Re: calorimeter document

[Elke-Caroline Aschenauer <elke@jlab.org>]

On Sat, 9 Feb 2008, Matthew Shepherd wrote:

Dear Matt,

thanks for taking the suggestions into account.

bye elke



> Date: Sat, 9 Feb 2008 11:18:15 -0500
> From: Matthew Shepherd <mashephe@indiana.edu>
> To: Elke-Caroline Aschenauer <elke@jlab.org>
> Cc: Hall-D Calorimetry <halld-cal@jlab.org>
> Subject: Re: calorimeter document
>
>
> Hi Elke,
>
> According to my notes from our phone call the other night, I have made
> the following changes:
>
> - removed my internal flag about "need to check consistency of SiPM
> parameters" and added the sentence:
>
> Based on the design specifications for the SiPM devices, the following
> method was used to estimate the electronics threshold.
>
> - explaining the background shapes in pi^0 and eta just got to be too
> vague and cumbersome to be useful so I didn't do it
>
> - tried to make clear that we are rejecting only pythia generated
> channels that exclusively match our signal
>
> To ensure that the sample is originates from pure background hadronic
> photoproduction processes, we examine the identities of the generated
> particles as provided by \pyth{} and discard events that match our
> {\em exclusive} signal final state topology.
>
> - sprinkled in a few more sentence around the dense text about our
> "poor man's" kinematic fit:
>
> The most effective method of suppressing remaining hadronic
> backgrounds is to employ a global kinematic fit that enforces four-
> momentum conservation and evaluate the goodness of fit for the signal
> candidate; however, such techniques have not yet been fully
> developed.  In lieu of a global kinematic fit, we simply place
> requirements on the total reconstructed energy and transverse momentum
> of the signal photons.  Figure~\ref{fig:e0pyt_etot} shows the total
> energy of the $\eta\pi^0$ candidate photons for events with only one
> candidate from \pyth{} background (top left) and from signal $\eta
> \pi^0$ (top right).
> The red points in the top right plot show the background from \pyth{}
> scaled to the signal based on the ratio of cross sections predicted by
> \pyth{}.  In order to mimic the energy conservation constraint that a
> full kinematic fit would enforce, we select events with $E(4\gamma) >
> 8.0$~GeV.  In addition, the total transverse momentum $p_{\mathrm{T}}$
> must sum to zero to conserve momentum.  The lower pair of plots in
> Figure~\ref{fig:e0pyt_etot} show, in the same style, $p_{\mathrm{T}}$
> of the signal $\eta\pi^0$ candidate and recoil proton after the
> $E(4\gamma)$ requirement.  To enforce conservation of momentum, events
> with $p_{\mathrm{T}}<100$~MeV/$c$ are selected.
>
> and added to the end of the paragraph:
>
> For the analyses presented here, we make no additional selection
> requirements although it is recognized that there exist additional
> techniques for further suppressing background, {\it e.g.,} selecting $
> \pi^0$ or $\eta$ candidates whose decay photon energies are not
> heavily asymmetric.
>
> Unfortunately I just do not have time to complete the following things:
>
> - alterations to conversion figure to indicate detector regions where
> conversions happen (it is noted in the caption)
> - addition of Beni's rainbow scatter plot showing conversions
> - addition of summary table for simulated and generated properties
>
> I will certainly include the first two in my talk.  I don't think the
> last is a disaster because the only place we could make a direct
> comparison between actual beam test and simulation would be in BCAL
> energy resolution.  The remainder of the items are either implemented
> in simulation and not completely independently verified or measured
> (like BCAL timing resolution) but not implemented in simulation.  Of
> course, I realize there is some value in collecting the numbers all in
> one place.
>
> Cheers,
>
> Matt
>
>
>

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