Magnetized Media as Detectors for Galactic Axions

Transcription

1 TRUCT AXMA BkU Magnetized Media as etectors for alactic Axions C. Braggio University of adova and for the AXMA collaboration March 7, 7

2 TRUCT AXMA BkU AX CUL AX-RM interaction detection of atomic transitions i in which axions are absorbed AXMA = detection of VS-R photons in rare-earth doped materials QUAX = axions are converted to magnons in a ferri-/para-magnet B = B m a QUAX and AXMA

3 TRUCT AXMA BkU AXMA - A UCVRS SCM AX-RM interaction detection of atomic transitions i in which axions are absorbed QUAX = axions are converted to magnons AXMA = axions are converted to VS-R photons RVW LTTRS BRUARY, 959 B = B m a b- y f of ) are ' igns ing ted /v«tcal UM R quontum A/Vi~ c )i h hv )& kt T- MULTLR.. nfrared quantum counter. Several ions of pump laser resonant with transition material transparent to the pump until an R photon is absorbed ( ) level is fluorescent = detection can be accomplished via conventional detectors (MT or ) such energy level scheme can be realized in wide bandgap materials doped with trivalent rare-earth ions. Bloembergen, hys. Rev. Lett., 8 (959)

4 n the nonrelativistic limit, q. () implies the interaction energy Let us define g i by AXMA - A UCVRS a ff ¼þ g Z f ~ ~p ~σ a SCM ~σ þ material transparent to the pump until an AX is f t a ; ðþ g a m i v m a ρ a d p d n f absorbed ( ) dp ð~pþjhijðg ~ e S þ g ~Þ ~pjij : ð7þ TRUCT AXMA BkU where m f is the mass of fermion f, ~p its momentum, transition and g i is a number takesofplace orderbetween one giving the coupling strength of ~S ¼ )i S ZMA SLT LVLS to allow for tunability ~σ its spin. The first term on the rhs of q. () is the target atom. t depends on the atomic transition used, similar to the coupling of the magnetic field to spin, with (B field) the indirection the interesting of polarization axion mass of therange atom, and the momen- fluorescent distribution = of the detection axions. can t varies be accomplished with time of day via and TCAL UM ~ a playing the role of the magnetic field. That interaction level istum causes magnetic dipole h (M) transitions in atoms. R The singleofphoton year since detectors the momentum distribution changes on those second term causes Δj ¼, Δl ¼, parity-changing transitions. As usual, l is the quantum number giving the time scales due to the motion of the arth. T- dopant (rare-earth ion) concentration compatible with MULTLR or a mole of target atoms, the transition rate on magnitude of orbital angular momentum, and j that of total transition rate by axion absorption R i for a ML of target resonance is angular momentum. c We will not use the second term atoms: because, starting from the ground state (l ¼ ), it causes transitions only if the energy absorbed is much larger than A R i ¼ g i Av ρ a R quontum A/Vi~ f minðt; t ;t a Þ hv )& the axion mass. f f ¼ e, the required kt a energy is of order ev. f f ¼ p; n, the required energy is of order MeV.. ρ ¼ a ev The groundbstate of most atoms is accompanied by sec ev=cm f a several other states related to it by flipping the spin of one or more valence electrons, or by changing the z component g v minðt; t ;t a Þ i z of the nuclear spin. The energy differences between these 6 ð8þ sec states can be conveniently tuned by the Zeeman effect. The interaction of the axion with a nuclear spin ~ may be written. Sikivie, where RL, A is Avogadro s () number. There is an (almost) equal transition rate for the inverse process, jii ji with a ¼ g a f ~ emission of an axion. t is proposed to allow axion % ~ target atoms/cm ðþ absorptions liter ACTV VLUM only by cooling the target to a temperature axion field

5 M TRUCT AXMA BkU 8 6 RY LVL ARAM R + R L 5 Q LaCl 9 5 J n 5/ Ce + r L M / B S 5 S A 7 C 9 S 5 B A 7 5 C R 7 5 9/ d + 5 W U T S L V X Y Z m M C 7 S 5 A 5 A R R S 5 T U V W X Y Z 6 5/ 5 Sm J C S u S7/ 7 d + 5 M C B 5 A Tb + 5 L 5 5 L J X Y Z 6 6 5/ B 5 C 6 B 5 9 A 7 A 6 W 9 y M L C Y 7 Z ' 5 5 S o M L Z 7 5 9/ 5/ r S 9 B 9 A Y ig..9 nergy level diagrams of trivalent rare earth ions of R + in LaCl ( ieke-diagram ) [.7] f electrons electrostatic interaction cm 6 Tm + 66 art C Coherent and ncoherent Light Sources art C. 5 7/ Yb + 5 nergy ( cm ) further 6 splitting C by 5 spin-orbit interaction 5 5 cm S 6 U T R Q M L M / B S 5 S A 7 C 9 S 5 B A R U T S R Q L M L C 7 S 5 J 5 C S A 5 A crystal field (Stark splitting) L C M 6 L B 5 A 7 J 5 M C B 5 L 5 5 A Z Y X W U V T S R Q L J Q M L 5 J L 8 M ' S 5 C U T S R 7 Q M L / S 9 B 9 S 6

6 TRUCT AXMA BkU R RAC MATRCS SSBL UCVRS SCMS r + A TCTR TRSC TRSL x - (cm - ) S / 9/ S / 9/ (A) pump at / S / (λ 8 nm) fluorescence at 5 nm 9/ 9/ ~8 ~5 / / ~ ~65 / / (B) pump at 5/ 9/ transition (λ nm) fluorescence at 65 nm 5/ 5/ = intrinsic threshold.7 ev TUABL UM LASRS

7 pendicular to c, theexperimental Zeemansplittings were8.6,6.5 TRUCT AXMA BkU and 5.8 cm and the best theoretical ones 8.6, 6.7 and.8 cm. The latter were obtained with a.t magnetic field oriented 8 away from a (or b) inthe(a,b) plane.ndeed,themagnetic field was strong enough to lower the axial symmetry in the R RAC MATRCS calculations. MRV T TCTR TRSC TRSL We also investigated the polarization of the transitions between Zeeman pump levelslaser in the tuned B toc case 5/,5/,+ where the original 9/,9/,+ axial site symmetry istransition preserved. (λ ach 89calculated nm) level was characterized by its crystal field R quantum fluorescence number μ, which can take the values ± / and x - (cm - ) x - ± / in d symmetry (ig. ). The selection rules for electric and (cm - ).5 T < B <.5 T 9/ 9/ z < ν a < z 9/ 9/ 8 µev < m a <.5 mev ( dressed e ) / / / / ~89 ~988 ~5 ~89 ~988 ~5 5/, 5/, + 5/ 5/, 5/, - B = B =

8 netic field was strong enough to lower the axial symmetry in the / TRUCT AXMA calculations. c B, c B, c B c BkU We also investigated the polarization of the transitions between Zeeman levels in the B c case where the original axial site symmetry is preserved. ach calculated level was characterized by its A RSS LCTR crystal field quantum number μ, which can take the values ± / and ± / in d symmetry (ig. ). The selection rules for electric and The r +, f shell electrons are dressed of their interaction with the matrix. Calculated Zeeman level energies as a function of B magnetic field parallel to c (solid lines) or to a (dashed lines) in r:yl. (a) / () and / () (b) 5/ () ig.. Calculated Zeeman level energies as a function of B magnetic field parallel ig. 5. igh resolution absorption spectra at. (a) 5() /() transition at zero magnetic field. nset: example of a central hole burnt in a transition between hyperfine levels and the corresponding side hole. A, B, and labels see

9 B = TRUCT AXMA BkU LASR-UC R LURSCC A AX TRAST r:yl (.%, % doping), oriented immersed in liquid e (. )/superfluid e (.5 ) = axion transition saturated tunable laser (Ti:Sa) infrared (.5 µm) fluorescence scheme B = 7 mt (permanent magnet) x - (cm - ) ~89 ~988 ~5 9/ 9/ / / 5/, 5/, + 5/, 5/, - identify Zeeman splitting investigate laser-induced noise (in a L scheme that involves phonon generation) r:yl S LASR

10 igure Transition! 9/,9/. Left: magnetic field is oriented the optical the crystal igure 5/,5, Transition 5/,5,! The 9/,9/. Left: The magnetic fieldalong is oriented alongaxis theofoptical axis of(b c); the crystal (B c); AXMA BkU Right: The magnetic field vector isfield perpendicular to the opticaltoaxis the crystal Measurements are c).crystal Right: The magnetic vector is perpendicular theofoptical axis of(bthe (B c). Measurements are performed for two polarizations of the incident wave c and c. c and c. performed for two polarizations of electromagnetic the incident electromagnetic wave TRUCT nm nm c c nm nm B=7 mt 89.9 nm B=7 mt nm 9/,9/ 5/,5/ 5/,5/ -> T= 88,95 -> 9/,9/ c B=7 mt 89.9 nm B= T= 89, 88,95 B c B=7 mt c 89,5 89, WavelengthWavelength [nm] [nm] 5/,5/ B=.5 µm luorescence [arb units] nm.5 µm luorescence [arb units] c.5 µm luorescence [arb units].5 µm luorescence [arb units] Bkc c 88.9 nm 88.9 nm c B=7 mt B=7 mt nm 89.9 nm nm 89.9 nm nm 89.5 nm c -> 9/,9/ T= 89,5 88,95 5/,5/ -> 9/,9/ B=7 mt B=7 mt B= B= T= 89, 88,95 89,5 89, WavelengthWavelength [nm] [nm] 89,5 λ λ = 88 pm 66.7 µev. z λ λ =. pm 78. µev 8.9 z - The band is centered cm-at, while reports it at 6 data) and at cm-at cm- The bandatis6 centered 6 literature cm-, while literature reportscm it at (experimental 6 cm- (experimental data) and 6 6 (calculated) []. The width of the band is. pm, while at it was.9 pm. ain: for the measurements without (calculated) []. The width of the band is. pm, while at it was.9λpm. ain: 6.5 forµev the measurements without λ = pm.7 z λ λ =.99 pm 6.5 µev 5. z magnetic field and no amplification for the measurements under magnetic field. magnetic field and no amplification for the measurements under magnetic field. By comparison with data in the literature we are able to identify the splitting of the ground state in the (A) or B c: or B c: upconversion scheme with B k c. 88,95 88,95 89, 89, 89,5! =! 89,5 =,!!" = 78.!!"# = 8.9!!"#

11 TRUCT AXMA BkU B c λ λ =. pm 78. µev 8.9 z λ λ =.99 pm 6.5 µev 5. z B c λ λ = 88 pm 66.7 µev. z λ λ = pm 6.5 µev.7 z ATMS T XCT STAT RQUST [ ] A e (ma/t) ma(ev) <. T = m = 5.6 m = B.6 field (thus m a) to operate at T m

12 TRUCT AXMA BkU LASR-UC BACRUS s the laser heating the crystal? / At which level is the transparency condition not satisfied? Measure the temperature of the active volume of the detector via L from the Stark levels. x - (cm - ) 9/ 9/ / Stark splitting of the free ion terms S LJ level umju exp (cm ) ~89 ~988 ~5 / 5/ 5/ 5/ 5/ / / 9/ 7/ / /

13 TRUCT AXMA BkU LASR-UC BACRUS Measure the temperature of the active volume of the detector via L from the Stark levels: L from (5/,5/) at two different temperatures scales as the ratio of the Boltzmann factors () 5/, 5/ ---> 9/, 9/ 5/, 5/ --> 9/, 9/ V (mv),,5,., 6 mw, c xc=88.99 nm+\-.6 pm w=.8 pm +\-. A=.5.9, mw, _ _ c xc=88.99 nm+\-. w=.9+\-. A=5 V_L (mv),,, wavelength (nm) wavelength (nm)

14 TRUCT AXMA BkU LASR-UC BACRUS Measure the temperature of the active volume of the detector via L from the Stark levels: L from (5/,5/) is linear with laser power x - (cm - ) x - (cm - ) S / 5 S / 9/ 9/ V_Lock (mv), T= Residuals 5 9/ / ~8 V (mv) 9/ / 5-5 Residuals ~89 ~988 ~5 / 5/ ~5 / 5/ (mw)

15 le TRUCT AXMA BkU e h ce MATC T AX LWT r- ed \ / or The \ linewidth/ f = /πτ + (τ + lifetime of the upper Zeeman level) of the transition between the S - Zeeman-split \ levels should be matched to Q a 6 n (axion linewidth) X, T SURAC, 7),, lt, ig.. Quantum-counter device geometry used in analysis of device performance. ) e x - (cm - ) e le. ion in d ch is 9/ 9/ / / τ + µs at T ( z/kz) is compatible with an efficient upconversion process ) rs a- d m he ls,., er lo-' ' lo lo5 UM WX (,), W/crn ~89 ~988 ~5 B = 5/, 5/, + 5/, 5/, -

16 TRUCT AXMA BkU CCLUSS AXMA results for a gas system ew J. hys. 7 (5) 5 upconversion in R-doped crystals Appl. hys. Lett. 7 (5) 95 solid crystals of inert gasses: demonstrated apparatus that allows high purity crystals growth and verified electrons emission through the solid-vacuum interface in s-e and s-c Currently investigating: laser-induced noise matching Q a with the Zeeman transition (τ m) upconversion efficiency and lifetime of the excited state

17 TRUCT AXMA BkU BACU SLS

18 TRUCT AXMA BkU AX TCT A AS SYSTM BC (buffer gas cooling). 6 cooled by collisions with a helium- thermal bath at temperature T e 8 m = W ba (B min ) = cm (. ev) magnetic field region: W ba saturates for B > B max = 8 T. ev< m a <.9 ev detection: RM (resonance-enhanced multi-photon ionization spectroscopy) refl = 5 to maximize the fraction of molecules that interacts with the laser beam = ( refl π w )/(h d + h ew J. hys. 7 (5) 5 tan θ) L Santamaria et al ew J. hys. 7 (5) 5 (+)RM ph to intermediate state + ph to ionize L Santamaria et ew J. hys. 7 (5) 5 igure. Schematic layout of the experimental apparatus. The 8 m 6 beam emerging from the BC source is subjected to RM spectroscopy. Any ionization product, only possible as a consequence of axion-driven a b absorption events, is eventually igure. nergy-level diagram involved in the (+)RM spectroscopic detection. The oxygen molecules promoted by the axion field into the ( =, J =, M J = ) level are subsequently ionized by using laser pulses tunable around 87 nm (violet arrows).

19 TRUCT AXMA BkU AS SYSTM: ULTRACL MLCULAR XY 6 n s, the number of oxygen molecules that have been exposed to the axion field is molec = nmax π(d/) v m, where v m = (8 k B T)/π m and n max (/) n e = 5 cm max molecular density that can be cooled to T e = the axion-induced absorption event number = molec h v m R ab (n days 6) n the worst case R ab = z/ A for an acquisition time of days... is it possible to increase the density?