Re: [Brahms-l] INEL trigger efficiency in pp

Thanks Hiro,

It's still not completely clear to me what the correct procedure for
this efficiency correction is.

We measure a number of tracks (Ntr) and a number of events (Nev) and
divide those out to get the yield (Ntr/Nev). We know that we only pick
up a fraction of the total cross section (72%) so we can divide Nev by
0.72 to get the total number of inelastic events, but what about the
tracks in these (28%) missing events? How do we evaluate the Ntr in
the missed events. If we just calculate the yields by dividing Nev by
the trigger efficiency (i.e. multiply the spectrum by 0.72) we somehow
assume that the missing events don't have any tracks. Is that fair?

I've tried to understand how STAR is doing it. It's not written
explicitly, but this is how I interpret them: They claim that they
measure 85% of NSD events and gives an uncertainty of 14% for the
normalization to their NSD spectrum - I guess the multiply their
spectrum by 0.85 and the 14% is for the tracks in the missed events
(it could in principle be zero or as abundant as in the measured
events). They also claim that the NSD and total inel yields are almost
identical (only a small difference at low pt) - I'm not sure I
understand that, since I wouldn't expect the single diffractive (SD)
events to contribute with very many tracks (in their acceptance) but
they are still events (and should go into Nev in the calculated
yield). In other words I wouldn't expect the same yield in SD events
as in NSD events.

I'm a bit confused - who knows about these things and what should the
official BRAHMS procedure be?

Cheers,

Claus


On Tue, 10 Feb 2004, Hironori Ito wrote:

> Ok.  JH pointed out to me that the option is IHPR2 not IHNT2.  I run
> hijing with non-single diffractive option.  Now, it produces dn/deta
> =2.5 at eta =0. This is right number.  Using this HIJING pp in our BRAG
> (GEANT), INEL counter efficiency is now 85%.  So, as a summary, this is
> my result.
>
> INEL efficency
> 72% in total inelastic cross section
> 85% in non-single diffractive cross section
>
> Hiro
>
> Hironori Ito wrote:
>
> > Hello.  I guess I made a mistake in efficiency in non-single
> > diffractive events since 10% increase in dn/deta is not the same as
> > 10% in cross section.  As JH suggested, I tried to run Hijing with
> > non-single diffractive option using IHNT2(13) =3 option.  But, I did
> > not see any change in dn/deta.  Therefore, I am not quite sure how to
> > run Hijing with this option.
> >
> > Hiro
> >
> > Hironori Ito wrote:
> >
> >> Hello.  Since so many people asked about INEL efficency, I just dig
> >> up my files.  (I thought these things are checked by someone who are
> >> writing Ph.d thesis. :)  )  Here is the conclusion I made.
> >> 1.  From the Hijing 1.383, our INEL counter is about 72% efficient.
> >> (see http://www4.rcf.bnl.gov/~hito/run03/hijing_pp_inel_efficiency.gif )
> >>
> >> 2.  Now, looking into what HIJING 1.383 really is for pp.  I looked
> >> at dn/deta from raw hijing output.  At, eta=0, it is  2.2 .  From UA5
> >> ppbar results (see  http://pdg.lbl.gov/2002/contents_plots.html  you
> >> can find a postscrip file there.), it shows 2.2 with the words saying
> >> "The number per pseudorapidity interval is about 10% higher if the
> >> rate is normalized excluding singly diffractive events rather than to
> >> the total inelastic rate." This tells me that Hijing pp produces the
> >> total inelastic collisions.   (This also means the following.  Since
> >> we don't trigger on  single diffractive events, what we can measure
> >> is 90% efficient at most.  Our INEL is 72/90=80 % efficient for
> >> non-single diffractive events.)
> >>
> >>
> >> If people need it, I can also dig my old files for dAu.
> >>
> >>
> >> Hiro
> >>
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