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

Data/Monte Carlo disagreement for Rustem’s Signal Fluctuation

variable in the Far Detector(Working Title)

Philip RodriguesOxford MINOS Group Meeting

15 Jan 08

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, ±40ns3. Take all strips in this window (track and non-track)4. Sort these strips by PH5. Find mean PH of lower half, mean PH of upper half6. Low/High = mean of lower half / mean of upper half

3

ND Recap

• Problems in ND investigated quite thoroughly:– Uncalibrated spectrometer– Low PH afterpulsing

• Use only calorimeter strips > 100 sigcor solves problem:

From docdb 4025 (Rustem)

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

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

Noise?

• No

Dogwood noise No noise Double noise

7

Noise (default)

• No

8

More Less ad hoc cuts

• Change strip and time windows• 1 strip window helps – something happening around

the track

Tim

e window

meaningless in

FD

?

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

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

Crosstalk

• Reco FD MC with optical and charge xtalk +10%

Default xtalk +10%

• Not quite perfect, but major improvement• Plots with +20% and +13% upcoming

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

Conclusions

• Starting to understand data/MC disagreement

• Crosstalk seems a likely candidate• Need to convince a skeptical public