ILL beam experiment Improved experiment with horizontal beam: (1) Reactor source,,(2)pulsed source Vertical experiment: DUSEL proposal

Transcription

1 Neutron-Antineutron Oscillation Search with Cold Neutrons M. Snow Indiana University/CEEM NANO Workshop ILL beam experiment Improved experiment with horizontal beam: (1) Reactor source,,(2)pulsed source Vertical experiment: DUSEL proposal Thanks for slides and calculations to: Yuri Kamyshkov, Geoff Greene, Hiro Shimizu

2 Neutron-Antineutron transition probability For H E V 2 E V P nn t 2 V 2 V 2 2 sin2 h where V is the potential difference for neutron and anti-neutron. Present limit on ev Contributions to V: <Vmatter>~100 nev, proportional to density <Vmag>=B, ~60 nev/tesla; B~10nT-> Vmag~10-15 ev <Vmatter>, <Vmag> both >> t For V 2 h t <<1 ("quasifree condition") P nn h t t nn Figure of merit= NT 2 N=#neutrons, T= quasifree observation time

3 Neutron Cooling: MeV to nev T30K T293K W(E n ) UCN Very cold Cold ThermEpitherm E n [ev]

4 N-Nbar search at ILL (Heidelberg-ILL-Padova-Pavia) Schematic layout of Heidelberg - ILL - Padova - Pavia nn search experiment at Grenoble Cold n-source 25 D2 (not to scale) fast n, background ILL 57 MW No GeV background No candidates observed. Measured limit for a year of running: Discovery potential : N 2 n t sec with L ~ 90 m and t 0.11 sec Measured limit : nn sec measured P nn nn nn sec Bended n-guide Ni coated, L ~ 63m,6x12cm 6 2 H53 n-beam ~ n/s Focusing reflector 33.6 m 58 Magnetically shielded 95 m vacuum tube Flight path 76 m < TOF> ~ s Annihilation target 11m 1.1m E~1.8 GeV 11 ~ n/s Baldo-Ceolin M. et al., Z. Phys. C63,409 (1994). Detector: Tracking& Calorimetry Beam dump

5 Quasifree Condition: B Shielding and Vacuum Bt<<ћ ILL achieved B <10 nt over 1m diameter, 80 m beam,one layer 1mm shield in SS vacuum tank, 1% reduction in oscillation efficiency (Bitter et al, NIM A309, 521 (1991). For new experiment need B <~1 nt If nnbar candidate signal seen, easy to turn it off by increasing B V opt t<<ћ: Need vacuum to eliminate neutron-antineutron ti t optical potential difference. P<10-5 Pa is good enough, much less stringent than LIGO QuickTime and a TIFF (LZW) decompressor are needed to see this picture.

6 The conceptual scheme of antineutron detector n A 5 pions (1.8 GeV) Annihilation target: ~100 thick Carbon film annihilation 4 Kb nc capture 4 mb

7 Better Cold Neutron Experiment (Horizontal beam) need cold neutrons from high flux source, access of neutron focusing reflector to cold source, free flight path of ~ m Improvement on ILL experiment by factor of ~1000 in transition probability is possible (but expensive) with existing n optics technology and sources D ~ 2-3 m L = 300 m

8 concept of neutron supermirrors: Swiss Neutronics neutron reflection at grazing incidence (< 2 smooth supermirror refractive index n < 1 total external reflection e.g. Ni c = 0.1 /Å c 2d sin reflectivity = 5 Å [ ] reflectivity d 3 >dd 2 >d d = 5 Å [ ] reflectivity = 5 Å [ ]

9 Supermirror Neutron Optics: Elliptical Focusing Guides Muhlbauer et. al., Physica B 385, 1247 (2006). Under development for neutron scattering spectrometers Can be used to increase fraction of neutrons delivered from cold source (cold source at one focus, nbar detector at other focus)

10 1ectivity Supermirrors : critical m critical Commercial Supermirror Neutron Mirrors are Available With m 3-4. Phase space acceptance for straight guide m 2, more with focusing reflector 1 ~ 1000 layers Refl c m c Multilayer mirror Items of commerce

11 Supermirror Neutron Optics: Higher m and reflectivity m=10! apan zu, KEK/Ja H. Shimiz From H. Shimizu

12 Prototype supermirrors with m~6 produced Useful neutron flux scales roughly as m 2 Image Courtesy; H. Shimizu

13 New Experiment at Existing Research Reactor? need close access to cold source to fully illuminate i elliptical l reflector Requests to all >20 MW research reactors with cold neutron sources Can a reactor be found? Not yet Cutaway view HFIR reactor at ORNL

14 Advantages of a Next-Generation Pulsed Neutron Source (ESS) for A Neutron-Antineutron Oscillation Experiment Possibility to use active neutron optics to partially correct for gravitational defocusing Possibility to optimize the target/moderator system with this experiment in mind, and take advantage of a colder cold source if moderator research is successful. Possibility to upgrade reflector with other developments in y pg p neutron optics (higher m higher reflectivity supermirrors, )

15 At a pulsed neutron source like ESS, neutrons of a given speed reach the mirror at a known time. We can therefore imagine an array of mirrors tiling an ellipse and phased to the source to condition the beam Piezodrivers This tilting can be used to counteract the defocusing of the beam from gravity, thereby reducing the beam/detector size and therefore reduce the cost of the experiment.

16 Nt 2 distribution vs vertical Y in the target plane m=4; x target <1m m. Radius of beam is smaller by~factor of 2 ->cost of experiment is smaller (scales generically as the area)

17 Supermirror Neutron Optics: Future Possibilities In the future one may consider varying the shape of the guides actively by means of piezo actuators. If used at pulsed sources, beam size and therefore the divergence for each wavelength during a neutron pulse can be optimized. This corresponds to a kind dof active phase space transformation at o that will allow the circumvention of Liouville s theorem. The combination of fast mechanical actuators with supermirror technology may become useful for active phase space transformation. P.Boni, NIM A586, 1 (2008). One could design the experiment to be able to take advantage of such advances in active neutron optics technology through modification of the reflector

18 Scheme of Vertical N-Nbar experiment ~3 MW TRIGA research reactor with vertical hole and cold neutron moderator vn ~ 1000 m/s Vertical shaft ~1000 m deep with diameter ~ 4-5 m at proposed US DUSEL facility Large vacuum tube, focusing reflector, magnetic shielding Detector (similar to ILL N-Nbar detector) at the bottom of shaft Letter of intent to DUSEL submitted 3.4 MW Annular Core TRIGA reactor 3E+13 n/cm2/s thermal flux Deuterium moderator Vacuum Tube L~1000m D~3-4m Neutron trajectory Approximate scales 100 m 1 m Beam dump Focusing Reflector L~150 m Magnetic Shield Annihilation Target D~2 m Detector

19 Annular core TRIGA reactor (General Atomics) for N-Nbar Nbar search experiment ~ 1 ft GA built ~ 70 TRIGA reactors MW (th) 19 TRIGA reactors presently operating in US (last commissioned in 1992) 25 TRIGA reactors operating abroad (last commissioned in 2005) some have annular core and vertical channel Wll Well-established tblihdtechnology annular core TRIGA reactor 3.4 MW with convective cooling, vertical channel, and large cold LD 2 moderator (T n ~ 35K). Courtesy of W. Whittemore (General Atomics)

20

21

22 Cold Neutron Source Example Made in PNPI, Russia Liquid hydrogen at 20K Inserted vertically into research reactor Delivered to new Australian research reactor, 18 MW power

23 3.4 MW annular core research TRIGA reactor with Liquid id D2 cold neutron moderator TRIGA = Training Research Isotopes from General Atomics

24 Vertical flight path Shaft diameter Focusing mirror reflector Vacuum chamber with Active + passive magnetic shield km ft 4 c 10 5 Pa 1nT Annular core TRIGA reactor 3.4 MW LD 2 cryogenic cold moderator; neutron temperature 35K Running time 3-5 years Robust detection signature nc several pions 1.8 GeV Annihilation properties are well understood LEAR physics Ati Active magnetic shielding hildi allows effect ON/OFF Free-n sensitivity increases more than 1000 Expected background at max sensitivity 0.01 event

25 1km Vertical Space Working Group NNbar: search for neutron to antineutron t transitions (Yuri Kamyshkov/UT) Study of diurnal Earth rotation (Bill Roggenthen/SDSMT) Physics of cloud formation (John Helsdon/SDSMT) Search for transitions to mirror matter (n n) (Anatoli Serebrov / PNPI) Cold atom interferometry for detection of gravitational waves (Mark Kasevich / Stanford U) Experiment Length Dia Pressure Mag. shield NNbar 1.5 km 4-5 m <10 Pa ~ 1 nt Purpose Mirror neutrons 1.5 km 4-5 m <10 Pa ~ 1 nt n disappearance Atom interferometry 1-4 km 0.3 m <.1 Pa ~ 1 nt grav. wave detection Cloud Form Physics km 3-5 m 0.2 atm N/A atm. physics facility Diurnal rotation km 1m <10 Pa N/A E&O Talks posted at

26 Sources of x1000 Improvement on ILL Experiment with Cold Neutrons -increased phase space acceptance of neutrons from source (using m=3 supermirrors): x~60 -increase running time: x~3 -increase neutron free-flight time (t 2 ): x~100 (vertical), ~4-10 (horizontal) -source brightness : x~1/20 (vertical 3.4 MW TRIGA) X~1/2 (horizontal, 20-60MW research reactor) For horizontal experiment: greater source brightness ~counteracted by (dispersive) gravitational defocusing of Maxwellian neutron spectrum

27

28 Sources of x1000 Improvement on ILL Experiment with Cold Neutrons from CW Source -increased phase space acceptance of neutrons from source (using m=3 supermirrors): x~60 -increase running time: x~3 -increase neutron free-flight time (t 2 ): x~4-10 (horizontal) -source brightness : x~1/2 (horizontal, 20-60MW research reactor) For CW horizontal experiment: greater source brightness ~counteracted by (dispersive) gravitational defocusing of Maxwellian neutron spectrum