Overview of Exotic Strange Quark Matter Search Experiments

Overview of Exotic Strange Quark Matter

Search Experiments

Symposium on Fundamental Issues inElementary Matter25-29 September 2000Physikzentrum Bad Honef

James Nagle

What is Quark Matter?

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QCD allows for bound states of quarks in color-singlet configurations

Nuclei are not single hadrons, but bound states of individual nucleons

Quark matter composed of up and down quarks for (A>1) is knownto be unstable, otherwise normal nuclei would decay into such quark matter.

What is Strange Quark Matter?Strange quark matter composed of up, down and strange quarks may be meta-stable or even stable in bulk.

States have a reduced Fermi energy, reduced Coulomb, no fission.Thus SQM states could range in size from A=2 to A > 106.

Witten proposed SQM could even be the ground state of nuclear matter and could exist in bulk as remnants of the Big Bang.

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gy L

evel

Strange Quark Mass

Quark Matter Strange Quark Matter

Where to findStrange Quark Matter?

1. Remnants from the early universe

2. Core of dense stars

3. Created by coalescence of multiple strange baryons

4. Created via a quark-gluon plasma formed in relativistic heavy ion collisions

1. Remnants of the Big Bang

SQM left over from the Big Bang could be seen in cosmic rays and may have a 10-7 concentration by mass in the Earth’s crust.

Many searches with null results.

Cosmological and Astrophysical SQM

2. Core of Dense Stars

Neutron stars may have quark matter core which could be SQM

E. Witten, Phys. Rev. D 30, 272 (1984).A. DeRujula and S.L. Glashow, Nature 312, 20 (1984).J.D. Bjorken and L.D. McLerran, Phys. Rev. D 20, 2353 (1979).

N. Glendenning and J. Scahffer-Bielich, Phys. Rev. C 58, 1298 (1998).

3. Coalescence of SQM

n

nn p

p

A. Baltz, C. Dover et al., Phys. Lett. B, 325, 7 (1994).

In p + p, p + A, A + A collisions, at freeze-out baryons and strange baryons can coalesce to form nuclei and hypernuclei.

If strange quark matter states are more stable than these hypernuclei, then the state can make a transition to form SQM.

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J. Schaffner et al., J. Phys. G 23, 2107 (1997)., S.A. Chin and A. Kerman, Phys. Rev. Lett. 43, 1292 (1979).H. Liu and G.L. Shaw, Phys. Rev. D 30, 1137 (1984), C.Greiner et al. Phys. Rev. Lett. 58 (1987) 1825.C.Greiner and H. Stocker, Phys. Rev. D 44 (1991) 3517.

Cools by hadron emissionat the surface

p

)( suK

Preferential emission of anti-strange quarks

Once cooled down, remaining quarks form a meta-stable state of SQM with:

(A= 2-100 and |S|=1-100).

4. Quark-Gluon Plasma

H-dibaryonThe H-dibaryon is a six-quark color singlet hadron.

It would be the lightest strange quark matter state, and there is no theoretical consensus about its mass.

p-

p , 0n

n

nn Very deeply bound, only S=2 decay, long lifetime > 105 seconds

Unbound, possibly a resonance similar to d* in proton-proton interactions

Very loosely bound, unclear distinction between H and bound state- possibly very short lifetime ~ 1/2

Bound H state, with lifetime ~ 10-8 seconds >

d

dsu

u s

“For all H masses except those near the threshold, we expect a true six-quark bound state.”Donoghue et al., Phys. Rev. D 34, 3434 (1986).

H Mass Threshold

What do we know about the H?

1. Carroll et al., Phys. Rev. Lett. 41, 777 (1978). p + p K K H2. Gustafson et al., Phys. Rev. Lett. 37, 474 (1976). p + A H X3. Shahbazian et al., Z. Phys. C39, 151 (1988). p + A HX 4. Alekseev et al., Yad. Fiz. 52, 1612 (1990). n + A HX5. Bawolff et al., Ann. Physik Leipzig 43, 407 (1986). + A HX6. Condo et al., Phys. Lett. 144B, 27 (1984). p + A HX ………….

A. E836 BNL-AGS E224 KEK

B. E888 BNL-AGS KTeV FNAL E910 BNL-AGS

C. E810 BNL-AGS E896 BNL-AGS

K- + 3He K+ + ( + p) + n K+ + + n

p + A ( + ) + X H + X

A + A ( + ) + X H + X

Best Limits to Date

“To conclude, in the context of published models, our [KTeV] result …. in conjunction with the result from experiment E888, rules out the [H dibaryon] model proposed by Donoghue et al. for all S=1 transitions.”

A. Alavi-Harati et al., Phys. Rev. Lett. 84, 2593 (2000).

pnn

E888KTeVE224E836

Plot from Ram Ben-David and D. Ashery

Let’s look in more detail….

Experiment 888Originally E888 had two possible H candidates, but further studies support the conclusion that they are consistent with known backgrounds.

Sensitive to: H n and H 0 n

< 60 nbE888 sensitivity

~ 1.0 bmodel prediction

J. Belz et al., Phys. Rev. Lett. 76, 3277 (1996).J. Belz et al., Phys. Rev. C 56, 1164 (1997).Cousins et al., Phys. Rev. D 56, 1673 (1997)

Experiment 888: Part IIE888 limit of H < 60 nb assumed H production peaked at midrapidity (like p+p).

Using transport model RQMDv2.3 shows an H distribution shifted towards target rapidity as suggested by Cole et al. This reduces the acceptance substantially and yields a limit of H < 1.2 b.

Rapidity

dN/d

y ( a

.u. )

p + pp + Pt

E888 acceptance

However, the predicted yield using a p + p type model for coalescence is H ~ 2 b.

In p + Pt collisions, there is significant strangeness enhancement and even greater enhancement of nearby baryons. The predicted yield should be H ~ 40 b.

Thus the ratio (limit/prediction) is still roughly the same. Nagle et al., Phys. Rev. C 53, 367 (1996).

Cole et al., Phys. Lett. B 350, 147 (1995).

E910 Lambda Distribution

nucl-ex/0003010 31 March 2000

distribution is shifted towards target rapidity.

p + Au at 18 GeV

Increasing number ofcollisions by the incoming proton

E799-II KTeV ResultNo candidates.

Sensitive to: H p

A. Alavi-Harati et al., Phys. Rev. Lett. 84, 2593 (2000).

< 12 pbKTeV sensitivity

Checking the Calculations

Rapidity

Inva

riant

Yie

ld (a

.u.)

p + Be at 800 GeV/cOriginal Model Calculation by Frank Rotondo. F. Rotondo, Phys. Rev. D 47, 3871 (1993).

Re-checked using transport model RQMD and coalescence. Agrees with previous prediction within a factor of 2.

< 12 pbKTeV sensitivity

~ 1.2 bmodel prediction

KTeV acceptance

E906 - HypernucleiIf one observes a double-lambda hypernucleus that decays by sequential weak decay, then it rules out all but the most weakly bound H dibaryon.

There are three isolated previous candidates - but the results are not consistent.

Recently E906 at the BNL-AGS reports a clear signal above background in the region where one expects to find the

4H.

Look for these results in the near future, and an upgrade proposal (Adam Rusek/Robert Chrien/Tomokazu Fukuda).

Double Lambda HypernucleiK- + (p) - + K+

- + (p) + + + A 4H + X

4H - + 4He

4He 3He + p + -

Beyond the H (|S| >2)Larger states of SQM can only be created with relativistic heavy ion collisions.

However, there are some issues:Too hot (higher energy)

- difficult to get multiple baryons close enough to fuseToo cool (lower energy)

- not enough strangeness production

AGS energies may be optimal, but there is still a large penalty for coalescence 1/48. Also, replacing a baryon unit with a strange baryon unit was predicted to be another ~ 1/5.

E864

Search for SQM with new Z/A

NA52 Experiment at CERN-SPS

No remaining candidates and thus set upper limits.

E886 (AGS) Adam Rusek

E878 (AGS) Mike Bennett

E864 (AGS) K.Barish, M.Munhoz, S.Coe, JN

E864 (AGS) Z.Xu, G.V.Buren, R. Hoverstein

NA52(CERN) R. Klingenberg, K.Pretzel

Lifetimes > 50 ns

T.A.Armstrong et al., Phys. Rev. Lett. 79, 3612 (1997)T.A.Armstrong et al., Nucl. Phys A 625, 494 (1997)D. Beavis et al., Phys. Rev. Lett. 75, 3078 (1995)A. Rusek et al., Phys. Rev. C 54, R15 (1996).R. Klingenberg et al., Nucl. Phys. A, 306c (1996).

No Evidence for SQM

A. Baltz et al., Phys. Lett. B 325, 7 (1994)H. Crawford et al., Phys. Rev. D 45, 857 (1992).H.C. Liu and G.L. Shaw, Phys. Rev. D 30, 1137 (1984).

Most plasma predictions ruled out by data

Sensitivity for SQM via coalescence up to states

A=6-7 , |S|=2-3

Nucleosynthesis Models

Quark Plasma Models

E864 Upper Limits

SQM Sensitivity

E864: Hypernuclei

If “SIGNAL”

invariant yield (2.6 + 1.2) 10-4 c2/Gev2

S = 1/28

If “LIMIT”

90% CL sensitivity 2.5 10-4 c2/Gev2

S < 1/30

Sotiria Batsouli, Yale University

(2.991 GeV)

e

J

.R.(e)= 25%

Y(A,|S|) = C x (1/48)A x (s)|S|

Unstable Nuclei5Li 4He + p (c ~ 100 fm/c)

Follows scaling law

Finite Size Effects

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Hep

H

2r

Heinz, Scheibl, Phys. Rev. C59,1585 (1998).

= 5 fm B.E.( - 2H) = 0.13 Mev

e : = 1.74 fmE. = 8 MeV

Assume ( 2H +) with b = d 9.8 fm e ( 2H +p) with b = pd 2.6 fm

Using R|| , R | from E917, E895

2r

2r2r

Thus, accounting for lower abundance of ‘s and finite

size effects leaves an additional penalty of 0.5

Antideuterons

Corrected for large contribution of

antilambdas to measured antiprotons

T.A. Armstrong, Phys. Rev. Lett. 85, 2685 (2000).

E864

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• Concept of a deeply bound H dibaryon may be on its last legs.• E906 and other KEK hypernuclei results will play a key role.• There is still a window at around 1/2 for a weakly bound H

dibaryon or bound state.• Or are the productions models really wrong (?)

• For A > 2 SQM almost final limits from fixed target programs.• In absence of observations, limits of a few 10-9 are reached.• Much harder to find many strange baryons close together than

initially predicted. Hypernuclei are also suppressed (?)

• RHIC is next step for heavy ion physics, but not SQM physics• Future experiments looking for multi-strange hypernuclei and

shorter lifetime SQM at Japanese Hadron Facility (?)

Conclusions and Future

Good Discussions

I want to acknowledge useful and fun discussions in preparing forthis talk with

Frank RotondoAdam RusekBill ZajcSebastian WhiteBob CousinsJosh KleinRam Ben-DavidJurgen Schaffner-BielichJack SandweissSotiria Batsouli

and many others……..

How does coalescence work?

Deuteron coalescence in p + A collisions

Deuteron coalescence in A + A collisions

Model Predictions for H dibaryon:How often are all the ingredients within the phase space (r, p) normally adequate to coalescence a deuteron from a proton-neutron pair.

p n

Nagle et al., Phys. Rev. C 53, 367 (1996).

= 2 fm B.E.( - 3H) = 2.04 Mev

e : = 1.4 fmE. = 29 MeV

Size effects not important

But weakly bound breaks easily

strong unstable nucleus

(2J + 1) = 4 , (2J + 1) = 10

Then, not much additional penalty for strangeness.

Other Hypernuclei

MeV

J

J

(3.92 GeV)

10412.04.0

4

4

Hn

H

2r

.R.(e)= 50%

2r