bari, bologna, boston, caltech, drexel, indiana, frascati, gran sasso,
DESCRIPTION
Surdo INFN - Lecce. Oscillations in Atmospheric Neutrinos. with. Bari, Bologna, Boston, Caltech, Drexel, Indiana, Frascati, Gran Sasso, L’Aquila, Lecce, Michigan, Napoli, Pisa, Roma I, Texas, Torino. Summary Analysis of High and Low energy neutrino events - PowerPoint PPT PresentationTRANSCRIPT
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 =
+