# Presentation: 516276

## Does Antares see neutrinos?

- Aart Heijboer

- results based on data <= feb13

##  Select events with >= 5 trigger hits, got (get's rid of minbias triggers, I think...)

-  Select events with >= 5 trigger hits, got (get's rid of minbias triggers, I think...)
-  684k events, Reconstructed 587k (=86%)
- 'AartStrategy':
- much effort went into speed: naglib minimizer + full analytical derivatives.
- typical 5h run reconstructs in <20 min:  ~0.1 s/evt.(could easily run online on 1 machine, if you'd want that for some reason...)
- Made two adaptations in likelihood wrt version in CVS:
- bg-levels in PDF are currently set to 1000 kHz for 1 spe, 100 kHz for 2 spe , 10 kHz for 3 spe.. etc.
- using time-PDF determined on 1 spe MC hits. (i.e. not using sharper PDF's for large ampl. hits)
- V1.1 detector, default calibration, **no alignment**

- Diffing FullPdfFitter.hh against CVS
- ===================================================================
- RCS file: /afs/in2p3.fr/throng/antares/src/CVS/reco/inc/FullPdfFitter.hh,v
- retrieving revision 1.3
- diff -r1.3 FullPdfFitter.hh
- 193c193,194
- <   max_k40_amp=3;
- ---
- >   max_k40_amp=5;        // modif for line 1&2
- >
- 199a201
- >
- 201c203,206
- <       double Psig = time_function( t, ampbin, dPsig_dt,0);
- ---
- >
- >
- >       int ampbin_dum = 0; // modif. for line 1&2: use A=1 for all pdfs's  (probably better for downgoing anyway)
- >       double Psig = time_function( t, ampbin_dum , dPsig_dt,0);
- 203c208,210
- <       double k40rate=6e4*1e-9;              //NB: hard-coded background value
- ---
- >
- >
- >       double k40rate=99e4*1e-9;              //NB: hard-coded background value - move to 99 kHz for line1&2
- 208,209c215,217
- <         k40rate *= pow( 7.5e-3, hit_amp-1);  // 7.5e-3 determined from MC (formula in
- <                                                // thesis is too idealized ;-(
- ---
- >
- >         k40rate *= pow( 0.1 , hit_amp-1);  // move to: very soft suppression for line 1&2
- >                                              // (untested guess).
- 211a220
- >

- Reconstruction.

- this was not intended:
- I meant to set it to 100kHz.
- See at the end of talk forcomments on what changes
- when using 100 kHz

## To very good approximation: true fraction of upgoing events is zero.

- here, just about half the events
- are reconstructed as up going:
- => reco is **not** doing anything useful
- (we're not even sure these events are
- muons at all... could be random k40)

- Let's use this fact to our advantage for a change
- => See how well reconstruction measures the number of up-going events

- here, (only) about 1% of
- events are reconstructed
- in wrong hemisphere.

- conclude:
-  we are measuring real muons.
- no surprise, but still: this plot is a nice illustration of that.
-  quantity  is doing it's job in data (like in mc):
- A high value of  means the event is wellreconstructed and has a low wrong-hemisphereprobability.

- One might be tempted to take this wrong-hemisphere-fraction and
- just multiply by the known ratio of up/down muon flux to get an estimate of
- the fraction of true neutrino events. This approach does not work, however,
- because for high , the acceptance for neutrino events is expected to be
- very different from the acceptance for downgoing muons. Downgoing
- muons are harder to reconstruct -because the detector is looking down-,
- and even if reconstructed well, they have a worse likelihood(lower ) -because
- more hits come from scattering and because there are sometimes
- multiple muons.

- Is the muon reconstruction working?

- 5 string data

- will discuss
- these later

## How can we know if we are seeing neutrinos?

- Loose cuts                       Stringent cuts

- PRD  66(2002) 012005: “Observation of High Energy Atmospheric neutrinos with AMANDA”

- Example from Amanda:

- Loose cut                               Stringent cut

- Look for kink in a plot of #upgoing events vs a background rejecting cut.
- A kink indicates atm 's popping up above atm  background

- Antares MC
- (12 strings, no trigger sim, no req on #trig. hits)

- kink

- kink

- similar plot in:
- Nature 410, 411-413

## The data...

- (kink at same value =-5.5). However, in light of the
- radically different bg-rate assumed it in the reconstr.
- of the data , it is not so clear if this means anything.
- It's still nice, though.
- Blue curve taken from 12 string MC, with normalization
- chosen to intersect  data at =-5.5.
- Data compatible with this curve (up to the
- region where we predict < 1 event)
- 'Muon' distribution falls off faster in data than MC:
- 105 per unit vs  103 per unitThis is tentatively
- understood: MC has pre-selection (ang. err<1 & Erec>0).
- (Would need to rerun reco to get Erec.)
- 12 string MC predicts 10  events with >-5.3 each day.
- We see only 3 events in 15 days. Don't understand this,
- but likely that rec. is suffering from real data conditions &
- absence of alignment (&bug)

- Assuming the component from atm. is an exponential,
- we can make a rough estimate of significance of the
- most -like events:
- where we expect 0.1 atm , we observe 3 events
- ->  p-value of 1.4 10-4 (**3.8******)
- where we expect 0.01, we observe 1 event
- -> p-value of this event alone = 1%. (2.6 )

- upgoing events
- (cos 

- 5 string data

- 12 string MC

- kink?

## Three events that are

- separated from main
- distribution.

- Same plot again....

- *********************************************
- *   run * frame idx *    Lambda *        dz *
- *********************************************
- * 25864 *    137249 * -5.251702 *  0.978547 *
- * 25922 *     53569 * -5.254281 *   0.86197 *
- * 25929 *     61770 * -5.015625 *  0.813989 *
- *********************************************

- all three have angular error < 1 deg.

- let's have a look at them...

- A closer look at the  candidates

## run 25864, frame 137249,  = -5.25

- right image only
- showing hits used
- for reconstruction

- run 25864, frame 137249,  = -5.25

## scanfit 

- scanfit
- reconstruciton:
- agrees!

- z vs t

- z-t diagrams with
- Ronald's scanfit
- reconstruction

- just the same
- picture as
- before – not
- using scanfit

## run 25922, frame 53569,  = -5.25

- run 25922, frame 53569,  = -5.25

## scanfit 

- scanfit
- reconstruciton:
- agrees!

## run 25929, frame 61770,  = -5.02

- run 25929, frame 61770,  = -5.02

## scanfit 

- scanfit
- reconstruciton:
- agrees!

##  Exciting excess in region of very well reconstructed up going events! 

-  See 3 events, where we expect O(0.1) for monotonously falling bg.
-  Quick and dirty significance estimate: 3.8(but: it is much less when  using lower bg rates in PDF).
- Signal should become more clear over next few weeks.
-  Shape & atm  ratio agree quite well with (12 string) MC
-  Visual inspection of the candidates: no obvious problems found.
- Hits used for reconstruction make sense (no large clusters unused)
- Event with largest  indeed looks most convincing
-  Normalization (#events) lower than MC for both atm  and 
- probably due to combination of my pre-selection (>4 trig hits), reconstruction not tuned for real data (e.g. high bg rates)...
-  Scanfit reconstruction agrees! And it may already have found more  neutrinos (see e.g. analysis elog entry by mieke of 7Feb)
- very useful to compare different algorithms in this way!

- Conclusion

## The traditional, bi-annual,  day-before-the-talk bug:

**I have set the k40-rates assumed in the PDF a **** factor 10 higher than I intended too: 1 MHZ / 10****#pe-1.**
- The k40 rate is effectively used to deweight hits in the fit: the high rate means that single-pe hits are assumed to have a high chance of being background, so they don't contribute much the likelihood, even if their residuals are small.
- This means that only hits with large amplitude give high  events.
- Indeed, the 3 events found so far all had many large hits.
- This is maybe not such a bad thing: large hits are good..
- but it is a significant difference between the rec. algorithm used for the data and the one used for the MC
- -> the nice agreement between data and mc should not be taken too seriously!
-  Redid reco with 100kHz spe rate: 100** **kHz / 10#pe-1.
- still find our three neutrino candidates: they are still reconstructed ~samebut the values of  change
- also find additional candidate(s) that look(s) quite convincing (!) -- see pictures in next few slides.
- but, unfortunately, the kink in the plot is less clear than in the 1Mhz case
- some unconvincing candidates around =-5.5 with muon next to detector (i.e. not traversing the instrumented volume)
- could also be just lucky (unlucky) in 1Mhz (100kHz) case.
-  It would be bad start trying lots of different selection tricks to reproduce   the 'kink' for the 100kHz case. If we want to optimize cuts for the kink-finding   method, we should do it on (realistic) MC.... not on data.

## Plots when 100kHz spe k40 rate assumed in PDF

- same
- events
- as before

- Not a very convincing kink
- in this case.

-  o---------------------------------------------o
-  | have a look at some of the wannabees        |
-  o---------------------------------------------o
- *************************************************************************
- * evinf.run * evinf.evn *    Lambda *  57.2*zen *  57.2*azi *     E_ang *
- *************************************************************************
- *     25864 *    137249 * -5.095270 * 11.793801 * 73.515520 * 0.4774286 *
- *     25895 *      9975 * -5.286803 * 73.500960 * -96.81535 * 1.0107569 * NEW
- *     25922 *     53569 * -5.085312 * 30.406404 * -15.22184 * 0.3522388 *
- *     25923 *    121051 * -5.270804 * 73.278992 * -10.32835 * 0.8019053 * NEW
- *     25929 *     61770 * -4.790475 * 35.451048 * 147.02832 * 0.2327608 *
- *     25934 *     18566 * -5.244625 * 72.668245 * -17.91373 * 2.1204676 * NEW
- *     25934 *     68307 * -5.288116 * 32.759485 * -5.569122 * 0.9079579 * NEW
- *************************************************************************

- for 250kHz
- in case you
- care...

## Plots for 100kHz spe k40 rate assumed in PDF: more candidates?

- If it was a real :
- expect some hits
- here in stead of
- here.

- maybe...

- 25895 *      9975

## Plots for 100kHz spe k40 rate assumed in PDF: more candidates?

- looks pretty good to me!

- 25895 *      9975

## Plots for 100kHz spe k40 rate assumed in PDF: more candidates?

- should
- be stuff
- here

- no way!

- 25934 *     18566

## Plots for 100kHz spe k40 rate assumed in PDF: more candidates?

- probably a horizontal muon skimming the detector

- 25934 *     18566