UCN transport and NN experiments R. Young and B. Wehring NCState University

The geometry: How do we model transport?

Transport Data: Where Does It Come From? Raw Data: TOF – proton start, detector stop LANSCE Prototype Source: Modeling strategy, model date using fit parameters: specularity (TOF very sensitive) loss per bounce, shape of SD2 and UCN lifetime in SD2 (use “bottle lifetime between source and valve A) For lifetime: study thin films so mfp in SD2 not important

Prototype Results Specularity: average probability that a reflection will be mirror-like Loss per bounce: average probability that UCN will be absorbed or upscattered during a collision 58Ni/Mo coated guides (approx. 305 neV) Specularity: 97.5% ( roughly 2% uncertainty) agrees with measurements of straight and curved guides we have performed at ILL Loss per bounce: .0025 conservative, set by 58Ni bottle lifetimes and source data PLD diamond coatings (250 - 300 neV, with 300 neV measured for at SPEAR) Specularity: >99% (data obtained at ILL recently for drawn quartz tubes) Loss per bounce < .00016 (data from ILL expts – negligible for our purposes)

The Monte Carlo Runge-Kutta numerical integration Gravity, magnetic fields (if needed), and wall reflections Non-specular reflections via various models (Gaussian, isotropic and Lambertian—(from Golub, Richardson, Lamoreaux) Spin dynamics if needed (depolarization on surfaces and spin dynamics in rf fields) (future effort: n-n phase evolution) Assume n annihilated on each collision

Preliminary results for base case (det eff = 1): A possible base case: NCState geometry, 4 cm thick SD2, 18 cm guides, .050s SD2 lifetime, a UCN energy cutoff of 430 neV initally Primary flux: 6.0 x 107 (below 305 neV) Box loading efficiency: 20 –32% Best case: diffuse walls, specular floor 3.5x10^9 discovery pot. 325 s avg. residency Straightforward gains: Source thickness x2 (see Serebrov’s geom): x 2 Source lifetime  .075s +10% Running time: 4 years (“real”) Speculative gains: Multiphonon: x1.5(?) Coherent amplification: x2 (?) Solid Oxygen: x5 (?)  5.5 – 7 x 109 Various diffuse regions, wall potentials, same “best” case as above