Barium daughter tagging using single molecule ﬂuorescence imaging Austin D McDonald, Fernanda Psihas For the NEXT Collaboration Currently, the only known method to determine the Majorana nature of the neutrino is a direct observation of neutrinoless double beta decay. The NEXT experiment employs a series of high-pressure xenon gas TCPs with energy resolution of ~0.7% FWHM at the Q value. The gas phase allows for accurate track reconstruc- tion. Sensitivity to the topology allows for discrimination between back- ground and signal. The theoretical spectrum for the two neutri- no and no neutrino spectrums. 2D diagram of the NEXT detector. Example of NEXT-new data events. The difference between signal and background are the large depositions at the end of electron tracks (two for signal). N N P P e – e – N N P P e – e – ν– ν– Ton-scale neutrinoless double beta decay (0νββ) experiments expect only a few events per year. Radioactive backgrounds in the form of alpha, beta, and gamma decays can mimic the double electron signal. Barium is not produced by any of the backgrounds to ββ decay. Edan Bainglass, Frank Foss, Ben Jones, David Nygren, Pawan Thapa Exploiting a bio-chemistry technique to enhance sensitivity to ββ decay !"#$%&'&"() !"#$%&'()*+,-)- *%+(#,-.$/'&"() ./01 ./01 We employ ﬂuorescent dyes to do Single Molecule Fluorescent Imaging (SMFI). The dye molecule con- sists of a ﬂuorophore, which naturally de-excites via ﬂuoresence, and a receptor, which quenches the ﬂuorescence. The dye molecules are non-ﬂuorescent in the ab- sence of ions. When bound to an ion, the energy levels for ﬂuorescent de-excitation become avail- able. The receptor may be ion speciﬁc and can be coupled to different dyes. Development of a dye for use in high pressure xenon gas is currently underway, in collabora- tion with the department of chemistry at UTA. This custom dye is based on PSMA, a molecule know to have high sensitivity to Ba++, and a good candidate for use in xenon gas. Our SMFI implementation may also allow for super-resolution reconstruction, since it local- izes molecule positions to within a few nm. FLUOROPHORE RECEPTOR O O O Cl O Cl HO CH3 N N CO2H CO2H CO2H CO2H FLUOROPHORE RECEPTOR O O O Cl CH3 O O O N N O O O O O O Cl HO Baa++ Total Internal Reﬂection Fluorescence (TIRF) utilizes evanescent wave excitation to excite the molecules that are a few wavelengths away from the surface. Left: Dye molecule used in our ﬁrst demonstration of single molecule barium sensitivity. Top: Un-chelated molecule (not ﬂuorescent). Bottom: Molecule chelated to Ba++ ion (ﬂuorescent). Right: Single molecule imaging setup at UTA. The 498 nm excitation light is delivered by a colimated laser, focused on the objective’s backfocal plane. The ﬂuores- cence emmision is collected by the CCD. The objective is used to convert the focused laser light into parallel rays at the critical angle. Single barium di-cation sensitivity has been achieved utilizing the method of Single Molecule Fluorescent Imaging (SMFI) described above. Solutions are made with a speciﬁc pH, and diluted to small ion concentration. Trace ions are then removed with a chelation agent. The molecules are immoblized for imaging by trap- ping them in a matrix. Typical TIRF image, showing single molecules located at various depths in the sample. Pixel sixe is 160 nm. The dye’s ﬂuorescence is diffraction limited, this allows for super-resolution reconstruction which localizes the molecule to ~2nm . TIRF was used to image near the surface and minimize ﬂuorescence from deep in the sample by means of evanescent wave excitation. Single barium ion ﬂuorescent tra- jectory, demonstrating the abrupt single step photobleaching. The analysis of barium rich vs no barium samples showed a signal over back- ground at the 12.9 sigma level. Single molecules are identiﬁed by the characteristic photobleaching process, where the molecule transitions to a non-ﬂuorescent state in one step. First demonstration of single Ba++ i