CLAS12 Particle Identification

CLAS12 Particle Identification

S. Stepanyan (JLAB)

Probing Strangeness in Hard Processes

INFN Frascati, October 18 – 21, 2010

Outline2

S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010

– CLAS12: physics and instrumentation

– PID in forward detector (baseline design)• e/ separation

• neutral particle identification

• charge hadron identification

– Charge hadron identification in central detector (baseline design)

– Improvements to the baseline design• K/ separation in forward detector

• neutron detection in central detector

• low energy recoil detector

– CLAS12 trigger

– Summary

CLAS12 physics program

3D Structure of the Nucleon - the new Frontier in Hadron Physics

Nucleon GPDs and TMDs – exclusive and semi-inclusive processes with high precision

Precision measurements of structure functions and forward parton distributions at high xB

Elastic & Transition Form Factors at high momentum transfer

Hadronization and Color Transparency

Hadron Spectroscopy – heavy baryons, hybrid mesons, …

Already approved experiments correspond to about 5 years of running

2/25/09


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Forward Central Detector Detector

Angular rangeTracks 50 – 400 350 – 1250

Photons 20 – 400 ---Resolutionp/p (%) < 1 @ 5 GeV/c < 5 @ 1.5 GeV/c(mr) < 1 < 10 - 20(mr) < 3 < 5 Photon detectionEnergy (MeV) >150 --- (mr) 4 @ 1 GeV ---Neutron detection

Neff < 0.7 (EC+PCAL) n.a.Particle ID

e/Full range ---p< 5 GeV/c < 1.25 GeV/c/K < 2.6 GeV/c < 0.65 GeV/c

K/pGeV/c < 1.0 GeV/cFull range ---

CLAS12 – Design ParametersForward Detector

Central Detector


€

L =1035cm−2s−1

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Detectors used for PID

High Threshold Cherenkov Counter (HTCC) for e/ separation, cGeVPth /7.4

Low Threshold Cherenkov Counter (LTCC) for e/ separation, cGeVPth /7.2

Scintillator counters (fTOF) @ ~650cm from the target, time resolution of 80ps

Electromagnetic calorimeters (PCAL&EC), 54 layers of lead and scintillators, 22 r.l.

CLAS12, Sector mid-plane

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Scintillator counters (cTOF) @ 50 cm from the target, time resolution of 60ps

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LTCC & HTCC


Working gas CO2 at 1 atm. Pion threshold P=4.9 GeV/c

Ellipsoidal mirror system

48 5’’ quartz window PMTs

Working gas C4F10 at 1 atm. Pion threshold P=2.7 GeV/c

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ECal (EC&PCAL)

Lead-scintillator sandwich with three stereo readout planes (UVW). Total of 22 r.l. thick, 54 layers (EC+PCAL) with longitudinal segmented 15+15+24

Transverse segmentation 4.5 cm in the first 15 layers and ~10cm in the last 39 layers. Light collection form one end of 5 to 420 cm long scintillator strips

U - plane

V - plane

W - plane

Inner PMTOuter PMT

Outer bundle

Inner bundle

LG


PCAL light readout with wavelength shifting fibers embedded in the scintillaotr strips

EC light readout with clear optical fibers connected to one end of scintillaotr strips


e/ separation LTCCxHTCCxEC for P < 2.7 GeV/c HTCCxEC (will be used in the trigger) for P < 4.9 GeV/c EC for P > 4.9 GeV/c (/e rejection better than few %)

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HTCC 3p.e.

HTCC 3p.e. and EC+PCAL > 0.4 GeV

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EEE 1.0

Electron detection with EC/PCAL

Added pre-shower calorimeter with 15 lead-scintillator layers will allow to retain good energy resolution for up to 11 GeV/c

ECAL for e/ separation for P > 4.9 GeV/c: cuts on the energy detected in PCAL and Inner part of EC, a cut on the total energy in ECAL

Ele

ctro

n de

tect

ion

effic

ien

cy 0.02

0.04

0.06

0.1

0.12

0.08

0.14

Pio

n d

ete

ctio

n ef

ficie

ncy

Cut on total energy in ECAL (GeV)

EC only

EC+PCAL



Neutron, , and 0 detection in PCAL+EC

Two cluster reconstruction from high energy 0 decays

Neutron detection efficiency

Neutron momentum (GeV/c)

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For neutron identification and momentum measurements, time-of-flight from the target to EC planes will be used. With time resolution of ~0.3 – 0.4 ns neutrons with P<3 GeV/c can be identified

4.5 cm transverse segmentation

10 cm transverse segmentation


Forward TOF systemExisting TOF, Panel 1a and 2a, time resolution t=150ps-180ps

New TOF plane, Panel 1b, time resolution t=80ps

CLAS/e2 – 12C run

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58 counters in each sector, 6x6 cm2 scintillator bars with lengths from 32 to 375 cm


Charged hadron ID with fTOF

In some limited cases, where exclusivity of the reaction can be used to aid kaon ID, LTCC can be used to veto charged pions with P>2.7 GeV/c.

t – time-of-flight difference

between different particles

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There is a gap in /K separation in forward detector for momenta above ~2.5 GeV/c.

Forward TOF at L~650 cm with t~80ps will allow clean (4-5) separation for /K with P< 2.6 GeV/c K/p with P<4 GeV /p with P<5 GeV/c


Charged hadron ID in central detector

Silicon TrackerScintillator Counters, t=60ps

5T SC Solenoid Magnet

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K-

p-K

, =0.06 ns

Momentum measurements in the solenoid field using silicon tracker and time-of-flight measurements with 60 ps time resolution in central TOF counters will provide /K and K/p separation for momenta up to 0.7 GeV/c and 1.2 GeV/c, respectively. Should be sufficient for the main physics program.

CLAS12

cGeVPth /9.4

cGeVPth /7.2

Low Threshold Cherenkov Counters (LTCC)

High Threshold Cherenkov Counter (HTCC)

Electromagnetic calorimeters

CLAS12 Torus

Drift Chambers

Forward TOF Counters

CLAS12 Solenoid


Large acceptance detector with excellent vertex reconstruction and good PID, capable of running with high energy electron beams on variety of targets - cryogenic, gausses, solid, polarized - at luminosity of ~1035 cm-2 s-1

Suitable for exclusive reactions with multi-particle final states

Forward TOF Counters

Si-tracker

There is always room for improvement!

/p

/KK/p

P, GeV/c3 4 5

detection in LTCCdetection in LTCC

fTOF

Charge kaons in FD


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at Pp = 4.5GeV /c, − t ≈ 8(GeV /c)2

K/p separation > 4 - 5 GeV/c should not be a problem, production of energetic nucleons is highly suppressed -

The biggest problem is charged kaon identification above ~2.5 GeV/c.

Cherenkov counters will not help, small inefficiencies for pions will cause big problems with kaon spectrum contamination.

RICH with a radiator of n≈1.03 will be the ideal choice to carry over charged hadron PID above limits of CLAS12 fTOF.


Neutron detection in CD Deeply exclusive reactions on neutron, e.g. DVCS on neutron - gives access to GPD E, the least known and least constrained GPD that appears in Ji’s sum rule

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80% of neutrons recoil at θlab > 40°, in momentum range 0.2 to 1.2 GeV/c

Spectator tagging method is luminosity limited (few x1033 to 1034 cm-2 sec-1)

Direct detection of neutrons in CD will fully utilize high luminosity of CLAS12

Central neutron detector – ~10 cm thick scintillator in the space between

CTOF and solenoid inner cryostat Neutron identification and momentum

measurement using TOF Expected momentum resolution dp/p~5%,

expected efficiency ~10-15%


Low energy recoil detector

Physics motivation: Neutron structure function – spectator tagging Nuclear DVCS – recoil (light) nuclei tagging Meson spectroscopy in coherent production on light nuclei

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Thin wall, e.g 30m kapton, high pressure (6-7 atm) gas targets

Lightweight target-tracking detector system will substitute dense target and central silicon tracker in the solenoid

RTPC based on cylindrical GEMs work well for 3 experiments with CLAS

Tracking detector


Very forward electron detection (LowQ) Electroproduction at very small values of Q2 is equivalent to photoproduction

using partially linearly polarized photons Forward angle electron detector together with CLAS12 will be excellent place

for baryon (e.g., and ) and meson spectroscopy. Part of the program can be run in parallel with electron running

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TorusHTCC

R1 DC

ECal

Target Moller absorber

Silicon tracker

Variable Range Resolution

E’ 0.5 GeV to 4 GeV

2

1.8o to 5.2o

Q2 0.01 to 0.2 GeV2

mrad8mrad1

3.0%5.1

EE

Detector system: tracker (can be combined with CLAS12 forward vertex tracker), calorimeter, fast scintilation detector

Trigger logic with fast clustering is necessary to reject high energy showers (>7 GeV) from elastic and Moller electrons


CLAS12 trigger CLAS12 will have free running DAQ system. ADCs and TDCs will collect data in

pipeline mode. Readout of data will be performed after trigger decision is made. Expected event readout rate ~10kHz. Inclusive electron rate at 1035 cm-2 s-1 is ~3kHz.

Available fast FPGA with flash-ADCs will allow to employ a multi layer trigger system in order to find clusters in ECal, reconstruct tracks in drift chambers and identify segments in Cherenkov counters and TOF counters

Trigger decision will be made after matching clusters, hits and tracks. The goal is: a) Achieve good electron selectivity using cluster energy cuts in ECal, momentum from

fast tracking, and hits in HTCC (+LTCC). Singles rates will be high, it is important to suppress accidentals. [CLAS Level 1 trigger for electrons is based on the total energy cut in EC and sector based ECxLTCC coincidence and only 7% of triggered events have electron at high energy runs]

b) Alow additional (multi-prong) triggers from photoproduction process –n tagged quasi-real photoproduction with LowQ setup n Qusi-real photoproduction of events when electron scattered at ~0 degree

[Some photoproduction reactions were successfully analyzed from CLAS high energy electroproduction data]

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Summary

In the baseline design, CLAS12 particle identification system includes gaseous threshold Cherenkov counters, scintillator counters for time-of-flight measurements, and electromagnetic calorimeters

Despite excellent design characteristics of each element, requirements of some class of experiments cannot be fulfilled with the baseline system

Important improvements to CLAS12 detector system for already proposed/approved physics program are: neutron detection in CD very forward electron detection low-energy spectator/recoil detection charged kaon identification in forward detector at momenta >2.7 GeV/c

Hopefully, this workshop will bring us one big step closer to build RICH detectors for CLAS12

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CLAS12 Particle Identification

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