Development Of The Recoil Detector For The HESR Day-One Experiment And Commissioning At COSY By Measuring Pp Elastic Scattering

The PANDA experiment is one of the future experiments at FAIR, it will pursue a broad physics program using a high quality antiproton beam in the momentum region from 1.5 to 15 GeV/c. The goal of the PANDA luminosity detector is to determine the absolute integrated luminosity with precision of â–³L/L≤3%. The parameters describing the antiproton-proton elastic scattering differential cross section:σtot,p and b are needed to calibrate the input to the PANDA luminosity determination in order to achieve this high precision for the absolute luminosity. However, the existing data of σtot,p and b in the PANDA beam momentum range are not sufficiently by precise for the PANDA luminosity calibration.The HESR Day-One experiment is dedicated to determine the parameters by mea-suring antiproton-proton elastic scattering in a large range of squared 4-momentum transfer,|t|. The HESR Day-One experiment will measure the elastically scattered an-tiprotons and recoil protons with the PANDA luminosity detector and a recoil detec-tor, respectively. One recoil detector consists of two silicon and two germanium sensors that cover the polar angle range from θ= 71° to 91.5°. The silicon detectors will mea-sure the recoil protons below T=12 MeV, and the germanium detectors will measure the recoil protons up to 60 MeV.A dedicated recoil detector for tests with proton beam at COSY has been built. After assembly, the silicon and germanium detectors have been tested in the laboratory with the radioactive source 244Cm. The optimal operation temperature,125 K, of the germanium has been determined. The energy resolutions of the silicon and germanium detectors at 125 K are better than 20 keV and 30 keV, respectively.The energy calibration of the silicon and germanium detectors has been studied. The uncertainties of the energy calibration of the silicon and germanium detectors have been estimated to be 0.33% and 0.31%, respectively. The dead-layer thicknesses of the germanium sensors have been determined.Simulation studies of proton-proton elastic scattering at 3.2 GeV/c has been per-formed. The detector’s acceptance has been obtained. The differential counts as a func-tion of |t| has been reconstructed with acceptance correction. The proton-proton elastic scattering differential parameters σtot,p and b as well as their systematic uncertainties have been determined by analyzing the characteristic shape of the |t| distribution.The recoil particle and kinematics measured in ppâ†'pp are the same as in ppâ†'pp. Thus, we can learn about behavior of the recoil detector for ppâ†'pp by measuring ppâ†'pp. Therefore, the recoil detector was installed at the ANKE cluster target station at COSY and commissioned by measuring proton-proton elastic scattering. Data were taken at beam momenta of 1.7,2.5,2.8 and 3.2 GeV/c. For 2.8 GeV/c and 3.2 GeV/c, the elastic scattering differential parameters and integrated luminosity have been deter-mined. The uncertainty of σtot and b were better than 1% and of p was about 2%. The absolute integrated luminosity was determined with precision of â–³L/L<3%. Comparing the measured σtot and p with existing data show agreement to better than 1.5%. The measured b values are however about 20% greater than the previously measured values. The differential cross sections at 2.8 GeV/c and 3.2 GeV/c have been obtained. The dσ/dt distribution of our results in the range of |t| ∈[0.02,0.095] (GeV/c)2 are in good con-sistent with the existing data at 3.0 GeV/c. These results demonstrate that the HESR Day-One experiment is feasible and that the data analysis method is reliable.