1. dE/dx measurement with Phobos Si-pad detectors - very first impressions (H.P Oct 17 1998)

2. What characterizes dE/dx in Si? In the MIP range: –measure momentum and and amplitude for which particles are minimum ionizing in thin silicon detectors In the high p range: –measure the relativistic rise of dEdx and compare it to predictions (Bethe Bloch, Geant) In the low p range: –measure the 1/beta-part of dE/dx for poins and kaons –characterize the energy straggling @ different momenta and particles for PID –try to measure the signal range for stopping particles

3. What do we need for this measurement The Silicon detector: –use final 4 planes of the spectrometer type 1 modules –small pads -> good and full tracking –high S/N -> good energy loss measurement –8 sensors & 96 chips -> minimize systematic error, give redundancy and allow cross checks The TOF: –provides pi/K seperation and particle identification in the low p range Cerenkow counters: –suppress e- back ground of secondary beams We need to do a real precision measurement! -> Use final PHOBOS calibration –allows to get very high precision dE/dx to better than 1%

4. Our setup: The high momentum beam line: –pi- beam from 0.5 to 8GeV/c The low momentum beam line (The E913 beam in C6) –pi-/K- beam line from 300MeV/c to 750 MeV/c Trigger scCerenkowPhobos4 planes of Spectrometer Paddletype 1 modules TOF start(Degarder)Phobos 4 planes of TOF stopCerenkow Paddle (Trg) type 1 modules

5. The Readout system Based on VME analog readout system developed by HEPHY/Vienna –repeater cards inplace of FEC and sends analog signals via 20m cables to dedicated VME ADCs (0.6 to 40MHz 12-bit) –uses 40MHz ADC to digitize TOF data –readout is based on 1 Pentium II and a simple PCI-VXI interface card and LabWindows The calibration is based on the final PHOBOS calibration card build by FH, Wr. Neustadt, Austria –uses 12 DAC voltage –switched with 20ns rise time on the calibration capacitor –linearity better than 0.5%

6. The system performance = Excellent! Si- system: –a 12 000 channel system –Signal/Noise was about 17:1 to 18:1 –about 60/12300 channel noisy –total efficiency about 98 % The TOF: –largely based on the PHOBOS paddle counter –resolution about 200ps (average over 2/3 of the paddle acceptance) (TDC intrinsic resolution about 120ps) The DAQ: –transfered RAW data in NON-SUPPRESSED mode with up to 100Hz ! –Limited only by CPU time and disk access

7. The PHAT analysis software is ready ALL analysis is based on standard PHAT routines Parts implemented: –all detector data unpacking routines are prepared –the full geometry is described –ready for track fitting –a first version for signal calculation is implemented Some parts still to go –implement calibration –tune signal calculation

8. Let’s get to the “first impressions” on the data quality The high p range: –aim to determine what a “MIP” is in thin silicon detector –measure dE/dx up from 0.5 to The beam and trigger –pi- beam –veto e- with Cerenkow –muon contents <2% –no protons –delta p/p = 0.5% –chross checked absolut energy with calorimeter - better an 4% Recorded 50000 tracks at each energy point:= 200k hits energies: 0.5, 0.75, 1.0, 2, 3, 4, 6, 8 GeV/c

9. Measurement precision WITHOUT good calibration already 1-2%!

11. The low p range and energy straggling: –aim to determine pi and K seperation –get energy straggling data at low momenta –test dE/dx PID The beam and trigger –pi-/K- beam (60:40) –veto e- with Cerenkow –muon contents <2% –delta p/p = 4% –use energy calibration files of E913 Recorded 50000 tracks at each energy point:= 200k hits energies: 285, 500, 620, 750 MeV/c and 4 degrader with lower energies for pi

12. Kaons Pions Not yet looked at!

13. YES - we did get stopping particles ! (pi-) –use paddle counter a veto –trigger now only on small area finger counter (1cm2) –use a 4.5 inch steel degrader –energy after degrader about 80MeV/c for cross check used detector part which is not in beam recorded data –with veto counter to enhance stopping events (low p tail selection) –without veto counter to cross check rates –with veto as trigger (high p tail selection) we have very limited data but can get more on monday

15. 30MIP signal 100MIP signal

16. Conclusion We have beautiful data! We measured: –the MIP point: measured –the relativistic rise: measured from 0.5 to 8GeV/c –dE/dx below one MIP: measured from 280 to 750 MeV/c for pi (500 to 750 MeV/c for K) –measured stopping particles and their signal range (try to get more statistics on Monday We can analyse: –energy loss over two orders magnitude in momentum! –Can fully characterise straggling over the full p range –Can explore our particle identification with REAL data –Can get ideas what to do with stopping particles …