11th Topical Seminar on Innovative Particle and Radiation Detectors 1-4//008, Siena, Italy The nuclear track detector CR39: results from different experiments M. Giorgini Bologna University and INFN 1
The Nuclear Track Detectors (NTDs) tecnique A very ionizing particle breaks the polimeric bonds around its trajectory. The produced damage is called latent track The latent track becomes visible and measurable after a chemical etching in a basic solution 00 A GeV S16+ Two (etch-pits) cones with the same dimensions or a hole develop around the particle trajectory
The nuclear track detector CR39 The most sensitive NTD employed in several scientific and technological applications is CR39 (PPG Ind. Inc.) More than 00 m of CR39 detectors were used in the MACRO [Eur. Phys. Jou. C 5 (00) 511] and SLIM experiments to search for massive rare particles in the cosmic radiation (magnetic monopoles, nuclearites, strangelets, Q-balls...) C1H18O7 ρ = 1.3 g/cm3 Accurate detector calibrations are required3
CR39 calibrations CR39 Detectors Fragments Incident beam Survived beam Fragments Target 50 cm Target CR39 Air gap Beams : 158 AGeV Pb8+ @ CERN-SPS 158 AGeV In49+ After exposure, the CR39 sheets were etched in 6N NaOH + 1% ethyl alcohol solution at 70 C for 40 h 4
Automatic and manual measurements Automatic image analyzer ELBEK (A. Noll et al., Nucl. Tracks Radiat. Meas. 15 (1988) 65) The base area, eccentricity and brightness are measured for each track Tracking : the trajectory of each ion is followed through the stack D L = (vt vb )t L (v T v B ) D = vbt (v T + v B ) D = 1+ 4 t L vb 4L 1 + D D and L are measured with a Leica optical microscope coupled to a CCD camera and a video monitor L is obtained multiplying the measured cone height by the 5 refractive index of the detector
Height and base area of conical tracks in CR39 exposed normally to In49+ and Pb8+ ions Z/β=75-8 Z/β=5 Z/β= Z/β=8 Z/β=80 Z/β=75 Z/β=83 Z/β=0 Z/β=30 Z/β= Z/β=46-49 Z/β=30 Z/β=40 Number of events Z/β=0 Z/β=49 Z/β=46 Cone height (arbitrary units) 6 Track area (pixel)
Best charge resolution Charge distribution for tracks present in at least out of 1 measured CR39 sheets located after the target σz = 0.05e 7
Calibration graph for CR39 Reduced etch rate p=vt/vb For each detected charge Restricted Energy Loss (REL) p=vt/vb de z Z 1 me c β γ Tmax δ REL= = K ln β I β A dx E< Tmax A unique calibration curve describes all the data REL (MeV cm g ) -1 8
Fragmentation cross sections of Fe6+, Si14+ e C6+ ions on CR39, CH and Al targets Nucl. Phys. A 807 (008) 06 Beam : Fe6+ (E = 0.3, 0.41, 1.0, 3.0, 5.0 AGeV) Si14+ (E = 1.0, 3.0, 5.0 AGeV) C6+ (E = 0.9 AGeV) Exposures @ BNL-AGS and HIMAC (Japan) CR39 sheets : area 11.5 11.5 cm thickness 0.65 mm Targets : CH, Al, CR39 thickness 1 mm After exposure, the CR39 sheets were etched in 6N NaOH aqueous solution at 70 C for 30 h 9
Total fragmentation cross sections AT ln(nin/nout) σtot = ρt tt NAV AT = mass number of the target ρt = density of the target tt = thickness of the target NAV = Avogadro's number Nin = number of incident ions before the target Nout = number of incident ions after the target Theoretical predictions : σ tot = σ nucl + σ EMD = π ro ( AT1 3 + A1P 3 bo ) + α ZTδ ZT = atomic number of the target Ap = mass number of the beam ro = 1.31 fm bo = 1.0 α = 1.57 δ = 1.9
Data-prediction comparison Fe6+ on CH [ Phys. Rev. C 56 (1997) 388 ] [ Phys. Rev. C 56 (1997) 388 ] Total cross section (mb) Total cross section (mb) Fe6+ on Al [ Phys. Rev. C 56 (1997) 388 ] [ Phys. Rev. C 56 (1997) 388 ] Target mass AT Total cross section (mb) Total cross section (mb) [ Phys. Rev. C 56 (1997) 388 ] Si14+ on Al Si14+ on CR39 Si14+ on CH [ Radiat. Meas. 34 (001) 37 ] [ Nucl. Phys. A 784 (007) 341 ] [ Nucl. Phys. A 784 (007) 341 ] [ Phys. Rev. C 39 (1989) ] [ Nucl. Phys. A 784 (007) 341 ] [ Phys. Rev. C 39 (1989) ] 0.9 A GeV C Present work [ Phys. Rev. C 66 (00) 014609 ] Target mass AT The quoted uncertainties are statistical standard deviations 11
Partial charge changing cross sections Average base areas for tracks present in at least out of 3 measured CR39 sheets located after the target Charge resolution σ ~ 0.e Z Z σ Z (mb) σ Z (mb) -1 - -3-4 -5-6 -7-8 -9 - -11-1 -13-14 338 ± 11 85 ± 11 5 ± 49 ± 197 ± 9 168 ± 8 13 ± 7 175 ± 8 7 ± 7 15 ± 6 5 ± 8 3 ± 6 81 ± 6 93 ± 18 177 ± 1 13 ± 11 1 ± 11 6 ± 8 117 ± 11 83 ± 9 90 ± -15 80 ± 6-16 50 ± 4-17 76 ± 5-18 86 ± 6 Partial charge changing cross sections for 1 AGeV Si14+ and 1 AGeV Fe6+ ions on the CH target 1
The SLIM experiment Chacaltaya laboratory (Bolivia, 530 m a.s.l.) Search for LIght Monopoles Intermediate mass (5 MM 1 GeV) Magnetic Monopoles Strange Quark Matter (nuclearites, strangelets) Charged Q-balls 13
Intermediate Mass Monopoles (IMMs) SO() 15 GeV 9 GeV SU(4) x SU()L x SU()R -35 s -3 s Virtual vector bosons X, Y? Electroweak Unification W, Z SU(3)C x [SU()L x U(1)Y]EW IMMs 5-1 GeV GeV - s Kephard, Shafi.et. al SU(3)C x U(1)EM Virtual photons and gluons Confinement region Magnetic field of a point MM A. De Rujula, CERN-TH 773/94 E. Huguet and P. Peter, hep-ph/ 901370 T. W. Kephart and Q. Shafi, Phys. Lett. B 50 (001) 313 S. D. Wick et al., Astropart. Phys. 18 (003) 663-5 -16-13 Radius (m) liquid H Energy losses of IMMs (a) β < -4 Elastic collisions (b) -4 < β < - Excitation (Medium as Fermi gas) (c) β > - Ionization (Bethe-Bloch) (Zeeq) = (gβ) 14
Strange Quark Matter (SQM) Phys. Rev. D 30 (1984) 7 ; Nature 31 (1984) 734 Aggregates of u, d, s quarks + electrons, n = /3 n 1/3 n 1/3 n Candidates for cold Dark Matter! Searched for in cosmic rays reaching the Earth e u d s [black points are electrons] R (fm) 3 4 M (GeV) ev 300 Z=1, A=580 Z=46, A=00 5 6 15 18 6-7 (b) ~ 57 4 x Z=14, A=300 1 Z=17, A=400 < N REL (MeVg cm ) 5 9 8. = M 17 14 AG (u.m.a.) N M = 6 6 ev 19 G ev qualitative picture (hep-ex/0004019) G 7 A 4 N M -1 s, ite ar N uc le -1 REL (MeV g cm ) Nuclearites : large neutral SQM bags. Core of u, d and s quarks with an electron cloud Typical galactic velocities : β -3 Dominant interaction: elastic collisions with atoms in the medium 4 3 g Strangelets : small charged SQM snuggets =,g o le op n Behave like ordinary nuclei same acceleration processes and energy loss Mo CR39Very Threshold low charge to mass Z/A ratio 3 D CR39 Threshold 1-5 -4-3 β REL vs β of nuclearites in CR39 - -5-4 -3 - β -1 0 15 REL vs β of strangelets in CR39
Q-balls Nucl. Phys. B 6 (1985) 63 ; Phys. Lett. B418 (1998) 46 Super-symmetric coherent states of squarks, sleptons and Higgs fields Candidates for Dark Matter! - Neutral Q-balls (SENS) : the main interaction process is the catalysis of proton decay. Not relevant for NTDs. - Charged Q-balls (SECS) are similar to nuclearites and strangelets and behave like ordinary nuclei same interaction processes Z = 13e A qualitative picture (hep-ex/0004019) -1 REL (MeVg cm ) Q SECS (charged) 3 ZQ =1e SENS (neutral) CR39 Threshold [black points are electrons, empty dots are s-electrons] -5-4 β -3 - REL vs β of SECS in CR39 16
The detector Nuclear track detectors Absorber Total area ~ 440 m One module (4.5 4.5 cm) 17
The search technique Strong etching* (large tracks, easy to detect) General scan of the top surface Soft etching** Scan in the predicted position measurement of REL and direction of incident particle. * 8N KOH + 1.5% Ethyl alcohol at 70 C for 30 h ** 6N NaOH + 1% Ethyl alcohol at 70 C for 40 h No candidate passed the search criteria 18
Upper limits for downgoing IMMs and dyons Flux upper limit (cm- s-1 sr-1) Analyzed area : 47 m Average exposure time : 4. years 90% C.L. upper limits for a downgoing flux of IMMs with g = gd, gd, 3gD and for dyons (M+p) : 1.3. -15 cm- s-1 sr-1 for β 4. - 19
Upper limits for nuclearites and charged Q-balls 90% C.L. upper limits for a downgoing flux of NUCLEARITES and charged Q-balls : 1.3. -15 cm- s-1 sr-1 for β > -4-14 - -1-1 Flux upper Limit (cm sr s ) -15-5 -4-3 β - 0
CONCLUSIONS The nuclear track detector CR39 was calibrated with different ions of different energies. A unique curve of p vs REL describes all the data. The best charge resolution obtained is σz ~ 0.05e. The total and partial fragmentation cross sections for Fe6+, Si14+ and C6+ ions on polyethylene, CR39 and aluminum targets were measured using CR39 The total cross sections for all the targets and energies used in the present work do not show any observable energy dependence There is a dependence on target mass, mainly due to the contribution of electromagnetic dissociation The SLIM experiment (47 m of CR39, with an average exposure time of 4. y) set 90% C.L. upper limits for a downgoing flux of : IMMs with g = gd, gd, 3gD and dyons : 1.3. -15 cm- s-1 sr -1 for β 4. - Nuclearites and strangelets : 1.3. -15 cm- s-1 sr -1 for β -4 Charged Q-balls : 1.3. -15 cm- s-1 sr-1 for β -4 1
SLIM scan L1 scan 3 X Mag, stereo microscope; scanned twice ~ 99% 0 40 X Mag L5 scan: 500 00 X Mag Coincidence area ~ 0.5 cm Measured with 6.3ob X 5oc Mag Event p and θ are equal within 0 %