PPAC Jonathan Olson University of Iowa HCAL November 11-13, 2004

Nov. 13, 2004PPAC J. Olson U. Iowa2 Example of low-pressure PPAC (Parallel Plate Avalanche Counter) Two flat plates Separated by 1 mm Filled with 80 torr isobutane 1000 V between plates Operates in avalanche mode MIPs often leave no signal Showers give large signal directly into 50 Ω

Nov. 13, 2004PPAC J. Olson U. Iowa3 PPAC in HE Three flat plates, separated by 1 ~ 2 mm Middle plate at high voltage Outer plates hold atmospheric pressure Gas flows in one side and out the other Plates can be made of same material as the absorber. Beam In

Nov. 13, 2004PPAC J. Olson U. Iowa4 Individual PPAC to replace Scintillators Coax and gas lines extend out of radiation area No organic materials in high-radiation region Beam In

Nov. 13, 2004PPAC J. Olson U. Iowa5 PPAC Readout - + Summing amplifier can be used to add PPAC signals, increasing the effective size of PPAC (without increasing the time width of the signals)

Nov. 13, 2004PPAC J. Olson U. Iowa6 Radiation damage A PPAC can be entirely metal and ceramic so that it will not be damaged by radiation levels expected with the SLHC upgrade. Also makes it a good choice for the ZDC. If PPACs are chosen for ZDC, we would have a significant investigation phase prior to HE upgrade

Nov. 13, 2004PPAC J. Olson U. Iowa7 Beam In Zero Degree Calorimeter The green is solid metal (W). Detectors that sample the shower are shown in blue. Detector near front end is for EM shower

Nov. 13, 2004PPAC J. Olson U. Iowa8 CONCLUSIONS PPACs in a ZDC Can be made radiation hard. Can provide transverse position information. Have good energy resolution. Have sub nanosecond time resolution. Can be integrated to give average luminosity. Can be replaced without removing the ZDC. ZDC can be left in place for both pp and PbPb

Nov. 13, 2004PPAC J. Olson U. Iowa9 1.8 ns 50 torr 790 V 7 mv into 50  Fast signals Single peak with considerable noise. The noise is large because of the small size of the signal using our 137 Cs source. With the much larger signals from high-energy showers, the noise will be negligible.

Nov. 13, 2004PPAC J. Olson U. Iowa10 PPAC ion signal Fast electron signal is followed by a small, slow (500 ns) signal from ions moving between the plates. The slow ion signal is easily removed.

Nov. 13, 2004PPAC J. Olson U. Iowa11 Ion collection time (1 mm spacing) 0.3  s 0.5  s 50 torr 790 V

Nov. 13, 2004PPAC J. Olson U. Iowa12 Poor for single, low-energy heavy ion Current per  m   is huge! Same size signal from shower has good energy resolution. Measure resolution with double PPAC Look at ratio between two sides Double PPAC for Energy Resolution

Nov. 13, 2004PPAC J. Olson U. Iowa13 Double PPAC for testing energy resolution

Nov. 13, 2004PPAC J. Olson U. Iowa14 Ion and electron signals with 2 mm spacing 168 pF 1.6  s 6.2ns 1.3  s Amplified signal using gamma source. Positive overshoot is from amplifier. Ion collection time is three times as long with the 1 mm spacing.

Nov. 13, 2004PPAC J. Olson U. Iowa15 For high speed, the RC time constant must be kept small. Only PPACs of small area are fast, ~1 ns R = 50 Ω (coax cable). C is the capacity between the plates Small PPAC ~1 ns C =.885 pF for 1 mm gap and area of 1 cm 2 Larger PPAC with C = 168 pF for 2 mm gap and area of 1 cm 2 rise time ~5 ns fall time ~7 ns Still fast enough for the HE where minimum beam crossing time is 25 ns. Speed vs Size

Nov. 13, 2004PPAC J. Olson U. Iowa16 Tests with double PPAC Test with EM showers using 80 ps bunches of 7 GeV positrons from the Advanced Photon Source, at Argonne National Laboratory Test with low energy hadron showers using the 120 GeV proton test beam at Fermilab

Nov. 13, 2004PPAC J. Olson U. Iowa17 PPAC Test at ANL IOWA double PPAC was tested for energy resolution with electron showers from the Advanced Photon Source (APS) at Argonne National Laboratory. The booster ring of the APS puts out 76 ps bunches of 7 GeV positrons at the rate of two per second, with 3.6 x positrons in each bunch. In normal operation the positrons are injected into the main storage ring where they are used to produce synchrotron radiation. There are maintenance and development periods during which the beam is directed into a beam dump. We set up our equipment next to the beam line just in front the beam dump. The entire beam bunch has an energy of 2.5 x eV, or 2.5 x 10 8 TeV, much more than we needed. The PPAC was close to the beam line and so was exposed to showers generated by the outer halo of the beam striking the beam pipe. Because of the small angle between the positrons and the wall of the beam pipe, the wall acted as an absorber with a thickness of several centimeters. The showers were developed in this absorber.

Nov. 13, 2004PPAC J. Olson U. Iowa18 Energy Resolution Data of PPAC Test at ANL Ratio E front to E back is constant to within ± 2%

Nov. 13, 2004PPAC J. Olson U. Iowa GeV proton test Measured signal size (into 50 Ω, no amplification) at shower maximum. Maximum signal from detector placed after 30 cm of iron was 17 mV. TeV hadron showering in copper would give a much larger signal.

Nov. 13, 2004PPAC J. Olson U. Iowa20 No “Texas tower effect” With above-atmosphere hydrocarbon gas occasional proton from n-p scattering gives huge signal. In PPAC, proton hits wall at almost full energy. PPAC signal mostly from low-energy electrons. We will test this with detailed simulations.

Nov. 13, 2004PPAC J. Olson U. Iowa21 Simulation Efforts Investigation using GEANT4