Bari, Bologna, Boston, Caltech, Drexel, Indiana, Frascati, Gran Sasso,L’Aquila, Lecce, Michigan, Napoli, Pisa, Roma I, Texas, Torino
with
Summary• Analysis of High and Low energy neutrino events• Sterile vs Tau neutrino oscillations (matter effects)
A. Surdo INFN - Lecce
MACRO @ Gran Sasso
• GUT Monopole and rare particle search• Cosmic ray physics• Neutrino bursts from stellar collapses• Study of atmospheric neutrinos• Neutrino astronomy• Indirect search for WIMPs
Data taking: Mar 1989 – Dec 2000(complete detector since Apr ’94)
Main features of Macro as detector
• Large acceptance (~10000 m2sr for an isotropic flux)
• Low downgoing rate (~10-6 of the surface rate )
• ~600 tons of liquid scintillator to measure T.O.F. (time resolution ~500psec)
• ~20000 m2 of streamer tubes (3cm cells) for tracking (angular resolution < 1° )
More details in Nucl. Inst. and Meth. A324 (1993) 337.
Up stop
In down
In up
Up through
Neutrino event topologies in MACRO
• Detector mass ~ 5.3 kton
(1) Up throughgoing (ToF)(2) Internal Upgoing (ToF)(3) Internal Downgoing (no ToF)(4) UpGoing Stopping (no ToF)
Absorber
Streamer
Scintillator
(1) (2)(3)
(4)
Energy spectra of events
detected in MACRO
• Emedian ~ 50 GeV for Throughgoing muons;
• Emedian ~ 4.5 GeV for Internal Upgoing (IU) ;
• Emedian ~ 3.5 GeV for Internal Downgoing (ID)
and for UpGoing Stopping (UGS) ;
Low energy events (IU, ID+UGS) allow to investigate the oscillation parameter space independently from throughgoing muons
1
T1 T2 T3 T4 c2L
+1
-1 T1
T3 T4
T2
L>2.5mStreamer tube track
Upward Throughgoing muons
Analysis and Data Set
* evaluation:
1) agreement between streamer track and scintillator counter hits (position from times at the ends)
2) -1.25 < 1/ < -0.75
3) 2m (~200 g/cm2) of absorber crossed to reduce at 1% level the bck due to ’s produced by muons (Astrop. Phys. 9 (1998) 105)
• Automated data selection procedure (no visual scan)
• 863 induced upward through-going muons during:
* Background rejection cuts:
Event selection based on time-of-flight method
Mar 89-Nov 91 (1.4y) Dec 92-Jun 93 (0.4y) Apr 94-Dec 2000 (5.5y)
1/6 lower detector Lower detector Complete detector
Phys. Lett. B357 (1995) 481 Phys. Lett. B434 (1998) 451 (until Nov ‘98)
Measured flux and comparison with Monte Carlo
• Data
number of events: 863 background (wrong ) 22.5 background (’s from muons) 14.2 Internal neutrino interactions 17
Total 809 events
• Monte Carlo prediction 1122 ± 17%
- Bartol atmospheric neutrino Flux (±14%)
- GRV-LO-94 PDF for DIS cross section (± 9%)
- Lohmann et al. muon energy loss (± 5%)
* Detector response simulation using GEANT
* Same analysis chain as the data
R = data/prediction = 0.721 ± 0.026stat ± 0.043syst ± 0.122theor
2 test on the angular distribution (10 bins) with prediction normalized to data :
• 2 = 9.6/9 d.o.f for with maximum mixing and m2 ~ 0.0025 eV2 P = 37 %
• 2 = 25.9/9 d.o.f. for no - oscillations P = 0.2 %
Upward Through-Going MuonsAngular Distribution
MACRO UPMUProbabilities for sterile
neutrino oscillations
P.Lipari and M.Lusignoli, hep-ph/ 9803440Q.Y.Liu et al, PLB440 (1998) 319,
• Sterile neutrino matter effectsreduction of angular distortion (max mixing)
Peak probability for the shape = 1.8%Peak probability for the combination = 8%
Probabilities lower than that for neutrinos
Ratio vertical / horizontalLipari -Lusignoli, Ph Rev D57 (1998)
Monte Carlo optimized:
)4.0)(cos(
)7.0)(cos(
N
NR
• The plot is for maximum mixing P(sterile) = 0.033% P() = 8.4%
• Sterile neutrino disfavored with respect to at >99% C.L. for any mixing (7% systematic on the ratio)
(Results in hep-ex/0106049, to be published on Phys. Lett.,)
(a) time-of-fligth between central / top SC layers
(b) topological criteria for vertex containment inside lower detector (~1 % bck after this cut)
Internal Upgoing ’s (IU)
Phys. Lett. B478 (2000) 5
Partially contained events
Selection criteria:
Internal Downgoing ’s (ID)+ Upgoing Stopping ’s (UGS)
(a) No T.o.F. measurement(b) topological constraints on track (bottom SC layer + track inside fiducial volume)(c) visual scan procedure for final selection(d) >100 g cm-2 of material crossed in the detector
UGS ID
IU events
From MC simulation:
• E ~ 5 GeV• ~ 87% due to -CC interactions
DATA: 5.5 live-y
DATA - Bck(1/) = 154 events
• From Apr. 1994 up to Dec. 2000• 1/ distribution after all analysis cuts:
Data vs Monte Carlo Predictions
• : Bartol flux with geomagnetic cutoffs
(error ~ 13%)• = Q.E. + 1 (Lipari et al., PRL74 (1995) 4384)
+ DIS (GRV-LO-94 PDF) (error ~ 15%)• (E,zenith): detector response and acceptance
(systematic error ~ 10 %)
DATA: 154 12stat
MC: 285 28sys 57theo
MC-oscill: 168 17sys 34theo
DATA: 262 16stat
MC: 376 38sys 76theo
MC-oscill: 284 28sys 57theo
Internal down + Upgoing stopping ’s
Internal Upward going ’s
• GEANT based program for the simulation of detector response • Simulated events processed through the same analysis chain as the data
E ,zenith
Angular Distributions
thsysstatIUMC
Data11.005.004.054.0
)(
thsysstatUGSIDMC
Data14.007.004.070.0
)(
maximal mixing , m2 = 2.5 x 10-3 eV 2
MC expectation (no oscillations)
• Data consistent with a constant deficit in all zenith angle bins (IU: 2 /d.o.f. = 3.1/4 on shape)
• Probability for NO oscillations (one side): RIU: ~ 2.3% R(ID+UGS) ~ 9.3%
InternalUpgoing
Ratio of event types at low energy
• Most of the theor. uncertainties canceled (<5%)• Systematic errors reduced (~6%)
Data: R = 0.59 ± 0.06stat
Expected (No oscillations): R = 0.76 ± 0.04sys ± 0.04th
>>> compatibility ~ 1.9%
Expected oscillations: R = 0.59 ± 0.04sys ± 0.03th
(maximal mixing and m2 = 2.5 x 10-3 eV2 )
InternalDowngoing
UpgoingStop
R =
+