1 Search for SQM in CRs at Chacaltaya O. Saavedra Dipartimento di Fisica Generale Universita di Torino and INFN sez. di Torino Collaboration (Bolivia, Canada, Italy, Pakistan) S.Balestra, S. Cecchini, F. Fabbri, G. Giacomelli, M.Giorgini, A. Kumar S. Manzoor, J. McDonald, E. Medinaceli, L. Patrizii, J. Pinfold, V. Popa, O. Saavedra, G. Sher, M. Shahzad, M. Spurio, V. Togo, A. Velarde, A. Zanini

2 Cosmic ray strangelets What are strangelets ? Could a significant cosmic ray strangelet flux exist and be measured ? Did we already detect them? A strangelet search at Chacaltaya with SLIM Preliminary results and conclusions

3 Strangelets (Small Lumps of Strange Quark Matter) Nucleus ( 12 C) Z=6, A=12 Z/A = 0.5 Strangelet A=12 (36 quarks) Z/A = That u,d, quark matter is not absolutely stable can be inferred by stability of normal nuclei-but this is not true for u,d,s quark matter. R (fm) M (GeV) [black points are electrons] Aggregates of u, d, s quarks + electrons, n e = 2/3 n u –1/3 n d –1/3 n s Ground state of QCD stable for  300 < A < A qualitative picture… Produced in Early Universe or in strange star collisions (J. Madsen, PRD71 (2005) )

4 Strangelets (Small Lumps of Strange Quark Matter) Roughly equal numbers of u,d,s quarks in a single ‘bag’ of cold hadronic matter. Stability can not be calculated in QCD, but is addressed in phenomenological models (MIT Bag Model, Color Flavor Locking…). For a large part (~half) of available parameter space, these models predict that SQM is absolutely stable in bulk Values of Bag Constant J. Madsen, PRL 87 (2001) Stable SQM Energy per baryon(MeV) Strange quark mass (MeV)

5 Color-flavor locked strangelets (J. Madsen) Predicts CFL strangelets have lower E/A than ‘normal’ strangelets, giving a charge/mass relation of Z~0.3A 2/3 (“normal” bag model strangelets have Z~.1A for A<<1000 Z~8A1/3 for A>>1000 Nuclea r Matter Fe 56

6 Important feature: Z /A « 1 M. Kasuya et al. Phys.Rev.D47(1993)2153 H.Heiselberg, Phys. Rev.D48(1993)1418 J. Madsen Phys. Rev.Lett.87(2001) A Z A 2/3 ~0.1A 8A 1/3 Nuclei 0.5A

7 Nuclearites, i.e. SQM “meteorites”: ~neutral, ß~10 -3 Main energy loss mechanism by atomic collisions dE/dx= -   medium v 2 N   cm 2 R N < 1Å     x R 2 N R N > 1Å Accessible (mass,  ) regions for nuclearites from above

8 Detection conditions in SLIM

9 Strangelets : small lumps of SQM - ~300 < A < 10 6 Produced in collisions of strange stars R. Klingenberg J. Phys. G27 (2001) 475 -charged Accelerated as ordinary nuclei G. Wilk et al. hep-ph/ (2000) J. Madsen et al. Phys.Rev.D71 (2005) Strangelets as ultra-high energy cosmic rays? Madsen & Larsen, PRL 90 (2003)

10 Did we already detect them? [1] P. B. Price et al. Phys. Rev. D18 (1978) 1382 [2] T. Saito et al. Phys. Rev.Lett 65 (1990) 2094 [3] M. Ichimura et al., Nuovo Cim. A106 (1993) 843 [4] V. Choutko (AMS Coll.) 28 ICRC (2003) 1765 Several “exotic“, unexplained, events from different CR experiments [1] Price’s “Monopole” re-analysis Z ~ 46 and A > 10 3 – 10 4 [2] HECRO-81 (Japan): CR composition on balloon (9 gr/cm 2 ) Č + Scintillator counter +Proportional tubes 2 events with: Z ~ 14 A ~ 350 and A ~450 [3] “Exotic Track” event : Balloon born emulsion chamber Z ~ 20 and A ~ 460, θ zenith = 87.4°  200 gr/cm 2 [4] AMS-01 Anomalous Cosmic ray: A ~ 17.5, Z/A ~ a) Direct measurements

11 PRL 35 (1975) 0486 MM with g= 137e β=0.5 The “ Price Event”: Balloon flight – 10 m 2 of passive detectors + emulsions and Č films.

12 Did we already detect them? [1] P. B. Price et al. Phys. Rev. D18 (1978) 1382 [2] T. Saito et al. Phys. Rev.Lett 65 (1990) 2094 [3] M. Ichimura et al., Nuovo Cim. A106 (1993) 843 [4] V. Choutko (AMS Coll.) 28 ICRC (2003) 1765 Several “exotic“, unexplained, events from different CR experiments [1] Price’s “Monopole” re-analysis Z ~ 46 and A > 10 3 – 10 4 [2] HECRO-81 (Japan): CR composition on balloon (9 gr/cm 2 ) Č + Scintillator counter +Proportional tubes 2 events with: Z ~ 14 A ~ 350 and A ~450 [3] “Exotic Track” event : Balloon born emulsion chamber Z ~ 20 and A ~ 460, θ zenith = 87.4°  200 gr/cm 2 [4] AMS-01 Anomalous Cosmic ray: A ~ 17.5, Z/A ~ a) Direct measurements

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14 b) Indirect measurements Centauro-like events low elettromagnetic high hadronic component 1.Long-lived cascades 2.strongly penetrating Penetrating chararter through the atmosphere. Colliding droplet of quark matter: Bjorken and McLerran 1979 More receintly A. Ohsawa, E.Shibuya and M.Tamada: N.Phys “Exotic Characteristics of Centauro-I”

15 EAS HADRON exp. by EAS measurements: Shaulov 1996,98 Can be interpretated as an indirect signature of unknow component Of cosmic radiation: hypothesis of SQM: Wilk and Wlodarczyk 1996 Neutron monitors in HADRON experiment : reveled extremely long delay neutrons associated to EAS. A tentative explanation: arrival of strangelets with gradual dispersion of energy through the atmosphere Gladysz-Dziadus and Wlodarczyk Muon bundles : DELPHI and ALEPH: Rybczynski, Wlodarczk and Wilk “Strangelets in cosmic rays”: Nucl.Phys.B 151 (2006)341 “Strangelets as cosmic rays beyong the GZK-cutoff” Madsen and Larsen P.Rev.lett. 90 (2003)

16 SLIM modules 24x 24cm 2 Nuclear Track Detector Arrays 440 m Chacaltaya, 5230 m asl 100 m Koksil, Himalaya, 4275 m asl

17 Nuclear Track Detectors: The track-etch technique CR39 and Makrofol Aluminium CR39 Makrofol  Fast MM Nuclear fragment Slow MM 200 A GeV S 16+ or β ~ MM =1 mm SQM nuggets Two etching have beed defined: Strong etching: 8N KOH % Ethyl alcohol 77°C 30 h Soft etching: 6N NaOH + 1% Ethyl alcohol 70° 40 h

18 New etching procedure, different from MACRO OLDOLD NEWNEW NaOH NaOH+ 1% ethylic alcohol New (very delicate!) etching procedure  higher signal/noise ratio The etching procedure

19 Detector Calibration: ion CERN, BNL detector foils target 160 AGeV In 49+ beam fragments Z/  =49 Z/  =20 CR39

20 Calibrations of NTDs CR39 threshold Makrofol threshold Reduced etch rate vs REL REL vs ß for nuclearites CR-39 Z/  =11

21 Total area ~ 440 m 2 One module (24  24 cm 2 ) In four years of exposure, for a downgoing flux of particles, the SLIM sensitivity will be about cm -2 s -1 sr -1

22 Absorber Nuclear track detectors Strong etching (large tracks, easy to detect) Soft etching Scan in the predicted position measurement of REL and direction of incident particle. The search technique Up to now, no double coincidences found

23 Preliminary results Φ SQM <2.1 x cm -2 sr -1 s -1 (90% CL) We analyzed 293 m 2 of CR39 with exp =3.8 y exposure at the Chacaltaya Lab. No double coincidence was found In a single NTD the backgrond is due to espalation due to muons, neutrons or pions Up to now, no SQM, no monopoles have been found.

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25 Nuclearites High altitude: SLIM :5300 m White Mountain: 4800 m Mt. Norikura: 2000 m Underground Ohya : 100 hg/cm 2 MACRO : 3700 hg/cm 2 Sea level White Mt. Mt. Norikura Ohya MACRO SLIM

26 SLIM CAKE Predicted Chacaltaya : 7x m -2 h -1 sr -1 for m N > 3 x 10 3 SLIM: tens of events in 4 y Model already ruled out… Strangelets If Abundance in CR:   M -7.5 HECRO ET event Price TREK Skylab HEAO-3 Ariel

27 1-Mass and size decrease A 0 at the top of the atmosphere Spectator-participant picture: only quarks in the geometrical intersection of colliding nuclei mass reduced (at most) to A 0 –A t until A = A crit (~300)  neutron evaporation  decay into normal matter Maximum depth reached before evaporation: Propagation of strangelets in the atmosphere Chacaltaya Ref. Strangelets at Chacaltaya G. Wilk et al. hep-ph/ Rybczynski et al. N.Cimento 24,645,2001

28 Conclusions Analysis completed by mid 2007 Upper flux limits for unexplored masses Rejection/confirmation of strangelets propagation models and abundances SLIM: still discovery potential for SQM