1. CLAS12 Particle Identification S. Stepanyan (JLAB) Probing Strangeness in Hard Processes INFN Frascati, October 18 – 21, 2010

2. Outline 2 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

3. 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 x B 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 S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010 3

4. ForwardCentral Detector Angular range Tracks 5 0 – 40 0 35 0 – 125 0 Photons 2 0 – 40 0 --- Resolution  p/p (%) < 1 @ 5 GeV/c < 5 @ 1.5 GeV/c  (mr)< 1 < 10 - 20  (mr)< 3 < 5 Photon detection Energy (MeV)>150---  (mr)4 @ 1 GeV--- Neutron detection N eff < 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/p  GeV/c< 1.0 GeV/c    Full range--- CLAS12 – Design Parameters Forward Detector Central Detector S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010 4

5. Detectors used for PID High Threshold Cherenkov Counter (HTCC) for e/  separation, Low Threshold Cherenkov Counter (LTCC) for e/  separation, 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 5 Scintillator counters (cTOF) @ 50 cm from the target, time resolution of 60ps

6. 6 LTCC & HTCC S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010 Working gas CO 2 at 1 atm. Pion threshold P=4.9 GeV/c Ellipsoidal mirror system 48 5’’ quartz window PMTs Working gas C 4 F 10 at 1 atm. Pion threshold P=2.7 GeV/c

7. 7 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 PMT Outer PMT Outer bundle Inner bundle LG S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010 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

8. S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010 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 %) 8 HTCC 3p.e. HTCC 3p.e. and EC+PCAL > 0.4 GeV

9. 9 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 Electron detection efficiency 0.02 0.04 0.06 0.1 0.12 0.08 0.14 Pion detection efficiency Cut on total energy in ECAL (GeV) EC only EC+PCAL S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010

10. Neutron, , and  0 detection in PCAL+EC Two cluster reconstruction from high energy  0   decays Neutron detection efficiency Neutron momentum (GeV/c) 10 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

11. S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010 Forward TOF system Existing TOF, Panel 1a and 2a, time resolution  t =150ps-180ps New TOF plane, Panel 1b, time resolution  t =80ps CLAS/e2 – 12 C run 11 58 counters in each sector, 6x6 cm 2 scintillator bars with lengths from 32 to 375 cm

12. S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010 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 12 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

13. S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010 Charged hadron ID in central detector Silicon Tracker Scintillator Counters,  t=60ps 5T SC Solenoid Magnet 13 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.

14. CLAS12 Low Threshold Cherenkov Counters (LTCC) High Threshold Cherenkov Counter (HTCC) Electromagnetic calorimeters CLAS12 Torus Drift Chambers Forward TOF Counters CLAS12 Solenoid S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010 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 ~10 35 cm -2 s -1 Suitable for exclusive reactions with multi-particle final states Forward TOF Counters Si-tracker There is always room for improvement!

15.  /p  /K K/p P, GeV/c 345  detection in LTCC fTOF Charge kaons in FD S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010 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.

16. S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010 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 16 80% of neutrons recoil at θ lab > 40°, in momentum range 0.2 to 1.2 GeV/c Spectator tagging method is luminosity limited (few x10 33 to 10 34 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%

17. S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010 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 17 Thin wall, e.g 30  m 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

18. S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010 Very forward electron detection (LowQ) Electroproduction at very small values of Q 2 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 18 Torus HTCC R1 DC ECal Target Moller absorber Silicon tracker VariableRangeResolution E’E’0.5 GeV to 4 GeV  22  1.8 o to 5.2 o Q2Q2 0.01 to 0.2 GeV 2 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

19. S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010 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 10 35 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 – 1)tagged quasi-real photoproduction with LowQ setup 2)Qusi-real photoproduction of events when electron scattered at ~0 degree [Some photoproduction reactions were successfully analyzed from CLAS high energy electroproduction data] 19

20. S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010 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 20