Upload
rusty
View
37
Download
1
Embed Size (px)
DESCRIPTION
Università degli Studi di Bologna. Neutrino Oscillation Studies with a Massive Magnetized Calorimeter. Marco Selvi. Neutrino Oscillations Status of the experimental scenario and need for new detectors Magnetized calorimeter performances Atmospheric neutrino physics CNGS beam physics - PowerPoint PPT Presentation
Citation preview
Neutrino Oscillation Neutrino Oscillation Studies with a Studies with a
Massive Magnetized Massive Magnetized CalorimeterCalorimeter
Università degli Studi di Università degli Studi di BolognaBologna
Marco Selvi
Massive Magnetized Detector M. Selvi – Università di Bologna
SummarySummary
• Neutrino Oscillations• Status of the experimental scenario
and need for new detectors• Magnetized calorimeter performances• Atmospheric neutrino physics• CNGS beam physics• -factory physics
Massive Magnetized Detector M. Selvi – Università di Bologna
Neutrino OscillationsNeutrino Oscillations
Massive Magnetized Detector M. Selvi – Università di Bologna
Neutrino OscillationsNeutrino Oscillations : 2 : 2 flavorsflavors
If neutrinos have mass the flavour eigenstates could not coincide with mass eigenstate:
|(0)> = cos |> + sin|>
|(0)> = -sin |> + cos|>
|(t)> = cos exp(-iE1t) |> + sinexp(-iE2t) |>
|(t)> = -sin exp(-iE1t) |> + cosexp(-iE2t) |>
After time evolution:
Massive Magnetized Detector M. Selvi – Università di Bologna
Neutrino OscillationsNeutrino Oscillations : 2 : 2 flavorsflavors
Oscillation Probability:P() = sin2 sin2(1.27 m2
L/E)
m2 = m22- m1
2
Survival Probability: P() = 1 - P()
sin2m2 =0.003 eV2
Massive Magnetized Detector M. Selvi – Università di Bologna
Atmospheric neutrinosAtmospheric neutrinos
Massive Magnetized Detector M. Selvi – Università di Bologna
Atmospheric neutrinosAtmospheric neutrinos
P + air --> (, K)
e + e
• < h > = 10 km
• ~ E-3.7
Massive Magnetized Detector M. Selvi – Università di Bologna
From Battistoni & Lipari (1998)
Updated NuMI beam
the LBL nightmareThe L/E rangeThe L/E range
L (down-going) ~ 10 km
L (up-going) ~ 104 km
E from 100 MeV up to 100 GeV
L
Massive Magnetized Detector M. Selvi – Università di Bologna
Status of neutrino studies Status of neutrino studies with Atmosphericswith Atmospherics
Massive Magnetized Detector M. Selvi – Università di Bologna
Status of atmospheric neutrino Status of atmospheric neutrino datadata
•Up/down asymmetry: robust indication of disappearance
(10)
(fixes the mixing in a model independent way)
•Disappearance occurs near the horizon
+ upgoing, througoing, multiring muon-like and NC-like, indication of appearance
+ MACRO, Soudan 2
Superkamiokande: 79.3 kty (Y. Totsuka, TAUP2001)
deficit increasing with Ldeficit increasing with L no anomalyfor eno anomalyfor e
Massive Magnetized Detector M. Selvi – Università di Bologna
Interpretation of atmospheric Interpretation of atmospheric neutrino dataneutrino data
• SK data interpreted as 2 oscillations in the channel • (Supported by MACRO,
SOUDAN2,CHOOZ)
• Pure–s oscillations excluded
• Pure –e oscillations excluded • Dinamycs of disappearance fit
an L/E law (FCNC, VLI, VEP excluded)
• Is pure - oscillation the end of atmospheric neutrino history?
Best fit:
m2 = 2.5 x 10-3 eV2 sin22 = 1
Massive Magnetized Detector M. Selvi – Università di Bologna
Explicit detection of Explicit detection of oscillation?oscillation?
• L/E resolution of SuperKamiokande not sufficient to detect oscillations explicitely
• Limited precision on m2
• There are viable alternative hypotheses with L/E law:
• Decay• Decoherence
• At least one full oscillation cycle has to be detected to prove oscillations (disprove alternative hypotheses).
The oscillation is damped by finite detector L/E resolution !!
Massive Magnetized Detector M. Selvi – Università di Bologna
Damped oscillationDamped oscillation
Perfect resolution
Damped Oscillation
Critical damping
sin2m2 =0.003 eV2
Massive Magnetized Detector M. Selvi – Università di Bologna
Physics Physics
with a Massive Magnetized with a Massive Magnetized Spectrometer Spectrometer
on Atmosphericon Atmospheric
Massive Magnetized Detector M. Selvi – Università di Bologna
New detector conceptsNew detector concepts
Overcome limitations of current atmospheric neutrino detectors:
•High L/E resolution•Fully exploit far/near source method
for disappearance•Systematic-free analysis of the oscillation pattern
Massive Magnetized Detector M. Selvi – Università di Bologna
Atmospheric: comparison Atmospheric: comparison up/downup/down
It is a good experimental rule that precise measurements are obtained by comparison with a reference
For E > 2 GeV • The atmospheric neutrino flux is up/down
symmetric at the source • The downward is not affected by oscillations (m2
< 10-2 eV2) reference near source• Upward flux is affected by oscillations: L/E goes
up to 6·104 km/GeV far source
Massive Magnetized Detector M. Selvi – Università di Bologna
Measurement of disappearanceMeasurement of disappearance
The disappearance probability can be measured with a single detector and two equal sources:
= P( ; L/E) N up(L/E)
N down(L’/E)
L’
L
L(up) = 2Rcos(up) L’(down) = L( –down)
= 1 - sin2 (2) sin2 (1.27 m2 L/E)
An oscillation pattern should appear in the experimental ratio of up to down fluxes (*)
*) method first suggested by P.Picchi and F.Pietropaolo
Massive Magnetized Detector M. Selvi – Università di Bologna
What affects the L/E What affects the L/E resolutionresolution
The L/E resolution is determined by the capability of the experiment to reconstruct the neutrino energy and the neutrino direction of flight (L ~ 2R cos):
But is not measured; just ... so events near the horizon are of no use: resolution is
spoiled by the tan2 term
Low L/E values must be obtained with high E
A detector with a modest hadronic energy resolution, but a good muon momentum measurement can be effectively used provided that low-y events are selected
• Limitation of SK: due to the limited acceptance at high energies, oscillations occur near the horizon
Massive Magnetized Detector M. Selvi – Università di Bologna
Detector choiceDetector choice
• Magnetized tracking calorimeterMagnetized tracking calorimeter E by range measurement for fully contained events
E by tracking in magnetic field for partly-contained
events
by tracking
Up/Down by time of flight (plus vertex identification)
high time resolution (< 2 ns) is also required
Massive Magnetized Detector M. Selvi – Università di Bologna
The Monolith DetectorThe Monolith DetectorLarge mass 34 ktonMagnetized Fe spectrometer B = 1.3 TeslaTime resolution ~ 1 ns (for up/down discrimination)Space resolution ~ 1 cm (rms on X-Y coordinates)Momentum resolution p/p ~ 20% from track curvature for outgoing ~ 6% from range for stopping Hadron E resolution Eh /Eh ~ 90%/Eh 30%
~52000 m2 of detector : Glass Spark Counters
8 cm
2.2 cm
Fe
Fe
29.5 m
13 m
14.5 m B B
Massive Magnetized Detector M. Selvi – Università di Bologna
Event selectionEvent selection
Event selection developed to optimise the observation of the oscillation pattern
(keep under control the relative L/E resolution)
1. E > 1.5 GeV
2. Fiducial selection of 40 cm on each side
FC events: inside fiducial volume
PC events: one single outgoing track with range > 4 m
3. Nb. of fired layers > 6
4. Selection on combination of the observables E, , Eh to ensure the required L/E resolution
Massive Magnetized Detector M. Selvi – Università di Bologna
L/E resolution in L/E resolution in MONOLITHMONOLITH
Contributions to L/E resolution
Angular spread
Energy measurement
Final L/E resolution
contribution of track fit error
Massive Magnetized Detector M. Selvi – Università di Bologna
Efficiencies and Efficiencies and resolutionsresolutions
• Selected CC (downgoing only!) after 4 y of data taking:
• Fully contained: 931
• Partially contained: 259
• Total: 1190
Massive Magnetized Detector M. Selvi – Università di Bologna
Effect of the Magnetic Effect of the Magnetic FieldField
Higher efficiency in the low L/E region Higher efficiency in the L/E region of physical interest (102-103) Slightly higher cost and complexity (anti-seismic rules for LNGS impose expensive mechanics anyway)
Massive Magnetized Detector M. Selvi – Università di Bologna
Expected L/E distributions Expected L/E distributions (1)(1)
Central value in each bin is obtained with a 26 years statistics.Event rates, error bars and contour lines correspond to 4 years.
99% C.L90% C.L.68% C.L.
m2 = 710-4 eV2
m2 = 210-3 eV2
Massive Magnetized Detector M. Selvi – Università di Bologna
Expected L/E distributions Expected L/E distributions (2)(2)
m2 = 510-3 eV2
m2 = 810-3 eV2
Massive Magnetized Detector M. Selvi – Università di Bologna
Monolith sensitivity – 4 yMonolith sensitivity – 4 y
•Comparison of MONOLITH sensitivity to oscillations with Kamiokande and SuperKamiokande• 90% C.L. allowed regions after 4 years for different m2 (left)• Exclusion regions if no effect is found (right)
Massive Magnetized Detector M. Selvi – Università di Bologna
Detection of the oscillation Detection of the oscillation patternpattern
Four simulated experiments of 4 years with m2 = 0.003 eV2
• best fit to oscillation• best fit to decay• best parametric fit
Massive Magnetized Detector M. Selvi – Università di Bologna
A staged approachA staged approach
15 m
13.1 m
14.5 m B
16 m
8.5 m
13.5 m B
1 module = 17 kt
Maximum size that fits in Gran Sasso Hall A (between LVD and GNO)
12 kt
Massive Magnetized Detector M. Selvi – Università di Bologna
L 2REarthcosE= E+Eh
=
Resolution comparable to the full detector (34
kt)
Efficiencies and resolution in a Efficiencies and resolution in a 12 kt module12 kt module
Efficiency loss < 20% w.r.t. the full detector (fiducial cut against cosmic muon background)
34 kt 17 kt
Massive Magnetized Detector M. Selvi – Università di Bologna
A 12 kt detector (4 years)A 12 kt detector (4 years)
Kamiokande
SK
0.007 eV2
0.003 eV2
0.001 eV2
10kt
90% C.L. allowed regions
Efficiency for decay model rejection at 95% C.L.
RMS Precision on sin22RMS Precision on m2
SK 90% C.L.
region
Massive Magnetized Detector M. Selvi – Università di Bologna
12 kt detector12 kt detector
Massive Magnetized Detector M. Selvi – Università di Bologna
34 kt detector34 kt detector
Massive Magnetized Detector M. Selvi – Università di Bologna
100 kt detector100 kt detector
3.0 10-3
1-3% precision in the oscillation parameters is achievable
Massive Magnetized Detector M. Selvi – Università di Bologna
Vertical vs horizontal Vertical vs horizontal layers for atmospheric layers for atmospheric neutrinos (FAQ)neutrinos (FAQ)
Selected atm. ’s events for fixed L/E resolution • Lower reconstruction
efficiency along the vertical direction with vertical plates
• About the same efficiency at small L/E (where the 1st minimum is expected):
• Events near the horizon filtered by resolution requirements!
• Need for an external VETO Pay on mixing, but marginally on m2
Massive Magnetized Detector M. Selvi – Università di Bologna
Physics Physics
with the with the
CNGS beamCNGS beam
Massive Magnetized Detector M. Selvi – Università di Bologna
CNGS beamCNGS beam
• from , K
• < E > ~ 20 GeV
• L = 732 km
• Optimized for tau appearence
• Rate CC ~ 2600/kt y
Massive Magnetized Detector M. Selvi – Università di Bologna
Detector layoutDetector layout
Massive Magnetized Detector M. Selvi – Università di Bologna
CNGS event exampleCNGS event example
Massive Magnetized Detector M. Selvi – Università di Bologna
Efficiencies and Efficiencies and resolutionsresolutions
Almost flat around 50% for E>10 GeV
Massive Magnetized Detector M. Selvi – Università di Bologna
L/E RangeL/E Range
L/E distributions after selections• 4 y atmospheric (shaded)• 1 y CNGS beam
High sensitivity to m2 values down to a few 10-4 eV2
AtmosphericsThe L/E distribution, resulting after
selections, is populated up to 5·103 km/GeV
The Log(l/E) distribution is more populated at high L/E
The sensitivity of the experiment decreases for
increasing values of m2
Can the beam help at high m2 ?• atmospheric no systematic• beam systematic to be understood
Massive Magnetized Detector M. Selvi – Università di Bologna
Monolith on CNGS beamMonolith on CNGS beam
CNGS beam will cover with very high statistics the region L/E < 100 km/GeV: ~ 40,000 events/year CC after selections vs. ~ 200 events/year from up-going atmospheric.
Systematic effects: a tough job!
10% bin per bin systematics assumed
Accordingly with BMPT .
Massive Magnetized Detector M. Selvi – Università di Bologna
Impact of CNGS beamImpact of CNGS beam
Atmo’s alone
Atmo’s + Beam
m2 =0.007 eV2
Massive Magnetized Detector M. Selvi – Università di Bologna
CNGS beam: CC/NC ratioCNGS beam: CC/NC ratio
m2 = 0.003 eV2
MONOLITH 12ktx5y
(CC
/NC
)ob
s /(
CC
/NC
)no-o
sc
Visible hadron energy (GeV)
CC/NC
Atm. full MONOLITH
90% allowed regions(includes uncertainties of beam shape and composition, detector effects, …)
CC/NC ratio can supplement atmospheric data constraints on sterile neutrinos
Massive Magnetized Detector M. Selvi – Università di Bologna
Physics at the Physics at the -factory-factory
with awith a
MonolithMonolith-like-like
DetectorDetector
Massive Magnetized Detector M. Selvi – Università di Bologna
Neutrino OscillationsNeutrino Oscillations : 3 : 3 flavorsflavors
If neutrinos have mass the flavour eigenstates could not coincide with mass eigenstate:
3 mixing angles: 12, 23, 13
2 mass differences: m212 m2
23
1 CP-violation fase:
Massive Magnetized Detector M. Selvi – Università di Bologna
One-mass scale One-mass scale dominancedominance
at terrestial distancesPe-= sin2(23 ) sin2(213) sin2(1.27 m2
23 L/E)
13 bounded by CHOOZ exp. to be smallsin2(213) < 0.1 (90% C.L.)
<<
Very high intensity beam needed
Massive Magnetized Detector M. Selvi – Università di Bologna
factoryfactory
Features:
• High intensity
• Well-known beam
• Both flavors
• Different helicity
Massive Magnetized Detector M. Selvi – Università di Bologna
•Circulating 50 GeV in a NuFactory(1021 decays in 5 years)
•Beam made by and e (ee)
•Search at LBL for wrong sign muons () coming frome oscillated into
sign of m2, study of matter effects, CP violation
Physics at a Physics at a FactoryFactory
Massive Magnetized Detector M. Selvi – Università di Bologna
Golden channel: wrong sign Golden channel: wrong sign muonsmuons
Massive Magnetized Detector M. Selvi – Università di Bologna
CC rate (background)CC rate (background)
eeee
XX
3.5 103.5 107 7
CCCCat 732 kmat 732 km
Massive Magnetized Detector M. Selvi – Università di Bologna
CC rate (signal)CC rate (signal)
eeee
oscillationoscillation
XX
1.1 101.1 105 5 CCCCat 732 kmat 732 km
Massive Magnetized Detector M. Selvi – Università di Bologna
Two main sources:
•Fake WSM (due to charge misidentification)
• WSM from hadrons
BackgroundsBackgrounds
Massive Magnetized Detector M. Selvi – Università di Bologna
o Generate interaction using Pythia + q.e. + 1 corrections (Lipari code).o Simulate the whole event in Geant:o Multiple scattering with Moliere theory option ON
(not just gaussian approximation)o Full B field description o Fit muon track using GEANE and Kalman filter approach
(a real reconstruction, not just smearing)
both for signal and background
Charge identificationCharge identification
Massive Magnetized Detector M. Selvi – Università di Bologna
B field detailsB field details
Massive Magnetized Detector M. Selvi – Università di Bologna
Long FC event example Long FC event example ((--))
Massive Magnetized Detector M. Selvi – Università di Bologna
background event background event example (example (++))
Massive Magnetized Detector M. Selvi – Università di Bologna
Wrong event exampleWrong event example
Large Large angle angle scatterinscatteringg• Overestimated in GEANT (~30) ...see OPERA
• Recognizable via Kalman filter (change in slope)
Massive Magnetized Detector M. Selvi – Università di Bologna
Selection cuts:
• Pfrom range > 7.5 GeV
•In each region:• At least 4 points•Track lenght > 300 cm
•Same charge assigned in each region
Charge identification: Charge identification: resultsresults
Fractional bkg.1 x 10-6
Efficiency 35%
Massive Magnetized Detector M. Selvi – Università di Bologna
Wrong sign muonsWrong sign muons
from hadronsfrom hadrons
Massive Magnetized Detector M. Selvi – Università di Bologna
Wsm from hadronsWsm from hadrons
Massive Magnetized Detector M. Selvi – Università di Bologna
Large Magnetic Detector people (Dydak et al.) showed (see NuFact '00)that it is possible to reject such bkg up to
~ 2 x 10-6 with 30% efficiency
just using two cuts:
• P > 7.5 GeV
• Qt > 1. GeV
Wsm from hadronsWsm from hadrons
Massive Magnetized Detector M. Selvi – Università di Bologna
• P cut may be easily reproduced: • good muon momentum resolution
• Qt depends on hadronic angular resolution• in LMD analysis they assume to have the same performances of MINOS
(MINOS proposal - chapter 7)
... What can Monolith ... What can Monolith say?say?
Massive Magnetized Detector M. Selvi – Università di Bologna
Angular ResolutionAngular Resolution
• From true vertex to true shower’s center of gravity
• From
reconstructed vertex to rec. shower’s center of gravity
Massive Magnetized Detector M. Selvi – Università di Bologna
Vertex resolutionVertex resolution
• Transverse resolution x = 5.6 cm
• Longitudinal res. y = 5.8 cm
• Vertical res. z = 5.1 cm
Massive Magnetized Detector M. Selvi – Università di Bologna
hadronic angular hadronic angular resolutionresolution
Reconstructing vertex:Reconstructing vertex:about twice about twice MINOSMINOS
Monolith fitMonolith fit3232.. 8.28.2
Massive Magnetized Detector M. Selvi – Università di Bologna
Second approachSecond approach
• Use LMD cuts (P >7.5 GeV; Qt > 1 GeV)
And take into account the different smearing
Charge id. CC e CC e NC
MONOLITH
1. 10-6 7.5 10-7 2.5 10-7 5.2 10-6 16.5 %
35 30 15 160
Monolith fitMonolith fit
3232.. 8.28.2
Massive Magnetized Detector M. Selvi – Università di Bologna
ImprovementsImprovements
• Higher granularity• Planes orientation
... perform the same cuts (P >7.5 GeV; Qt > 1 GeV) and modify the fractional bkg accordingly with the obtained hadronic direction smearing
Efficiencies are considered to be the same (16.5%)
Very conservative hypothesis: improvements are expected in both cases
Massive Magnetized Detector M. Selvi – Università di Bologna
Horizontal plates – 4 cm Horizontal plates – 4 cm thickthick
Monolith fitMonolith fit2323.. 12.12.
Massive Magnetized Detector M. Selvi – Università di Bologna
Vertical planes – 8 cm Vertical planes – 8 cm thickthick
...Against ~5 cm in HOR configuration
Massive Magnetized Detector M. Selvi – Università di Bologna
Vertical plates – 8 cm Vertical plates – 8 cm thickthick
Monolith fitMonolith fit1515.. 12.12.
Massive Magnetized Detector M. Selvi – Università di Bologna
Test beam with the Baby-Test beam with the Baby-MonolithMonolith
prototype: prototype:
Hadronic angular resolutionHadronic angular resolution
Massive Magnetized Detector M. Selvi – Università di Bologna
Experimental setupExperimental setup
Beam of e, of2, 4, 6, 8, 10 GeV
Massive Magnetized Detector M. Selvi – Università di Bologna
Event display: Event display:
Massive Magnetized Detector M. Selvi – Università di Bologna
hadronic angular hadronic angular resolutionresolution
Resolution better than the Resolution better than the requested one.requested one.
Baby-Baby-Monolith fitMonolith fit1010..44 10.10.11
Massive Magnetized Detector M. Selvi – Università di Bologna
SinSin22(2(21313) sensitivity) sensitivity
• Oscillation probability:Pe-= s23
2 sin2(213) sin2(1.27 m2 L/E)
• Fix 23=45°, change 13 and m2
• Compare number of signal events (efficiency corrected) with the error in the surviving background events(statistical + 5% syst.)
• Draw a 4 region
Massive Magnetized Detector M. Selvi – Università di Bologna
SinSin22(2(21313) sensitivity – 4) sensitivity – 4
Strong muon momentum cut
P > 20 GeV
P > 7 GeV
Qt > 1 GeV
8 cm VERT plane
P > 7 GeV
Qt > 1 GeV
Massive Magnetized Detector M. Selvi – Università di Bologna
Baseline: 3500 kmBaseline: 3500 km
Baseline 732 km
Vertical layers
Baseline 3500 km
Vertical layers
Bkg ~ L-2 (fluxes)
Signal ~ L-2 (fluxes) x L2 (oscillation) = L0
... up to O(3000 km)
Massive Magnetized Detector M. Selvi – Università di Bologna
ConclusionsConclusions
We show that a massive magnetized calorimeter can significantly contribute to the actual and
future neutrino physics framework:
• Explicitely prove the oscillation pattern in L/E
• Precisely measure the osc. parameter values (if oscillations)
• CNGS beam can help in disappearence analysis and NC/CC ratio, especially if m2 > 0.005 eV2
• The proposed detector is well-suited for the wrong sign muons detection on a -factory beam.