The Lightweight Straw Tube Tracker for PANDA Detector at GSI Andrey Sokolov *,1, James Ritman 1, Peter Wintz 1, Paola Gianotti 2, Dario Orecchini 2 1 Institut für Kernphysik, Forschungszentrum Jülich 2 Laboratori Nazionali di Frascati, Italy

PANDA detector Target spectrometer: MVD + STT/TPC + MDC Time Of Flight DIRC + RICH Electro-Magnetic Calorimeter Muon detection Superconducting solenoid Forward spectrometer: Dipole magnet MDC or STT RICH EMC Hadron calorimeter Muon detection STT or TPC Bernd Ketzer HK57.1

Requirements to the Central Tracker  Almost full angular coverage;  High momentum resolution, δp/p~1% ;  High spatial resolution, σ rφ ~150μm, σ z ~1-3mm ;  Minimal detector material budget, X 0 ~1% ;  High rate capability, 10 7 ev/s ;  Resistance against aging effects, 1-2 C/cm/year ;

Central Tracker Options Time-Projection Chamber (Christian Höppner, HK 38.2) Straw Tube Tracker

Straw Tube r Typical spatial resolution μm ~2 kV Ar+CO 2

Straw Tube

Pressure Stabilized Straw Tube Elongation 1.5mm +50 μ m P abs =2 atm Overpressure gives the stability and rigidity to the straw tube, but it also change straw tube dimensions. That should be taken into account in the tracker design.

COSY –TOF Straw Tube Tracker One double layer Pressure Stabilized Straw Tube Tracker

Spatial Resolution Spatial resolution of the COSY-TOF straw tube tracker Ar+20%CO 2

Proposed PANDA pressure stabilized straw tube tracker Pressure Stabilized Straw Tube Tracker 1.5m

Aging Phenomena in Straw Tube  Gas gain in the straw tube can deteriorate and dark current (noise) can increase with a time due to aging effects, namely: –deposit of the conductive polymers on the wire surface; –formation of an insulation coating on the cathode (Malter effect); –anode wire swelling by the free radicals; –oxidation of the conductive layer on the cathode surface.  These aging phenomena are typically observed for the accumulated charge values > 1-3 C/cm, depending on the gas mixture.

Aging Phenomena in Straw Tube Anode wire surface after irradiation [ATLAS TRT, NIM A512(166)]

Longitudinal Hits Projection 1000 events of pp collisions (DPM generator) protons

Hit/Charge Density Along Straw Length

Conclusions and Outlook  New design for the PANDA Straw Tube Tracker has been proposed;  The total weight of the tracker will be only about 50 kg;  The spatial resolution is about 150μm using Ar+10%CO 2 gas mixture;  The background simulation shows the very high radiation load;  The beam test is under preparation;  The test and simulation results of the PANDA straw tube tracker demonstrate the feasibility of the chosen detector concepts.

 Total number of tubes - ~5000 ;  Radial dimensions – 16-42cm ;  Length – 1.5m ;  Tube diameters – 10mm ;  Tube wall material – Mylar, 30μm ;  Anode wire – W/Re, 20μm ;  Spatial resolution – σ rφ ≈150μm, σ z ≈3-10mm ;  Gas filling – Ar+10%CO 2 ;  Gas absolute pressure – 2 bar ;  Thickness - ~1% X 0. STT parameters

Longitudinal Coordinate Measurement  Skewed layers –1-4 mm precision;  Charge sharing: –10-20 mm precision;  Time of charge propagation: –10-20 mm precision. One planar double-layer with the skewed straw tubes

HESR: High Energy Storage Ring Beam Momentum GeV/c High Intensity Mode: Luminosity 2x10 32 cm -2 s -1 (2x10 7 Hz)  p/p(st. cooling)~10 -4 High Resolution Mode: Luminosity 2x10 31 cm -2 s -1  p/p(e- cooling)~10 -5

Straw Tube Straw Tube Tracker