1. Rejection Of Background For the detection of Prompt Neutrinos
Newt Ganugapati
&
Paolo Desiati

2. Why?What? and Where?
The Conventional muon and neutrino fluxes come primarily from the decay of the relatively long lived pi and K mesons but with increasing energy the probability increases that such particles interact in the atmosphere before decaying.
This implies that even small fraction of short lived particles can give dominant contribution to the high energy Neutrino flux.These short lived ‘charmed’ particles or prompt muons and neutrinos arise through semi leptonic decays of hadrons containing heavy quarks most notably charm
At about 1 TeV the contribution of prompt neutrinos taking into account the LVD bound is as high as 10%.Between 1 TeV and 100 TeV these become the biggest source of uncertainty in the atmospheric neutrino flux and would limit the search for diffuse neutrinos.

3. There is a huge amount of uncertainty in the models for the prediction of prompt atmospheric fluxes as can be seen.Most of these models have been generated from QCD by modeling the interactions.
Note that the crossing between conventional to prompt muon fluxes happens between 40TeV and 3 PeV.
Out of these the most widely accepted models are the RPQM and QGSM model.(LVD bound)

4. Prompt Neutrinos VS Prompt Muons
Discuss the physics
of point 1.
Due to the charmed particle decay kinematics and the same branching ratios into prompt electrons and muon neutrinos.The flux of prompt muons and prompt neutrinos are essentially the same until 100TeV.
Prompt muons are much easier to detect than prompt Neutrinos since the later have to produce a charged particle inside the detector on the other hand we have lots of prompt muons.

5. Prompt muon Montecarlo
I generated a MC using a E^-1 spectrum at the surface of the earth and propagated using our regular codes of AMASIM,MMC etc.The surface generator is muo0 and was written by S.Hundertmark.It generates muons along a plane at the surface of the earth according to a specified energy spectrum,zenith,azimuth and then these were reweighted to the spectrum of charm predicted by the RPQM model.
We already have a MC for conventional muons which will be a background to our detection of the charm muons.The observable space will be studied to design our cuts to improve our signal to background ratio and to know the regions where to look for our signal.Possible separations of signal will be looked at by studying the distribution of these observables.

6. Quality Cuts Show zenith distribution before and after cut on the
plot.
Give number of events
before and after cuts.
The quality cuts we use are
Abs(smootallphit(2))<0.26
Jkrchi(2)<7.8
Ldirb(2)>120.
The plot shows how the quality cuts change the distribution of the error of reconstruction for zenith angle in our Montecarlo.

7. Plot also in cos(zenith)
ENERGY SPECTRA
ZENITH ANGLE SPECTRA
(QUALITY CUTS APPLIED)
(QUALITY CUTS APPLIED)
BACKGROUND
EVENTS=91450
SIGNAL EVENTS=147.7
ECPD(OF THE BUNDLE)
ZENITH(2)

8. Whatis the livetime for this table?.
COS
(ZENITH)
0-0.2
SIGNAL
EVENTS
0.9744
15.18
33.07
45.37
53.26 BG 36
1248
7922
23620
58634
SIGNAL/BG
0.027
0.0121
0.0041
0.0019
0.0009
Put table ins standard powerpoint format.
It must be clear from the above table that an effective way to search for charm is to look for it at large zenith angles(Nearly horizontal events).Note that the ratio of signal events for zenith>67degrees to entire zenith is 16.15/147.85~0.11

9. Use titles
Use such table format

10. Energy spectra At 5 TeV, the ratio is about 1/5 not 1/15
The plot shows the energy spectra of conventional muons (single, multiple) and of the charm muons (RPQM) for all zenith angles.
Multiple muons are the dominant background above energy of 5 TeV.
At an energy greater than 5TeV the ratio of signal to background is about 1/15.
At 5 TeV, the ratio is
about 1/5 not 1/15
Muon energy [Log10(GeV)]

11. Energy spectra for q>67°
The plots shows the energy spectra of conventional muons(single,multiples) at large zenith angles(greater than 67degrees).For a true energy cut of 5TeV
Number of single muons=7
Number of multiples=30
Number of charm=3.3
signal/background~1/12
(combination of zenith and energy cuts increases the ratio by 10 times)

12. HOW DO WE TRANSLATE THE ENERGY CUT INTO OBSERVABLE SPACE?
Any parameter that is nicely correlated with the muon bundle’s energy at center of detector can be used.Possible parameters are NCH(number of OM’S hit),Amount of light collected(ADC’S).Number of hits etc.We will look into some of the scatter plots and correlations before we can decide which observables we can cut on to execute the energy cut.

13. A new energy estimator
I will be looking at the time delay or also called time residual distributions of hits for different energy ranges of muon bundles and will come up with a new way to parameterize it.This parameter will be used as an energy estimator.The use of this parameter to NCH will be elucidated later.

14. Time delay distribution (obtained from MC)
The plot shows the normalized time delay
distribution of hits for various energies(each bin of the histogram shows the fraction of hits in that time range).I will define a new parameter which will be the number of hits between ( ns) and study its correlation with energy.I call this parameter “lateres”.
(0-1)TeV
(1-2)TeV
(2-4)TeV
(4-5) TeV
(5-10)TeV
GT 10TeV
Tail goes up with
increasing energy
Lateres= Nhits ( ns)
Time Delay(ns)

15. Montecarlo and data description of time delay distributions
The figure describes the agreement of the Monte Carlo with the data.In particular note the agreement in the ns region where ‘lateres’ is defined
Show log plot
show with quality cut
show with nch energy cut
Time delay(ns)

16. The following is a scatter plot of the number of channels hit vs the energy of the muon bundle at centre of detector.
for nch>100
Number of events greater than 5TeV=599
Number of events less than 5TeV=1700
for nch>135
Number of events greater than 5TeV=351
Number of events less than 5TeV=361

17. Number of events greater than 5TeV=359
The following is a scatter plot of lateres vs the energy of the muon bundle at center of detector.
for lateres>45
Number of events greater than 5TeV=359
Number of events less than 5TeV=129
Using this as a cut(for reasons shown and reasons that will come) is preferred over NCH as an energy estimator
lateres Vs log10(ecpd)(muon bundle)

18. Correlation plots of number of OM’S hit and lateres with energy of the muon bundle at center of detector

19. Nch VS Lateres(Energy estimators)
<1TeV
<1TeV
1-3TeV
1-3TeV
3-5TeV
3-5TeV
>5TeV
>5TeV
True Energy
True Energy
N-Channel(nch)
‘Lateres’

20. Comment by AK
Need to demonstrate why the new energy estimator is better than nch. This is a big topic.
You risk confusing the case for prompt muon analysis with the energy resolution analysis.
Risk: More sensitive to Monte-Carlo and Ice properties.
You will have to do the entire prompt muon analysis with the nch parameter. Once that works, you are free to demonstrate that lateres improves this analysis further

21. A cut on lateres>45 imposed BG events left =487 (entire zenith)
ZENITH ANGLE DISTRIBUTION OF BACKGROUND AFTER CUT ON ‘lateres’(energy cut)
A cut on lateres>45 imposed
BG events left =487
(entire zenith)
Also imposing a zenith cut
>67degrees
BG events left =19
( cosine(zenith)<0.4)
Data or MC??????

22. ZENITH ANGLE DISTRIBUTION OF SIGNAL AFTER CUT ON ‘lateres’(energy cut)
Please put numbers on
previous and this slide
in a table so that is
easy to compare.
ZENITH ANGLE DISTRIBUTION OF SIGNAL AFTER CUT ON ‘lateres’(energy cut)
A cut on lateres>45 imposed
signal events left =6.22
(entire zenith)
Also imposing a zenith cut
>67degrees
signal events left =0.556
( cosine(zenith)<0.4)
signal/background=0.556/20.0
~3/100
Events(zenith>67) =0.556/6.22=0.09
Events(entire zenith)

23. Pandel and patched Pandel functions at a distance 20m from the track
This graphical illustration is
misleading and misses the
point.
What is wrong with this
picture? Think about it.
Pandel and patched Pandel functions at a distance 20m from the track
Patched Pandel

24. If a hit is the first hit in an OM in the vicinity of the track(0-50m) and has a negative time residual(less than –15ns) and occurs with a large adc (> 3.0p.e.)(in other words implying that it hasn’t got scattered much) then it means that it is more likely to be a multiple muon event by the method described previously.I call the number of such hits per each event as “earlyres”.
The 3.0p.e. above is the expected adc in the vicinity of the track for hits produced by unscattered photons.

25. What does “number of hits =7.6” mean?
Livetime?
What does “number of hits =7.6” mean?
Time delay distribution of high adc hits in the vicinity of the track(for signal) (after reweighting)
Time delay distribution of high adc hits in the vicinity of the track(for background)
Number of hits=7.61
Number of
hits=930
Time delay(ns)
Time delay(ns)
Y-axis shows the number of hits corresponding to the delay

26. Montecarlo and data description of time delay distributions in the vicinity of the track
Note the agreement between the data and the Monte Carlo for time delays less than –15ns.This would be the region of interest where the parameter ‘earlyres’ is defined.This distributions are taken only for large adc(3.0pe) in the vicinity of the the track(less than 50m from track).It should be note that these histograms are normalized with the entire time residual distribution and not –50ns to 50ns shown.
Time delay(ns)

27. I suggest to call these hits “early hits” not “earlyres”
Distribution of ‘earlyres’ for background conventional muons(large zenith angles and high energy)
The x-axis gives the value of ‘earlyres’ and the y-axis shows the number of events .This plot shows the distribution of ‘earlyres’ for the 19 conventional muon events for large
zenith angles (>67degrees) high energy(lateres>45)
As expected most of these events have one or more early hits.
earlyres(number of hits)

28. single logarithmic plot.
Distribution of ‘earlyres’ for signal charm muons(large zenith angles and high energy)(reweighted)
The x-axis gives the value of ‘earlyres’ and the y-axis shows the number of events .This plots shows the distribution of ‘earlyres’ for the 0.45 charm muon events for large
0.2<cosine(zenith)< high energy(lateres>45)
As expected most of these events have no early hits.
Superimpose previous
plot and this plot in a
single logarithmic plot.
earlyres(number of hits)

29. Number of single muons(like signal)
The below table shows the number of muons that pass the cut of earlyres=0 (no high adc, early hits in the vicinity of the track).In a zenith bin 0.2<cosine(zenith)<0.4 for different ranges of true energy.It can be seen that the method gets more and more effective at higher energies as more percent of multiples get rejected.Thus if a 1 TeV muon for instance passes our energy cut(‘lateres’) than most likely it will not be rejected by the other cut(‘earlyres’) and will remain as a background. The opposite is true for high energy muons(>5TeV)
True
Energy(TeV)
1-2
2-4
4-7
7-10
>10
Number of single muons(like signal)
91/108
27/36
9/15
2/3
0/0
Number of multiple muons(background)
65/101
34/68
4/31
1/7
0/7

30. Summary Restructure previous table so it becomes readable: True
Energy(TeV)
1-2
2-4
4-7
7-10
>10
Single muons before cut
91/108
27/36
9/15
2/3
0/0
Multiple muons after cuts
65/101
34/68
4/31
1/7
0/7
Single muons before
Multiple muons after cuts
Single/multiple before
Single multiple after cuts

31. ZENITH ANGLE DISTRIBUTION OF SIGNAL(AFTER ALL CUTS)
The plots shows the zenith angle distribution of signal after all our cuts. For zenith angle greater such that cos(zenith)<0.4 we have an expected events of 0.39.The total number of events in the entire zenith range is 2.19.The ratio is 0.39/2.19
~1/6(this increase is due to the fact that at larger zenith angles we have lesser stopping muons inside our detector)

32. ZENITH ANGLE DISTRIBUTION OF B.G.(AFTER ALL CUTS)
Previous plot and this plot must
be superimposed.
ZENITH ANGLE DISTRIBUTION OF B.G.(AFTER ALL CUTS)
It can be seen that as we go into horizontal region we will find that signal starts to dominate over background(have to verify this!!!!with large statistics though).The expected background for cos(zenith)<0.4
is zero.This yields a prediction of 0.39 signal events on a background of zero in the horizontal high energy muons after all cuts.

33. CONCLUSIONS AND OUTLOOK
With all my cuts I calculate an expected signal of 0.4 events on a background of zero for a generation time of 1 hour.This needs to be tested on a huge statistics of Montecarlo generated at large zenith angles and high energy.
Most of my cuts were obtained just by inspection at distributions and optimization of this cuts need to be done by using the MRF(90%.C.L)
I studied a few other parameters based on delay time and these can be used too to reject more background.
The time residual distributions predicted from MC should be made sure that they agree with the data.The ice-model and the Photon propagation codes in the MC should be made sure that the describe the data well.
Generation of a large amount of statistics and calculating the sensitivity will be the next step.

34. More Comments by AK:
Make a better case for the separation of multiple muons from single muons.
This topic should become almost a standalone presentation.
Show the lateral disttribution of muons at large zenith angles (>67) and compare it to small zenith angles (<30°). [Why am I asking this?)
Do an analysis based on nch.