The BoNuS Detector. A Radial-Drift GEM TPC. Howard Fenker TPC R&D Meeting LBL, March 24, 2005

Transcription

1 The BoNuS Detector A Radial-Drift GEM TPC Howard Fenker TPC R&D Meeting LBL, March 24, 2005

2 Barely Off-shell Nucleon Structure This work was partially supported by DOE Contract No. DE-AC05-84ER40150 under which the Southeastern Universities Research Association (SURA) operates the Thomas Jefferson National Accelerator Facility (Jefferson Lab).

3 Motivation Purpose Provide almost-free neutron target to improve our understanding of neutron structure.

4 Method af t er e Measure slow protons e before n p p? Identify spectator protons to tag e - d events in which the neutron was struck. Measurement of proton momentum vector tells the initial state of the neutron.

5 Spectator Proton Angular distribution is isotropic. Backwards proton almost certain to be a spectator. Momentum distribution favors low values. Characteristics

6 Relative Ionization Yields Spectator tracks are 20x - 50x minimum ionizing. -> Detector can be made almost insensitive to lighter particles.

7 How to do it? Spectator must escape target Low density detector media. Minimal insensitive material Acceptance Large Symmetric about the target Detector sensitive to spectators, insensitive to background.

8 Big Picture Track secondary e - in CLAS. Locate e - interaction point in target. Link p spectator with electron vertex (need σ z ~8mm).

9 Narrow Target Optical properties of the CEBAF beam allow the use of a very narrow target. Spectator protons can escape the target and be detected.

10 Conventional TPC Advantages for BoNuS: Cylindrical Very low mass. Most energy de/dx is in sensitive materials. Many measurements of each track.

11 Conventional TPC Radial TPC Shorter drift path. Tolerates non-uniform B-field.

12 STAR Radial TPC

13 BoNuS Detector Concept

14 Why GEM Readout? Uniform acceptance Reduced mechanical strength required Less massive components It is interesting! First use of GEMs at JLab First use of curved GEMs anywhere

15 Availability of GEMs Both CERN and 3M have produced high quality GEM foils. CERN s priority is the internal program; they have limited capacity. 3M s priority is Return on Investment: mass production is possible. Tech Etch (Plymouth, MA) applying for R&D Funding. We (and others) have tested both 3M and Tech-Etch GEMs. Tech-Etch: Have supplied working custom GEMs for the BoNuS detector.

16 Problems with GEMs Gain Uniformity Seen to vary ~10% over a 10cm x 10cm CERN GEM Study of GEM Characteristics for Application in a Micro-TPC B. Yu, V. Radeka, G. C. Smith, C. L. Woody, and N. N. Smirnoff Gain Stability over time Short term- charge-up Long term- gain drift Rate dependence

17 Short-term: Charge-Up From A Comparative Study of GEM Foils from Different Manufacturers, Bob Azmoun (BNL), G. Karagiorgi(FIT), C. Woody (BNL)

18 Long-term: Gain Drift

19 Rate Dependence of Gain

20 Gain variations are a potentially serious problem for de/dx measurements We are considering various calibration options Not so serious for tracking. NEVERTHELESS we proceed.

21 Sample Event: Proton ID by de/dx & Curvature 100 MeV/c pion 100 MeV/c proton

22 Cosmic Tracks Proton Tracks box size represents Q( x,t ) 20mm x 19mm 20mm x 19mm x pad #

23 Production Model: Exploded View

24 Production Model

25 BoNuS in CLAS

26 Detector Parameters Geometric Acceptance Sensitive over 296 deg. In phi, 20cm in Z. Momentum Acceptance Protons from ~70 MeV/c Proton Identification (next slide) Vertex Z resolution <~ 10mm Track Momentum Resolution dp/p <~30% Track E information from de/dx Rate & Timing to handle ~2000 events/s

27 Detector Development Prototype flat, standard GEMs Test Prototype curved, standard GEMs Test Prototype flat, custom GEMs Test Production curved, custom GEMs June test run in CLAS

28 Prototypes

29 Prototype Construction Curved Prototype Test Fit GEM HV Connections ULTEM Frame Parts Drift Region Cathode Field Cage Electrodes (GEMs and Readout Board are not shown)

30 GEMs CAN be Curved

31 GEMs CAN be Curved

32 Curved GEM E-Fields 60mm radius Negligible change in E-field Curving the GEMs should not be an issue. LOCAL FIELD DEFORMATION NEAR CURVED GEM IS NEGLIGIBLE

33 and Curved GEMs do work.

34 Operation of a Curved-GEM Radial TPC, at least with the modest resolution requirements of BoNuS, has been successful. The challenge is construction.

35 Electronics Development Commercial CAMAC Modules 8 ch. (5/03) Test the whole concept Cosmic / Source / TUNL Run1 (11/03) Milestone: choose ALTRO readout (12/03) ALTRO Test Board 16 ch. Overcome signal polarity issue Cosmic / Source / TUNL Run 2 (5/04) ALTRO Production System 128 ch. (12/04) Cosmic / Source / TUNL Run 3 (3/05) Final ALTRO System 3200 ch. (6/05)

36 BoNuS Signal Readout System

37 ALICE and BoNuS Readout System ALICE RCU ALICE FEC Ribbons To RTPC BoNuS Carrier Card

38 prtpc w/ Inverter/Driver Cards Ribbons To Readout System

39 Detector System Tests Readout 128 channel tests Analog Electronics Prototype test results. Software Straight tracks de/dx

40 de/dx Analysis from TUNL

41 de/dx Analysis from TUNL

42 de/dx Analysis from TUNL

43 Software/Analysis Challenges DAQ: Interface w/clas data structure Event visualization OK and improving Track Fitting - Straight Tracks OK and improving Need to incorporate Vdrift(R) (ongoing) B-Field & its Non-Uniformity Lorentz angle R HIT vs. Time Bin (V drift varies with R) Curved e - Drift N.B.: non-uniform B

44 Bonus Detector Outlook Detector Parts Delivery 4/1 Detector Assembly 4/1-5/1 Electronics Fabrication now - 5/1 Assemble Detector, Target, Support, Readout 5/1-5/15 Checkout: 5/15 5/30 Hall-B Install & Engineering Test 5/31 6/8 Physics Run October 20 December 22, 2005!

45 BoNuS Detector Much done. Used GEMs Curved GEMs. Made TPC and RTPC. Developed readout. Plenty to do!