Summary to date

This work has been ongoing for the last year or so, off and on because of classes. I'll try to summarize what's been done so far in this post.

Talks that I've given on Kshort reconstruction, containing a lot of background info, are located at my colorado HEP website:

http://www-hep.colorado.edu/~drell/CMS-talks

I'm still doing fairly simple simulations of V0 events, namely 5 GeV Pt Kshorts coming from the IP. I've implemented an EDFilter, called KshortChargedDecayFilter, which looks at the simulated event and checks to see if it's a simple K0s->pi+pi- event. If it isn't, it stops processing for that event, i.e. reconstruction of that event does not take place. This filters out K0s->pi0pi0 as well as any events where the decay product charged pions undergo nuclear interactions within the silicon tracker material. We have a lot of material on CMS, so this happens fairly often. For a 10000 event sample in a recent release of CMSSW (CMSSW_1_2_3) I obtained 4675 good K0s->pi+pi- events with no nuclear interactions.

I then feed these good events into the different reconstruction algorithms, the Combinatorial Track Finder (CTF) and RoadSearch (RS). I've been running the reconstruction algorithms through a long history of CMSSW releases, starting with 0_6_0 and going all the way to the most recent release as of this post, CMSSW_1_3_3. I've been comparing reconstruction efficiency of the Kshort tracks across the two reconstruction algorithms.

I should note that the CTF has a couple of seeding algorithms implemented. The one that will be used in the mainline reconstruction chain is called the Mixed seeding algorithm. CTF also has a seeding algorithm that uses the silicon strip detectors instead of the inner pixel layers. The strip detectors have worse z-resolution, so the invariant mass plots generated using this seeding algorithm are broader, but the efficiency is much higher. This seeding algorithm was designed to be used for reconstruction during the engineering runs, when we were to have only a partial pixel detector installed, but as it seems that there will be no colliding beam in the engineering run, it's not clear to me what the pixelless seeding will be used for. It seems a good fit for V0 reconstruction, but the overhead is significantly higher, so it isn't likely to be included in the main reconstruction chain.

To reconstruct the Kshorts, after I use the CTF and RoadSearch, I take the reconstructed tracks and use the KalmanVertexFitter to vertex the tracks. From this, I can make invariant mass plots, etc.

I'm now trying to track down a loss of RS efficiency that may or may not be caused by a bug in the RS code in the CMSSW_1_3_2 release. So, I've upgraded to CMSSW_1_3_3, recently released on the CERN lxplus machines, and I'll attempt to see if we can regain the efficiency I'd seen in the CMSSW_1_2_3 release.