atmospheric n ’s in a large lar detector
DESCRIPTION
Atmospheric n ’s in a large LAr Detector. G.Battistoni, A.Ferrari, C.Rubbia, P.R.Sala & F.Vissani. Motivations to continue the study of atmospheric neutrinos. There is still interest in continuing the study of atmospheric neutrinos: - PowerPoint PPT PresentationTRANSCRIPT
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!!
LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni 3
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)
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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)
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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)
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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
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The “standard” analysis:
Beware of containment:but we have good news about the possibility of using MS to measure muon energy
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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
LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni 9
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 >
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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
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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
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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
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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
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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)
LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni 15
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…)
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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)
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In graphic form...
13 = 0o
13 = 3o
13 = 5o
13 = 10o
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Results for 13 = 0
23 = 40o
23 = 50o
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Results for 13 = 0
RatioNe/Ne0 23 = 40o
23 = 50o
0.037 +/- 0.006
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Results for 13 > 0
13 = 5o 13 = 10o
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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
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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
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For example (13 = 0) :
00 /
/
NN
NN
e
e
it could be possible to achievea 3 separation
even for ~500 kton yr
LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni 24
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
LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni 25
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,...).