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Revised pythia estimates

Updated on Tue, 2008-04-08 21:43. Originally created by jwebb on 2008-04-08 19:25.
Abstract: I have Comparison with Cross Sections (Pythia estimates, prompt photon yields) shown projections for single photon yields in the pp2006 data which were flawed.  They overestimated the luminosity for a fixed sample size by a factor of ~3.  The problem was due to misinterpreting the definition of "tried" and "accepted" events in pythia 8.1.  New projections are presented for a cross check with yields extracted from data.

 
1.0 Pythia Configuration
 
Configure pythia to simulate pp collisions at root(s) = 200 GeV. Turn on all prompt photon processes, and require a minimum partonic pT = 3.0 GeV (aka CKIN(3)=3.0).
 
// Generator. Process selection. RHIC initialization.
rootS=200.0 * GeV;
Pythia pythia;
pythia.readString("PromptPhoton:all = on");
pythia.readString("PhaseSpace:pTHatMin = 3.");
pythia.init( 2212, 2212, rootS );

 

2.0  First  Run

Accumulate an event sample of 10k gammas w/in the acceptance of 1 < eta < 2, and with pT > 5.2 GeV.  Pythia reports:
*------- PYTHIA Event and Cross Section Statistics -------------------------------------------------------------*
| |
| Subprocess Code | Number of events | sigma +- delta |
| | Tried Selected Accepted | (estimated) (mb) |
| | | |
|-----------------------------------------------------------------------------------------------------------------|
| | | |
| q g -> q gamma (udscb) 201 | 907889 280753 280753 | 3.934e-04 3.496e-07 |
| q qbar -> g gamma 202 | 103023 37462 37462 | 5.234e-05 1.274e-07 |
| g g -> g gamma 203 | 570 208 208 | 3.051e-07 1.091e-08 |
| f fbar -> gamma gamma 204 | 460 162 162 | 2.363e-07 9.048e-09 |
| g g -> gamma gamma 205 | 253 84 84 | 1.516e-07 7.875e-09 |
| | | |
| sum | 1012195 318669 318669 | 4.465e-04 3.724e-07 |
| |
*------- End PYTHIA Event and Cross Section Statistics ----------------------------------------------------------*
Luminosity for this 10k event sample is therefore:  L = (318669) / (4.465E-4 mb) = 0.7137 pb^-1
 
 
 

3.0 Scale it up

Next we want to scale up the event sample to 4.3 pb^-1.  Simply run 10k*(4.3/0.7137).  And create the plots.
 
Figure 3.1 -- dN/dpT for inclusive gammas w/ in 1.0 < eta < 2.0 and pT > 5.2.
 
Figure 3.2 -- dN/dpT for gammas w/ in 1.0 < eta < 2.0 and pT > 5.2, with a jet pointing in -0.9 < eta < 1.9 (left).  x1 vs x2 (right).
 
 

 

Ok... sanity check here.  2665 events w/ pT > 10 GeV and a jet in -0.9 < eta < 1.9, for 4.3 pb^-1.  This extrapolates to 198k events w/ same cuts for 320 pb^-1. 
This may be on the high side.

 

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