- Email: [email protected]
SIMPLE-icity in Direct Dark Matter Searches
Nuclear Physics B (Proc. Suppl.) 173 (2007) 129–132 www.elsevierphysics.com
SIMPLE-icity in Direct Dark Matter Searches F. Giuliania∗ , T Morlata , A.R. Ramosa b , TA Girarda , M. Felizardo da Costab c , J.G. Marquesb a , R.C. Martinsc , H.S. Mileyd , D. Limagnee and G. Waysandef a
Centro de F´ısica Nuclear, Universidade de Lisboa, 1649–003 Lisbon, Portugal
b
Instituto Tecnol´ ogico e Nuclear, Estrada Nacional 10, 2686-953 Sacav´em, Portugal
c
Department of Electronics, Instituto Superior T´ecnico, Av. Rovisco Pais 1, 1049–001 Lisbon, Portugal
d e
Pacific Northwest National Laboratory, Richland, WA 99352 USA
INSP ( UMR CNRS 7588) Universit´es Paris 6 & 7, 75015 Paris, France
f
Laboratoire Souterrain a` Bas Bruit (Universit´e de Nice-Sophia Antipolis), 84400 Rustrel–Pays d’Apt, France Recent activity in the SIMPLE dark matter search program is described, to include the recent development of a ”heavy” detector for application in spin-independent searches.
SIMPLE [1] is the European WIMP search based on Superheated Droplet Detectors (SDDs). An SDD consists of an emulsion of metastable liquid droplets in an organic gel, each of which operates on the same principle of the bubble chamber. The SDD technique has been demonstrated to yield competitive restrictions with very low exposure: with only 0.42 and 2 kgd respectively, the two SDD-based WIMP searches, SIMPLE and its North-American counterpart PICASSO [2] obtained constraints comparable to the 44.9 kgy NAIAD [3]. The reason for this competitiveness is the insensitivity of the SDDs to the majority of the backgrounds which plagued the more traditional search activities, which allows competitive results without using sophisticated background discrimination techniques to go below the level of the intrinsic radioimpurities of the detector composition. The SDD background insensitivity derives from the thermodynamic response of the device to incident radiation [4]. The critical energy (Ec (T, P )) necessary to nucleate a bubble needs to be deposited within a path length of the order
∗ [email protected]
0920-5632/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2007.08.036
of the critical vapor embryo radius (rc (T, P )), i.e.
arc
Ec = 0
dE dE dx ≈ arc (Ethr ) dx dx
(1)
where Ethr (T, P ) is the energy threshold, a is the Harper parameter for the refrigerant, and typically arc 0.1 − 1 μm. This sets a temperature and pressure dependent dE/dx threshold of Ec /(arc ) which can be kept high while Ethr (T, P ) is low. Recoil energy spectra can be obtained by varying the operating temperature during the measurement, as has been done in calibrating the SDD response to α’s [5] and neutrons [6]. For the refrigerants currently employed, these calibrations confirm the calculated requirement of a dE/dx 150 keV/micron for bubble nucleation, eliminating the contributions of minimally ionizing particles. The device itself is of simple construction: for SIMPLE, this is an emulsion with 1-3% concentration of refrigerant, instrumented with a simple microphone which records the nucleation events. A measurement consists of a mosaic of 1 liter devices kept at the selected (T, P) using a pccontrolled water bath which also acts as radiation
130
F. Giuliani et al. / Nuclear Physics B (Proc. Suppl.) 173 (2007) 129–132
shield; the same pc supports a Labview-based DAQ for up to 32 detectors (∼20 ke/setup). The advantage of the SDD technique is a device which can operate continuously up to 40 days without recompression, unlike a bubble chamber which must be recompressed after each nucleation event. The advantage of the gel-free bubble chamber approach is an ability to easily instrument a large active mass, which COUPP is pursuing with some considerable success in extending the metastability lifetime of the refrigerant [7]. The organic gel of SIMPLE’s SDD is composed of water, gelatine, PVP and glycerine, all of which are also employed in pharmaceutical/food productions, making them readily available with a high degree of purity at relatively low cost (∼ 100 e/liter module, including instrumentation). The gel acts as a built-in neutron and α shield, as it moderates neutrons down to below the detection threshold. Due to the high stopping power of α’s in the gel, the main α background contribution arises from impurities in the gel itself. Chemical purification techniques already allow reduction of the actinide concentrations in the gel below 5 x 10−5 pC/g, resulting in an intrinsic α background of better than 0.5 cts/kgd. In fact, thanks to the peak stopping power of 200 keV/μm at 700 keV, at 2 atm below ∼8 o C α’s can only be detected through nuclear recoils. The main beta source of the SDD is the 14 C contained in the gel and freon, which beta decays with Q = 156.5 keV, insufficient for yielding a signal either directly, via nuclear scattering or other reactions like 35 Cl(β − ,ν)35 S. As a consequence, the β’s from 14 C and tritium are not a concern. SDDs are known to be generally insensitive to b γ’s for temperatures such that s ≡ TTc−T −Tb < 0.5 where Tc is the critical temperature and Tb the boiling temperature at the operating pressure [8]; SIMPLE usually operates at s = 0.3. The main background of SIMPLE is traditionally due to microleaks of the nitrogen (used for pressurizing the detectors at 2 atm) into the water bath used to both regulate the SDD operating temperature and to shield neutrons, which are recorded by the piezoelectric sensor and are indistinguishable from a nucleation event. While the majority of these are eliminated by coinci-
dence between the detector microphone and the hydrophone, this problem is being solved through capping improvements: a preliminary test of the new caps showed no microleaks in three weeks, yielding a 90% C.L. upper limit of ∼0.11 microleaks/detector/day, corresponding to ∼11 microleaks/kgd for a 10 g/detector loading, versus the previous 0.5-1 microleaks/detector/day. The possibility of discriminating the microleaks through pulse shape discrimination is also being explored [9]. The bubble nucleation process is a four-stage process [10], the last stage of which generally provides the recorded signal. The third stage of the process however depends on the nature of the incident radiation, but is significantly faster. The feasibility of measuring this stage as a discrimination technique using ultrasound technology is being explored. The choice of refrigerant depends on the search objective. The WIMP-nucleus zero momentum transfer cross section σA is the sum of a spinindependent (SI) and a spin-dependent (SD) contributions, σA = σSI + σSD , with
σSI = π4 G2F μ2A [(gp Z + gn N )2 ] 2 2 2 J+1 σSD = 32 π GF μA [(ap Sp + an Sn ) J ]
(2)
where GF is the Fermi constant, gp,n (ap,n ) are the SI (SD) WIMP couplings with the proton (neutron) respectively, Sp,n are the expectation values of the proton (neutron) group’s spin, μA is the WIMP-nuclide reduced mass, and J is the total nuclear spin. Eq. (2) shows that the SI channel basically scales as A2 , while the SD channel depends on the spins of the proton and the neutron group. Thus spin-dependent investigations generally favor light refrigerant nuclei with spin, whereas spin-independent investigations require heavy nuclei. The current SD limits on a 50 GeV mass WIMP of the traditional C2 ClF5 -based SIMPLE are shown in Fig. 1 in comparison with those of PICASSO and several leading experiments [11,3,12,13]. The C2 ClF5 -based search is tailored to detect WIMPs through the SD channel because the involved nuclei are light but with significant
F. Giuliani et al. / Nuclear Physics B (Proc. Suppl.) 173 (2007) 129–132
Figure 1. Current results for MW = 50 GeV/c2 from a C2 ClF5 run of the SIMPLE experiment (SIMPLE ”light”), along with PICASSO and various leading search experiments. The dashed lines are projections for C2 ClF5 and CF3 I SDDs (see text).
proton group spin. This is clearly seen by comparing the significant SD impact of the current SIMPLE ”light” results in Fig. 1 with its poor SD cross section restrictions observed in Fig. 2. Fig. 1 also shows (dotted lines) projections for a 3 kgd SIMPLE ”light” experiment currently in preparation, assuming the current SIMPLE radiation background of ≤1 evt/kgd. Projections are for both the case of 3 undiscriminated events (outer set), consistent with the assumed background, and that of no events after discrimination (inner set). In either case, the next SIMPLE ”light” results should supersede NAIAD in reducing the CDMS-allowed parameter space. The following phase of SIMPLE ”light”, projected for 2007, is a 30-100 kgd exposure. The C2 ClF5 refrigerant, being a chlorofluorocarbon, is environmentally discouraged by European regulations, eliminating most suppliers of the material. Most recently we have prototyped
131
a new SDD emulsion using C4 F10 . This is the same refrigerant as used by PICASSO, but employs SIMPLE’s gel without the use of heavy salts for density-matching and a priori yields an intrinsic background of < 0.5 evts/kgd after purification. This will be gradually phased into use as the current C2 ClF5 supply is depleted. The insensitivity of the SDD can be exploited in spin-independent measurements using heavy refrigerants. Although several readily available candidates exist (eg. CF3 Br, CF3 I, XeF6 ...), the most obvious difficulty with such a ”heavy” SDD lies in its fabrication, since current devices rely on density matching of the gel (ρ ∼ 1 − 3g/cm3 ) with the refrigerant in its liquid phase in order to produce a homogeneous suspension of droplets. SIMPLE ”heavy” [14] is based on a recently prototyped superheated emulsion of CF3 I in the same gel of SIMPLE ”light”, with agarose as an additive to modify the viscosity and shift upwards the sol-gel transition temperature, potentially enabling twice the SDD continuous operation lifetime [15]. Hence the shielding and background considerations qualitatively also apply. A prototype measurement is scheduled for later this year, with a 3-8 kgd exposure planned for 2007. The potential impact of a CF3 I-based search in the SI channel is shown in Fig. 2, where two 34 kgd projections assuming a 1 evt/kgd background are shown in comparison with the current, equal exposure, CDMS results [11]. The first projection assumes that all expected 34 kgd events are observed, but not identified, so that the upper limit on the WIMP counts is given by the error bar of the ”measured” rate. The second, instead, assumes perfect discrimination, so that all the background events can be rejected. This is close to, but not better than, the current CDMS results in which all events are identified as background. The difference between the two, despite the equal exposures and that 127 I has a higher σSI than Ge, results from CF3 I containing a significant fraction of lighter elements. This is not a disadvantage, since both 19 F and 127 I are known spin-dependent sensitive nuclei, and the former has a better form factor due to the generally lower momentum transfer. A CF3 I search will hence have also a significant impact in this
132
F. Giuliani et al. / Nuclear Physics B (Proc. Suppl.) 173 (2007) 129–132
Cavaillou of the Laboratoire Souterrain a` Bas Bruit (Universit´e de Nice-Sophia Antipolis). This work has been supported by the grant no. POCTI/FIS/57834/2004 of the Portuguese Funda¸c˜ao para a Ciˆencia e a Tecnolog´ıa cofinanced by FEDER. REFERENCES
Figure 2. CF3 I spin-independent projections for 34 kgd exposure and a) 34 undiscriminated events (dotted) and b) all events removed by discrimination (dashed). The current C2 ClF5 SI result is in the top.
sector, as projected in Fig. 1, again for 34 kgd exposure, 1 evt/kgd background and two different sets of 19 F spin matrix elements, from Pacheco [16] and Divari [17]. Summarizing, the SDD-based searches have demonstrated the ability of this technique to reduce (but not eliminate) the concerns regarding backgrounds typical of dark matter searches. The two part construction (gel + refrigerant) permits a low background generic gel matrix with interchangeable targets, which allows a tuning of the device with respect to both its sensitivity to SI- or SD-WIMP interactions, and its operating conditions to achieve this sensitivity. In the SD sector, the at least one order of magnitude less exposure required to achieve the same sensitivities as the more traditional search activities suggests a capacity of the SDD technique to rapidly improve on the limits so far achieved by either NAIAD or DAMA/NaI. The simplicity of the technique is similarly applicable to the SI sector. We thank M. Auguste, D. Boyer and A.
1. T.A. Girard, F. Giuliani, T. Morlat, et al. Phys. Lett. B, 621:233, 2005. 2. M. Barnab´e Heider, M. DiMarco, P. Doane, et al. Phys. Lett. B, 624:186, 2005. 3. G.J. Alner, H.M. Ara´ ujo, G.J. Arnison, et al. Phys. Lett. B, 616:17, 2005. 4. F. Seitz. Physics of Fluids, 1:2, 1958. 5. J.I. Collar, J. Puibasset, TA Girard, et al. Phys. Rev. Lett., 85:3083, 2000. 6. F. Giuliani, C. Oliveira, J. I. Collar, et al. Nucl. Instr. & Meth. A, 526:348, 2004. 7. L. Bond, J. I. Collar, J. Ely, et al. Nucl. Phys. B (Proc. Suppl.), 138:68, 2005. 8. F. d’Errico. Nucl. Instr. & Meth. B, 184:229, 2001. 9. M. Felizardo, R.C. Martins, A.R. Ramos, et al. In IEEE, Instrumentation and Measurement Technology Conference, volume 2, page 1551. IEEE Instrumentation and Measurement Society, May 2005. 10. Yu. N. Martynyuk and N. S. Smirnova. Sov. Phys. Acoust, 37:376, 1991. 11. D. S. Akerib, M. J. Attisha, C. N. Bailey, et al. Phys. Rev. Lett., 96:011302, 2006. 12. A. Benoit, L. Berg´e, A. Broniatowski, et al. Phys. Lett. B, 545:43, 2002. 13. G. J. Alner, H. Araujo, G. J. Arnison, et al. Astrop. Phys., 23:444, 2005. 14. F. Giuliani et al. Preprint physics/0511158. 15. T. Morlat, D. Limagne, G. Waysand, and J.I. Collar. Nucl. Instr. & Meth. A, 560:339, 2006. 16. A. F. Pacheco and D. Strottman. Phys. Rev. D, 40:2131, 1989. 17. P. C. Divari, T. S. Kosmas, J. D. Vergados, and L. D. Skouras. Phys. Rev. C, 61:054612, 2000.
SIMPLE-icity in Direct Dark Matter Searches F. Giuliania∗ , T Morlata , A.R. Ramosa b , TA Girarda , M. Felizardo da Costab c , J.G. Marquesb a , R.C. Martinsc , H.S. Mileyd , D. Limagnee and G. Waysandef a
Centro de F´ısica Nuclear, Universidade de Lisboa, 1649–003 Lisbon, Portugal
b
Instituto Tecnol´ ogico e Nuclear, Estrada Nacional 10, 2686-953 Sacav´em, Portugal
c
Department of Electronics, Instituto Superior T´ecnico, Av. Rovisco Pais 1, 1049–001 Lisbon, Portugal
d e
Pacific Northwest National Laboratory, Richland, WA 99352 USA
INSP ( UMR CNRS 7588) Universit´es Paris 6 & 7, 75015 Paris, France
f
Laboratoire Souterrain a` Bas Bruit (Universit´e de Nice-Sophia Antipolis), 84400 Rustrel–Pays d’Apt, France Recent activity in the SIMPLE dark matter search program is described, to include the recent development of a ”heavy” detector for application in spin-independent searches.
SIMPLE [1] is the European WIMP search based on Superheated Droplet Detectors (SDDs). An SDD consists of an emulsion of metastable liquid droplets in an organic gel, each of which operates on the same principle of the bubble chamber. The SDD technique has been demonstrated to yield competitive restrictions with very low exposure: with only 0.42 and 2 kgd respectively, the two SDD-based WIMP searches, SIMPLE and its North-American counterpart PICASSO [2] obtained constraints comparable to the 44.9 kgy NAIAD [3]. The reason for this competitiveness is the insensitivity of the SDDs to the majority of the backgrounds which plagued the more traditional search activities, which allows competitive results without using sophisticated background discrimination techniques to go below the level of the intrinsic radioimpurities of the detector composition. The SDD background insensitivity derives from the thermodynamic response of the device to incident radiation [4]. The critical energy (Ec (T, P )) necessary to nucleate a bubble needs to be deposited within a path length of the order
∗ [email protected]
0920-5632/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2007.08.036
of the critical vapor embryo radius (rc (T, P )), i.e.
arc
Ec = 0
dE dE dx ≈ arc (Ethr ) dx dx
(1)
where Ethr (T, P ) is the energy threshold, a is the Harper parameter for the refrigerant, and typically arc 0.1 − 1 μm. This sets a temperature and pressure dependent dE/dx threshold of Ec /(arc ) which can be kept high while Ethr (T, P ) is low. Recoil energy spectra can be obtained by varying the operating temperature during the measurement, as has been done in calibrating the SDD response to α’s [5] and neutrons [6]. For the refrigerants currently employed, these calibrations confirm the calculated requirement of a dE/dx 150 keV/micron for bubble nucleation, eliminating the contributions of minimally ionizing particles. The device itself is of simple construction: for SIMPLE, this is an emulsion with 1-3% concentration of refrigerant, instrumented with a simple microphone which records the nucleation events. A measurement consists of a mosaic of 1 liter devices kept at the selected (T, P) using a pccontrolled water bath which also acts as radiation
130
F. Giuliani et al. / Nuclear Physics B (Proc. Suppl.) 173 (2007) 129–132
shield; the same pc supports a Labview-based DAQ for up to 32 detectors (∼20 ke/setup). The advantage of the SDD technique is a device which can operate continuously up to 40 days without recompression, unlike a bubble chamber which must be recompressed after each nucleation event. The advantage of the gel-free bubble chamber approach is an ability to easily instrument a large active mass, which COUPP is pursuing with some considerable success in extending the metastability lifetime of the refrigerant [7]. The organic gel of SIMPLE’s SDD is composed of water, gelatine, PVP and glycerine, all of which are also employed in pharmaceutical/food productions, making them readily available with a high degree of purity at relatively low cost (∼ 100 e/liter module, including instrumentation). The gel acts as a built-in neutron and α shield, as it moderates neutrons down to below the detection threshold. Due to the high stopping power of α’s in the gel, the main α background contribution arises from impurities in the gel itself. Chemical purification techniques already allow reduction of the actinide concentrations in the gel below 5 x 10−5 pC/g, resulting in an intrinsic α background of better than 0.5 cts/kgd. In fact, thanks to the peak stopping power of 200 keV/μm at 700 keV, at 2 atm below ∼8 o C α’s can only be detected through nuclear recoils. The main beta source of the SDD is the 14 C contained in the gel and freon, which beta decays with Q = 156.5 keV, insufficient for yielding a signal either directly, via nuclear scattering or other reactions like 35 Cl(β − ,ν)35 S. As a consequence, the β’s from 14 C and tritium are not a concern. SDDs are known to be generally insensitive to b γ’s for temperatures such that s ≡ TTc−T −Tb < 0.5 where Tc is the critical temperature and Tb the boiling temperature at the operating pressure [8]; SIMPLE usually operates at s = 0.3. The main background of SIMPLE is traditionally due to microleaks of the nitrogen (used for pressurizing the detectors at 2 atm) into the water bath used to both regulate the SDD operating temperature and to shield neutrons, which are recorded by the piezoelectric sensor and are indistinguishable from a nucleation event. While the majority of these are eliminated by coinci-
dence between the detector microphone and the hydrophone, this problem is being solved through capping improvements: a preliminary test of the new caps showed no microleaks in three weeks, yielding a 90% C.L. upper limit of ∼0.11 microleaks/detector/day, corresponding to ∼11 microleaks/kgd for a 10 g/detector loading, versus the previous 0.5-1 microleaks/detector/day. The possibility of discriminating the microleaks through pulse shape discrimination is also being explored [9]. The bubble nucleation process is a four-stage process [10], the last stage of which generally provides the recorded signal. The third stage of the process however depends on the nature of the incident radiation, but is significantly faster. The feasibility of measuring this stage as a discrimination technique using ultrasound technology is being explored. The choice of refrigerant depends on the search objective. The WIMP-nucleus zero momentum transfer cross section σA is the sum of a spinindependent (SI) and a spin-dependent (SD) contributions, σA = σSI + σSD , with
σSI = π4 G2F μ2A [(gp Z + gn N )2 ] 2 2 2 J+1 σSD = 32 π GF μA [(ap Sp + an Sn ) J ]
(2)
where GF is the Fermi constant, gp,n (ap,n ) are the SI (SD) WIMP couplings with the proton (neutron) respectively, Sp,n are the expectation values of the proton (neutron) group’s spin, μA is the WIMP-nuclide reduced mass, and J is the total nuclear spin. Eq. (2) shows that the SI channel basically scales as A2 , while the SD channel depends on the spins of the proton and the neutron group. Thus spin-dependent investigations generally favor light refrigerant nuclei with spin, whereas spin-independent investigations require heavy nuclei. The current SD limits on a 50 GeV mass WIMP of the traditional C2 ClF5 -based SIMPLE are shown in Fig. 1 in comparison with those of PICASSO and several leading experiments [11,3,12,13]. The C2 ClF5 -based search is tailored to detect WIMPs through the SD channel because the involved nuclei are light but with significant
F. Giuliani et al. / Nuclear Physics B (Proc. Suppl.) 173 (2007) 129–132
Figure 1. Current results for MW = 50 GeV/c2 from a C2 ClF5 run of the SIMPLE experiment (SIMPLE ”light”), along with PICASSO and various leading search experiments. The dashed lines are projections for C2 ClF5 and CF3 I SDDs (see text).
proton group spin. This is clearly seen by comparing the significant SD impact of the current SIMPLE ”light” results in Fig. 1 with its poor SD cross section restrictions observed in Fig. 2. Fig. 1 also shows (dotted lines) projections for a 3 kgd SIMPLE ”light” experiment currently in preparation, assuming the current SIMPLE radiation background of ≤1 evt/kgd. Projections are for both the case of 3 undiscriminated events (outer set), consistent with the assumed background, and that of no events after discrimination (inner set). In either case, the next SIMPLE ”light” results should supersede NAIAD in reducing the CDMS-allowed parameter space. The following phase of SIMPLE ”light”, projected for 2007, is a 30-100 kgd exposure. The C2 ClF5 refrigerant, being a chlorofluorocarbon, is environmentally discouraged by European regulations, eliminating most suppliers of the material. Most recently we have prototyped
131
a new SDD emulsion using C4 F10 . This is the same refrigerant as used by PICASSO, but employs SIMPLE’s gel without the use of heavy salts for density-matching and a priori yields an intrinsic background of < 0.5 evts/kgd after purification. This will be gradually phased into use as the current C2 ClF5 supply is depleted. The insensitivity of the SDD can be exploited in spin-independent measurements using heavy refrigerants. Although several readily available candidates exist (eg. CF3 Br, CF3 I, XeF6 ...), the most obvious difficulty with such a ”heavy” SDD lies in its fabrication, since current devices rely on density matching of the gel (ρ ∼ 1 − 3g/cm3 ) with the refrigerant in its liquid phase in order to produce a homogeneous suspension of droplets. SIMPLE ”heavy” [14] is based on a recently prototyped superheated emulsion of CF3 I in the same gel of SIMPLE ”light”, with agarose as an additive to modify the viscosity and shift upwards the sol-gel transition temperature, potentially enabling twice the SDD continuous operation lifetime [15]. Hence the shielding and background considerations qualitatively also apply. A prototype measurement is scheduled for later this year, with a 3-8 kgd exposure planned for 2007. The potential impact of a CF3 I-based search in the SI channel is shown in Fig. 2, where two 34 kgd projections assuming a 1 evt/kgd background are shown in comparison with the current, equal exposure, CDMS results [11]. The first projection assumes that all expected 34 kgd events are observed, but not identified, so that the upper limit on the WIMP counts is given by the error bar of the ”measured” rate. The second, instead, assumes perfect discrimination, so that all the background events can be rejected. This is close to, but not better than, the current CDMS results in which all events are identified as background. The difference between the two, despite the equal exposures and that 127 I has a higher σSI than Ge, results from CF3 I containing a significant fraction of lighter elements. This is not a disadvantage, since both 19 F and 127 I are known spin-dependent sensitive nuclei, and the former has a better form factor due to the generally lower momentum transfer. A CF3 I search will hence have also a significant impact in this
132
F. Giuliani et al. / Nuclear Physics B (Proc. Suppl.) 173 (2007) 129–132
Cavaillou of the Laboratoire Souterrain a` Bas Bruit (Universit´e de Nice-Sophia Antipolis). This work has been supported by the grant no. POCTI/FIS/57834/2004 of the Portuguese Funda¸c˜ao para a Ciˆencia e a Tecnolog´ıa cofinanced by FEDER. REFERENCES
Figure 2. CF3 I spin-independent projections for 34 kgd exposure and a) 34 undiscriminated events (dotted) and b) all events removed by discrimination (dashed). The current C2 ClF5 SI result is in the top.
sector, as projected in Fig. 1, again for 34 kgd exposure, 1 evt/kgd background and two different sets of 19 F spin matrix elements, from Pacheco [16] and Divari [17]. Summarizing, the SDD-based searches have demonstrated the ability of this technique to reduce (but not eliminate) the concerns regarding backgrounds typical of dark matter searches. The two part construction (gel + refrigerant) permits a low background generic gel matrix with interchangeable targets, which allows a tuning of the device with respect to both its sensitivity to SI- or SD-WIMP interactions, and its operating conditions to achieve this sensitivity. In the SD sector, the at least one order of magnitude less exposure required to achieve the same sensitivities as the more traditional search activities suggests a capacity of the SDD technique to rapidly improve on the limits so far achieved by either NAIAD or DAMA/NaI. The simplicity of the technique is similarly applicable to the SI sector. We thank M. Auguste, D. Boyer and A.
1. T.A. Girard, F. Giuliani, T. Morlat, et al. Phys. Lett. B, 621:233, 2005. 2. M. Barnab´e Heider, M. DiMarco, P. Doane, et al. Phys. Lett. B, 624:186, 2005. 3. G.J. Alner, H.M. Ara´ ujo, G.J. Arnison, et al. Phys. Lett. B, 616:17, 2005. 4. F. Seitz. Physics of Fluids, 1:2, 1958. 5. J.I. Collar, J. Puibasset, TA Girard, et al. Phys. Rev. Lett., 85:3083, 2000. 6. F. Giuliani, C. Oliveira, J. I. Collar, et al. Nucl. Instr. & Meth. A, 526:348, 2004. 7. L. Bond, J. I. Collar, J. Ely, et al. Nucl. Phys. B (Proc. Suppl.), 138:68, 2005. 8. F. d’Errico. Nucl. Instr. & Meth. B, 184:229, 2001. 9. M. Felizardo, R.C. Martins, A.R. Ramos, et al. In IEEE, Instrumentation and Measurement Technology Conference, volume 2, page 1551. IEEE Instrumentation and Measurement Society, May 2005. 10. Yu. N. Martynyuk and N. S. Smirnova. Sov. Phys. Acoust, 37:376, 1991. 11. D. S. Akerib, M. J. Attisha, C. N. Bailey, et al. Phys. Rev. Lett., 96:011302, 2006. 12. A. Benoit, L. Berg´e, A. Broniatowski, et al. Phys. Lett. B, 545:43, 2002. 13. G. J. Alner, H. Araujo, G. J. Arnison, et al. Astrop. Phys., 23:444, 2005. 14. F. Giuliani et al. Preprint physics/0511158. 15. T. Morlat, D. Limagne, G. Waysand, and J.I. Collar. Nucl. Instr. & Meth. A, 560:339, 2006. 16. A. F. Pacheco and D. Strottman. Phys. Rev. D, 40:2131, 1989. 17. P. C. Divari, T. S. Kosmas, J. D. Vergados, and L. D. Skouras. Phys. Rev. C, 61:054612, 2000.