New Search for Mirror Neutrons at HFIR

Transcription

1 New Search for Mirror Neutrons at HFIR L. J. Broussard Oak Ridge National Laboratory May 17, International Workshop on Baryon and Lepton Number Violation

2 Search for neutron disappearance Neutron disappearance would signal new physics with implications for BNV and dark matter Prior searches with ultracold neutrons (UCN) Fairly strong limits if B =0 (τ > 448 s) 1 Conflicting measurements if B 0, τ ~ 2 12 s 1 A. P. Serebrov et al, NIMA 611 (2009) 137 2

3 Search for neutron disappearance Neutron disappearance would signal new physics with implications for BNV and dark matter Prior searches with ultracold neutrons (UCN) Fairly strong limits if B =0 (τ > 448 s) 1 Conflicting measurements if B 0, τ ~ 2 12 s 1 A. P. Serebrov et al, NIMA 611 (2009) 137 3

4 Neutron Lifetime Discrepancy Count the dead 1 Count the survivors 2 8 s (4 σ) discrepancy between methods 3 1 A. T. Yue et al., Phys. Rev. Lett. 111, (2013) 2 D. J. Salvat et al., Phys. Rev. C 89, (R) (2014) 3 J. D. Bowman et al., arxiv:1410:5311 4

5 Losses in UCN traps UCN material bottles involve large corrections for losses Material bottles = absorption/upscattering on walls, impurities, residual gas, etc hard to model accurately Large lifetime discrepancy: neutron disappearance not ruled out as source Systematics relevant to disappearance search: rely on conditions changing slowly between measurements 5

6 Idea for new experiment UCN disappearance effect can be interpreted as Mirror Matter oscillations 1 : n n (more in L. Varriano talk) MM oscillation can be unambiguously tested with existing high-intensity cold neutron beams Several possible neutron sources can be considered Technique: Scan lab B field and tune to unknown B : look for counting resonance signature 1 Z. Berezhiani et al, arxiv:

7 Neutron Regeneration n Monitor Disappearance region n Regeneration region Detector/ Beamstop n Low bkgd Detector High cold neutron flux + long, large area guides P(n n n) t Dis τ 2 treg τ 2 (on resonance) Disappearance: precise monitoring of changes in transmission Different systematics from UCN disappearance Regeneration: large area, low background detector Magnetic field uniformity and control 7

8 BL13 SNS NIST 15 m BL14B 60 m 15 m x 2 BL14A HFIR CG2 14 m 20 m 8

9 GP-SANS at HFIR 14 m Disappearance and 20 m Regeneration beamlines Large area detector in shielded chamber Ample room for B control coils, monitors 9

10 GP-SANS cold neutron flux 4 cm 4 cm aperture, 0.3 divergence n/s expected Divergence: ±20 cm at detector TOF measurements confirmed spectrum, planned normalization measurements in June Simulated Φ = At τ = 12 s: expect 10 4 n n /s; 0.01 n n n /s n cm 2 s data from L. Crow 10

11 Neutron transmission monitoring Require 10-7 level or better monitoring of neutron transmission for disappearance Use current-integrating detector provided by n- 3 He Spin Rot. expt. (Indiana U.) n+ 3 He t+p Large signal, well defined amplitude, insensitive to gamma radiation Flux monitoring nearly statistics limited 2 ( 1.1 N) Optimal monitoring scheme being investigated 1 S. D. Penn et al, NIMA (2001) 2 W. M. Snow et al, Rev. Sci. Instrum (2015) C. Haddock and M. Snow 11

12 Regeneration detector Flux monitoring requirement ~1% Sensitivity depends on signal to background 1 m x 1 m 3 He, position-sensitive detector 1 5 mm x 5 mm position resolution >90% 5 Å 2 x 10-4 cps/cm 2 background Primarily from thermal neutrons from cosmics Rely on position cuts and additional shielding/veto 1 K. D. Berry et al, NIMA 693 (2012)

13 Magnetic field uniformity Measured ~20 mg nonuniformity + some hot spots Goal <1 mg uniformity/control Beamline upgrade in 2018: include considerations for B field uniformity/control This summer: detailed mapping for cancellation coil design Deviation from ambient field Solenoid: Cos-theta coil: with J. Barrow, C. Crawford 13

14 Neutrons/MWs Optimizing B field scans B not known: scan over B field/direction, search for disappearance/resonance Optimum step size ~10 mg for regeneration, ~20 mg for disappearance Scan B in 2 directions: worst case = 90 ; 4x loss Best sensitivity = scan B in 4 directions: worst case = 60 Improve sensitivity in regeneration mode by 2.5x Effect of misalignment of B and B in regeneration (5 mg steps) x 4x B field (mg) B. Rybolt 14

15 Goal Sensitivity Assumptions: Simulated flux (0.3 x/y divergence, n/s) Regeneration: measured unshielded bkgd (0.3 cps over 40 x 40 cm 2 ) Disappearance: stats limited monitoring (50% duty in, 6.5 hr per point) Confirm/refute UCN anomaly in 2 weeks beamtime τ < 12 s (90% C.L.) Note: GP-SANS heavily subscribed Simulated positive signal at τ = 12 s, 7 days regeneration mode (5 mg steps), 7 days disappearance mode (10 mg steps) Assume worst case B, β 15

16 Plan: Implement staged approach Phase 0: Demonstrate feasibility Determine flux normalization, stability Prototype short section of magnetic field control Demonstrate flux monitoring capability Measure background with shielding Investigate systematics Phase 1: Disappearance Collimation section upgrade in 2018 Flux monitor characterizations (10-7 level) Implement mg-level magnetic field control Phase 2: Regeneration Implement mg-level magnetic field control (limited access chamber) Implement additional background detectors, shielding, active veto system Total anticipated cost <$1M 16

17 Conclusion Mirror Matter is a viable candidate for Dark Matter with testable predictions in n-n oscillations. New search using GP-SANS: small, low cost, short beamtime, large potential impact Controversy in UCN storage experiments will be resolved Pursuing ORNL partial support through LDRD program Stepping stone to future parasitic experiment at SNS Second Target Station or ESS Dark Sectors 2016 Workshop: Community Report 17

18 nn Collaboration K Bailey, B Bailey, L Broussard, V Cianciolo, L DeBeer-Schmitt, A Galindo-Uribarri, F Gallmeier, G. Greene, E Iverson, S Penttila Oak Ridge National Laboratory J Barrow, L Heilbronne, M Frost, Y Kamyshkov, C Redding, A Ruggles, B Rybolt, L Townsend, L Varriano University of Tennessee Knoxville C Crawford University of Kentucky Lexington I Novikov Western Kentucky University D Baxter, C-Y Liu, M Snow Indiana University A Young North Carolina State University Z Berezhiani Laboratori Nazionali del Gran Sasso, Università di L Aquila 18