An Improved Limit on the Muon Neutrino Mass from Pion Decay in Flight

Carmen-Miruna AnăstăsoaieAlex Eduardo de BernardiniSven LafèbreMartin Vlček

NuMass Experiment

International Summer School on

Particle and Nuclear Astrophysics

in Nijmegen 2003

What is the aim of the project?

NuMass will improve the value of the upper limit of the mass of the muon neutrino.

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)

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improvement by NuMass by order of 20 to m() < 8 keV

History of the Muon Neutrino Mass Limit

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Why is this measurement so important?

verification of theoretical backgrounds- neutrino mass generation mechanism- complementary information to neutrino oscillation results- neutrino decays understanding - chiral left-right symmetry

improvement of the theoretical description of the Fermi constant understand some loopholes in cosmology

- lack of dark matter- limits to the density of Universe

minimal left-right model verification some propagation phenomena related to supernova pulses it is, after all, a fundamental constant !

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Highlights of the experimental technique

“origin”

In a perfectly uniform magnetic field any charged particle returns to origin independent of B or p or angle

Uniformity is more important value of B

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Highlights of the experimental technique

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

S1 S2

Trigger Hodoscope

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observed event by eventwe will need SEB

Highlights of the experimental technique

NuMass will use the existing G-2 Storage Ring in the BNL facility at Brookhaven with only minor modifications

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Highlights of the experimental technique

Embedded Scintillator:2 mm Prescale Strips

Trigger pads

BerylliumDegrader

S2

S1

Silicon μ-strip Detectors

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Endpoint structure

Expected distance between first pass pion and second pass muon (in mm)

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Sources of background

Beam-gas scatters => vacuum is 10-6 torr

Injected p (27 %) => rejected in embedded scintilators ΔT = 7 ns / turn slower

Injected e (12 %) => rejected in J-veto, calorimeter or position, lose 1 MeV / turn

μ → e=> rejected by g-2 calorimeter

< 10-4 of good π-μ events π → e=> rejected by calorimeter in inner

J-veto

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J-Veto

S1 S2

g-2 Cal’s

C-Veto

Advantages of NuMass

run in dedicated mode or in conjuction with K-decay (E949) or MECO experiment

another project may run nearly immediately after our beamtime, there are only minor changes on beam

pure 2 body decay no model dependent nuclear/atomic environment

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Responsibilities

Beamline and Ring BNLSSD and readout electronics CERN, MinnesotaActive Vetoes and Scint Trigger BU, Illinois, Tokyo ITFeedthrus and positioners Tokyo IT, Heidelberg, BNLDAQ and g-2 electronics Minnesota, BUField Measurements Yale, Heidelberg, BNLOrbital dynamics, Monte Carlo Cornell, BNL, Yale, NYU,

Minnesota, BUAnalysis The team!

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Budget

$ 770k BNL- modifications on G-2 and SEB- improved sensitivity for the V1 beamline

instrumentation- beam time

$ 330k CERN, Universities- silicon detectors, degrader, active vetoes- feedthrus, positioners- electronics, DAQ

$ 1.1 M TOTAL COST

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Scheduling Year 2000

build 2-SSD detectors plus removable degrader unitbuild active vetos or simple prototypewrite software for new electronics readout and integrate with g-2

Year 2001install and test prototype detectors by running parasiticallyunderstand the π-μ orbital parameterstest AGS/beamline modifications for slow extraction to g-2build and test final silicon detector + degrader

Year 2002commission slow extraction to g-2run the experiment parasitically with E 949

Year 2003dedicated experiment or further parasitic running to completion

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Thank you for your attention ...

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Neutrino oscillation

Neutrino oscillation experimental results are theoretically dependent. Some effects surrounding the standard formulation of neutrino oscillation phenomena:

Neutrino oscillation Δm2 DIRECT !!!

(flavor) quantum number oscillation

existence of sterile neutrino

understanding of the mixing angles

chiral oscillation

Dirac formulation of neutrino oscillation

matter effect

wave packet description

I’m

If you believe atmospheric neutrino result:

=>with onlym2~.002

Then this experiment reduces the neutrino mass limit

by 3 orders of magnitude!

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Neutrino oscillation

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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Some background configurations

5 mm endpt (q=70 MeV/c)

SR shrinks it 2 mm

e

e

g-2 Calorimeters

J-Calorimeter

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Cross section of g-2 superconducting magnet

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Cross section of the field

Contours every 1 ppm of field gradient represents lines every 1.5 μTesla

Magnetic field is 1.45 Tesla

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Proposed Parasitic Running with AGS Crystal ExtractionProposed Parasitic Running with AGS Crystal Extraction

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.)

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