Craig Woody BNL RHIC Detector Advisory Committee Review December 19, 2002 A Fast, Compact TPC for Dalitz Rejection and Inner Tracking in PHENIX

Craig Woody BNL

RHIC Detector Advisory Committee ReviewDecember 19, 2002

A Fast, Compact TPC for Dalitz Rejection and Inner Tracking in PHENIX

C.Woody RHIC Detector Advisory Committee Review 12/19/02 2

Physics goals Description of the combined TPC/HBD detector Main R&D Issues Goals, milestones, funding

Outline


• Low mass lepton pairs and vector mesons

• Charm and B physics with resolved secondary verticies - low mass tracking just outside vertex detector - allows measurement in both heavy ion and pp running

• Improved inner tracking for PHENIX - increased h and f coverage (needed for jet and g-jet physics) - tracking through the magnetic field (improves momentum resolution, the ability to measure real low pT tracks, and to reject high pT background tracks)

Physics measurements addressed by this detector


e+

e-

TPC / HBD e-

e+

p

p

p

V0

measured in outer PHENIX

detectors(Pe > 200 MeV/c)

• Operate PHENIX with low inner B field to optimize measurement of low momentum tracks

• Identify signal electrons (low mass pairs, r,w,f, …) with p>200 MeV in outer PHENIX detectors

• Identify low momentum electrons (p<200 MeV) using Cherenkov light from HBD and/or dE/dx from TPC

• Calculate effective mass between all opposite sign tracks identified as electrons (eelectron > 0.9, prej > 1:200)

• Reject pair if mass < 130 MeV

Must provide sufficient Dalitz rejection (>90%) while preserving the true signal

Strategy for Low Mass Pair Measurement


Dalitz Rejection and Vector Meson Survival Probability

K. Ozawa

Survival probability of is ~85% for Dalitz rejection ratio of 90%.

Central Au+Au collisionsee = 100%, prej = 1:200 (HBD,RICH)


PHENIX Tracking

a

decays

conversionsB

DC

- DC only- PC1-PC3 matching- Random background

PT distribution of charged tracks

Drift Chamber

Momentum determined by measuring a angle

Tracking through the magnetic fieldwill help eliminate backgroundsfrom decays and conversion whichare problematic at high PT

PHENIX presently has no tracking inside magnetic field


PHENIX Inner Magnetic Field

± Configuration

BR

BZz=20cm

field from CDR scaled to 0.78 Tm

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 50 100 150 200 250 300 350

R (cm)

Bz

(Tm

)

++ 1.25 Tm

+ 0.73 Tm

+- 0.22 Tm

DC at 220 cm

B dl to drift chamber

Field Integrals Inner Coil creates a “field free” (∫Bdl=0) region inside the Central Magnet

Inner field itself is non-uniform

Tracking with TPC will aid in electron

id in HBD


Tracking at High Field and Vertex Resolution

Momentum resolution Impact parameter resolution

V. Rykov ++ Configuration B = 9 KG


TPC/HBD Detector

• Fast, compact TPC R<70 cm, L< 80 cm, Tdrift 4 msec

• Serves as an inner tracking detector in both HI and pp, providing tracking through the central magnetic field Df = 2p, |h| 1.0 Dp/p ~ .02p

• Provides electron id by dE/dx e/p separation below 200 MeV

• HBD is a proximity focused Cherenkov detector with a ~ 50 cm radiator length

• Provides electron id with minimal signals for charged particles

“Hadron Blind Detector”

GEMs are used for both TPC and HBD

TPC ReadoutPlane

CsI Readout Plane

Drift regions

Readout Pads


Rates and Occupancy

100 MeV e-

C.Aidala

35 pad rows, 80K channels DR ~ 1 cm, RDf ~ 2 mm DZ ~ 2.5 mm (140 samples)

11M voxels

Innermost pad row ~ 3% occupancy

Requirement: The TPC should work at the highest HI and pp luminosities

Au-Au : L ~ 8 x 1027 cm-2s-1

L x s = 8 x 1027 x 7.2 b = 58 kHz dNch/dy = 150 (min.bias) ~ 250 trks/evt, 15 trks/msec Nhits/evt ~ 100K occupancy ~ 1%

p-p : L ~ 2 x 1032 cm-2s-1

L x s = 2 x 1032 x 60 mb (Ss = 500 GeV) = 12MHz ~ 50 events in 4 msec drift time dNch/dy = 2.6 ~ 5 trks/evt, 52 trks/msec


R & D Issues for the TPC

Performance of GEM detectors• Stability, gain uniformity, aging• Studies of fast drift gases (CF4, CH4, mixtures…)

- Drift velocities, drift lengths, diffusion parameters, dE/dx, ion feedback,… - Optical transmission into the VUV for use with HBD

• Optimize spatial resolution

Detector component design• Readout plane • Field cage • Understand E x B effects for drifting charge in non-uniform magnetic field• Understand space charge effects (do we need gating ?)

Electronics

Infrastructure issues • Requires engineering and integration study (additional manpower needed)


GEM Detectors at BNL

Several multistage GEM detectors have been obtained from Sauli’s group at CERN and are currently being used for detector studies at

BNL

B. YuHigh precision (100 mm) scanning x-ray source


Double GEM Gas Gain Uniformity

5.4keV collimated x-rays (~1mm2) scanned with a 1mmx1mm grid over 9cmx9cm area.

90 100 110 120 130 140 150

Relative Amplitude

Good gain uniformity and energy resolution is important for particle id using dE/dx

p

k

pe

0.2 1.0 P (GeV/c)

miniTPC35 pad rows CH4

dE/d

x (k

eV/c

m)

e/p separation below 200 MeV

N. SmirnovB. Yu


GEM Spatial Resolution

J.Va’vra et.al., NIM A324 (1993) 113-126

Diffusion LimitsL~ 80 mm/35cm ~ 500 mm

GEM’s produce inherently good spatial resolution due to direct collection of electron signal

Must keep channel count low


Interpolating Pad ReadoutTwo Intermediate Strips

Single Intermediate Zigzag

-100

-80

-60

-40

-20

0

20

40

60

80

100

3000 3500 4000 4500 5000 5500 6000 6500 7000

Reconstructed Position [µm]P

os

itio

n E

rro

r [µ

m]

Overall position error: 93µm rms Including ~ 100µm fwhm x-ray p.e. range,

100µm beam width, alignment errors

Fine “Zigzag” pattern

B. Yu


Test Drift Cell

Drift Stack E-Field calculation

C. Thorn

Joint R&D with LEGS

Will be used to study

• Drift velocities• Drift lengths• Diffusion parameters• Energy loss (dE/dx)• Study impurities• Readout structures• Field cage design


TPC Readout

Readout Pads 35 pad rows, 5K ch/planeDR ~ 1 cm, RDf ~ 2 mm

Number of pads 80KPad size 2x10 mm2

Drift time 3.5 msecSampling rate 40 MHz (25 ns)Sampling resolution 2.5 mm, 8 bits Number of samples 140Unsuppressed data volume 11 MBSuppressed data volume (~1/10) 1 MBActual data volume 100 KBBuffer latency 4 msecReadout time 40 msecData transmission rate 200 Gbit/secPower per channel 100 mWTotal power 8 KW

200 ch readout card

15 cm

5 cm

R&D Issues

• Need to minimize power• Distribution of analog and digital signals• Low noise, zero suppression• Data volume (triggering)

Readout features


TPC Readout Electronics

Options• Commercial ADC + FPGA

• ALICE ALTRO chip

• Custom ASIC (may only need for preamp/shaper)

Considerations• Speed (need ~ 40 Mhz)

• Power (< 100 mW/ch total)

• Compatibility w/PHENIX readout

• Cost and availability

AD9289 Serial ADC4 ch / 65MHz / 8 bit

ADC each channel

AMU/ADC

C-Y. Chi


HBD Readout Electronics

Options• Separate (slow) ADC + TDC

• Fast ADC used to extrapolate T0 measurement

Considerations• Low noise (signal ~ 40 p.e.’s)

• Low mass (inside PHENIX accept.) (signals brought to edge of detector)

• ~ 5K channels - too few for ASIC

• Needs time measurement ~ few nsC-Y. Chi


FY03 R&D Goals

• Complete TPC test cell• Carry out gas studies of TPC with GEM readout• Preliminary design of TPC field cage & readout plane• Carry out CsI photocathode studies with GEMs• Measure CF4 scintillation (NSLS Feb ’03)• Carry out aging studies (GEMs, CsI, CF4)• Measure HBD response to hadrons and electrons• Define HBD detector configuration• Preliminary engineering design and integration study• Preliminary design of TPC and HBD electronics• Build test setup for TPC and HBD electronic components• Improved Monte Carlo simulations


• Demonstrate proof of principle of TPC with GEM readout

• Demonstrate proof of principle of CsI + GEM operation

• Determine feasibility of operation in pure CF4 (or choose alternative gas)

• Demonstrate feasibility of combined TPC/HBD detector concept

• Decide on ALICE ALTRO chip, commercial ADC+FPGA or ASIC for TPC

• Decide on slow ADC+ TDC or fast ADC for HBD readout

FY03 R&D Milestones


R&D Goals & Milestones for FY04 & FY05

FY2004

• Construct TPC/HBD prototype detectors• Construct gas system for prototype detectors• Build prototype HBD and TPC electronics• Build test setup for TPC and HBD electronics• Carry out detailed engineering design and integration study• Carry out further detailed Monte Carlo simulations

FY2005• Complete engineering and integration design• Complete TPC detector design • Complete design of TPC readout electronics


R&D Budget RequestCategory Description FY03 ($K) FY04($K) FY05($K)

Salaries Post Doc 45 45 45(incl. fringe) Electrical Engineer (1.0-1.25 FTE) 100 125 125

Electrical Tech (0.25 FTE) 20 20 20Mechanical Engineer (0.25 FTE) 25 25 25Mechanical Designer (0.25 FTE) 20 20 20Mechanical Tech (0.25 FTE) 20 20 20

Supplies Lab equipment 30 20 15Electronics ASIC fabrication 30 60 75

Test equipment 15 25 15Total 305 360 360Total (incl 40% overhead) 427 504 504

Related R&D Efforts

• Joint effort with STAR (includes additional equipment costs)• LEGS TPC• Detector R&D at FIT*• TPC w/GEM readout for NLC/TESLA

Additional institutional manpower contributions

*Florida Institute of Technology - 2 physicists, 1 student interested

BNL Weizmann Stony Brook Columbia TokyoPhysicists 1.50 1.50 0.25 0.25 0.25Physics Associates 0.50Post docs 0.25 0.5Students 1.00 1.00 0.5Technicians 0.25Electrical Engineers 0.25 0.25Mechanical Engineers 0.25Mechanical DesignersFTEs 2.50 2.75 1.50 0.50 1.25Total FTEs 8.50


Additional Slides


20 cm

55 cm

70 cm

CsI Photocathode

C.Aidala

Single 100 MeV/c electron track

GEANT Simulation of TPC/HBD

TPC/HBD detector in PHENIX PISA simulation package


Fast drift gases - CH4 and CF4

10 cm /ms

12 cm /ms

40 cm drift ~ 3-4 ms Requires high drift field

1 V / cm / Torr

CF4 -Ar

1 KV / cm

C2 H6

CH4

C2 H2 P10

CF4


Ion Feedback in GEMs

ElectronsIons

F.Sauli

B.YuTriple GEM


Space Charge Distortions

Emax ~ 1.7V/cmEmax ~ 1.4V/cm

Distortion field components in TPC volume.

Radial Axial

200 GeV Au+Au Ion feedback 10%

q ~ 2.5 x 10-3 radDx ~ 0.5 mm for 40 cm drift

G ~ 103

r ~ 10-8 C/m3

B. Yu


GEM Aging and Discharge Rates

Experience from COMPASS

• Triple GEM greatly reduces discharge probability rate• no discharges over months of operation• no loss of gain or resolution due to aging

S.Kappler, 2001 International Workshop on Aging Phenomena in Gaseous Detectors http://www.desy.agingworkshop

S.Bachmann et.al., NIM A479 (2002) 294

Triple GEM

Aging rate at RHIC

• Min bias 1.3 x 107 trks/sec• dE/dx = 80 ion pairs/cm (CH4)• Gain = 2 x 103

• dQ/dt = 64 C/yr, A= 8247 cm2

dQ/dA = 0.08 mC/mm2/yr

Triple GEMArCO2, G~8.5x103


Used for measurements of VUV gastransmission and CsI quantum efficiency

VUV Spectrometer

Ratio of Quantum Efficiencies Before and After Exposure to Gas

0

20

40

60

80

100

120

140

1150 1250 1350 1450 1550 1650 1750

Wavelength [Angstroms]

QE

(Aft

.)/Q

E(B

ef.)

[%

]

1. Ar (1 min.)

2. Ar (5 min.)

3. Ar (10 min.)

4. CF4 (1 min.)

5. CF4 (5 min.)

6. CF4 (10 min.)

(Au-Ni-Cu-G-10 Substrate)

B.Azmoun


Commercial ADC

C-Y. Chi


Use of ALTRO Chip in PHENIX

Backend of the ALTRO chip15 write clocks

signalL1 trigger

(write to buffer)

L1 (W)L1 (W)

L1 (W)L1 (W)

L1 (W)L1 (W)

L2 trigger

(keep the buffer)

Read or drop L2 events

L1 (W)L2 (keep)

L1 (W)L2 (keep)

L1 (W)L2 (keep)

ALTRO’s event buffer could be divided to

8 * 512 word blocks or

4 * 1024 words blocksTime

C-Y. Chi

Problem for PHENIX a) no overlapping event buffers (space between L1 triggers could be as short as 4 beam clocks) b) L1 trigger delay is too short (i.e., 15*25 ns = 375 ns)


• We need to generate a fake L1 trigger every 512*25ns = 12.8s. ( used as L1 delay buffer)

• Our L1 trigger will become ALTRO chip’s L2 trigger.• We read the L1 data buffers to a FPGA/ASIC. We will parse our

data blocks from ALTRO data buffers

Two overlapping TPC data block

ALTRO 512 words buffers

TPC data block PHENIX L1 Two PHENIX L1

Use of ALTRO Chip in PHENIX

C-Y. Chi


Implementation Plan

Construction (2 years)

• Detector: $250K• Gas System: $250 K• Detector mounted electronics: $4.0M (80K Readout Channels @ $50/ch)• Other readout electronics: $500K

Total: $5.0 M

FY 2003

FY 2004

FY 2005

FY 2006

FY 2007

FY 2008

HBD TPC

R&D

Operation

Construction

R&D

Construction

Operation

R&D (3 years)

Total: $1.4M

(LDRD for $100K in FY 2001 & FY 2002)

Documents

Craig Woody BNL RHIC Detector Advisory Committee Review December 19, 2002 A Fast, Compact TPC for Dalitz Rejection and Inner Tracking in PHENIX