters magic numbers.

Solution of the Schrodinger equation determines energy levels of the states and hence the magic numbers.

Modification by the tensor force Tensor force first introduced

by Yukawa through exchange of p mesons.

Spin orbit partners attract each other. Similarly “anti-partners”

repel each other.

T Otsuka et al. PRL 105, 032501 (2010)

Direct Reactions

R Lemmon private communication

Spectroscopic factors Nuclear structure can be determined for the

differential cross-section of the reaction for a give state.

Important quantity is to measure is the spectroscopic factor. The spectroscopic factor describes how close the state is

to being a pure shell model state.

Controversy over whether spectroscopic gives true indication of orbit occupancy. Measurements only in asymptotic region.

calculatedjn

measured ddS

dd

.

Spectroscopic factor controversy Many arguments over whether spectroscopic

factors are a “good” measurement of shell structure. Direct reactions only measure at the periphery of

the nucleus where the measurements are biased towards 100% occupancy of the state.

A better measurement would be relative spectroscopic factors or ANC’sPossible way round this is to use

high energy direct reactions which can probe deeply bound states i.e. QFSRemoval of weakly bound nucleons result in no reduction of spectroscopic factor

A Gade et al. PRC 77 044306 (2008)

Quasi-free scattering QFS takes place at high energies ~ 1 GeV/nucleon.

(p,2p), (p,pn), (p,pa) (e,e’p)

Set kinematic conditions so that nucleons come out back to back c.f. elastic scattering

Detect complete spectroscopy in inverse kinematics Allows final state interactions to be measured

GSI Helmholtz Centre

Reactions with Relativistic Radioactive Beams (R3B)

A/Z

Z11Be

11Be

10Be

8Li

M Barr private communication, J Taylor PhD thesis

Facility for Antiproton and Ion Research (FAIR)

R3B experiment

Located on the high energy branch of FAIR at GSI. Detection of all reaction channels.

Study of nuclear and astro-physical reactions Main reactions of interest are quasi-free scattering reactions with hydrogen target

(p,2p), (p,pn), (p,pa), etc

J Taylor PhD thesis

Initial Design Main requirements were for high resolution for

momentum and energy Good intrinsic energy resolution High resolution spectroscopy in both energy and

position High granularity

At least 2 layers were required to track particle. Also gives E-DE particle identification

Detector designed for QFS but needs large angular coverage able to cope with other reaction requirements e.g. elastic scattering, coulex, etc.

Initial Design First layer 2.5 cm from beam axis

100 mm thick 2 x 10 cm

Second layer 10 cm from beam axis 300 mm thick 4 x 10 cm

Simulations done in the R3BSim package

Full energy of the protons detected using a “perfect” calorimeter CALIFA energies not included

Simulation Development• R3BSim developed by the USC and Daresbury– Based on Geant4 + ROOT

• 2 geometries of calorimeter• 2 geometries of tracker• ALADIN, LAND, ToF Wall, etc

– Working (p,2p) event generator– Existing analysis code

• R3BROOT developed at GSI– Based on ROOT + Geant3/4 + FLUKA

• 2 geometries of calorimeter• 1 geometry of tracker• ALADIN, LAND, ToF Wall, etc

– No (p,2p) event generator implemented– No analysis code

Simulations of Elastic Scattering

Elastic scattering event generator written for R3BRoot Compare well with R3BSim simulations

Pitch (cm)

CALIFA E() (%)

R3BRoot DEsep (MeV)

R3BSimDEsep (MeV)

0.1 3 4.8 4.10.1 1 4.6 40.05 1 2.2 2.20.05 0.5 2.2 2.10.01 0.5 0.6 0.5

Efficiency

Efficiency of detecting two protons from (p,2p) events As energies increase get more forward focusing of protons If end cap included get ~ 90% efficiency

Design constraints Must detect protons at

most forward angles Inner layer as thin as

possible At least 3 layers

Strip redundancy Inner layer as close to

target as possible Accurate determination of

reaction vertex Distance to outer layers

large as possible No shielding between

detector and target

The two designs

Barrel Detector Geometry 3 layers of Si strip

detectors Orthogonal strips 58, 109 and 119 mm from

beam axis 2 end cap detectors

300 and 350 mm from target position

Easy analysis of positions Asics chips positioned at

forward angles

The two designs

Lampshade Detector Geometry• 3 layers of Si strip

detectors– Stereoscopic strips– 69 mm (14o), 194 mm (33o)

and 196 mm (33o) from beam axis at zero position

– 9.8 mm gap between layer 2 and 3

• All electronics can be placed before target

• Analysis of positions more difficult

3 layers of Si strip detectors Stereoscopic strips 69 (14o), 194 (33o) and 196

(33o) mm from beam axis at zero position

9.8 mm gap between layers 2 and 3

All electronics can be placed before target

Analysis of positions more difficult and loss of efficiency

Comparison of ResolutionsBarrel Detector Lampshade Detector

Resolution is almost the same for both detectors Given the advantage of the lampshade detector design, this will be the

detector geometry we went for

Lampshade resolutions with CALIFA Separation energy

calculated by Si + CsI energies.

Background from protons punching through CALIFA.

Gate on highest energy CsI energies to cut out background

DEsep = 2.8 MeV Eff(m>=2) = 71%

Background Contribution Energy profile of

particle 1 does not look like detected energies, whereas particle 2 does

Detected energies dominated by CsI energy peak at 0.15 GeV

Proton punch through ~320 MeV

Recovery of events needed or extend CALIFA crystals

Detection of protons and gammas 12C(p,2p)11B*(5 MeV)

11B in ground state 11B in 5 MeV state

Reduction in background due to thicker CsI crystals Broad peak is unresolved triplet

Cascade through 2 MeV state Gate on gamma energies in CALIFA

Detection of protons and gammas 12C(p,2p)11B*(5 MeV)

CALIFA barrel onlyCALIFA + perfect end-cap

CALIFA barrel low in efficiency but collects full energy

End-cap technology yet to be decided

Detection of protons and gammas 12C(p,2p)11B*(5 MeV)

CALIFA barrel CALIFA end-cap

Gammas pushed forward in reaction Mostly detected in end-cap

“Lampshade” design The inner detector module (green) has

6 detector modules, each with 2 silicon wafers

The outer detectors (blue) are formed from 2 layers of 12 detector modules, each with 3 silicon wafers Manufacturing masks are shared

between one of the outer and inner detector modules slices to reduce costs.

View from beam direction

3rd layer 300 mm

2nd layer 300 mm1st layer 100 mm

Outer and Inner silicon modules

Silicon Design

Strips are stereoscopic rather than perpendicular strips Reduced capacitance due to non-metalization Diamond shaped pixels 50mm pitch

Inner layer Max distance from beam axis = 69 mm Tilt angle = 14o

Outer layers Max distance from beam axis = 194/196 mm Tilt angle = 33o

Mechanical Design

Si Tracker

Cryogenics

CALIFA

Target

Vacuum chamber

Si Tracker

R3B Slow Control

To R3B DAQ

Si Inner

Si Middle

Si Outer

ASIC

ASIC

ASIC

ASIC

ASIC

ASIC

120k strips912 ASICs

Si Inner

ASIC

ASIC

Si Middle

ASIC

ASIC

Si Outer

ASIC

ASIC

x6

x12

x12

FPGA enet

enet

FPGA enet

enet

FPGA enet

enet

FPGA enet

enet

FPGA enet

enet

FPGA enet

enet

Vacuum Air

Switc

hSw

itch

DAQ PC(s)

30-912 FEE cards

CALIFA Timestamp & trigger links

Further Work Implementation of full tracking and analysis

code Prototyping of Si starts in April

Call for tender put out in October ASICS design is set and manufacturing has

started Full detector should be in place by mid 2014 GLAD moved to cave C this year New tracking detector coupled to CALIFA

demonstrator in 2014 Full experiment at FAIR in 2017 Design of next generation tracker

Collaboration

And the R3B collaboration