Gas detectors in a ZDC (at LHC) Edwin Norbeck and Yasar Onel University of Iowa For7 th CMS Heavy-Ion meeting at Delphi June 2003

E. Norbeck U. of Iowa Gas-ZDC Delphi June 11, TAN Neutral Energy Absorber Between beam pipes 140 m from IP For pp receives ~210 W of neutrons and photons Radiation levels up to 50 Grad/yr Use neutral flux to measure and optimize luminosity. For PbPb use to measure impact parameter Measure with a Zero Degree Calorimeter, ZDC

E. Norbeck U. of Iowa Gas-ZDC Delphi June 11, ZDC signal vs impact parameter

E. Norbeck U. of Iowa Gas-ZDC Delphi June 11, 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

E. Norbeck U. of Iowa Gas-ZDC Delphi June 11, Requirements for detectors in TAN Energy measurements within 25 ns (for pp) 100 ns (for PbPb) Timing to within 300 ps Four quadrants for beam location (Neutral “beam” is about 2 cm in diameter) Fit within 8 cm x 8 cm x 100 cm (along beam) Simple, reliable, radiation hard Require little or no maintenance

E. Norbeck U. of Iowa Gas-ZDC Delphi June 11, Detectors and absorbers in TAN W tungsten metal (generates showers) P PPAC (time) IC ion chamber (energy) Neutrons and photons come in on left end. Beam people want one IC in TAN at all times. We must at least consider the logical extension presented here.

E. Norbeck U. of Iowa Gas-ZDC Delphi June 11, Typical low-pressure PPAC Two flat plates Separated by 2 mm Filled with 10 torr isobutane Most MIPs leave no signal 700 V between plates Timing resolution better than 300 ps Not useful for HEP until LHC (Parallel Plate Avalanche Counter)

E. Norbeck U. of Iowa Gas-ZDC Delphi June 11, for PPAC in TAN Three flat plates, separated by 2 mm Middle plate at high voltage Outer plates hold atmospheric pressure Not separated into quadrants Filled with torr of a suitable gas Gas flows in one side and out the other Timing resolution better than 300 ps Use in Zero level trigger Plate composition chosen to maximize signal, i.e. maximize conversion of soft photons to electrons

E. Norbeck U. of Iowa Gas-ZDC Delphi June 11, Test PPAC and electronics At heavy-ion facility (NSCL, GANIL…) Chose energy of heavy-ion beam so that after passing through the outer plate it will have an energy that will produce a signal the same size as a shower at LHC. Rough calculation finds that 35 A MeV Ar gives the same signal in a PPAC as the shower maximum from one 2.75 TeV neutron. The heavy-ion laboratories use many PPACs and have a good supply of gas handlers, etc.

E. Norbeck U. of Iowa Gas-ZDC Delphi June 11, 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

E. Norbeck U. of Iowa Gas-ZDC Delphi June 11, Parameters for an ionization chamber module. Active area per quadrant 40mm x 40mm Plate gap 0.5 mm No. of gaps 60 (6 series x 10 parallel) Capacitance/gap 28.3 pF Gas Ar+N 2 (1%), 4x760 Torr Gap voltage 150 V Electron gap transit time 21.7 ns Integration time constant 2.0 ns Time between bunches 25 ns mip per pp int. 268 Electron/ion pairs/cm-mip 388 S/N for average pp int. 6

E. Norbeck U. of Iowa Gas-ZDC Delphi June 11, Optimization of IC for PbPb Increase time constant to 20 ns in front end electronics. Ample time Time between bunches is 100 ns. Possibly increase gas pressure

E. Norbeck U. of Iowa Gas-ZDC Delphi June 11, Detectors and absorbers in ZDC Need simulations to optimize location of first two modules. (Might need four modules.) Radiation length only 0.35 cm in W 7 nuclear interaction lengths of tungsten Energy in ICs from a neutron depends on the location of first interaction. W metal + detectors has more stopping power than the copper metal it replaces.

E. Norbeck U. of Iowa Gas-ZDC Delphi June 11, PPAC energy resolution Poor for single heavy ion Current per  m   is huge! Same size signal from shower may have good resolution. Measure resolution with double PPAC Look at ratio between two sides Perhaps use PPACs also for energy

E. Norbeck U. of Iowa Gas-ZDC Delphi June 11, CONCLUSIONS Zero Degree Calorimeter of W and gas: Is radiation hard Can be left in place for both pp and PbPb Provides good energy and time resolution, but how does it compare to a quartz fiber ZDC?