The Time Projection method is an ideal candidate to track low energy release particles. Large volumes can be readout by means of a moderate number of channels providing a complete 3D reconstruction of the charged tracks within the sensitive volume. It allows the measurement not only of the total released energy but also of the energy release density along the tracks that can be very useful for particle identification and to solve the head-tail ambiguity of the tracks. Moreover, gas represents a very interesting target to study Dark Matter interactions. In gas, nuclear recoils can travel enough to give rise to tracks long enough to be acquired and reconstructed

Baracchini, E.

Cavoto, G.

Di Marco, E.

Mancini, C.

Marafini, M.

Mazzitelli, G.

Pinci, D.

Renga, F.

Tomassini, S.

English

arXiv

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MPGD Optical Read Out for Directional Dark Matter Search

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ISTITUTO NAZIONALE DI FISICA NUCLEAREINFN-19/1/LNF11 January 2019MPGD Optical Read Out for Directional Dark Matter SearchG. Mazzitelli1, E. Baracchini1,2, G. Cavoto2,3, E. Di Marco2,M. Marafini2,4, C. Mancini2, D. Pinci2, F. Renga2 and S. Tomassini11 INFN, Laboratori Nazionali di Frascati, Frascati (RM), Italy2 INFN, Sezione di Roma, Italy3 Sapienza Università di Roma, Dipartimento di Fisica, Italy4 Museo Storico della Fisica e Centro Studi e Ricerche E.Fermi, ItalyAbstractThe Time Projection method is an ideal candidate to track low energy release particles.Large volumes can be readout by means of a moderate number of channels providing acomplete 3D reconstruction of the charged tracks within the sensitive volume. It allowsthe measurement not only of the total released energy but also of the energy release densityalong the tracks that can be very useful for particle identification and to solve the head-tailambiguity of the tracks. Moreover, gas represents a very interesting target to study DarkMatter interactions. In gas, nuclear recoils can travel enough to give rise to tracks longenough to be acquired and reconstructed.PACS: 29.40.Gx, 29.40.Cs, 29.90.+r, 95.35.+d, 26.65.+tPublished byLaboratori Nazionali di FrascatiConference Record of 2018 IEEE NSS/MIC/RTSDpresented by G.Mazzitelli1 IntroductionThe use of large Time projection Chamber (TPC) in High Energy Physics (HEP) havevarious application and feature. Although with very small efficiency, those detectors offeramong the best energy resolution and particle identification capability (PID), as well asa very good tracking and spacial resolution. This is pushing an international community,called CYGNUS, to study the application of such technology to the search of directionalDark Matter (DM) and the detection of neutrinos coming form the Sun.In Italy the National Institute for Nuclear Physics (INFN) is promoting the Phase-0for the construction of 1 m3 demonstrator based on Micro Gas Pattern Detector (MGPD),namely a triple large Gas Electron Multiplier (GEM), optically read by means of a sCMOSlow noise and high granularity sensor.During the Phase-0 many prototypes, based on triple GEM optical readout, havebeen tested showing promising results to access the Phase-1 that will start in 2020 withthe construction of the 1 m3 demonstrator to be hosted in the National Laboratory of GranSasso (LNGS). A Phase-2 is foreseen to realize a 30-100 m3 detector, as a brick of aworld distributed observatory for DM and neutrinos within the CYGNUS internationalcollaboration.Hence, The purpose of the Phase-0 is to demonstrate the validity and capability oflarge electron TCP at atmospheric pressure (He based) equipped with high ganularity andsensitivity MGPD optilal read outMGPD optical readout is relay changing the paradigm:• optical sensors offer higher granularity with respect to electron sensitive devices;• optical coupling allows to keep sensor out of the sensitive volume reducing theinterference with high voltage operation and lowering the gas contamination;• the use of suitable lens allow to acquire large surfaces with small sensors;Moreover, in last years, optical sensors had a huge development and are able to providelarger granularity along with very low noise level and high sensitivity. Recently meanytest has been done with different prototype (NITEC [1], ORANGE [2], [3], [6], [4],LEMOn [5], [7], [8]) at electron beam test facility, neutron beam and with various ra-dioactive sources.2 Recent LEMOn ResultsThe LEMOn prototype is completely realize in 3D printing, (Fig. 1) and the heart consistsof a 7 liter active drift volume surrounded by an elliptical field cage (200×200×240 mm3)and a 200×240 mm2 rectangular triple GEM structure, with two 2 mm high transfer gapsamong them. An ORCA-Flash 4.0 camera was placed 52 cm away from the last GEMto acquire images of light produced in GEM channels. This is based on a CMOS sensor2with a high granularity (2048×2048 pixels), very low noise (around two photons perpixel), high sensitivity (70% of QE @ 600 nm) and linearity. This camera is instrumentedwith a Schneider lens (f/0.95-25 mm) and each pixel was looking at an effective area of125×125m2.Figure 1: Engineering sketch of the tested prototypeThe prototype has been tested with the 450 MeV electron of the Frascati Beam Testfacility [9] with a maximum drift field of 0.6 kV/cm and 60:40 HeCF4 gas mixture:• an intrinsic XY resolution of about 70 µm, degraded of 10µm/cm as function of thedrift distance• an energy resolution of 20-30% in the keV energy range• a drift diffusion of about 130 µm/sqrt(cm)• a longitudinal (Z) resolution exploiting the XY diffusion of 7%• a longitudinal (Z) resolution exploiting the PMT light diffusion of 10%The slop of 10µm/cm (Fig. 2) is strongly determined by the drift field and is lim-ited in LEMOn by High Voltage connectors and the power supply. The new prototype,LIME, under construction at the National Laboratory of Frascati will be able to provide1kV/cm over 50 cm of drift length. LIME will be also equipped with a 33×33 cm GEMamplification stage constituting one of the 18 modules of the Phase-1 1 m3 of CYGNOdemonstrator.The energy resolution (Fig. 3) is obtained by cutting the 450 MeV single electrontracks in slides of given length and assuming an energy lost per sub-track length is 0.24keV/mm as predicted by means of Garfield simulation for 60:40 HeCF4 gas mixture.3Figure 2: XY resolution vs depths (Z) obtained with a drift field to 0.6kV/cmFigure 3: energy resolution @ depths (Z), in the few keV region a relative resolution of20-30% is achievedThe diffusion (Fig. 4) is well in agreement with the expected value obtained withGarfiled simulation from where is also expected a better behaviour ad higher drift field upto 2kV/cm. In Fig. 4, data @ 0.45 kV/cm were collected with a different (not optimized)field applied on the triple GEM system, the intercept at zero of 400µm is typical for threeGEM stack.Transverse (Fig. 5) and longitudinal (Fig. 6) diffusion gives precision order 10%.The exploitation of this characteristic could be very useful for the fiducialization of thedetector: anode (where the GEM are located) and cathode are the most radioactive area4Figure 4: electrons drift diffusion in HeCF4 for 0.30, 0.45, 0.60 kV/cmFigure 5: measured transverse diffusion and relative error σZ ' 12%in the detector, and a possible solution to avoid this noise is to trash the events close tothem. A second method is to use minority carrier produced with negative ion by meansof the introduction of SF6 or CS2 in the gas mixture. This solution, much more accurateand sophisticated see the support of an European Commission grant with the INITIUMproject and will be investigated in Phase-1.Moreover, a campaign of measurements with 55Fe has been started to study detec-tion capability, energy resolution and efficiency at keV energy.In order to investigate the detection capability different clustering methods are under5Figure 6: measured longitudinal diffusion and relative error σZ ' 7%study. The clustering method is fundamental to determinate the energy threshold anddiscriminate between 55Fe photons and background due to cosmic rays and environmentalradioactivity that at see level for a 7 liters active volume start to be a significant noise. Inthe following the preliminary data obtained with the Nearest Neighbor Clustering (NNC)method are shown (Fig. 7).Figure 7: Example of 55Fe cluster identification obtained with NNC clustering methodol-ogyThe NCC method is CPU demanding and is not optimized at all on the possibleshape of the track, is a zero order method used in parallel with HDBSCAN and MachineLearning approach that are under implementation to improve the energy threshold andPID.Referring to Fig. 8, the energy spectra fit provides 0.12 ph/eV. Assuming a pedestaljitters based on average of the run within 55Fe source in the detector of 5 σ (75 photos),an energy threshold of 625 eV with a resolution of about 33% (2 keV) in agreement withexpected and measured value at the Frascati BTF.6Figure 8: 55Fe energy spectrum obtained with NNC method obtained with GEM voltageof 460 V3 Nuclear RecoilLast but not least, some preliminary tests have been performed with AmBe neutron sourcead at the FNG ENEA neutron Facility [10]. A deep analysis of the data is ongoing,preliminary results show the very good capability of TPC-MGPD optical readout detectorto identify particles.Figure 9: (left) example of row image collected with AmBe and 55Fe sources; (left/box)a zoom of millimeters high ionizing recoil (about 105 keV and 17 keV); (right) clus-ter reconstruction and Particle identification - 55Fe Compton electrons and radioactivitybackground (yellow), p (green), α (red) - by means of average photons detected per pixel.The AmBe neutron source was located outside the detector on the right side of the picture;the orange elliptic rings represents the location of the field cage plastic ringsIn figure 9 a typical image collected with an AmBe neutron source is shown. TheAmBe source was located at the right side of the image together with an 55Fe source7located inside the detector in the opposite upper side. The AmBe source was shieldedby means lead breaks in order to strongly reduce the associated emission of gamma andMeV electron and enhance the neutron interactions. In the right side of the figure theNCC cluster restriction is shown, where the different color, 55Fe Compton electrons andradioactivity background (yellow), p (green), α (red), are identifying particles by meansof average photons detected per pixel (less then 10 ph/pixel; between 10 and 15 ph/pixel;above 15 ph/pixel). The long nuclear recoil in the center of the figure (red) release aboutfour time the energy of the particle (green) that candidate the first one to be an α and thesecond to be a proton produced by the interaction of neutron with the ASAP field cagering, the yellow dots are due to 55Fe photon interactions, cosmic rays and radioactivebackground. In the box two zoom of a millimetric and nuclear recoil of about 100 keVand 20 KeV are shown.Figure 10: Nuclear Recoil in LEMOn (125 µm resolution) produced by a neutron of FNGENEA source, head-tail and the brag pick are clearly visibleIn figure 10 a typical long nuclear recoil (namely a proton from the ASAP box)is shown where 550 ph/mm are released. Exploiting the results obtained with 55Fe cal-ibration and GEM voltage of 440 V 0.06 ph/eV are expected, that means an energy de-position of 9.2 keV/mm. These results are consistent with the expectation of detectinghighly ionizing millimeter traces with sufficient resolution, as required for a directionalDM detector.4 ConclusionThe work done during 2018 for the Phase-0 of the CYGNO project is confirming thepotentiality of large TCP based equipped with an high granularity and sensitivity MPGDoptical readout. Spacial end energy resolution, improvable with a stronger drift field, as8well as the capability to identify nuclear recoil to avoid background looks very promising.Phase-0 is foreseen to be completed in 2019 with the constriction of LIME prototype, amodule completely equivalent to 1/18 of the CYGNO 1 m3 demonstrator.AcknowledgmentA special thanks to M. Chiti and A. Esposito of the Servizio Radioprotezione LNF-INFNand to A. Orlandi, M. Iannarelli and E. Paoletti of the Servizio progettazione rivelatoriLNF-INFN. Morever, we are grateful to the BTF staff for the excellent and stable beamand the Frascati Enea FNG group, M. Pillon and S. Fiore, for their inexhaustible support.References[1] Baracchini, E. and Cavoto, G. and Mazzitelli, G. and Murtas, F. and Renga, F.and Tomassini, S.”, Negative Ion Time Projection Chamber operation with SF6at nearly atmospheric pressure, JINST (2018), 13,P04022, doi: 10.1088/1748-0221/13/04/P04022[2] M. Marafini et al., “ORANGE: A high sensitivity particle tracker basedon optically read out GEM,” Nucl. Instrum. Meth. A 845, 285 (2017).doi:10.1016/j.nima.2016.04.014[3] M. Marafini et al., “High granularity tracker based on a Triple-GEM opticallyread by a CMOS-based camera,” JINST 10 (2015) 12, P12010 doi:10.1088/1748-0221/10/12/P12010.[4] M. Marafini, V. Patera, D. Pinci, A. Sarti, A. Sciubba and E. Spiriti, “Optical readoutof a triple-GEM detector by means of a CMOS sensor,” Nucl. Instrum. Meth. A 824,562 (2016). doi:10.1016/j.nima.2015.11.058[5] D. Pinci et al., “Cygnus: development of a high resolution TPC for rare events,” PoSEPS -HEP2017 (2017) 077. doi:10.22323/1.314.0077[6] V. C. Antochi et al., “Combined readout of a triple-GEM detector,” JINST 13(2018) no.05, P05001 doi:10.1088/1748-0221/13/05/P05001 [arXiv:1803.06860[physics.ins-det]].[7] Mazzitelli, G. and E. Baracchini and M. Marafini and G.Cavoto and C. Voena andF. Renga and E. Di Marco and D. Pinci and S. Tomassini and C. V. Antiochi, A highresolution TPC based on GEM optical readout, Under pubblication in IEEE NuclearScience Symposuim Medical ImagingConference, 2017[8] D. Pinci, E. Baracchini, G. Cavoto, E. Di Marco, M. Marafini, G. Mazzitelli, F.Renga, S. Tomassini, C. Voena, High resolution TPC based on optically readout9GEM, Nuclear Instruments and Methods in Physics Research Section A: Accel-erators, Spectrometers, Detectors and Associated Equipment, 2018, ISSN 0168-9002,https://doi.org/10.1016/j.nima.2018.11.085.[9] G. Mazzitelli et al, “ Commissioning of the DAΦNE beam test facility” Nucl. In-strum. Meth. A 515 (2003) 524542.[10] Martone, M., Angelone, M., Pillon, M., The 14 MeV Frascati neutron generator,Journal of Nuclear Materials 212-215(PART B), pp. 1661-1664 (1994)10

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