dE/dx measurement with PhobosSi-pad detectors

- very first impressions

(H.P Oct 17 1998)

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

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%

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 sc Cerenkow Phobos 4 planes of SpectrometerPaddle type 1 modules

TOF start (Degarder) Phobos 4 planes of TOF stop CerenkowPaddle (Trg) type 1 modules

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%

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

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

Let’s get to the “first impressions” on thedata 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

p [GeV/c] S0 S1 S2 S3 S4 S5 S6 S7 average dE/dx sigma dE/dx average dE/dx sigma dE/dx0.5 21238.22 20971.32 21443.33 21021.41 23878.66 24074.86 24009.35 23714.51 21169 216.724056 23919.34479 159.05830.5 20858.97 20776.54 20947.53 20706.72 23650.25 23725.51 24073.04 23651.61 20822 104.0525394 23775.10135 201.7117

1 20732.55 20257.13 20823.58 20643.78 23117.31 23695.13 23436.18 23022.58 20614 249.1460318 23317.79954 307.54298 21554.27 21315.44 21691.23 21461.98 24086.3 24682.43 24837.26 24783.87 21506 158.0009563 24597.46259 346.77514 21016.99 20880.43 21505.31 21273.16 24017.08 24378.64 24455.15 24280.64 21169 277.087385 24282.87894 191.04992 20985.39 20711.62 21381.36 20769.65 23809.44 24074.86 23945.67 23714.51 20962 303.3671669 23886.12009 157.5835

1.5 20858.97 20516.84 21009.51 20643.78 23601.8 23998.91 23945.67 23400 20757 219.5863265 23736.59447 285.18463 21427.85 20971.32 21381.36 21147.28 24086.3 24226.75 24391.46 23714.51 21232 212.7543865 24104.7558 288.51096 21598.51 21360.88 21939.13 21461.98 24293.94 24530.54 24582.52 24280.64 21590 252.2226337 24421.90804 156.981

0.75 20732.55 20607.73 21133.46 20769.65 23740.23 23847.02 23818.3 23274.19 20810.84865 225.9487339 23669.934 267.661

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Measurement precisionWITHOUT good calibration already1-2%!

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• 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

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Kaons

Pions

Not yetlooked at!

• 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

30MIP signal100MIP signal

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 …