High Resolution Hypernuclear Spectroscopy at Jefferson Lab, Hall A: the Experimental Challenge

IXth International Conference on Hypernuclear and Strange Particle Physics (HYP06) - Mainz, Germany, 10 -14 October, 2006

•Hall A Experimental setup modification•The Septum Magnets

•Optics of new High Resolution Spectrometer setup• The Jlab Hall A RICH

• Layout• Electronics Read Out and DAQ• Performance and results during experiment e94-107 – electroproduction of Hypernuclei• Rich upgrade for higher momenta and faster acquisition

• Conclusions

Francesco Cusanno, INFN Gruppo Sanità, Sezione di Roma

Jefferson LAB Site Location and the CEBAF facility

Hall A

Francesco Cusanno – HYP06 – Mainz, Germany, 10 – 14 October 2006


Optimization of Optics: the Database

Four Optical Elements (QQDQ)

Design Resolution 10-4 FWHM momentum resolution

Previously best obtained 2.5 10-4 FWHM momentum resolution

Multiple Coulomb Scattering is the reason for the difference

Typical HRS System

Both Spectrometers Have Demonstrated ~ 10-4 FWHM δ Resolution

Old D.B.


New D.B.

Performances of New Setup and Database

Hadron Identification through Aerogel

AERO1 n=1.015

AERO2 n=1.055

p

k

KAONS = AERO1 • AERO2

p k

All events

ph = 1.7 : 2.5 GeV/c

Pions = AERO1 • AERO2

Protons = AERO1 • AERO2


KAON Id Requirements – Physics case

Process Rates

signal (e,e’K) bound state

10-4 – 10-2

accidentals (e,e’)(e,)

(e,e’)(e,p)(e,e’)(e,k)

1001000.1

Very forward angle high background of and p

TOF and 2 threshold Cherenkov aerogel are NOT

sufficient for unambiguous K identification

RICH DETECTOR

Signal Vs. BackgroundHypernuclear spectroscopy


Freon Radiator: 1800x400x15 mm3 single box with quartzwindows glued on neoceram housing

Grid plane: 100 m positive wires (collects electrons ionized in the gap)

Wire chamber : composed by 20 m anode wires plane sandwitched between a cathode plane formed by 100 m wires and the cathode plane formed by the photocathodesThree Photocathodes :

403x640 mm2 each, divided in 8.4 x 8 mm2 size pads evaporated with a 300 nm CsI layer

JLAB Hall A RICH layout – similar to ALICE HMPID RICH


JLAB Hall A RICH MonteCarlo Simulations

, K Separated by , K Separated by

– K = 30 mrad

mrC

4.4

, K Separated by , K Separated by 6.8 6.8

Separation powerSeparation power

c n12

N. of detected N. of detected photoelectronsphotoelectrons

20sin370 2.. ELN

iicep


JLAB Hall A RICH: some components


Photocathode positioning in the glove box


JLAB Hall A RICH: the evaporation system

Photocathode

110 cm

120

cm

10-6 mbar vacuum2 nm/s CsI deposition at T = 60ºC (CERN experts indications). Vacuum - heating conditions starts 15 – 24 h before evaporation. A post-evaporation heat treatment is done for 12 hours.

crucibles

Quantum Efficiency

MeasurementSystem

details in : F.Cusanno et al.NIM A502(2003)251


RICH front end electronics and DAQ system

3 PhotoCathode each divided in 80*48=3840 pads 11520 tot. channels

FEE arranged in 8*6 = 48 rows each each rows handling 240 channels with 15 GASSIPLEX chips (for amplification, holding and multiplexing analogue signals – 16 pads per gassiplex chip)

Readout using CAEN System with CAEN V550 CRAMS and V551 Sequencer

240 pads (15 Gassiplex chips multiplexed signal with zero suppression) per CRAM channel (10 bit FADC)

total number of 24 VME modules + 2 VME V551 Sequencer in two VME CRATES.

2 MHz clock speed

no data buffering foreseen in CRAMS - CRAM memory read out for each trigger

Achieved performance :

sampling 120 s (clock) + 10 s = 130 s

VME (60 hits) 54 s

overhead 16 s 200 s deadtime per trigger

Experience : 20 – 25 % deadtime with 1kHz random trigger


JLAB Hall A RICH Event Display during data taking


JLAB Hall A RICH OPERATING conditions

Gas: Pure Methane (Minimize Photon Feedback, High Q.E.)

High Voltage: ~ 2100 Volts for a gain of 8x104

Grid Voltage: 250 - 450 Volts

Optimal trigger to read-out delay: ~ 400 ns (peaking time of gassiplex response)

MIP charge and hit size cluster charge and hit size


Rich Performances – key parameters :

mrad c

5

Angular resolution :Npe /p ratio :

66.01

122

22

n

n

N

N P

clus

Pclus

Npe for and P Cherenkov angle reconstruction

Cherenkov average angle (rad)Nclusters


Aero Selected

Aero Selected P

Aero Selected K (!)

Aero Selected Kon a large sample of filtered data

Separation power

cK 6

mrad c

5Angular resolution

/K population ratio

100

Kaon selection:cK 3

This would accept ~ 10-4 pions x /K ratio

1/100 pion contamination

…. But NON GAUSSIAN TAILS GIVE AN

IMPORTANT CONTRIBUTION !

Rich Performances – PID :


Rich – PID – Kaon selection results :

P

K

Time of coincidence for Aerogel Selected Kaons w/o and w/ rich :

AERO K AERO K && RICH K


Rich – PID – Pion rejection factor :

Time of coincidence for Aerogel Selected Pions: effect of Rich Kaon selection

N.Evts in the peakBackgnd subtr. =

64656

N.Evts in the peakBackgnd subtr. =

63

Pion rejection~ 1000

AERO && RICH KAERO


Rich Possible improvements :

• MWPC stability for high rates

For single rates ≤ 60 KHz HV=2100 V is OK

In the range 60 KHz – 100 KHz HV=2075 V is OK

Above 100 KHz HV must be reduced further

MWPC stability (and mechanics) needs to be studiedfor high rates running

However running at reduced gain with moderately goodperformance seems to be feasable

• /K separation for p>2.5 GeV/c

Doable “just” replacing the radiator C5F12 in liquid phase (<24°C)

• DAQ rate bottleneck (~1kHz) can be overcome replacing front-end


Rich /K separation for p > 2.5 GeV/c

Radiator C6F14 n=1.29 Ch ~ 5mr

Radiator C5F12 n=1.24 Ch ~ 5mr

4 separation at ~ 2.5 GeV/c 4 separation at ~ 3.0 GeV/c


Rich /K separation Vs. proximity Gap lengthwith C5F12 (n=1.24) radiator - MonteCarlo Simulations


Rich /K separation with C5F12 (n=1.24) radiator (14 cm proximity gap)

>20 separation at ~ 2 GeV/c ~ 4 separation at 3.0 GeV/c

MonteCarlo Simulations


Rich electronics upgrade :

VMEto

Local BusInterface

SegmentController

fbD[31..0]

LOC_ADD[11..0]

LOC_CS

LOC_R/Wn

fbD[27..0]

LOC_CS

LOC_R/Wn

LOC_ADD[3..0]

Column Controller

(1 to 8)

DILO 5 Boards

(ADC and DILOGIC)

RCB BOARDSEGMENT

GA

SS

IPL

EX

The HMPID ALICE RICH DAQ scheme

Front end digitization/multiplexing

On board

48 multiplexed channels

(instead of 240) Clock rate up to 10 MHz


Conclusions:

Septum Magnets has been successfully operated,

High Resolution Spectrometers with Septum Magnets provide momentum

resolution of 10-4 FWHM

The RICH detector has been successfully operated during the

hypernuclear experiment at JLab

It is a powerful tool for Particle Identification

Average Cherenkov angle resolution ~ 5 mr in good agreement with

Monte Carlo simulations

Clean kaon identification is possible with a pion rejection ratio ~1000

Upgrade foreseen both to increase the max DAQ rate limit and to increase

momentum range for /K separation


Documents

High Resolution Hypernuclear Spectroscopy at Jefferson Lab, Hall A: the Experimental Challenge