[Halld-physics] Ashot, Re: Primakov eta hadronic background

[Ashot Gasparian]

   Dear Sascha,

  This is a great progress on the way of background
  simulations for the eta-Primakoff proposal.
  It certainly shows that with the multi-function and
  ~4pi GlueX setup one can effectively separate an
  elastic channel at the end of the spectrum, at list.
  I will take a more careful look on your plots, but from
  the first look they are already very promising. I agree
  that we need more statistics for this background
  estimation.
  I will also double check the cross sections you are using
  for the Primakoff part and contact to you soon.
  In regard to n,eta,pi+ channel: can we use the information
  from the forward time-of-flight detectors and effectively
  suppress this background? There should be an easier ways
  for the charged channels.

  Thank you for your efforts and contributions to this project.

  Ashot


.............................................................
Ashot Gasparian                    Phone:(336)285-2112 (NC A&T)
Professor of Physics
Physics Department                       (757)-269-7914 JLab
NC A&T State University              Fax:(757)-269-6273 JLab
Greensboro, NC 27411               email: gasparan at jlab.org
.............................................................


On Tue, 1 Dec 2009, Alexander Somov wrote:

> Hello Ashot,
>
> Finally, I took a quick look on the hadronic bg for Primakov
> eta. I considered bg from inclusive eta photoproduction
> predicted by Pythia ( The inclusive eta background should
> dominate combinatorial bg)
>
>
> I put a few plots to
>
> http://www.jlab.org/~somov/primex
>
>
>
>
> ---MC sample----
>
> The MC sample corresponds to 2 10^7 Pythia events generated
> in the beam energy range of 9 GeV < E_gamma < 12 GeV
> (I selected events containing at least one eta in the final
> state  with an angle < 1.6 deg, and processed these events
> through Geant). The magnetic field was switched OFF.
>
>
> This sample corresponds to about 32 reconstructed 'Primakov'
> eta's in the eta->2gamma decay channel.
>
> N_prim_eta(0 - 0.5 deg)_produced =  2e7 * 7.2e-4 / 122 = 118
> N_prim_eta_rec = 118 * 0.71 * 0.39 ~ 32,
>
> where 7.2 ub -  is the Primakov production Xsection p(0. - 0.5 deg)
>      122 ub -  is the total photoproduction Xsection
>      0.39   -  is the branching fraction for eta -> 2 gamma
>      0.71   -  is the prim eta acceptance (according to Aram).
>
>
> --Eta reconstruction--
>
> - considered events with only 2 clusters in the FCAL
> - eta p elastic decays were excluded from the sample
> - Primakov signal region was defined as:
>                    E_beam - E_2gamma > -0.4 GeV
>  (more than 3 sigma region  according to the eta mass constrained fit).
>                    Angle(gamma gamma) < 0.5 deg.
>
>
> Below are descriptions to plots
> -------------------------------
>
>     angle_vs_energy.pdf
>     -------------------
>
>     Reconstructed angle of 2 photons versus ( E_beam - E_2gamma )
>
>     top right plot: veto events with the bcal total energy (summed
>                     over all reconstructed photons) larger than
>                     60 MeV. This cut removes most background from
>                     p eta pi0 decays. Remaining bg originates mainly from
>                     n eta pi+
>
>  Note: 99% of the p eta (eta->gamma gamma) elastic decays survive this
>        cut.
>
>
>     bottom left plot: Exclude events where the reconstructed eta and
>                       a track candidate having a hit(s) in the SC are
>                       positioned NOT back-to-back in phi, i.e.,
>                       delta_phi < 170 deg or delta_phi > 190, where
>                       delta_phi = Phi(2gamma) - Phi(HIT_SC).
>                       ( If there are no hits in the SC, we keep this
>                        event ).
>
>                       The delta_phi distribution for the reconstructed
>                       p eta decays is shown in the file  eta_dphi.ps.
>                                                           -----------
>                       The remaining event close to the signal region is
>                       p eta pi+; I need large statistics to study it in
>                       detail. We can presumably measure p eta pi+ decays
>                       and subtract them from the 'Primakov' signal
>                       region.
>
>
> All in all, I don't see large background in the Primakov signal region
> (If here is no bug in my code, of course ). I hope that you know the ABC 
> store close  to the lab... :)
>
> We can discuss more details during the meeting. I will need to check evrth. 
> and generate a large sample...
>
>
> Cheers,
>      Sascha
>
>