window of opportunity there are mysteries in the neutrino mass spectrum which a complementary,...
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Window of Opportunity
There are mysteries in the neutrino mass spectrum which a complementary, direct measurement can help unravel.
Oscillation Exp. only sensitive to m2
disappearance => oscillation => mass2-flavor mixing is much easier to write down
Astrophysics/Cosmologyno sterile standard model interactions, stable
Supernovaeonly applies to Dirac neutrinosmodel-dependent at supernuclear densities
… … Physics ...Physics ...
… … Experiment … Experiment … G-2 storage ring: state-of-the-art spectrometer at bargain prices
Beamline can be parasitic with SEB, easily switched to RHIC, FEB
An order of magnitude improvement in a fundamental constant
A stricter limit is part of this decade’s focus on neutrino physics
PRESENT
Atmospheric: =>Xand m2 ~.0012 - .008 eV2 SuperK: => slightly favored)
Solar Neutrino: e =>X and m2 ~eV2 or is it 10-11 eV2 ? (SNO may help)
LSND => e and m2 ~ .03-1.0 eV2
FUTURE
MINOS - Beams early 2004 CERN - Beams early 2005
K2K - 220 evts by 2005 (if m2 large)
MiniBoone in 2003, Boone in ??
The next Supernova - Tools to interpret and limit
Neutrino decay
e e e via Lo (minimal LR symmetric model) consistent with
Mass Density of Universe Primordial nucleosynthesis Microwave Bkgd Diffuse -ray Bkgd SN1987a
as long as m() > 35 keV (from Z-width)
Supernovae
For mX)> 10 keV, t ~ day => pulse is below background if SNO sees no delayed pulse, then take your pick: No X produced? Oscillated to (sterile)? They decayed? is massive?
Check out all those 17 keV papers for more exotic loopholes
Closing LoopholesClosing Loopholes
GF mm2
GF
mm2
0.5 ppmMuLan
0.38 ppm 10 ppm
It is, after all, a Fundamental Constant !It is, after all, a Fundamental Constant !
Its uncertainty affects our knowledge of other fundamental constants
For example:
* Mass of the pion as measured by decay of stopped ’s
* Gfermi
theoretical precision negligible compared to experimental variablesother electroweak variables, such as MZ, continue to improve
Direct Measurements are …more direct!
Current Limits
m(e) 4.35 - 15 eV Tritium -decay endpoint 23 eV TOF spread from SN1987A 0.5 - 9 eV Double -decay for Majorana ’s
m(170 keV (stopping ’s)
m( 18.2 MeV Inv. Mass of hadrons (e+e- Colliders)
Pure 2-body decay No model-dependent nuclear/atomic environment
Pions live a reasonably long time
DIRECT MEASUREMENTS OF M(
Pion Decay at RestParent momentum is well-known
Limited by the uncertainty in the pion mass
Pion Decay in FlightNeed to measure
pp Momentum Resolution limited by mult.scattering in detectors
Pion Decay at Rest
Series of experiments at PSI
1979: Daum et al. (Phys Rev D20 p.2692) Solution A Solution B
1984: Abela et al (Phys Lett B146 p.431)Solution A Solution B
1996: Assamagan et al. (Phys Rev D53 p.6065)Solution A Solution B
m2( 0.163 + 0.080 MeV/c2)2
m()250 keV/c2
m2(+ 0.13 + 0.14MeV/c2)2
m()570 keV/c2
m2(0.143 +0.024 0.016 + 0.023MeV/c2)2
m()170 keV/c2
1982: Anderhub et al. Phys Lett B114 p.76
Pion Decay in Flight
m2( 0.14 + 0.20MeV/c2)2
m(500 keV/c2
2002: BNL g-2 Neutrino Mass Experiment?
m(8 keV/c2
If SuperK definitively proves =>m2~.007) Then this experiment reduces the neutrino mass limit
by 3 orders of magnitude!
Highlights of the Experimental Technique
• Translate p to r in 0.1 ppm uniform B-Fieldno multiple scatteringno need to measure decay angle or location
• Reference each to parent slow extraction
• In situ alignmentprotons (7 ns/turn late) prescaled undecayed pionsremote positioning of active vetoesremote angular adjustment of detector
• Position resolution from silicon1.4 m SSD
• Time resolution from scintillators and PMT’stight triple coincidence triggerTDC’s on all vetoes and embedded
hodoscope
In a perfectly uniform B-fieldAny charged particle returns to origin independent of B, p,
* Origin can produce a range of angles and momenta * Uniformity is more important than value of B* 1st harmonic (and other nonuniformities) are always monitored using residuals of prescaled pions and undecayed protons
“origin”
G-2 Storage Ring
G-2 Experiment Weak-focussing Storage Ring: Muons stored for 800 s
Quadrupoles Muon Kicker
NuMass Experiment Spectrometer: observed evt-by-evt
No Quads Pion kicker
Same Momentum - 3 GeVretain excellent shimming and B-field uniformity0.1 ppm over 4.5 cmTrolley runs in vacuum to map fieldFixed probes to track changes
Active shimming and thermal insulation to minimize change
“Pion Kicker”
p = -16.2 MeV/c X/Xo = 14.7 % (rms) = 1.56 mr
Put pions on orbit using dE/dx Injection
5.2 cm Beryllium
orbit with degrader
orbit withoutdegrader
D
D
D depends on m()
undecayed
pions
decay ’s
Forward-going decay muons orbit a larger diameter byD
CM
q = 29.7 MeV/c
D p - p0.7 MeV/c 3.26 mm D p3 GeV/c 14 m
D -m2
D 2 q m
non-zero mshrinks D
0.04 mm for current limit
Conceptual Design
D undecayed
pions
decay ’s
Forward-going decay muons orbit a larger diameter byD
CM
q = 29.7 MeV/c
D p - p0.7 MeV/c 3.26 mm D p3 GeV/c 14 m
Conceptual Design
D
D -m2
D 2 q m
non-zero mshrinks D
0.04 mm for current limit
D depends on m()
Non-forward going muons are lower momentum
They move to the inside of S2
Also vetoed offline by the g-2 calorimeters and J veto
J-Veto
S1 S2
g-2 Cal’s
Injection
decay orbit
24 g-2 calorimetersrestrict late decays
identify electron bkginitial beam tuning C-veto: restrict
incoming ’s
J-veto: restrict early ‘s at large angles
J-cal: 2nd turn electron id
Beam counter
Experimental MethodExperimental Method
S1 S2
Trigger Hodoscope
2.56 cm
6.4 cm
Embedded Scintillator:2 mm Prescale Strips
Trigger pads
BerylliumDegrader
S2
S1
Silicon strip Detectors (S1, S2)(1.28 cm long vertical strips at 50 m pitch)
32 strips per Viking chipserial readout into 1 ADC
@40MHz = 0.8 s
Sample & Hold Readout System
Simple Standard Cheap
Beam Counter
S1 (ch 6)
S2 (ch 6)
S1 (ch 71)
S2 (ch 71)
Hodoscope
Trigger:latch data
O
O
O
O
150 ns
225 ns
1st turn:
1st turn:
2nd turn:
2nd turn:
Parasitic RunningParasitic Running
E949 Running Conditions25 Gev protons70 TP in a 4.1 s spill / 6.4 s cycle
E952 Parameters2.8 x 106 into g-2 ring/TP5.4 x 1012 for an 8 keV result
Triggers Offline
Entering Ring Detector +vetoes
8 x 106 part/s 1 x 106 part/s 1.8 x 105 s-1 910 s-1 42 s-1
400 Hz/strip 55 s/SSD 11 ms/SSD
100 MB/s 0.5 MB/s
Prescale in trigger
Instantaneous rates (100% extr. eff.)
Running Time
5% of SEB beam => 492 hrs (crystal extr. eff.)
Scintillator Hodoscope
Radial segmentation = 2 mm Vertical segmentation = 12.8 mm
• 4 ns gate for 3-fold coincidence triggerAccidentals at 0.004, flagged by beam counter
• Veto events r < 2mm to enrich eventsx 50 prescale => 0.5 MB/s or 37 DLT tapes
• Select readout SSD0.7% dead time1/10 data volume
• 1 ns timing resolution (TDC) + 2mm segmentationreject accidentals offline (another factor of .002)
Sources of Background
• Beam-gas scattersvacuum is 10-6 torr
• Injected p (27%)7 ns/turn slower
• Injected e (12%)lose 1 MeV/turn from SR (4.7 mm inward)identify in J-Veto calorimeter (or position)
• => e (= 64 s)injected (1%) and =>< 10 -4 of good events rejected by g-2 calorimeters
• => e(BR=1.2 x 10-4)low tail out to ~ 5 mm calorimeter at inner J-Veto
5 mm endpt (q=70 MeV/c)
SR shrinks it 2 mm
e
e
g-2 Calorimeters
Some Background Configurations
J-Calorimeter
ScheduleSchedule
Summer 2000 Test individual SSD’s at CERN
Spring 2001 Do tests at end of g-2 run (fast extraction)
Insert 2 SSD’s in rigid frame with removable “degrader” -inj, low intensity, no quads, no kickerNo degrader:J-veto Degrader: J-veto
Summer 2001 Test of crystal extraction for Slow Beam
2001 Build mosaic of SSDCustomize VA readout (chip run)Tests of detector at CERN test beam
2002 Engineering run - parasitic with E949 Crystal extraction: slow beam down V-lineFinal 5x5 SSD configuration with degrader in ring
2002 Physics run - parasitic or dedicated
Responsibilities
Beamline and Ring BNL
SSD and readout electronics CERN, Minnesota
Active Vetoes and Scint Trigger BU, Illinois, Tokyo IT ??
Feedthrus and positioners Tokyo IT, Heidelberg ??, BNL
DAQ and g-2 electronics Existing (Minnesota, BU)
Field Measurements Yale, Heidelberg, BNL
Orbital dynamics, Monte Carlo Cornell, BNL, Yale, NYU, Minn, BU
Analysis The team!
Goals of the 2001 Test Run
• Check out trigger and DAQ modifications
• Read out silicon microstrip prototype detector in g-2 conditions
• Beamline settings for pion injection link to position of pion and muon at detector and J-vetomost efficient angle thru inflector
• Map scattering background in g-2 Cal, FSD, J-Veto
• Practice tightening profile using beamline
• Practice tightening profile using current shims
• Inject positive pions at 0.5% above magic momentum
• Observe trigger hodoscope (TDC and ADC gives 2 rough profiles 150 ns apart)
• No degrader Find 1st pass pion distribution and 2nd pass muon distribution Some storage: tune on fast rotation in detectors Check lifetimes of lost muons vs positrons in FSD’s See pions at Flash Counter on 1st turn
• Degrader Find 1st pass pion and 2nd pass pion distribution No storage: Check lifetime of lost muon distribution No pions on Flash Counter Muons scraped off inner J-Veto after 1st pass and pions after 2nd
• Read out microstrip detector as well, but unable to do residuals..yet
• Gradually reduce emittance and then reduce intensity How low a rate can we get? Can we find the on-orbit protons 7 ns later?
• Watch FSD, PSD and CAL detectors, collect information on the scattered background - electrons? muons?
• Delay S2 microstrip trigger to remove 1st pass in S2
Problems: Fast extraction, high intensity, sec shaping timeConditions: No vacuum, no kicker, no quads, reverse B-field
PSD tiles
Removable Copper sheets
S2 Prototype SSD’s from CERN
g-2 Test setup
S1
12.8 mm
12.8 mm
Trigger tiles
Using VA-2 chip: 800 ns shaping time
Beam Counter
S1 (ch 6)
S2 (ch 6)
S1 (ch 71)
S2 (ch 71)
Hodoscope
Trigger S1
O
O
O
O
150 ns
225 ns
1st turn:
1st turn:
2nd turn:
2nd turn:
Trigger S2
More Accidentals and More Deadtime
Inflector
No Degrader
T0 J-Veto
collimator
Pion hits inflector
pion => muon residual profile
Muon on orbit
Flash Counter
Inflector
Degrader
T0 J-Veto
collimator
Pion on orbit
pion => pion residual profile
Muon hits J-Vetoon 1st turn
Flash Counter
pion 2nd time around
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