Mitglied der Helmholtz-Gemeinschaft Hit Reconstruction for the Luminosity Monitor March 3 rd 2009 | T. Randriamalala, J. Ritman and T. Stockmanns

February 24, 2009 Folie 2 Outline  Reminder: Luminosity Monitor Telescope Geometry Parameters of the Sensor Digitization  Reconstruction : Simulation setup Geane task Results  Conclusion

February 24, 2009 Folie 3 At the position z = 10.5 m downstream: the luminosity monitor is designed to detected the outgoing antiproton resulting from the elastic pbar-p scattering :  8  mrad. Luminosity Monitor Telescope R~8 cm 31 cm ~70 cm D=89mm Vacuum Tracking stations beam

February 24, 2009 Folie 4 Sensor Parameters used for the digitization Double sided silicon strip sensor:  Pitch = 50 μm  Thickness = 300 μm  Front side skew angle = 30 degrees  Back side skew angle = - 60 degrees 50  m 300  m 30° -60° A portion of a sensor

February 24, 2009 Folie 5 Digitization Charge per hit is shared among the strips fired depending on the path length they contain, then diffused over the sensor by a Gaussian distribution with 8 μm width. Add noise of 5 keV (  ) and set the threshold to 10 keV. Consider only events in which the outgoing antiproton hits all 4 stations: tracks are nearly normal to the LM detector surface

February 24, 2009 Folie 6 How to reconstruct the position in the strip? Hit multiplicity = 1: Reconstructed position is the center of the strip fired. Hit multiplicity > 1: Reconstructed position is obtained by fitting the charge ratio variation as a function of the MC postion.

February 24, 2009 Folie 7 Reconstruction Run 100,000 events : 1 antiproton per event, with momentum 6.2GeV/c and polar angle 2 mrad to 10 mrad. Temporary solution: Solenoid field only. The dipole field bends particles away from the LM. (see next slide) Problem: Beam pipe without chicane. Magnetic field: Full map of the PANDA magnetic field (dipole, solenoid and transition region) is now available in pandaroot.

February 24, 2009 Folie 8 Full magnetic field system : Tracks are bent by dipole magnetic field. With the current status of the beam pipe, the LM does not observe any hits.

February 24, 2009 Folie 9 Without the dipole magnetic field: Tracks go through the LM And hits are observed ! MC Points

February 24, 2009 Folie 10 Geane and LM It takes into account 3 effects : energy loss (affects mean values and errors), Coulomb multiple scattering (affects errors only) and magnetic field (affects mean values only). If track hits the 1 st station: Input : hit position, momentum, charge and plane definition. What is Geane? It is a track follower: it predicts the trajectory of a charged particle in terms of mean values and errors. How does Geane work for LM? Hit positions prediction at the next three planes are done by giving the configurations of these lasts.

February 24, 2009 Folie 11 Geane and LM Geane can be used as reference for the LM reconstruction results. At LM region, B=0. Tracks follow straight lines Difference between Geane hit and MC hit positions at the 3 last planes. Plane #2Plane #3Plane #4  cm  cm  cm

February 24, 2009 Folie 12 Results(1) Difference between reconstruction hit and MC hit positions at the 4 stations Plane #1Plane #2Plane #3 Plane #4 mult = 1  ~ 10  m) mult >1 (  ~ 2  m)

February 24, 2009 Folie 13 Results(2)  Geane -  MCPoint MC points have been fitted linearly and have been compared with Geane tracks.  Geane := angle between Geane track and horizontal  MCPoint := angle between fit line of MCPoint and horizontal With Geane : t Geane – t MCPoint  mrad

February 24, 2009 Folie 14 Results(3) t Reco - t MCTrack  Reco -  MCTrack Remark: MC Track only from the IP RecoPoints have been fitted linearly and have been compared with MCTracks.  MCTrack := angle between MCTrack and horizontal  Reco := angle between fit line of RecoPoints and horizontal With reconstruction :  mrad

February 24, 2009 Folie 15 Conclusion  The RMS of the deflection angle  of a singly charged particle with momentum p and velocity  is given by : ~ 0.09 mrad   ~  Reco  mrad) Reconstruction work !!!  The corresponding track hit difference (MCTrack – RecoTrack) at the last station has  track = 90  m (~ 2 x pitch) Current design: bad resolution !!! Detector optimization

February 24, 2009 Folie 16 With others values of thickness Thickness = 150  mThickness = 50  m   ~0.07 mrad  track ~ 57  m   ~0.05 mrad  track ~ 40  m