In this paper I will briefly introduce the idea of using Carbon Nanotubes
(CNT) as target for the detection of low mass WIMPs with the additional
information of directionality. I will also present the experimental efforts of
developing a Time Projection Chamber with a CNT target inside and the results
of a test beam at the Beam Test Facility of INFN-LNF.Comment: 3 figures, IFAE2017 poster session proceeding

Antochi, V. C.

Baracchini, E.

Cavoto, G.

Di Marco, E.

Mazzitelli, G.

Pinci, D.

Polosa, A. D.

Renga, F.

Voena, C.

English

arXiv

In this paper we will briefly introduce the idea of using Carbon Nanotubes (CNT) as target for the detection of low mass WIMPs with the additional information of directionality. We will also present the experimental efforts of developing a Time Projection Chamber with a CNT target inside and the results of a test beam at the Beam Test Facility of INFN-LNF

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DOI 10.1393/ncc/i2018-18070-3Colloquia: IFAE 2017IL NUOVO CIMENTO 41 C (2018) 70Carbon nanotubes as target for directional detection of lightWIMPV. C. Antochi(1)(2), E. Baracchini(3), G. Cavoto(1)(2), E. Di Marco(2),G. Mazzitelli(3), D. Pinci(2), A. D. Polosa(1)(2), F. Renga(2) and C. Voena(2)(1) Dipartimento di Fisica, Università di Roma - Roma, Italy(2) INFN, Sezione di Roma - Roma, Italy(3) INFN, Laboratori Nazionali di Frascati - Frascati (RM), Italyreceived 21 April 2018Summary. — In this paper we will briefly introduce the idea of using CarbonNanotubes (CNT) as target for the detection of low mass WIMPs with the addi-tional information of directionality. We will also present the experimental efforts ofdeveloping a Time Projection Chamber with a CNT target inside and the results ofa test beam at the Beam Test Facility of INFN-LNF.1. – The ideaAs the Solar System moves through the Galaxy, if we assume a dark matter halo,as astrophysical evidence suggests, made of cold weakly interacting massive particles(WIMPs), we expect a wind of these particles coming from the direction towards theSun is moving, the Cygnus constellation. The Earth’s revolution around the Sun wouldalso be expecting to have a consistent effect of modulating a possible signal of darkmatter, as seen by Dama/LIBRA experiment at INFN Gran Sasso, Italy [1]. So, in orderto assure the nature of possible interactions due to WIMPs, a directional information ofthese events is needed.In order to solve the problem of directional detection of dark matter, we explore thepossibility of using a large array of aligned Carbon Nanotubes (CNTs) open at one end astarget inside a Time Projection Chamber (TPC). The concept is that a WIMP interactswith a carbon nucleus inside a CNT elastically and then the recoiling nucleus, if therecoil direction is close to the CNT axis, has a good chance to be channeled towards theopen cap and inside the gaseous TPC [2-4].The ideal detector would be a TPC with a CNT wall inside with the axes of thenanotubes directed towards Cygnus at all times and a drift field perpendicular to theCNT axes. The objective for this kind of detector is to be able to observe recoil eventsdown to a threshold of 1 keV. This way, assuming no signal events and rejection of allbackground, in 3 years of exposure time and a 10 kg CNT target the detector would reacha cross section sensitivity of 10−44 cm2 for WIMPs of mass 1–2 GeV.Creative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0) 12 V. C. ANTOCHI et al.(a) (b)Fig. 1. – Simulation in ANSYS Maxwell of the TPC with the target of semiconductive Sisubstrate only (a), and Si + a sheet of conductive graphite to resemble the CNTs (b). The driftfield (intensity indicated by colour gradient and direction by arrows) in (a) shows very smalldistortion effects while in (b) it is very distorted by the conductive graphite.2. – The experimental set-upA prototype was developed in order to study the CNT characteristics and response.This prototype consisted in a 3D-printed field cage with a 5 cm drift gap, with silverrings spaced 1 cm apart in order to mantain a uniform drift field. Triple thin GEMs [5],3 cm×3 cm wide, were used as amplification and a TimePix chip [6] was used as read-outto collect the charge from the GEMs.The CNT target used was a 2 cm × 2 cm silicon substrate with 200 μm thick multi-wall carbon nanotube forest on one side, grown perpendicularly. The target was placedvertically in a minimal 3D-printed plastic support inside the drift gap.The first tests with the CNT target were performed at the Beam Test Facility(BTF) [7] at LNF. The TPC was placed inside an inox steel vacuum vessel whith athin berillium window for the beam, the vessel was set on the micrometric table of theBTF. This way beam height could be easily controlled remotely. The vessel was thenfilled with different gas mixtures for different performance tests, but the main resultsFig. 2. – Images of the projection of the beam passing through the field cage at different heightsfrom the base. The beam is straight at 1 cm and 2 cm from the base of the drift gap, but whengetting closer to the CNT target it shows distortions of the drift field (3, 4 and 5 cm). Thedifferent colours, red to blue, are proportional to the height of the beam and measure the timedifference between the time of arrival and the LINAC’s t0.CARBON NANOTUBES AS TARGET FOR DIRECTIONAL DETECTION OF LIGHT WIMP 3were achieved with the Ar:CO2:CF4 (40:55:5) and pure SF6 at low pressures.The BTF beam used was 450 MeV electron beam with the possibility to modify itsintensity and its dimensions, and to monitor it directly with a MediPix chip.3. – First results3.1. Drift field simulation. – Before the experimental tests, we performed simulationswith the ANSYS Maxwell software of the entire geometry of the TPC in order to verify theuniformity of the drift field and study possible distortions introduced by the CNT target.The CNT target, allegedly semiconductive material grown onto a silicon (semiconductive)base, was simulated first as a semiconductor, then as a conductive graphite sheet onto asemiconductive silicon base.In the first case the simulation showed very little distortion of the drift field closeto the edges of the semiconductive target, but in the second case the graphite distortedheavily the drift field (see fig. 1).3.2. Experimental results. – At the BTF the configuration with the vertical CNTtarget was tested. The electron beam was sent at various heights through the drift gapin order to study the response of the CNTs when the beam passed close to them. TheTimePix chip recorded the projection of the ionization produced by the beam in theTPC. Below the target the beam projection was recorded straight wihtout any distortioneffect from the CNTs, but going higher and closer to the target, strong distortion effectswere observed as seen in fig. 2, comparable to those seen in the simulation with theconductive graphite sheet. The experimental behaveour of the CNT target, in a driftfield of ∼0.8 kV/cm in both Ar:CO2:CF4 and SF6, resembled more a conductor than asemiconductor.New configurations are being studied in order to minimise the field distortion andnew tests will be performed at the BTF in July 2017.REFERENCES[1] Bernabei R., Belli P., Cappella F. et al., Eur. Phys. J. C, 73 (2013) 2648.[2] Cavoto G., Cirillo E. N. M., Cocina F. et al., Eur. Phys. J. C, 76 (2016) 349.[3] Capparelli L. M., Cavoto G., Mazzilli D. and Polosa A. D., Phys. Dark Univ., 9-10(2015) 24; 11 (2016) 79(E), arXiv:1412.8213 [physics.ins-det].[4] Cavoto G., Luchetta F. and Polosa A. D., arXiv:1706.02487 [hep-ph].[5] Sauli F., Nucl. Instrum. Methods A, 805 (2016) 2.[6] George S. P., Murtas F., Alozy J., Curioni A., Rosenfeld A. B. and Silari M.,JINST, 10 (2015) P11003.[7] Ghigo A., Mazzitelli G., Sannibale F., Valente P. and Vignola G., Nucl. Instrum.Methods A, 515 (2003) 524.

Carbon nanotubes as target for directional detection of light WIMP

Carbon nanotubes as target for directional detection of light WIMP

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