Measurement of the neutron lifetime with a Magneto Gravitational trap Gilles Ban LPC-Caen, ENSICAEN–CNRS/IN2P3 Université de Caen Basse-Normandie Caen, France

People and institutions Present Russian-French collaboration V.Ezhov1, A.Z.Andreev1, G.Ban2, B.A.Bazarov1, P.Geltenbort3, A.G.Glushkov1, M.G.Groshev1, V.A.Knyazkov1, N.A.Kovrizhnykh4, O.Naviliat-Cuncic2, V.L.Ryabov1 1 Petersburg Nuclear Physics Institute, Gatchina, Russia 2 LPC-Caen, University of Caen, ENSICAEN, Caen, France 3 Institut Laue-Lagnevin, Grenoble, France 4 Institute of Electro-physical Apparatus, St-Petersburg, Russia Supported in part by RFBR ECO-NET “ONELIX”

OUTLINE 1. Motivations for precision measurements of tn 2. Ultra cold neutrons, and source 3. Neutron lifetime experiment 4. Conclusion and outlook

Motivations 1) Value ? PDG tn = 885,7 ± 0,8 s 2) CKM Matrix, Vud Strength of weak interaction u and d quarks 3) BBN input Helium abundance directly related to tn

Present status of tn PDG 2004- 2010: (885.7±0.8) s All recent storage experiments (including the most precise) used material storage of UCN (although not under the same conditions). A.Serebrov et al. PLB 605 (2005) 72 PRC 78 (2008) 035505 878.5 ± 0.8 s A. Pichlmaier et al PLB 683 (2010) 880.7 ± 1.8 s

tn accepted value ? From the Particle Data Group K Nakamura et al. JPG 38 (2010) http://pdg.lbl.gov/2010/listings/rpp2010-list-n.pdf « It is up to workers in this field to resolve this issue. Until this major disagreement is understood our present average of 885.7 ± 0.8 s must be suspect » New experiments are underway, beam, material walls, magnetic trapping since 2005…

Vud, CKM and SM ) 3 1 ( sec 2 4908 l t + × ± = V Neutron lifetime, axial/vector strength, up and down mixing are related  Knowing 2 gives the other one ) 3 1 ( sec 2 4908 l t + × ± = ud V (Marciano, Sirlin 2006) l=Ga/Gv extract from A measurement t experiments Other way 0+0+ ,very high precison 0,97425 ± 0.00022 (Towner & Hardy PRC 79, 2009)

BBN Input As the universe expands, the temperature drop results in a departure from equilibrium conditions (neutron-proton inter-conversion breaks). Neutrons are free to decay. Nucleosynthesis begins effectively below the photo-dissociation threshold for deuterons (2.23 MeV). Nearly all surviving neutrons end up in bound 4He nuclei. The experimental parameter most important in determining Yp is the neutron lifetime, which normalizes (the inverse of) Γn↔p. Courtesy A. Coc Still even a few seconds difference in t won’t strongly affect the knowledge of Yp Or constraint more Astrophysical observations

Techniques Cold neutrons Beam ( p Penning trap), Protons and/or beta detection  Fiducial volume, detection efficiency Materials or magnetic bottles Ultra cold neutrons Protons/beta detection, surviving neutrons  Losses, wall interaction or depolarisation

Ultra Cold Neutrons Ultra Cold Neutrons, UCNs Fast neutrons En~ MeV up to ~1 GeV  ~ 10-7 eV= 100 neV Very Cold Moderator (<30K) Liquid or solid D, SF He 100 neV  1 meter in the gravitational field  1 T, 60 eV/T  few m/s (slower/faster than you ?)  Collective interaction, containment, guiding For example copper Ef=170 neV Most Powerfull user source Institut Laue Langevin , ILL , Grenoble

Institut Laue Langevin, HFR, UCN Source ILL, Grenoble, France the only multi-user UCN source in operation high flux reactor(thermal power: 58.3 MW) thermal n-flux: 1.5 ×1015n/s/cm2 cold neutron source: 20 l of LD2at 25K vertical neutron guide 13m, 7×7 cm2, (58Ni coated) UCN source: rotating turbine UCN density at experiment: ρ= 20 /cm3

3D magnetic trapping For mn  -60.3 neV/T, a 2T field generates a 120 neV barrier. Force due to field gradient, F = -m (dB/dz), repels only one spin state. Use permanent magnets. Step 3: 3D confinement Step 1: 1D confinement - top (gravity) - bottom (magnetic shutter) 1 – permanent magnets 2 – magnetic poles Step 2: 2D confinement Add magnetic shutter

…in real life 20 segments; 560 NdFeB magnets; FeCo poles inner walls covered with Fomblin oil (reflect “wrong” spin neurons during filling and depolarized neutrons during storage) field gradient near wall: 2 T/cm 15 l total- (9 l storage-) volumes

Experimental setup Main elements: lift, trap, solenoid, shutter, detector to vacuum pump material shutter magnets and poles yoke outer solenoid UCN detector absorber lift cylinder UCN Lift: Fomblin coated Al cylinder + PE disk Trap: Fomblin coated magnets and poles [V.F. Ezhov et al., NIM A 611 (2009) 167]

Normalized time spectra stop storage measurement (start 100 s background measurement) Storage time 1000 s 1300 s 1800 s → Continuous monitoring of “leaking” neutrons (which are forced depolarized in the trap, reflected by the Fomblin coated walls and detected)

Systematics Depolarized neutrons not detected (Absorbed by walls) = missing : beta decay like Forced depolarisation to monitor the lost neutrons which are not detected Vaccuum : measurements at different pressure 1s precision = 7.5 10-6torr >>Work pressure= 1.5 10-6 torr Systematics studies limited by number of UCN Need of strong source (>100 /cm3)

Result tn = 877.9 ± 2.0 ± ?.?(syst) [s] Coming soon

Future plans Final Value Construction of a new trap with a 90 l storage volume 60 segments disposed on a Ø80x40cm2 cone, Ø6cm guide NdFeCo magnets and FeCoNi poles Fill trap from top with adapted “lift” Use forced depolarization to change trapping conditions (leaks) Add spin analysis system with UCN detection Project funded (France/Russia) Runs in at ILL in 2011

Summary The use of permanent magnets has provided so far the most sensitive value for the neutron lifetime with magnetically stored UCNs. Key features of the trap for the measurement of the neutron lifetime are: - filling of the trap from top with a slow lift - continuous monitoring of leaking neutrons - tuning leaks by depolarizing neutrons inside the trap A final value of the neutron lifetime is expected to be issued soon from measurements performed with the prototype trap. Lower than PDG to what extent (??) An improved setup is under construction which will enable to reach a statistical precision below 1s (and hopefully solve the existing puzzle). Move to a stronger stronger source for systematics studies (??)

THANK YOU FOR YOUR ATTENTION !!

Trap filling sequence 1.Fill lift volume 3.Move lift down 4.Open lift and move lift up 2.Close lift volume vlift << vn lift cylinder material shutter UCN UCN detector 3 He

Vud, CKM and SM To be competitive with this value t and l have to reach 10-4 precision ~10 times better precision for both Using Vud and l values one gets (S. Paul NIM A 611 2009) 880.1 ± 1.3 s < t < 887 ± 3.46 s