Our resolution comes from 3 sources:
With the help of Juan Romero and Gulshan, the first two of these were
implemented. Given a pion of a certain momentum, I start
it randomly in the target and propogate through the material-- energy loss
and MCS then give me the new momentum (of course it is a random process).
For cross-checking, Juan and I ran some identical sets of particles through
our independent codes. He posted both of our results on
this page.
(Note -- previously I had the wrong page listed here-- thanks Juan.)
For the "intrinsic" resolution of our detector (this means that after the target and scintillator, the particle has some new momentum-- how well do we measure this new momentum?), I had been using our canonical "dp/p=1%". However, this seemed too good as compared to my old slow simulator simulations (which were flawed for other reasons), and I wanted to get a resolution estimate from the data itself.
Dieter and Paul both have nice peaks, and their widths are pretty much consistent with each other. I use Dieter's to estimate the intrinsic resolution. To do this, I decay 10,000 lambdas and 10,000 kaons using a geant routine, boost the particles to the system c.m. frame (i.e. ycm of the Au+Au system), and then smear the particles' momentum by:
px --> px*(1.0 + resolution*Gauss)
py --> py*(1.0 + resolution*Gauss)
pz --> pz*(1.0 + resolution*Gauss)
where Gauss is a random number from a gaussian distrib of unit sigma, and resolution would be 0.01 for 1% resolution.
Beam Energy |
L width (MeV/c) |
K0 width (MeV/c) |
d p/p (p) (%) |
d p/p (p) (%) |
2 |
1.17 |
4.6 |
1.5 |
2 |
4 |
3 |
6 |
3 |
3 |
6 |
3.5 |
8.7 |
3 |
4 |
8 |
4.4 |
7.9 |
3 |
4 |
Note that we do NOT expect the fits to converge as we increase our dp/p estimate. They can/should change. The above plots are to show the sensitivity to our estimate.
Update - with the parameterized resolution, we our corrected fits fall somewhere in between the 1% and 3.5% estimates - see this discussion for details.