Point Source Search with

2007 & 2008 data

Claudio Bogazzi AWG videconference 03 / 09 / 2010

Documentation available

• Note: http://csdweb.cern.ch/record/1284531 ANTARES-PHYS-2010-008• Web site: http://www.nikhef.nl/~t61/pnt/index.shtml here you can find also the previous talks and

the answers to the questions we received.

Outline

1) Quick review of the analysis

What’s new?

2) “Fixed” search with the 24 candidate sources

Live times

Live time in days of the data used in the analysis (number of runs in parentheses).

Excluded

2007 & 2008 basic runs with some exceptions (see row 3, 4, 5 and 6 in the table below)

Time offset• We use atmospheric muon tracks.• Random selection of a “probe line” which is not to be used in

the reconstruction.• Muon tracks reconstructed using the hits of the remaining

lines• Time residuals on the probe line recorded in histograms.

Peak fitted with a gaussian: the mean is interpreted as the relative time offset of the line

Time offset: iteration of the procedure

=> offsets obtained in the last iteration are applied to the data before reconstructing.

Measured offsets as a function of the iteration number.

Maximum change in offsets in the last iteration is 0.5 ns

Validation

Green: before applying line timing corrections.Black: after.

More events at the highest value of lambda.

Resolution and acceptance studiesWhat? - We have studied the behavior of MC while varying 2 quantities: 1) OM acceptance: additional MC produced with a 15% overall reduction of the photon detection probability of the Oms.

2) time resolution: hit-times smeared by random numbers drawn from a Gaussian with σ = 1, 2, 3 ns.

Comparison with data to constrain allowed values for a systematic range.

Results• For a detailed description of our method, see our note

(chapter 4.2).

• Main conclusion: our data seems incompatible with a 3ns smearing!

Angular resolution

Median resolution for an E-2

spectrum for different MC sets. In the x-axis the hit time smearing applied

Acceptance relative to the MC used in the analysis (2ns smearing, 100% OM acceptance).

85%OM acc

0.5 ± 0.1 15% systematic on the acceptance

Data/MC comparison

-- data-- MC-μ-- MC-υ

Cumulative Λ distribution for upgoing events with angular error estimate below 1°

At Λ > -5.4 we have:2040 data738 muons1093 neutrinos

Data / MC = 1.11

Data/MC comparison

-- data-- MC-μ-- MC-υ

Zenith angle distribution for the events selected after the final cuts applied in the analysis:Λ > -5.4 β < 1°

POINT SOURCE SEARCH METHOD

Search algorithm

• Unbinned likelihood-ratio method

To compute the likelihood we need 2 ingredients:1 Point Spread Function ( F )2 Background rate ( B )plus3 Effective area – acceptance to convert from μsig to the flux.

β

Pseudo-experiment generation

• Generate background events according to the parameterization in the sin(δ) distribution

• Add zero or more (up to 30) signal events at some position in the sky

(used PSF declination-dependent)

FULL SKY SEARCH

Full sky: results of the likelihood fit

3σ 5σ --- Nsig = 3--- Nsig = 6--- Nsig = 9--- Nsig = 12

On average 435 clusters.

Discovery potentials

Source intensity needed for a 50% chance of a 3σ (red) and 5σ (blue) as a function of the source declination. On the left plot it is expressed as the mean number of events produced by the source while on the right plot as the neutrino flux.

Full sky search: Λ>-5.4 & δ = -70°

3σ

3σ

5σ

5σ

FIXED SEARCH

Fixed: results of the likelihood fit

Fixed: point by point sensitivity

Median upper limit that can be set on the mean number of signal events (left) and on the neutrino fulx as a function of the declination if no signal is present. The dashed lines is the no-systematic case.

sys - - - - no sys

sys - - - - no sys

5% effect of systematic uncertainties

Fixed search: Λ>-5.4

Systematic uncertainties

• Absolute pointing: 0.13° for φ, 0.06° for θ (see Garo’s talk in Erlangen). To take into account these values, we smear the θ and ϕ angles by two random variables from a Gaussian distribution with the above sigmas

• Angular resolution: 15% . We take into account this number by generating a resolution-scale factor drawn from a Gaussian distribution with mean 1 and width equal to the uncertainty

• Background model: vary the background rate used for PE generation according to 2 different spline fits to the data.

• Acceptance: 15%. Not done in the PE but in the limit setting code

α=-180° α=-120° α=-60°α=0°

α= 60° α=120°α=180°

SS 433

3C279 HESS J1837-069

LS 5039

W28

Galactic Center

RX J1713.7-3946

GX 389Centaurus A

HESS J1614-518

ESO 139-G12RCW 86

Cir X-1

PSR B1259-63

PKS 2005-489

RGB J0152+017

PKS 2155-304 H 2356-309

HESS J0632+057

ES 0347-121

PKS 0548-3221ES 1101-232

RX J0852.0-4622

HESS J1023-575

“FIXED” SEARCH WITH THE 24 CANDIDATE SOURCES*

* NEW!!!

What? - Fixed search looking at 24 points in the sky

(candidate sources from previous analysis)

- Select events in 20° cone around each candidate.

- Likelihood fit of the selected events for each candidate.

- Select the source with the highest Q

(likelihood ratio).

More in details- For EACH pseudo experiment we define 24 clusters (one for every candidate source).

- The signal events (up to 30 as usual) are always added for the source HESS J1837-069 * [δ = -6.95°, α = 279.41°]

- Likelihood fit for each candidate (1 paramater: μsig).

- Select the candidate with the highest Q

20°

* This source has been chosen only for example

Q-distribution

Likelihood ratio distribution: the solid yellow histogram shows the distribution for background only experiments.The lines are the distributions for the case in which we add 1,2..7 signal events.

Q3σ = 6.76 Q5σ = 14.4

HESS J1837-069 [δ = -6.95°, α = 279.41°]

Discovery potentials HESS J1837-069 [δ = -6.95°, α = 279.41°]

Probability of 3σ (red) and 5σ (blue) discovery as a function of the mean number of signal events injected.

For this source, the number of events required to make a 3σ(5σ)discovery in 50% of the experiments is 3.9 (6.7)

Full sky search “candidate search”

3σ 7 3.9

5σ 10.5 6.7

Trial factor for having 2 analysis not included yet

Conclusions

• We present a search for cosmic sources of high energy neutrinos using 2007 & 2008 data.

• Integrated live time analyzed is 295 days.• Studies of detector timing and angular

resolution has been performed.• Angular resolution is estimated to be 0.5 ±

0.1.• Neutrino flux sensitivity is about 7.5 x 10-8 (E/GeV)-2 GeV-1 s-1 cm-2

BACKUP

Background rate

+ data-- spline fit-- spline sys

Distribution of sin(δ) for the selected data events (Λ > -5.4).

The solid line shows the spline parametrization used in the pe generation and in the likelihood fit

The dashed line is used for the background model systematic

Point spread function

Λ > -5.4

log(βυ)

(log) angle between the neutrino direction and the reconstructed track for an E-2 spectrum

Point spread function distribution for MC-υ events (E-

2 spectrum).

The line is the spline parametriziation used in the likelihood.

Acceptance

Λ > -5.8

Λ > -5.2Λ > -5.4

Constant of proportionality between the flux and the number of detected events as a function of the sin(δ)

The value on the y-axis corresponds to the number of detected events for a flux ϕ = 10-7 (E/GeV)-2 Gev-1 cm-2 s-1

(consisting of 50/50 neutrinos and anti-neutrinos)

At low declinations, this flux produces 3.1 events for the cut Λ > -5.4.

Discovery potentials

3σ

5σ

Full sky search: Λ>-5.4 & δ = -70°

Probability of a 3σ (red) and 5σ (blue) discovery as a function of the mean number of signal events for a source at a declination δ= -70°

Probability of a 3σ (red) and 5σ (blue) discovery as a function of the mean number of signal events for a source at a declination δ= -70°

Fixed search, no trial factor: Λ>-5.4 & δ = -70°

3σ

5σ

No systematic uncertainties here.

Probability of a 3σ (red) and 5σ (blue) as a function of the source declination. On the left plot it is expressed as the mean number of events produced by the source while on the right plot as the neutrino flux.

5σ

5σ

3σ

3σ

Fixed seach, no trial factor: Λ>-5.4 & δ = -70°