Atmospheric n ’s in a large LAr Detector

Atmospheric Atmospheric ’s in a’s in alarge LAr Detectorlarge LAr Detector

G.Battistoni, A.Ferrari, C.Rubbia, P.R.Sala & F.Vissani

LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni 2

Motivations to continue the study of atmospheric neutrinos

•There is still interest in continuing the study of atmospheric

neutrinos: •the confirmation of SK results with a technology having a

large reduction of experimental systematics with respect to

water Čerenkov

•the search for subleading contributions in the mixing matrix;

•a possible (in principle) precision measurement of 23

•a possible discrimination of Normal vs Inverted Hierarchy of

masses

•Can a very large LAr detector be the tool to perform these new

investigations (“Precision Physics”)? How does it compare to SK?

Tiny effects!!


This work:

FLUKA + NUX with 3-f oscillations with matter effects

Atmospheric neutrino Fluxes (2002) @LNGS

m223 = 2.5 x 10-3eV2 (positive)

m212 = 8.x10-5eV2

12 = 34o

23 = 40o, 45o , 50o

13 = 0o, 3o , 5o , 10o

CP = 0o

Earth density profile:PREM model

A.Strumia & F.V. hep-ph/0503246

1000 Kton year exposure

(A.Rubbia)


Event selection and definition

LAr Super-Kamiokande

Thresh. for e event 10 MeV 100 MeV

(single prong)

Thresh. for muon

event

50 MeV 200 MeV

(single prong)

600 MeV

(Multi-prong)


E = 653 MeV Pe = 500 MeV/c

Pp = 525 MeV/c

e CC Simulated Event Gallery

Pp = 278 MeV/c

E = 568 MeV Pe = 493 MeV/cE = 323 MeV

Pe = 294 MeV/cP = 398 MeV/c

E = 949 MeV Pe = 479 MeV/cE = 806 MeV Pe = 789 MeV/c

Pp = 424 MeV/cE = 534 MeV

Pe = 416 MeV/c

Pp = 401 MeV/cE = 340 MeV

Pe = 241 MeV/c

Pp = 336 MeV/c

E = 961 MeVPe = 493 MeV/c

Pp = 416 MeV/c

Pp = 399 MeV/c

Pp = 504 MeV/c

E = 585 MeV

Pe = 433 MeV/c

P = 303 MeV/c

E = 840 MeVPe = 509 MeV/c

How SubGeV e events will appear in ICARUS in one of its projective views (full detector desponse simulation using FLUKA)


e CC Simulated Event Gallery

E = 510 MeV

Pe = 471 MeV/c

E = 799 MeV

Pe = 745 MeV/c

E = 422 MeV

Pe = 378 MeV/c

E = 954 MeV

Pe = 637 MeV/c

P = 136 MeV/c

E = 849 MeVPe = 595 MeV/cE = 549 MeV

Pe = 609 MeV/c

E = 743 MeV

Pe = 727 MeV/c

P = 116 MeV/cE = 770 MeV

Pe = 409 MeV/c

P = 198 MeV/cE = 978 MeV

Pe = 528 MeV/c

Pp = 543 MeV/c

E = 220 MeV

Pe = 195 MeV/c


The “standard” analysis:

Beware of containment:but we have good news about the possibility of using MS to measure muon energy


A slightly less standard opportunity

Direction reconstructionusing lepton+recoiling proton

In general:•a superior capabilityin pointing•a better resolutionin L/E

Minimum Goal: ~50-100 kton yr


The Precision Physics case

•Solar and KamLAND experiments contributed to determine with relatively high precision m2

12 and 12

•At present the only determination of 23 come from atmospheric neutrinos and has a large uncertainty. How close is 23 to /4? Is it larger or lower than /4? (“octant ambiguity”)

23 < /4 >


The determination of 23 in atm. neutrino exp.

)(

)(12

)(

)(122sin

0232

downN

upN

upN

upN

Essentially the best determination of 2 23 comes from the analysis of Multi-GeV muon-like events

At present: 36° < 23 < 54°

The “solar” (12) sector generates significant effects on Sub-GeV neutrinos which might help resolve the octant ambiguity. This is true even in case 13 = 0

(in SK ~ 6 ev/Kton yr)

DIscussion previously proposed by P.Lipari


Oscillation effects in e-like events in the 13 = 0 approximation

Fosce = F0

e P(e e) + F0 P( e)F0

e ,F0flux w/o osc.

= F0e [ P(e e) + r P( e) ] r = F0

/ F0e : /e flux ratio

= F0e [ 1 – P12 + r cos2 23 P12 ] P12 = |Ae|2 : 2

transition probability e in matter

driven by m212

(Fosce / F0

e) – 1 = P12 (r cos2 23 – 1)

screening factor for low energy (r ~ 2)

~ 0 if cos2 23 = 0.5 (sin2 23 = 0.5)

< 0 if cos2 23 < 0.5 (sin2 23 > 0.5)

> 0 if cos2 23 > 0.5 (sin2 23 < 0.5)

Important only in SubGeV region

wherem2

12L/E is sufficiently large


A new measurement of 23

120

12023

2

2

1

2

1111sin

PN

N

PrN

N

r e

e

e

e

Also the rate is affected but this would be an extra term which adds to the “standard” 2-flavor oscillations

However, the general case of non vanishing 13

(and possibly CP) plus matter effects is more complex

SubGeV: r~2


12 = 34° 13 = 0° 23 = 40°

e e

e

e 12 = 34° 13 = 0° 23 = 50°

e e

e

e 12 = 34° 13 = 3° 23 = 50°

e e

e

e

To give an idea:osc. web calculator based on the code of F.V. (thanks to V.Vlachoudis CERN) http://pceet075.cern.ch/neutrino/oscil/

’s fromnadir


Implications:

The knowledge of the absolute level of SubGeV e can provide the best possible measurement of 23 and of its octant.

Of course, from the point of view of statistical significance, this requires a very high exposure.

How large?

The unique features of a large LAr detector (>50 kton?) can provide an important measurement of of SubGeV e with null or largely reduced experimental systematics. The ICARUS tecnology can explore for the first time the region with Pe<100 MeV/c (to be demonstrated by T600)


Other possibilities

There are 13 induced oscillations which instead affect the MultiGeV region: these could be used to discriminate the hierarchy of masses (sign of m2

23) if and anti- could be distinguished (MSW resonance is present for when m2

23>0 or for anti- (when m2

23<0)

This measurement, which requires /anti- separation, might be more problematic for a LAr detector (magnet…)


e + e SubGeVCC interaction rates (kton yr)-1

40o 45o 50o

0o52.2

(63.9)

51.3

(62.8)

50.2

(61.7)

3o51.7

(63.3)

50.9

(62.5)

49.7

(61.2)

5o51.4

(63.0)

50.6

(62.2)

49.6

(61.1)

10o50.8

(62.00)

50.4

(61.9)

49.3

(60.8)

23

13E<1 GeV

Plepton<1 GeV/c

No Osc.: 51.3 (62.8)


In graphic form...

13 = 0o

13 = 3o

13 = 5o

13 = 10o


Results for 13 = 0

23 = 40o

23 = 50o


Results for 13 = 0

RatioNe/Ne0 23 = 40o

23 = 50o

0.037 +/- 0.006


Results for 13 > 0

13 = 5o 13 = 10o


The problem of systematics

Leaving aside for a moment the question if such an extremely large exposure can be achieved:

The proposed measurement requires an absolute no-oscillation prediction affected by a systematic uncertainty not exceeding 1%. Is this achievable? (absolute level, e ratio)

•Primary c.r. fluxes (maybe we can take this ~under control)•Neutrino-nucleus cross sections•Hadronic interactions and atm. shower development is exactly 2 at low energy only if just are there! K/?

/e


A less naive method...

Of course it is hard to believe that one could rely on the absolute level of Ne prediction... (the c.r. flux normalization remains one of the most important uncertainties)

A better analysis is the ratio: so that many common systematics cancel out

The important topic remains the uncertainty as a function of energy

00 /

/

NN

NN

e

e

/e


For example (13 = 0) :

00 /

/

NN

NN

e

e

it could be possible to achievea 3 separation

even for ~500 kton yr


Considerations from SK

This topic has been debated at the end of 2004 in the context of a dedicated workshop

http://www-rccn.icrr.u-tokyo.ac.jp/rccnws04/

Requirements for SK: the measurement of 23 octant can be done with an exposure of at least 20 years of SK (depending on 13) to distinguish (~2) between the 2 mirror values of corresponding to sin223 = 0.96 with the present level of systematics


Conclusions

•A very large LAr TPC, in principle, can give new important contributions to neutrino physics, also with atmospheric neutrinos

•It allows to detect low energy neutrinos with null or negligible experimental systematic error. An exposure of 50-100 kton yr would allow be the minimum goal for this topic.

•the sector of SubGeV e, in particular, offers the possibility of performing new interesting measurements.

•To perform new precision measurements a very large exposure (>500 kton yr) is anyway needed

•Such a large exposure might be in part useless without an effort to reduce the existing systematic uncertainties ( fluxes, cross sections,...).

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Atmospheric n ’s in a large LAr Detector

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