Significance of TAU observation in OPERA

Luca Stanco – INFN - Padova 22 September 2010 1

Significance of TAU observation in OPERA

Questions to OPERA:

1. Does it exist the – oscillation ?

2. Is it coherent with expectation ?

We compute it as function of observed EVENTS(instead of the canonical dependence of LUMINOSITY)


Scenarios.

1.Standard: 5.3(2008+09) + 4.2(2010) + 4.2(2011) = 13.7*1019 p.o.t

2.Small compensation in 2011: 5.3+4.2+4.5 = 14.0

3.More in 2010&2011: 5.3+4.7+5.0 = 15.3

4.Add MTE in 2011: 5.3+4.7+5.5 = 15.5

5.Add 2013 with MTE: 5.3+4.7+5.5+5.0 = 20.5


SIGNAL: for each scenario the 95% C.L. on the corresponding Poisson pdf is computed: - lower and higher limits on the TAU events we may observed- corresponding significance is computed(use Proposal efficiencies * 0.8, use 20% of error)

BACKGROUND: use Proposal * 0.8(we factorize out the different CC and NC efficiencies).Use 50% of error (not so relevant).

This is a CONSERVATIVE choice (also because all channel are taken in a whole)

And of course, we do not consider here the improvement in the background estimation with the increase of statistics


Check for 2008+2009 Data Sample: Ntau=0.8*10.4*5.3/22.5=1.96±0.39 Nbck=0.8*0.75*5.3/22.5=0.14±0.07

95% of C.L.

0

12

3

4


and the obtainable significance is quite fluctuating !

#

# N

indication

evidence

observation

(but, remember, only with largest bck)


#

# N

limit of computationand use Feldman-Cousins

Conclusions: if > 5-6 events we find “observation” anyway even with 20.5*1019 p.o.t we may not “observe”

Scen. 1Scen. 5

Mean expect.

(but, remember, only with largest bck)


1.Similar to curves of Proposal2.At present really missing deeper studies with better Analysis and Monte Carlos3.My conclusion is however similar: Luminosity does not really matter for the signal4.We have to point towards BACKGROUND

This is valid while answering question no. 1….

Luca Stanco – INFN - Padova 22 September 2010 8Luca Stanco – ISTITUTO NAZIONALE di FISICA NUCLEARE - Padova 6 Maggio 2010 8

2. “Coherence” of the OPERA oscillation measure

5.3x1019 p.o.t

13.7x1019 p.o.t15.5x1019 p.o.t

20.5x1019 p.o.t90% C.L.95% C.L.

# of observed events

FEW events: difficult but affordable

# “distant” from MINOS

(remember, Tau with 80% efficiency)

Need 2013-14 !!


Conclusions:

OPERA is dominated by statistics,but...

the Physics Results can be extractedafterwords,

only once the Full DATA Sample has been exploited


Backup


13.7

14.0

15.3

15.5

20.5

Significance of TAU observation in OPERA

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