1. Measuring the Position Resolution of a COMPASS Drift Chamber Prototype Rojae Wright 1, Ihnjea Choi 2, Caroline Riedl 2, Matthias Grosse Perdekamp 2 (1) Alabama A&M University, (2) University of Illinois in Urbana Champaign Introduction Drift ChambersResults Acknowledgements Beam Test at DESY Drift chambers are wire chambers that are built to detect the passage of charged particles by means of ionization of gas atoms and molecules. Planar drift chambers generally feature a row of alternating sense and field wires between two cathode planes. The anode wires are at positive electrical potential compared to the cathode planes and field wires. The chamber is filled with a mixture of 45% Ar, 50% Ethane and 5% CF 4. When a charged particle passes through a drift chamber it creates electron-ion pairs. The applied high voltage creates an electric field and prevents electrons from recombining with the ionized molecules or atoms. The field causes the freed electrons to drift towards the anode sense wires and the positively charged ions to drift towards the field wires and the cathode planes. On average electrons drift at a constant velocity. Knowing the difference between initial and arrival time, Δt, the relation Δx= v × Δt yields the location of the passage of the charged particle. The drift velocity in the gas can be accurately computed and the use of high-resolution timing electronics (TDC) allows the track position to be determined from the drift time of the electrons. COMPASS is a fixed target experiment at CERN in Geneva, Switzerland which investigates the quark and gluon structure of proton. The experiment will study the transverse spin- and momentum dependent quark structure for the proton through pion-induced Drell-Yan scattering off transversely polarized proton targets. The observed Sivers asymmetries are indicative of quark orbital angular momentum inside the proton. UIUC is designing and building a drift chamber to replace aging straw chamber stations in the COMPASS spectrometer. UIUC has built two drift chamber prototypes, A and B. Prototype A consists of a single anode plane with 8 wires, prototype B has two anode planes with 16 sense wires each. Electron beams with momentum of 4-5 GeV at DESY, Hamburg and cosmic rays are used to measure the position resolution of the drift chamber prototypes A and B. This poster describes the details of the experimental method and steps that will lead to the measurement of the position resolution with cosmic rays. This research was supported by NSF Grant PHY-1062690 and Alabama A&M University <The Drell-Yan process is the creation of a lepton-antilepton pair from the annihilation of a quark-antiquark pair through a virtual photon. The drift chamber prototype B in the UIUC clean room. <The diagram shows the cross section of prototype A. The pitch between sense wires is 8 mm. Prototype A, Beam Test at DESY Conclusion and Future Work The position resolution for prototype A is found to be better than 200 micro meter. The frontend electronics needs to be shielded carefully to reduce noise levels. Prototype B will be used to evaluate the performance of the second generation FEE using cosmic rays. Prototype B, Cosmic Ray Test at UIUC 4 - 5 GeV electron beam 5 x 5 mm incident beam size Beam telescope, 6 layers of silicon detectors, reconstruct electron tracks. - position resolution ~ 6 um Prototype A placed between silicon beam telescopes for measuring the position resolution & chamber efficiency Prototype A Beam Telescope Electron beam 20~30kHz Distance (R) -Time (T) correlation from beam illuminated channel (ch3) Position resolution vs. drift time Close to sense wireClose to field wire Signal from Prototype B Cosmic ray trigger Cosmic Ray Signal with Trigger Time of cosmic ray signal – Time of trigger [ns] Cosmic ray signal Rate [lHz] Noise rates Electron beam illuminates Ch3 DC-A Channel #