PPAC in ZDC for Trigger and Luminosity Edwin Norbeck University of Iowa Luminosity Workshop November 5, 2004

Nov. 5, 2004PPAC E. Norbeck 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. 5, 2004PPAC E. Norbeck U. Iowa3 PPAC in Zero Degree Calorimeter Three flat plates, separated by 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 heavy metal (W alloy) so as to be part of the absorber. Beam In

Nov. 5, 2004PPAC E. Norbeck U. Iowa4 Radiation damage Parts of the ZDC will receive huge amounts of radiation, ~100 Grad. A PPAC can be entirely metal and ceramic so that it will not be damaged by 100 Grad. With PPACs the ZDC will not need to be removed during the life of the LHC.

Nov. 5, 2004PPAC E. Norbeck U. Iowa5 Individual PPACs can be replaced if necessary Rigid coax and gas lines extend to top of TAN No organic materials in high-radiation region Beam In

Nov. 5, 2004PPAC E. Norbeck U. Iowa6 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. 5, 2004PPAC E. Norbeck U. Iowa7 First PPAC provides trigger and horizontal position information. The other PPACs would not be divided horizontally. 6 HV plates in the first PPAC Beam In

Nov. 5, 2004PPAC E. Norbeck U. Iowa8 1.8 ns 50 torr 790 V 7 mv into 50  Fast signals can provide timing for trigger 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. 5, 2004PPAC E. Norbeck U. Iowa9 ZDC signal vs impact parameter With heavy ions, impact parameter is related to neutron multiplicity (proportional to total energy deposited in ZDC)

Nov. 5, 2004PPAC E. Norbeck U. Iowa10 In All of the PPACs except the first would be used to measure the neutron multiplicity and/or luminosity

Nov. 5, 2004PPAC E. Norbeck U. Iowa11 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. To measure time averaged luminosity the total current can be integrated over several  s.

Nov. 5, 2004PPAC E. Norbeck U. Iowa12 Ion collection time (1 mm spacing) 0.3  s 0.5  s 50 torr 790 V

Nov. 5, 2004PPAC E. Norbeck U. Iowa13 Beam An ion chamber could be added to measure the average luminosity Ion Chamber

Nov. 5, 2004PPAC E. Norbeck U. Iowa14 Four quadrants Beryllium-copper plates Ceramic and sapphire insulators Plated strip on ceramic circuit board plate bias connections Isolated instrumentation ground and local ground shielding enclosures Ionization Chamber W.C. Turner et al., NIM A 461 (2001) 107

Nov. 5, 2004PPAC E. Norbeck U. Iowa15 S.N.White NIM A 417 (1998) 1 Absolute luminosity for PbPb Use correlated forward-backward neutrons. Cuts out beam-air and beam-wall collisions.  1n,1n =.535 b  1n,xn = 1.89 b  xn,xn = 14.8 b

Nov. 5, 2004PPAC E. Norbeck U. Iowa16 Double PPAC One side could be used for fast signals and the other for integrated luminosity. Two independent PPACs in the same gas volume.

Nov. 5, 2004PPAC E. Norbeck U. Iowa17 PPAC energy resolution 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

Nov. 5, 2004PPAC E. Norbeck U. Iowa18 Double PPAC for testing energy resolution

Nov. 5, 2004PPAC E. Norbeck U. Iowa19 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. 5, 2004PPAC E. Norbeck U. Iowa20 For high speed, the RC time constant must be kept small. Only PPACs of small area are fast, ~1 ns The segments in the segmented PPAC of slide 5 are small enough to be fast. R = 50 Ω (coax cable). C is the capacity between the plates C =.885 pF for 1 mm gap and area of 1 cm 2 For our larger PPAC with C = 168 pF rise time ~5 ns fall time ~7 ns Fast enough for the Zero Degree Calorimeter where minimum beam crossing time is 25 ns.

Nov. 5, 2004PPAC E. Norbeck U. Iowa21 Tests with double PPAC Test with EM showers using 80 ps bunches of 7 GeV electrons 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. 5, 2004PPAC E. Norbeck U. Iowa22 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. 5, 2004PPAC E. Norbeck U. Iowa23 Energy Resolution Data of PPAC Test at ANL Ratio E front to E back is constant to within ± 2%

Nov. 5, 2004PPAC E. Norbeck 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 hadrons showering in tungsten would give a much larger signal.

Nov. 5, 2004PPAC E. Norbeck U. Iowa25 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. 5, 2004PPAC E. Norbeck U. Iowa26 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