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    User name R. Michaels

    Log entry time 22:32:04 on October14,2010

    Entry number 334922

    keyword=expected rates = measured rate, I think.

    Question: what is the elastic rate for protons
    expected for our kinematics ?

    E = 5.552 GeV, theta_p = 37 degr. theta_e = 21.9 degr

    I have a code that runs on ifarml4 to compute the
    elastic e-p rate. You have to feed it the beam energy
    and the electron angle and the current (3 uA).

    /home/rom/bgr/2010/epelast

    Now, it actually computes the electron rate into the HRS
    using a 15 cm LH2 target, but we are observing the protons
    and the solid angle may be different.

    Anyway, it gives 32.6 Hz for electrons at 3 uA.

    We can scale the rates by the old DVCS kinematics (ca. 2004)
    to check the proton rate and account for the possibly
    different acceptance for protons.

    (ca 2004): E = 5.75, theta_p = 39.41, theta_e = 19.4

    electron rate = 70 Hz

    The observed proton elastic rate in 2004 was 57 Hz at 3 uA.

    So, scaling by the computed electron rate we expect
    the proton rate now (2010) to be

    57 * (32.6 / 70.) = 27 Hz at 3 uA.

    The observed rate is 30 Hz.

    So, I think we may be ok at the 10% level !
    But someone else may check.