Presentation on theme: "Update on diffuse extraterrestrial neutrino flux search with 2000 AMANDA-II data Jessica Hodges, Gary Hill, Jodi Cooley This version of the presentation."— Presentation transcript:
Update on diffuse extraterrestrial neutrino flux search with 2000 AMANDA-II data Jessica Hodges, Gary Hill, Jodi Cooley This version of the presentation has been expanded to include work done after the meeting – where part of the nch problem was found to be related to no cross-talk cleaning in the cascade fit
Review of previous work Jodi Cooley’s thesis work – presented Mons October 2003 Basic quality cuts 2-D cut against coincident muons 2-D cut against nch>50 and positive smoothness – likelihood ratio track/shower vs ldirc 2-D on cogz versus l.r. track/shower model rejection potential optimised on nch
Review of previous work Cuts developed on 50% of data After nch>80 cut – 6 events on atmospheric background of 3.3 Second 50% of data yielded 4 events Combined 100% data nch>87 – 9 events on atmospheric background of 4.5 One event believed to be a coincident muon What does this excess mean?
New developments Reinvestigation of coincident muons using new dcorsika simulations Discovery that the nch>50, positive smoothness cut isn’t justified (which was suggested by others earlier!) Very recently started checking things with second 50% data, but only for nch less than 80 (less than where the cut would be)
"name": "The 50
Distributions of the 34 events Maybe a pileup toward low speed and high smoothness
Distributions of the 34 events No obvious disagreement
My conclusions about nch>50, positive smoothness Some of the 34 events are some kind of unsimulated background, some are good track events The difference between the two data halves is certainly a fluctuation on these underlying distributions Hard to imagine a periodic signal that just happens to coincide with our data separation by file numbers
My conclusions about nch>50, positive smoothness Some of these events are very nice tracks with long direct lengths Eliminate the original cut – maybe look at cutting on line fit velocity vs smoothness Tighten other cuts Good events will survive to higher levels Bad events will get eliminated elsewhere See what happens in subsequent years
Passing rates with tightened cuts Start with cuts just described Tighten gradually until events disappear Examine passing rates of data and simulation
Passing rates with tightened cuts l.r. up to zenith-weighted downgoing fit - jkchi(12)-jkchi(11) = 35 - 53 ldirb(11) = 10 - 28 ndirc(11) = 155 - 200 | smootallphit(11) | = 0.275 - 0.05 10 cut sets defined (40 - 49)
Limit setting potential versus cut level E 2 (E) < 2.35 10 -7 GeV -1 cm -2 s -1 sr -1
The cut against coincident muons Original cut: slope 18 New cut: slope 4
The cut against coincident muons Original cut: slope 18 MRF : 0.2348
The cut against coincident muons New cut: slope 4 MRF : 0.2379
Outlook for the 2000 diffuse analysis Some sort of weird effect was seen in the 1 st 50%, but not in the 2 nd Eliminate the problematic cut Tighten cut against coincident muons
Explanation of one part of the nch>50, positive smoothness problem Clue (Doug Cowen) – cascade fit is very sensitive to noise hits If the Monte Carlo and data have slightly different noise, then a cascade fit comparison might not make sense
The cascade fit was performed before the cross talk filter was applied! Cascade fits on data have been done with all the cross talk present Monte Carlo contains no cross talk Likelihood ratios based on different hit selections make no sense
track/shower l.r. before nch>50 cut Dramatic improvement in the agreement of this variable!
Bump in nch, correlates with excess at positive smoothness
track/shower l.r., ldirc vs t/s l.r. for nch>50, positive smoothness
Same plots, with consistent cross talk cleaning
New conclusions Once the cascade fit is correctly performed using the cross talk filtering selection, the excess of events at nch>50 and positive smoothness moves to the low l.r. / low ldirc corner of the 2D plot - which could be indicative of background However, this is the region where the E -2 signal prediction is expected to cluster We cannot cut this region away!