MACRO Results on Atmospheric Neutrinos
G. Giacomelli
University of Bologna and INFN
NOW2004, 11-18 September 2004
1. Introduction. Atmospheric n. Oscillations
2. MACRO. Events
3. Early analyses
4. Monte Carlo
5. nm ns
,
nt ;
L/En
6. Final analyses. Discussion
MACRO: Bari, Bologna, Boston, Caltech, Drexel, Frascati, Gran Sasso,
Indiana, L’Aquila, Lecce, Michigan, Napoli, Pisa, Roma, Texas, Torino. Oujda
1984 MACRO Proposal
2. MACRO
• Large acceptance (~10000 m2sr for an isotropic flux)
• Low downgoing m rate (~10-6 of the surface rate)
• ~600 t of liquid scintillator (time resolution ~500 ps)
• ~20000 m2 of streamer tubes (angular resolution < 1° )
Nucl. Instr. Meth. A324 (1993) 337; A486(2002)663
Upthroughgoing
In up
Absorber
Streamer
Scintillator
DATA SAMPLES(measured)
(Bartol96 expected)
__________________________
Upthrough(1)
In down
Upstop
1)
In up(2)
4)
3)
2)
In down(3)+
Up stop(4)
857
1169
157
285
262
375
Effects of nm oscillations on
upthroughgoing events
Flux reduction depending on zenith
angle for the high energy events
m
n
underground detector
Upgoing Muons E>1 GeV
1
Earth
dm2=0.0001 eV2
Pn mn m

m 2  L 
 1  sin 2  sin 1.27

E
n


2
2
From MC: distortion of
the angular distribution
Reduction factor
0.9
0.8
dm2=0.001 eV2
0.7
dm2=0.01 eV2
0.6
0.5
dm2=0.1 eV2
0.4
-1
-0.8
-0.6
-0.4
Cos(zenith)
-0.2
0
Experimental
checks on upthroughgoing muons
•
•
•
•
•
•
Analysis with scintillators only (PHRASE)
Separation of upmuons from downmuons : 1/b
Background estimates
Data versus azimuth (flat distribution)
Cross checks using 2 independent analyses
Uncertainties Scale systematic errors (MC, ..)
{ Point to point errors
• ......
3. Early physics analyses
Upthrough m only
{
{
Angular distribution
Absolute value
(Bartol96 MC)
m2=0.0025 eV2
Maximal mixing
Phys.Lett. B434(1998)451
Phys.Lett. B517(2001)59
Lower energy topologies consistent with upthrough m
nm energy estimate through Multiple Coulomb Scattering
of upthrough muons
Phys.Lett. B566(2003)35
4. Atmospheric n flux. Monte Carlos
-Until 2001
Bartol96
(Honda96)
-After 2001
FLUKA2001-3
(Honda2001-3)
Both
3-dimensional
improved interaction models
new cosmic ray fit, .....
They agree to ~5%
But: Predictions of new Honda and FLUKA MCs
H.E. 25% low ; L.E. 12% low
-Angular distributions of Bartol96, new Honda and
FLUKA MCs agree to ~<6%
Pn mn m
2


m
 L
2
2
 1  sin 2  sin 1.27

En 

From the muon
zenith angle
distribution.
L(cosQ=-1)~13000 km
L(cosQ=0)~500 km
MACRO
MonteCarlo
n1
Monte Carlo
nm
nt or nm
nsterile ?
Phys. Lett. B517 (2001) 59
Eur. Phys. J. C36 (2004) 357
OSCILLATION HYPOTHESIS
nm
nsterile hypothesis
min
Minimum value for nm
nt : Rt =1.61
disfavoured at 99.8 % C.L.
Minimum value for nm
nsterile : Rstmin =2.03
with respect to nm
nt
PROBABILITY FOR R < Rmin :
Pt = 7.2% ; Psterile = 0.015%
Pt/Psterile = 480
nm energy estimate through Multiple Coulomb Scattering of
muons in rock in lower MACRO
(Phys. Lett. B566 (2003) 35)
En = 13 GeV
En = 36 GeV
No oscillation Bartol96
En = 88 GeV
En =146 GeV
MC predictions for
nm
nt oscillations
with the MACRO
parameters
L/En distribution
Pn mn m
2


m
 L
2
2
 1  sin 2  sin 1.27

En 

From the muon
zenith distribution
From the measurement
of the muon energy using
Multiple Coulomb
Scattering
Upthr. m data
IU m data
MC predictions for nm
oscillations with the best
MACRO parameters
nt
12% point-to-point syst. error
Low Energy Neutrino Events
Internal Up
Internal Down
+ Up-stopping m
Measured (points) and expected number (dashed lines: MC Bartol96) of upgoing
semicontained events (left) and up-stopping plus downgoing semicontained m (right).
Solid lines: oscillations with the best fit parameters sin22Q=1 and m2=0.0023 eV2.
En=2.3 GeV . Monte Carlo scale uncertainty 23%
6. Final analyses. Discussion
Use ratios with uncertainties of ~5%, indep of MCs
H.E.
Zenith distribution
En estimate
R1= N(cos Q < -0.7) /N(cosQ > -0.4)
R2= N(low En) / N(high En)
L.E.
IU, ID and UGS m
R3= N(ID+UGS) / N(IU)
{
Best fit parameters for nm  nt
No oscillation hypothesis
ruled out by ~ 5 s
m2 = 2.3 10-3 eV2 ; sin2 2 =1
Eur. Phys. J. C36(2004)357
Absolute values referred to Bartol96 MC :
R4=(Data/MC)H.E.
;
R5=(Data/MC)L.E.
With these informations, the no oscillation hypothesis is ruled out by ~ 6 s

MACRO

Exotic oscillations
Lorentz invariance violation (LIV)
Mixing between flavor and velocity eigenstates
 dependence LEn  LIV is not dominant
We computed upper limits of LIV parameters
dv/2=(v3-v2)/2 , sin2 2θv using the formalism of
Coleman-Glashow PL B405(1997)249; hep-ph/0407087 ,
taking the Nlow, Nhigh samples of low and high energy
upthroughgoing data,
fixing n mass oscillation parameters to the MACRO values
and using the Feldman-Cousin procedure
Violation of the equivalence principle
Similar results as for LIV, but with parameter fg
[ g difference of coupling constants of n to grav pot f]