# Presentation: 598491

## Searches for States of Exotic Hot and Cold Quark Matter

- James Nagle
- Columbia University

## Outline

**Motivations for Studying Heavy Ion Collisions**
**	**Creation of **Hot** Quark-Gluon Plasma
- 	Creation of **Cold** Strange Quark Matter
**Probes of these Phenomena**
- 	Strange Anti-baryon Production
- 	Antideuteron Production
- 	Search for Strange Quark Matter (Strangelets)
**Experimental Results**
**	**Experiment E878 and
-                                 E864 at the Brookhaven AGS
**Conclusions**
**	**What are the Answers?

## Dense Nuclear Matter

- A gold nucleus has a volume of ~1400 fm3

- The individual nucleons are ~ 4.6 fm3   x 197

**~ 65% of the total volume occupied!**

- However, if you compress a nucleus to **ten** times nuclear matter density, the individual nucleons overlap.

- It becomes unclear to which proton or neutron a quark belongs.

- Baryon =
-      3 Quarks

## Phase Transitions

**Deconfinement**

- Normally quarks are bound together (confined) in particles such as protons and neutrons.
- QCD (the theory of strong interactions) states that there can be no free individual quarks.
- However, QCD predicts that at high density      (5 to 10 ) and high temperature (~ 150-200 MeV ~ 1012 oF), the quarks are no longer confined, but form a **plasma of quarks.**

- u

- u

- d

- u

- u

- d

- u

- d

- d

- d

- u

- u

- u

- d

- d

- u

## Chiral Symmetry

- If the individual nucleons disappear,
- and the system is a plasma of individual quarks, one expects that the quarks will act as nearly massless objects.
- This transition to nearly massless quarks is called the restoration of approximate **Chiral Symmetry**.
- The up and down quark are expected to have masses of ~ 5 MeV, while the strange quark is reduced to a mass of       ~ 150 MeV.

**Up       Down    Strange  Charm   Bottom  Top**

## Heavy Ion Collisions

- 1) Collision of Nuclei

- 2) Compressed and
- Heated Nuclear Matter

- 3) Expansion and Cooling

- ? Quark Phase
- ? Chiral Symmetry

## Enhanced Antibaryons

- What measurable effects might result in heavy ion collisions from a hot plasma state with nearly massless quarks?
- It will be easier to produce antibaryons (such as antiprotons) in a plasma.  The production of strange antibaryons (such as antilambdas) will be even more enhanced in part due to Pauli blocking of light quark pair production.

- U. Heinz *et al*., Nucl. Phys. 12 (1986) 1237.
- J. Ellis *et al.,* Phys. Lett. B 233 (1989) 233.
- P. Koch, B. Muller, J. Rafelski, Phys. Rep.142, 167 (1986).

**baryon**

**antibaryon**

**Quark - Antiquark**

**Quark - Antiquark**

- Anti-Strange Quark

## What Happens Next?

- K0

- K+

- K+

- K+ (u s)

**Bubbles of Hot Strange QM**

**Cools into Cold Lump of **
**Strange Quark Matter**

- C.Greiner *et al.* Phys. Rev. Lett. 58 (1987) 1825.
- C.Greiner and H. Stocker, Phys. Rev. D 44 (1991) 3517.

**s**

**s**

**s**

**s**

**s**

**s**

**s**

**s**

**s**

**s**

**s**

**s**

**s**

**s**

**s**

**s**

**s**

**Plasma has enhanced s s **
**content, but no net strangeness**

**Strangeness Separation**

**s**

**s**

**s**

**s**

**s**

**s**

**s**

**s**

## Strange Quark Matter

- The existence of quark states with more than three quarks is allowed in QCD.  The stability of such quark matter states has been studied with lattice QCD and phenomenological bag models, but is not well constrained by theory.
- The addition of strange quarks to the system allows the quarks to be in lower energy states despite the
- additional mass penalty.

- u

- d

- u

- d

- s

- Energy Level

- Strange Quark Mass

_**Quark Matter**_**    **_**Strange Quark Matter**_

- There is additional stability from reduced Coulomb
- repulsion.  SQM is expected to have **low Z / A**.

## Strange Quark Matter Stability

- Strange Quark Matter detection for
- mass > 10 GeV would be a smoking gun signature of **hot quark plasma** formation !

- Also, theorists have speculated that strange quark matter might exist in the core of neutron stars and other astrophysical objects.
- E. Witten proposed that large lumps of strange quark matter might be **even more** stable than nuclear matter (55Fe) and thus could exist as remnants from the Big Bang and help to explain the **Dark Matter** question.

## Where is the Experiment?

- Brookhaven National Laboratory

- Accelerator:  AGS (Alternating Gradient Synchrotron)

**Experiment E878 and E864**

## E864 Collaboration

- G. De Cataldo, N. Giglietto, A. Raino, P. Spinelli
**University of Bari/INFN**
- C.B. Dover
**Brookhaven National Laboratory**
**K.N. Barish**, H.Z. Huang
**University of California, Los Angeles**
**J.L. Nagle**
**Columbia University**
- J.C. Hill, **R.A. Hoverstein**, B.P. Libby, F.K. Wohn
**Iowa State University**
- P. Haridas, I.A. Pless, **G.Van Buren**
**Massachusetts Institute of Technology**
- T.A. Armstrong, R.A. Lewis, G.A. Smith, W.S. Toothacker
**Pennsylvania State University**
**R.R. Davies**, A.S. Hirsch, N.T. Porile, A. Rimai, R.P. Scharenberg, M.L. Tincknell
**Purdue University**
- M.S.Z Rabin
**University of Massachusetts**
- S.V. Greene, **T. Miller**, J.D. Reid, **A. Rose**
**Vanderbilt University**
- S.J. Bennett, T.M. Cormier, P. Dee, **P. Fachini**, B. Kim, **M.G. Munhoz**, C.A. Pruneau,    K.H. Zhao
**Wayne State University**
- A. Chikanian, **S. Batsouli**, **S.D. Coe**, G.E. Diebold, **L.E. Finch**, **N.K. George**, B.S. Kumar**,**** J.G. Lajoie**, R.D. Majka, **J.K. Pope**, F.S. Rotondo, J. Sandweiss, A.J. Slaughter
**Yale University **

## Slide 13

## E864 Details

**Overall Design**

-  Multi-purpose detector
-  Measures mass from momentum and velocity
-  High data rate (samples 105 interactions/sec)

**Specifics**

**Six planes of Straw Tube tracking chambers **
**Time-of-Flight Hodoscopes with ********(time) ~ 120-150 ps**
**Hadronic Calorimeter for independent mass measurement with energy resolution ~ 40%/sqrt(E) and ********(time) ~ 400 ps **
**High Mass Trigger (requiring late-energy in calorimeter) **

## E864 Pictures

- Time-of-Flight Detectors

- Simon Bennett and the
- Calorimeter

## E864 Particle Identification

**Excellent Antiproton Signal to Noise Ratio**

**Good Z=2 Identification**

**Neutral Particle Measurement Using the Hadronic Calorimeter**

## E864 Antiproton Data

- The production level increases for more central collisions.

**Excellent agreement for the 10% most central data between independent analysis efforts.  Note:  different triggers, different magnetic fields, different people**
**(J.G. Lajoie, J.N.)**

- T.A. Armstrong et al., Phys. Rev. Lett.  79, 3351 (1997).
- J.L. Nagle et al., J. Phys. G:  Nucl. Phys. 23 2145 (1997).

**Accepted in Phys. Rev. C**

## Data Comparison

- There is no statistically significant disagreement for the most peripheral collisions.
- The two data sets disagree to a significant extent for more central collisions.

- E864 (1996)
- E864 (1995)
- E878

## Do the Experiments Measure the Same Thing?

- There are many particles which decay into antiprotons at various distances from the interaction target.

- Target

- Incoming Au beam

- 

- p

- 

- Number of strange anti-quarks

## Decay Contributions

- E878 has a very small opening aperture and thus
- the relative acceptance for  and 0 is ~ **14%** for + ~11%.   No calculations for |S|=2,3 objects has been done.
- E864 has a large opening aperture and thus the relative acceptance for all these decay products is ~ **100%.**

- E878 ~  p

- E864 ~  p + frac()

## Ratio of Strange Antibaryons to Antiprotons

- Peripheral Collisions are consistent with elementary particle collisions ratios for strange antibaryons.
**However, for more central collisions there is a significant enhancement.**

**Strange Antibaryons / Antiprotons**

## Other Preliminary Results

- Two other experiments (**E877** and **E866**) have measured antiprotons and have calculated their relative acceptance for strange antibaryons.  So far the picture is consistent!

## Other Measurements and Other Systems

**Preliminary - Exp. 859 (Y. Wu)**

**Si + Au central collisions**
****** ****--****>   p + ********+**
**Indicate significant enhancement**

**Au + Au central collisions**
**Awaiting final results!**

**Pb + Pb central collisions **
**at CERN SPS (higher energy)**
****** ****--****>   p + ********+**
**NA35, NA49, WA97 **
**and also**
******and******
**WA97**

## Model Comparisons

- E859 and NA49 results are preliminary
- Published theoretical results

## More on Thermal Models

- In a simple model assuming chemical and thermal equilibration in the hadron phase, Y/p > 2 is obtained in some parameter space....
- Although there are serious questions about the model assumptions.

- Temp.       = 120 MeV
- (up)        = 200 MeV

- Strangeness chemical potential set by conservation of strangenes.

## More on Transport Models

- The annihilation probability is large due to the strong attraction between the proton and antiproton.

- Calculations indicate antiproton losses
- on the order of **90-95%**

**Escape path**

- Extreme calculation with no annihilation for strange antibaryons in RQMD yield Y/p ~ 3
- This has a dramatic effect of Pt distribution

## Why does the QGP model work so well?

- The QGP model predictions were published well before any strange antibaryon results for Au + Au and Pb + Pb were available

- The QGP model assumes that in the deconfined state
- s = 0
- independent of temperature and baryon density

- Now the problem is when we apply hadrochemistry in the Grand Canonical Ensemble how do be conserve strangeness?????

-  If hadronization occurs quickly the relative abundances of mesons and baryons stays fixed “because processes which convert mesons into baryon-antibaryon pairs are relatively slow.”  Thus, the model fixes the meson to baryon ratio in order to conserve strangeness.

## What have we learned?

- Very interesting results indicating large enhancement of strange antibaryons.
- Presently, these yields are difficult to explain in a purely hadronic picture.
- Enhancement easily understood in quark plasma model; **however**, a consistent picture is still lacking.

- Direct measurement of  is needed with pt dependence.
-       (E866/E917 analysis is far along...)
- Also, more comparisons with
- data at higher energies
- (**CERN and RHIC**)!

## What about Antideuterons?

- No statistically significant signal observed
- Set upper limit on coalescence parameter

- Coalescence if antiproton and antineutron close in phase space; therefore antiprotons from weak decay of strange antibaryons do NOT contribute

## Preliminary Mass Distribution

- Data Analysis of Gene Van Buren

- Preliminary

- True measure of the coalescence rate gives...
- 	1) Information about strange antibaryons
- 	2) Information about the spatial distribution 	         and collective flow of antinucleons

- J.L. Nagle et al., Phys. Rev. Lett. 73 (1994) 1219.
- J.L. Nagle et al., Phys. Rev. C 53 (1996) 367.
- H. Sorge, J.L. Nagle and S.Kumar, Phys. Lett. B 355 (1995).

## What else is there?

- Many other interesting observations:
-      First Neutron Yields
-      **Coalescence of Light Nuclei up to A=7**
**     ****First Reconstruction of Unstable Nuclei**

- A= 1    2    3      4        5      6      7

- Evan Finch, Zhangbu Xu, Nigel George

## Search for Z< 0 Objects

- We identify over **50,000**** **antiprotons from tracking
- and observe a number of Z=-1 high mass candidates.

- However, using the hadronic calorimeter reveals these candidates as **background**...

## Strange Quark Matter Limits

- Strangelets/Event < **10****-9**
- Lifetimes >  50 ns

- uuuuuu
- dddddd
- ssssss

- T.A. Armstrong *et al*, Phys. Rev. Lett. 79, 3612 (1997).
- T.A. Armstrong *et al*,. Nucl. Phys. A 625, 494 (1997).

**E878 Limits**

**E864 Published**

**E864 Final Limits**

## SQM Production Mechanisms

- 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).

**Coalescence**

- Strange and non-strange nucleons
- combine into composite objects in near final-state interaction.
**Only viable for low mass  range **

**QGP Distillation**

- Plasma charges up with net strangeness and cools off into meta-stable SQM droplet.
**Only mechanism for high mass**

**QGP Prediction**

## What is the Experiment Doing Now?

-  Final strange quark matter limits
-  We recorded over 280 Million events for the reconstruction of **H****4****** (bound state of p-n-n-) decaying to 4He + 
-  Think about future experiments at JHF

**Cold Quark Matter Search**

**Hot Quark Matter Search**

-  Final antiproton results in Phys. Rev. C
-  Working on antideuteron invariant yields
-  Look forward to results from E866/E917 and E896 and more theoretical developments
-  RHIC results on strange antibaryons should be very exciting!

## Cold

**Cold**

**Hot**

- No Strangelets 10-9

- Intriguing Strange
- Antibaryon Signal

## Neutral Candidates

- Candidates understood to result from overlapping neutron showers and neutrons originating from secondary Au interactions in the target.

## Slide 38

## Other Ideas and Explanations

- Antiprotons can be converted to strange antibaryons by associated production.

- p +  + K

- However, cascade models such as RQMD include such processes and only get ratios for /p ~ 0.4.

- Strange antibaryons might have a lower annihilation probability than antiprotons

- One expects the cross section to be somewhat lower due to less available phase space and possibly other reasons (quark content).

- p

- 

- initial

- final

## RQMD/Coalescence Au + Au central collisions

## RQMD/Coalescence Calculation for Antideuterons

**Good agreement with existing published**
**deuteron and antideuteron data.**

- J.L. Nagle et al., Phys. Rev. Lett. 73 (1994) 1219.
- J.L. Nagle et al., Phys. Rev. C 53 (1996) 367.
- H. Sorge, J.L. Nagle and S.Kumar, Phys. Lett. B 355 (1995).

**Awaiting new data at CERN from **
**NA44 in Pb + Pb**

## Antideuteron Tracking Results

- No statistically significant signal
- above background.