[Halld-physics] PYTHIA Lam0 K+ events

[Kei Moriya]

Hi,

Just to follow up on the discussion,
I looked at 2.5M PYTHIA events from the data challenge.

For final state p pi+ pi-, I get
18k events for p pi+ pi-,
268k events for p rho0.
The measured cross section for this final state from SLAC
is 14.7 mub, so with a total hadronic cross section of
124 mub, there is rough agreement.

For p K+ K- events, I also get good agreement between
SLAC's numbers (0.58 mub/124mub) and the PYTHIA results
(13k/2.5M). Most of the p K+ K- events are categorized
as p phi production.

For K+ Lambda, I get ~50 events in the coherent peak
so that the fraction is 2e-5, roughly 2.5 nb, which
agrees with Eugene's numbers.

I think the p pi+ pi- and p K+ K- numbers verify that
PYTHIA is giving roughly good agreement with measured data,
and that Paul's code is getting the numbers correctly.
Although it's not too big of an issue, PYTHIA is probably
underestimating the cross section for K+ Lambda, since
scaling 100 or 40 nb by 1/s from 4 GeV to 9 GeV in Ephoton
still gives much larger values than 2.5 nb.

	Kei

On 3/25/13 5:43 PM, Eugene Chudakov wrote:
> Concerning the discussion at the physics meeting today on the reason
> for no gamma+p --> L0 K+ events from PYTHIA.
>
> The cross section for a 2-body exclusive reaction is typically
> dropping with energy. The L0K+ cross section was measured at 4 GeV of
> about 100nb.
>
> I looked at the PYTHIA-simulated 400k events in the beam energy range
> of 3-12GeV. There were about 80 L0K+ events, mostly at low beam
> energies (see the plot attached). There are some events in the
> coherent peak region, of about 3e-5 of all interactions (about 3nb).
> At 4 GeV the PYTHIA result is about 40nb.
>
> Eugene
>
>
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