1. Data/Monte Carlo disagreement for Rustem’s Signal Fluctuation variable in the Far Detector (Working Title) Philip Rodrigues Oxford MINOS Group Meeting 15 Jan 08

2. 2 Low/High variable Rationale: muon tracks small variation between planes, non-muon tracks larger variation Construction: 1.Exclude first 30% of track planes (to veto shower) 2.Find window around reco’d track: ±4 strips, ±40ns 3.Take all strips in this window (track and non-track) 4.Sort these strips by PH 5.Find mean PH of lower half, mean PH of upper half 6.Low/High = mean of lower half / mean of upper half

3. 3 ND Recap Problems in ND investigated quite thoroughly: –Uncalibrated spectrometer –Low PH afterpulsing Use only calorimeter strips > 1 00 sigcor solves problem: From docdb 4025 (Rustem)

4. 4 Far Detector Very similar problem appears in FD: more low PH hits in data Ad hoc 175 sigcor (~2.5 pe) cut helps quite a lot: But why? We think we understand the FD It pays to understand this: –concerns that it may affect other aspects of the analysis (docdb 4024, slide 3)

5. 5 But why? Why has this never come up before? –The low/high variable is doubly sensitive to data/MC disagreements –Non reco’d strips (not track or shower) are used in its construction –Taking low/high ratio amplifies data/MC disagreement So, unlikely to affect anything else Candidates: –Noise: seems unlikely. My noise studies show good data/MC agreement –Crosstalk: seems unlikely. Lots of test stand studies –Afterpulsing: seems unlikely. FD timing very different to ND –Real Physics?: seems unlikely. We know what tracks do

6. 6 Noise? No Dogwood noise No noise Double noise

7. 7 Noise (default) No

8. 8 More Less ad hoc cuts Change strip and time windows 1 strip window helps – something happening around the track Time window meaningless in FD?

9. 9 Transverse variable ~ (PH in track) / (PH around track + PH in track) Timing cut makes “halo” narrower: –Early/late hits are mostly around track

10. 10 Mini-conclusion Should only use track hits for this variable (no window): –The physics rationale depends only on the track itself (cf transverse variable) –Track modelling is better than detector modelling(?) I plan to recommend this to Rustem/the CC group

11. 11 Crosstalk Reco FD MC with optical and charge xtalk + 1 0% Default xtalk +10% Not quite perfect, but major improvement Plots with +20% and + 1 3% upcoming

12. 12 Being sure How can we be certain it’s crosstalk? –xtalk-tagging code somewhere – knows about PMT pixels, etc –Plot strip distributions in time and space to look for physics –Learn about xtalk –Any other ideas?

13. 13 Conclusions Starting to understand data/MC disagreement Crosstalk seems a likely candidate Need to convince a skeptical public