1 / 9

K 0 s Reconstruction at ZEUS

K 0 s Reconstruction at ZEUS. Before and after the upgrade. Mark Bell. Introduction. HERA was upgraded in 2001 to deliver greater luminosity. ZEUS used the opportunity to install a Micro Vertex Detector (MVD).

salvador-thompson
Download Presentation

K 0 s Reconstruction at ZEUS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. K0s Reconstruction at ZEUS Before and after the upgrade Mark Bell

  2. Introduction HERA was upgraded in 2001 to deliver greater luminosity. ZEUS used the opportunity to install a Micro Vertex Detector (MVD). After the upgrade: How has the performance of the tracking and vertexing changed? What impact has the MVD had? To study this, use K0s: Produced copiously at HERA. Easy to detect through π+ π- decay, using Central Tracking Detector (CTD) and MVD. π+ π- K0s

  3. Tracking packages Before the upgrade, CTD was the only major tracking component. Now MVD used as well. There are different software track finding packages to use different detector components. • CTD: uses CTD only to find tracks and vertices using standard ZEUS VCTRAK package. • REG: uses MVD as well as CTD using VCTRAK. • ZTT: uses MVD and CTD but uses Kalman filtering to find tracks. This claims to fit tracks more accurately and hence should find more K0s.

  4. Event selection Sample of data taken from before the upgrade (22.8pb-1), and one from after (6.3pb-1). Old data normalized to that of new data for results. Data taken through a third level trigger for DIS and also requiring |zvtx| < 60 cm. K0s→ π+ π- found by looking for secondary vertex with two oppositely charged tracks. Make kinematic cuts on pion tracks and other variables in the event: 1) |zvtx| < 50 cm – rejects events not from interaction region. 2) cos(α) > 0.99 – ensures K0s comes from primary vertex. 3) Pion tracks: pT > 0.1 GeV and reach at least SL3 – gives well measured tracks. 4) M(e+e-) > 0.1 GeV – eliminates photon conversion electrons. 5) M(pπ) < 1.125 GeV – eliminates Λ’s. 6) s < 35cm – reduces background from interactions with CTD.

  5. K0s mass peak CTD (2000) CTD (2003/4) Half as many K0s in new data using CTD tracking. Width of signal wider in new data. Yield of K0s recovered when using MVD in REG tracking. ZTT tracking fails to find as many K0s. REG ZTT Invariant K0s mass after selection cuts

  6. MVD effective close to interaction point MVD finds K0s secondary vertices closer to the interaction point than the CTD alone. All extra K0s in new data are found closer to the interaction point. Distance from primary to secondary vertex

  7. ZTTfailure ZTT tracking comparable to REG tracking when few tracks in an event. Finds fewer K0s as N increases. Problem identified to be an error in vertexing routine. Has now been put right. Distance from primary to secondary vertex N = total number of tracks in event

  8. Conclusions K0s found in old and new data – tracking and vertexing compared. • Multiple scattering in the extra material of the MVD reduces the yield of K0s when only the CTD is used for tracking and vertexing. • Using the MVD as well as the CTD recovers the same yield of K0s. • Using Kalman filtered tracks fails to find as many K0s because of an error in the vertex finding algorithm. • The MVD is successful in finding secondary vertices closer to the interaction point. MVD enhances overall tracking and vertexing performance of the detector.

  9. Future work • Reanalyse the new data with the fixed ZTT vertexing routine to see if it is as or more effective than REG tracking for finding K0s. • The tools for tracking, vertexing and particle identification can be used in many areas of data analysis, opening up different avenues for potential research.

More Related