First Results from the UCNA Experiment B. PlasterLANL 2008 Brad Plaster, University of Kentucky LANL P-25 — November 5, 2008 Leah Broussard (Duke/TUNL) Kevin Hickerson (Caltech) Adam Holley (NCSU) Russ Mammei (Virginia Tech) Michael Mendenhall (Caltech) Robert Pattie (NCSU) Raymond Rios (Idaho/LANL) Anne Sallaska (U Washington) Riccardo Schmid (Caltech) Sky Sjue (U Washington) Junhua Yuan (Caltech) Yanping Xu (NCSU) Several New Collaborators as of 2008 Run

This talk B. PlasterLANL 2008 Not talk about Detailed design/performance of the Area B UCN source Mark Makela, Chris Morris, Andy Saunders Will talk about Physics motivation for UCNA Analysis techniques/results from 2007 run Status report on 2008 run Review of UCNA experiment

Neutron β-decay B. PlasterLANL 2008 σ ne θeθe p e θpθp g V = f 1 (q 2  0 ) G F |V ud |weak magnetism g A = g 1 (q 2  0 ) G F |V ud | = gAgA gVgV e iφe iφ O (5%) lattice QCD = 1 (CVC)

Correlation coefficients B. PlasterLANL 2008 σ ne θeθe p e θpθp spin e− correlation −0.103(4) electron, β- asymmetry −0.1173(13) neutrino- asymmetry 0.983(4) a 0 = 1 – A 0 = − B 0 = Highest Sensitivity to

Neutron lifetime B. PlasterLANL 2008 nn 1  G F 2 |V ud | 2 ( ) (1 + RC) “Master Formula” Marciano and Sirlin (2006) ± (0.0008) δ(V ud ) = ±

Status of A and B. PlasterLANL 2008 PERKEO II ILL-TPC IAE-PNPI PERKEO I ΔA/A [ % ] PDG Mean1.1 Published PDG 2008 Average of 4 published A results + 1 simultaneous A/B result [ Mostovoi et al. (2001) ] = − ± [0.23%] PERKEO II update: H. Abele, Prog. Part. Nucl. Phys. 60, 1 (2008) 0.28%

Status of  n and neutron V ud B. PlasterLANL 2008 Serebrov et al. (2005) Still no new (published) results since PDG 2008 neutron V ud = (4) τ (18) (2) RC V ud

Status of V ud B. PlasterLANL 2008 Improvement in neutron sector V ud ? Resolve discrepancies in A  If achieve agreement,, factor of 2 improvement Plus improvement in bottom-line precision on A: 0.6%  ?? But must resolve  n discrepancy !! 0 +  0 + neutron PDG nuclear mirror transitions 19 Ne, 21 Na, 35 Ar pion Naviliat-Cuncic and Severijns, arXiv:

Why measurement of A via UCN ? B. PlasterLANL 2008 PERKEO I (1986) Systematic Corrections [ % ] ILL (1997) PNPI (1997) PERKEO II (2002) Polarization / Spin-Flip 2.6 Backgrounds ~ 32.9 Other ~13 ~15 magnetic mirroring  cos θ  ~ 3 small ~3  cos θ 

Why measurement of A via UCN ? B. PlasterLANL 2008 Advantages of UCNA experiment (A via UCN) 1) Polarization Expect to achieve ~100% polarizations via transport of UCN through 7-Tesla magnetic fields Spin-state selected via μ B interaction, ± 60 neV/Tesla T < 335 nano-eV, v < 8 m/s, stored in material bottles

Why measurement of A via UCN ? B. PlasterLANL 2008 Advantages of UCNA experiment (A via UCN) 2) Beam-related backgrounds Greatly reduced by operating “pulsed mode” spallation source coupled to superthermal UCN source T < 335 nano-eV, v < 8 m/s, stored in material bottles prompt backgrounds environmental

Why measurement of A via UCN ? B. PlasterLANL 2008 Advantages of UCNA experiment (A via UCN) 3) New approach to electron detection T < 335 nano-eV, v < 8 m/s, stored in material bottles Low-threshold MWPC for detection of low-energy-deposition Coulomb backscattering events MWPC + plastic scintillator Low sensitivity to gammas (primary bkg’d in cold neutron expt’s) MWPCscintMWPC scint β-decay electron

Why measurement of A via UCN ? B. PlasterLANL 2008 Advantages of UCNA experiment (A via UCN) 4) Reduced neutron-generated backgrounds T < 335 nano-eV, v < 8 m/s, stored in material bottles Long storage times for UCN in apparatus For given rate, need relatively smaller number of stored UCN as compared to cold neutron beam

UCNA experiment B. PlasterLANL 2008 W(θ)  1 + vβvβ c P n A cos θ 0.6-T field expansion Angular Distribution

UCNA experiment B. PlasterLANL 2008 photograph 12/ Tesla Polarizers UCN 1-Tesla Electron Spectrometer UCN Beamline muon vetoes spin flipper

UCN spin polarization B. PlasterLANL Tesla Polarizer/Spin-Flipper Field Profile Spin-flipping via Adiabatic Fast Passage [AFP] 420 neV μB barrier UCN flux 1-Tesla AFP spin-flip region Resonator with nominal frequency of ~29 MHz Spin-flipping cancels systematic errors

Spin-flip efficiency B. PlasterLANL 2008 UCN flux g UCN detector AFP resonator + Cu foil

Spin-flip efficiency B. PlasterLANL 2008 Transmission measured to be 0.40 ± 0.05 % Spin-Flip Efficiency > 99.6%

In-situ depolarized fraction B. PlasterLANL T electron spectrometer B UCN from SD2 source 7-T Polarizer AFP off UCN detector β-decay running drain “right spin” on look for “wrong spin”

In-situ depolarized fraction B. PlasterLANL 2008 Spin Flipper State Change  t for switcher leakage signal Upper Limit of 0.65% on Depolarized Fraction Present During Any Run Quote 1.3% Systematic

Electron detection B. PlasterLANL 2008 Baseline requirements Low-sensitivity to backgrounds Minimal electron backscattering Reasonable energy resolution 2007 Geometry e 25-μm entrance and exit windows 3.5-mm plastic scintillator: energy, trigger low-pressure MWPC with low-Z fill gas 2.5-μm mylar foil Cu decay trap

Electron spectrometer B. PlasterLANL m long superconducting solenoid 1.0-Tesla field 0.6-Tesla field-expansion region 3-m long Cu decay trap [ BP et al., NIMA 595, 587 (2008) ]

Electron detection B. PlasterLANL 2008 PMT MWPC 100-Torr neopentane 2.54-mm wire spacing on anode and 2 cathode planes (163 х 163) mm 2 active area Scintillator PMTs in 100-Torr N 2 Axial fields ~300 Gauss (x,y) reconstruction [ T.M. Ito et al., NIMA 571, 676 (2007) ] Fiducial volume definition

Spectrometer performance B. PlasterLANL 2008 suppression of gamma background [ PERKEO II dominant background ] 113 Sn 368 keV MWPC: gamma suppression 2007 calibrations: 113 Sn (368 keV), 207 Bi (503 keV, 995 keV) ~310 p.e. / MeV, 5.6% at 1 MeV [ ~ 100 p.e./MeV in PERKEO II ]

Spectrometer performance B. PlasterLANL 2008 fiducial volume radius cut [decay trap walls] reconstruction of the center of Larmor spiral 113 Sn 368 keV

Event reconstruction B. PlasterLANL 2008 MWPC scintillator Correct Type I Type III Type IIMISID Type IVMISID scintillator decay trap foil + scattering off of decay trap foils + “lost events”

Monte Carlo: GEANT4 / PENELOPE B. PlasterLANL ) Reconstruct β-decay energy on event-by-event basis from measured “visible energy” deposition in scintillators “Invisible energy” loss in decay trap foils, MWPC windows/interior, and scintillator dead layer 2) Form experimental asymmetry, A exp (E recon ) = P  β cos θ  A residuals small, ~5 keV E vis (E true )  E recon (E vis )

Monte Carlo: GEANT4 / PENELOPE B. PlasterLANL ) Correct experimental asymmetry for subtle effects β cos θ “acceptance” Unobservable backscattering  β cos θ  for all triggering events energy loss tail in steep part of β-decay spectrum A exp (E recon )  β cos θ  Global Backscattering

Systematic corrections B. PlasterLANL 2008 analysis window  β cos θ  Backscattering 2007 Correction −1.6% +1.1%

Uncertainties in corrections B. PlasterLANL 2008 Uncertainty in correction for  β cos θ  acceptance ? How well is dE/dx energy loss modeled ? Assign (conservative) 25% uncertainty for geometry considerations

Uncertainties in corrections B. PlasterLANL 2008 Uncertainty in backscattering correction ? GEANT4 PENELOPE Simulations tend to under- predict backscattering Assign 30% uncertainty to correction

β-decay energy spectra B. PlasterLANL 2008 UCNA 2007 S/N 21:1 PERKEO II S/N 7: (6.6) (6.2)

Asymmetry extraction B. PlasterLANL 2008 Recoil-order corrections were applied to asymmetries (weak magnetism, g A g V interference, nucleon recoil) Standard calculational procedure of Wilkinson (1982) Included Fermi Function

UCNA 2007 result B. PlasterLANL 2008 UCNA 2007 A = − ± ±

UCNA 2008 running B. PlasterLANL Run 25-μm MWPC windows, 2.5-μm decay trap foils 0.781M β-decay events 0.396M passed cuts (tight fiducial cut), 4.1% statistical error Need ~8.5-10M events for 1% result (depending on fiducial cut) 2008 Run : Statistics + Systematics < 1% Run I: 25-μm MWPC windows, 0.7-μm decay trap foils Completed July–September, ~10.5M collected Run II: 25-μm MWPC windows, 13-μm decay trap foils Completed Monday 6AM, ~10.0M collected Run III: 6-μm MWPC windows, 0.7-μm decay trap foils Starts this weekend, thru end-of-run “Calibrate” MCs Optimal Geometry

Reduction in 2008 systematics B. PlasterLANL 2008 Decay Trap Foils 0.7 μm 13 μm  β cos θ  1.5% 3.4% Backscattering −0.5% −2.7% 25 μm MWPC Windows6 μm MWPC Windows Factor ~2 Bias to Asymmetry

UCNA 2008 running B. PlasterLANL 2008 Run I Run II

Projected impact of 2008/09 results B. PlasterLANL 2008

Summary B. PlasterLANL 2008 UCNA experiment has reported first-ever measurement of any neutron β-decay correlation parameter with UCN 2008 data collection proceeding well Poised to produce very interesting and competitive result at 1% level 4.5% “proof-of-principle” result Sub-1% level in 2009 running Higher rate: improved Fermi potential, beam current, SD2

Backgrounds vs. Spin State AFP off AFP on 0 – 800 keV background rates (all event types) EastWest ± ± ± ± no evident correlation (AFP-induced noise)

Decay Trap (x,y) Spectra 40 mm cut

Background Muons

GMS Gain Corrections LED box optical fibers β-scintillator light guides to β-PMTs NaI GMS reference PMT 60 Co gain correction factor for i th β-PMT position of LED peak in GMS reference PMT position of 60 Co peak(s) in GMS reference PMT position of LED peak in i th β-PMT

GMS Gain Corrections MeV MeV East 60 Co West 60 Co