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Search for SQM in CRs at

Chacaltaya

O. SaavedraDipartimento 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

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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

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Strangelets (Small Lumps of Strange Quark Matter)

Nucleus (12C)

Z=6, A=12

Z/A = 0.5

Strangelet

A=12 (36 quarks)

Z/A = 0.083

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) 102 103 104 105 106

M (GeV) 106 109 1012 1015 1018

[black points are electrons]

•Aggregates of u, d, s quarks + electrons , ne= 2/3 nu –1/3 nd –

1/3 ns

Ground state of QCDstable for 300 < A < 1057

A qualitative picture…

Produced in Early Universe or in strange star collisions (J. Madsen, PRD71 (2005) 014026)

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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. M

adse

n, P

RL

87 (

2001

)

Stable SQMEn

erg

y p

er b

aryo

n(M

eV)

Strange quark mass (MeV)

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Color-flavor locked strangelets (J. Madsen)

Predicts CFL strangelets have lower E/A than ‘normal’ strangelets, giving a charge/mass relation of Z~0.3A2/3

(“normal” bag model strangelets have Z~.1A for A<<1000

Z~8A1/3 for A>>1000

Nuclear

Matter

Fe56

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Important feature: Z /A « 1

M. Kasuya et al. Phys.Rev.D47(1993)2153 H.Heiselberg, Phys. Rev.D48(1993)1418J. Madsen Phys. Rev.Lett.87(2001)172003

A

Z

10

102

103

0.3A2/3

~0.1A8A1/3

Nuclei 0.5A

103

104

105

106

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Nuclearites, i.e. SQM “meteorites”: ~neutral, ß~10-3 Main energy loss mechanism by atomic collisions

dE/dx= - medium v2N 10-16 cm2 RN < 1Å

x R2N RN > 1Å

Accessible (mass,) regions for nuclearites from above

L

0dx

Mexp)0(v)L(v

c

L

0 v)0(vlnMdx

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Detection conditions in SLIM

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Strangelets : small lumps of SQM - ~300 < A < 106 Produced in collisions of strange stars

R. Klingenberg J. Phys. G27 (2001) 475

-charged Accelerated as ordinary nuclei

G. Wilk et al. hep-ph/ 0009164 (2000)J. Madsen et al. Phys.Rev.D71 (2005) 014026

Strangelets as ultra-high energy cosmic rays?

Madsen & Larsen, PRL 90 (2003) 121102

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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 > 103 – 104

[2] HECRO-81 (Japan): CR composition on balloon (9 gr/cm2)

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, θzenith= 87.4° 200 gr/cm2

[4] AMS-01 Anomalous Cosmic ray: A ~ 17.5, Z/A ~ 0.114

a) Direct measurements

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PRL 35 (1975) 0486

MM with g= 137e β=0.5

The “ Price Event”: Balloon flight – 10 m2 of passive detectors + emulsions and Č films.

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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 > 103 – 104

[2] HECRO-81 (Japan): CR composition on balloon (9 gr/cm2)

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, θzenith= 87.4° 200 gr/cm2

[4] AMS-01 Anomalous Cosmic ray: A ~ 17.5, Z/A ~ 0.114

a) Direct measurements

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b) Indirect measurements

Centauro-like events

• low elettromagnetic• high hadronic component1. 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. 2006

“Exotic Characteristics of Centauro-I”

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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 1997.

•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) 121102

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SLIM

modules 24x 24cm2

Nuclear Track Detector Arrays440 m2 @ Chacaltaya, 5230 m asl100 m2 @ Koksil, Himalaya, 4275 m asl

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Nuclear Track Detectors:

The track-etch technique

CR39 and Makrofol

Aluminium

CR39

Makrofol

Fas

t MM

Nuclear fragment

Slow MM

200 A GeV S16+ or β ~ 10-2 MM

=1 mm

SQMnuggets

Two etching have beed defined:

Strong etching:

8N KOH + 1.25% Ethyl alcohol 77°C 30 h

Soft etching:

6N NaOH + 1% Ethyl alcohol 70° 40 h

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New etching procedure, different from MACRO

OLD

NEW

NaOH NaOH+ 1% ethylic alcohol

New (very delicate!) etching procedure higher signal/noise ratio

The etching procedure

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Detector Calibration: ion beams @ CERN, BNL

detector foils detector foils

target

160 AGeV In 49+

beam

fragments

Z/=49

Z/=20

CR39

nn

1

20

Calibrations of NTDs

CR39 threshold

Makrofol threshold

Reduced etch rate vs REL REL vs ß for nuclearites

CR-39

Z/ =11

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Total area ~ 440 m2

One module (2424 cm2)

In four years of exposure, for a downgoing flux of particles, the SLIM sensitivity will be about 10-15cm-2s-1sr-1

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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

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Preliminary results

ΦSQM<2.1 x 10-15cm-2sr-1s-1 (90% CL)

We analyzed 293 m2 of CR39

with <t>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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Nuclearites

High altitude: SLIM :5300 m White Mountain: 4800 m Mt. Norikura: 2000 m

Underground Ohya : 100 hg/cm2 MACRO : 3700 hg/cm2

Sea level

White Mt.

Mt. Norikura

Ohya

MACRO

SLIM

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AMS 5y

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

0 2000 4000 6000 8000A

N(A

)[c

m-2

h-1

sr-1

]

SLIM

CAKE

Predicted Flux @ Chacaltaya : 7x 10-6 m-2 h-1 sr-1 for mN > 3 x 103

SLIM: tens of events in 4 y

Model already ruled out…

Strangelets

If Abundance in CR: M-7.5

HECRO

ET event

Price

TREK

SkylabHEAO-3

Ariel

2727

1-Mass and size decrease

A0 at the top of the atmosphere

• Spectator-participant picture: only quarks in the geometrical intersection of colliding nuclei

• mass reduced (at most) to A0 –At until A = Acrit (~300) neutron evaporation

decay into normal matter

• Maximum depth reached before evaporation:

3/1

air

0airN

2

A

A

3

4cm/g

Propagation of strangelets in the atmosphere

Chacaltaya

Ref. Strangelets at Chacaltaya

G. Wilk et al. hep-ph/0009164

Rybczynski et al. N.Cimento 24,645,2001

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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