Transcript Atmospheric neutrinos in T1800

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:
•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 q23
•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?
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This work:
(A.Rubbia)
FLUKA + NUX with 3-f oscillations with matter effects
Atmospheric neutrino Fluxes (2002) @LNGS
 Dm223 = 2.5 x 10-3eV2 (positive)
 Dm212 = 8.x10-5eV2 A.Strumia & F.V.
 q12 =
hep-ph/0503246
34o
Earth density profile:
PREM model
q23 = 40o, 45o , 50o
q13 = 0o, 3o , 5o , 10o
1000 Kton year exposure
dCP = 0o
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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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ne CC Simulated Event Gallery
How SubGeV ne events will appear in ICARUS in one of its projective
views (full detector desponse simulation using FLUKA)
En961
568
MeV
E=n =
949
MeV
= 500
MeV/c
MeV
P
=eP=
509
MeV/c
=
493
MeV/c
e 479
Pe = 416 P
MeV/c
P
MeV/c
n==653
e
EEnE
MeV
e
=
585
MeV
Pe = 789 MeV/c
Enn =En806
MeV
= 340
840
Pe = 493 MeV/c
323 MeV
Pp =
MeV/c
Pp401
= 504
MeV/c
336 MeV/c
p = MeV/c
Pe = P
433
Pp = 424 MeV/c
En = 534 MeV
398MeV/c
MeV/c
Pp = 416 MeV/c PeP=p =241
278MeV/c
MeV/c
PPep==294
303MeV/c
MeV/c
p==525
Pp = 399 MeV/c
PP
p
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ne CC Simulated Event Gallery
En =E849
MeV
= 220
510
799
422
954
549
743
770
978
MeV
n
Pp P
=e198
MeV/c
= 595
MeV/c
P
116
MeV/c
p =
P
=
471
745
609
195
MeV/c
Pep = P543
637 MeV/c
e = MeV/c
=P528
378
MeV/c
MeV/c
e =
PpP=e 136
MeV/c
Pe = 727 MeV/c
Pe = 409 MeV/c
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The “standard” nm 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 reconstruction
using lepton+recoiling proton
In general:
•a superior capability
in pointing
•a better resolution
in L/E
Minimum Goal: ~50-100 kton yr
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The Precision Physics case
•Solar n and KamLAND experiments contributed to
determine with relatively high precision Dm212 and q12
•At present the only determination of q23 come from
atmospheric neutrinos and has a large uncertainty.
How close is q23 to p/4? Is it larger or lower than p/4?
(“octant ambiguity”)
q23 < p/4  |<nm|n3>| > |<nt|n3>|
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The determination of q23 in atm.
neutrino exp.
DIscussion previously proposed by P.Lipari
Essentially the best determination of 2 q23 comes from
the analysis of Multi-GeV muon-like events
 N m (up)  
N m (up) 
sin 2q23  21  0
  21 

 N m (up)   N m (down) 
2
(in SK ~ 6 ev/Kton yr)
At present: 36° < q23 < 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 q13 = 0
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Oscillation effects in e-like events in
the q13 = 0 approximation
Fosce = F0e P(ne  ne)
+ F0m P(nm  ne)
= F0e [ P(ne  ne) + r P(nm  ne) ]
= F0e [
1 – P12
F0e ,F0m : n flux w/o osc.
r = F0m / F0e : m/e flux ratio
+ r cos2 q23 P12 ]
P12 = |Aem|2 : 2n
probability
transition
ne  nmt in matter
driven by Dm212
(Fosce / F0e) – 1 = P12 (r cos2 q23 – 1)
screening factor for low energy n (r ~ 2)
~0
if cos2 q23 = 0.5 (sin2 q23 = 0.5)
<0
if cos2 q23 < 0.5 (sin2 q23 > 0.5)
>0
if cos2 q23 > 0.5 (sin2 q23 < 0.5)
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Important only in
SubGeV region
where
Dm212L/E is
sufficiently large
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A new measurement of q23
1 DN e 1
 1  DN e 1
sin q23  1    0
  0
 r  N e r P12 2 N e 2 P12
2
SubGeV: r~2
Also the nm 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 q13
(and possibly dCP) plus matter effects is more complex
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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/
nne nne
ee
ee
nne nnm
nee  nmm
nne nnt
nee  ntt
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qq12 ==34°
12 =34°
q
34°
qq1312
==0°3°
13 = 0°
qq23q13
==50°
q2323 =50°
40°
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n’s from
nadir
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Implications:
The knowledge of the absolute level of SubGeV ne can
provide the best possible measurement of q23 and of its
octant.
The unique features of a large LAr detector (>50 kton?)
can provide an important measurement of of SubGeV ne
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)
Of course, from the point of view of statistical
significance, this requires a very high exposure.
How large?
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Other possibilities
 There are q13 induced oscillations which instead affect
the MultiGeV region: these could be used to
discriminate the hierarchy of masses (sign of Dm223) if
n and anti-n could be distinguished (MSW resonance
is present for n when Dm223>0 or for anti-n (when
Dm223<0)
 This measurement, which requires n/anti-n separation,
might be more problematic for a LAr detector
(magnet…)
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ne + ne SubGeV
CC interaction rates (kton yr)-1
No Osc.: 51.3 (62.8)
En<1 GeV
q23
q13
0o
Plepton<1 GeV/c
3o
5o
10o
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40o
45o
50o
52.2
(63.9)
51.7
(63.3)
51.4
(63.0)
51.3
(62.8)
50.9
(62.5)
50.6
(62.2)
50.2
(61.7)
49.7
(61.2)
49.6
(61.1)
50.8
(62.00)
50.4
(61.9)
49.3
(60.8)
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In graphic form...
q13 = 0o
q13 = 3o
q13 = 5o
q13 = 10o
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Results for q13 = 0
q23 = 40o
q23 = 50o
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Results for q13 = 0
Ratio
Ne/Ne0
q23 = 40o
q23 = 50o
0.037 +/- 0.006
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Results for q13 > 0
q13 = 5o
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q13 = 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 nooscillation prediction affected by a systematic uncertainty not
exceeding 1%. Is this achievable? (absolute level, ne/nm ratio)
•Primary c.r. fluxes (maybe we can take this ~under control)
•Neutrino-nucleus cross sections
•Hadronic interactions and atm. shower development
ne / nm is exactly 2 at low energy only if just p are there!
K/p?
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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)
Ne / Nm
 A better analysis is the ratio:
0
0
so that many common
Ne / Nm
systematics cancel out
 The important topic remains the
as a function of energy
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n e / nm
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uncertainty
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For example (q13 = 0) :
Ne / Nm
0
e
0
N / Nm
it could be possible to achieve
a 3 s separation
even for ~500 kton yr
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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 q23 octant
can be done with an exposure of at least 20 years of
SK (depending on q13) to distinguish (Dc2~2) between
the 2 mirror values of corresponding to sin2q23 = 0.96
with the present level of systematics
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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 ne, 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 (n fluxes, cross
sections,...).
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