General Meeting Minutes 2/19/10

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A. Accardi, J.P. Chen, D. Gaskell, H. Gao, V. Guzey, R. Ent, T. Horn, N. Kalantarians, P. Nadel-Turonski, Kent Paschke, A. Prokudin, C. Weiss

Discussion on proper cuts to use for various physics processes

Rolf's slides‎

DIS (ep) - y cuts for e- and hadron remnant detection

  • Several methods exist for DIS event reconstruction. Each method is associated with different uncertainties in the kinematic variables. The uncertainties factorize into a detector-dependent part such as the electron energy resolution, and a pre-factor for each measured quantity that depends on the event kinematics (not their uncertainties). The latter follows from error propagation, and has been worked out in detail for the methods employed at HERA in a convenient NIM paper‎.
  • The kinematic coverage in (x, Q2) is in practice limited by the large errors at extreme values of y. Based on the HERA experience, a range where reasonable range is 0.8 < y < 0.1. If the electron energy resolution can be kept below 1-2%, methods combining the detection of the electron and all hadronic remnants seem to offer the best performance over the full range of y. This emphasizes the need for a hermetic detector even for DIS.

DIS (eA) and SIDIS

  • The kinematical limitations for SIDIS and in the case of nuclear targets (where one could encounter different challenges for hadron detection) need to be investigated.

Exclusive Reactions

  • Reconstruction of exclusive events relies on kinematic fitting and detector hermeticity. The missing mass resolution deteriorates with energy. For the MEIC it will be in the GeV range and can thus not alone determine exclusivity. However, the phase space available for the multi-meson backgrounds also increases, reducing the contribution at small values of the missing mass (missing energy), which still makes it a useful tool. The hermeticity of the detector ensures that ideally all produced particles will be detected. In reality, some particles could escape down the beam pipe or hit dead zones, but the better the hermeticity, the stronger the constraint on the event reconstruction. Detecting all outgoing particles in the reaction of interest, making it kinematically overdetermined, allows the use of kinematic fitting for the event reconstruction. Knowing the errors on each measured quantity and the acceptance of the detector (and thus the region where no particles were detected) makes it possible to calculate a confidence level for each assignment of particles to the tracks in the event, as well as the one where one or more particles were missing. Ambiguous events can then be discarded. Since the confidence level is a statistically well defined quantity, the yields (and asymmetries) can be corrected accordingly, creating a clean exclusive sample if sufficiently good resolutions can be achieved.

Detector and Interaction Region Documentation

  • Documentation will be prepared for the user's meetings summarizing the considerations for the detector and interaction region. An outline can be found in the detector writeup.