Search

The E895 Collaboration has investigated a number of mixed-particle correlations involving neutral strange particles (K0s and Λ) in 2, 4, 6 and 8 A GeV Au + Au collisions at the AGS. The first measurements for pΛ correlations indicate a correlation magnitude of about 50% with a 26 MeV width. Detailed comparisons between data and theory suggest an emitting source with an effective Gaussian radius close to 4.5 fm. This radius is much larger than the value of 2.8 fm predicted by the relativistic transport code ART. Pairs of pK0, π−Λ and π−K0 are found to display essentially zero correlation at 6 A GeV. The latter observations are not unexpected considering that the proton–K0 interaction has a very small scattering length and there are no very well known interactions between pions and Λs or K0s.

Directed flow measurements for {Lambda} hyperons are presented and compared to those for protons produced in the same Au+Au collisions (2A, 4A, and 6AGeV; b

Transverse and radial flow measurements are presented for Λ hyperons along with Λ-P correlations from Au + Au collisions at AGS energies. The flow measurements are compared with those of co-produced protons. The measurements indicate that Λ hyperons flow consistently in the same direction as protons but with a smaller magnitude for all beam energies. Comparisons with RQMD calculations show that the experimentally determined Λ sideward flow is consistently larger compared with the calculated value obtained from scattering processes only. The experimental transverse flow ratio Λ/P is consistent with predictions ( 2/3) of the quark counting rule at 2 A GeV but is found to decrease with increasing beam energy. These observations may be related to the detailed features of the Λ-nucleon potential for the nuclear densities produced. At 6 A GeV, Λp correlation functions are observed to be essentially flat (within statistical uncertainty), indicating little or no correlation between Λs and co-produced protons. This suggests that Λs may have a spacetime emission pattern which is different from that for protons. Further evidence from radial flow measurements also indicates that 6 A GeV Λ hyperons (at mid-rapidity) do not share the same emitting source characteristics as co-produced protons.

We have measured the sideward flow of neutral strange (K{sup 0}{sub s} ) mesons in 6A GeV Au +Au collisions. A prominent antiflow signal is observed for an impact parameter range (b(less-or-similar sign)7 fm ) which spans central and midcentral events. Since the K{sup 0}{sub s} scattering cross section is relatively small in nuclear matter, this observation suggests that the in-medium kaon vector potential plays an important role in high density nuclear matter. (c) 2000 The American Physical Society.

We present the first excitation function of ${\ensuremath{\pi}}^{\ensuremath{-}}$ intensity interferometry at Alternating Gradient Synchrotron (AGS) energies (2--8 A GeV). The sensitivity of the multidimensional correlation functions to the geometry and dynamics of the pion-emitting system provides a stringent test of transport models of heavy ion collisions. Detailed comparisons with a realistic transport model, both with and without an explicit nuclear mean field, suggest that the beam energy evolution in the reaction dynamics is different in the model than in the data. A significantly increased ${\ensuremath{\pi}}^{\ensuremath{-}}$ emission time scale, which has been suggested as a signal of the onset of the transition to quark-gluon plasma, is not observed.

We present some of the latest results from the E895 experiment conducted at the BNL AGS accelerator. Au+Au collisions were recorded by the EOS Time Projection Chamber (TPC) at beam energies of 2, 4, 6, and 8 A GeV. The TPC detector permitted the reconstruction of individual collision events with almost 4π acceptance and good particle identification. This capability allowed E895 to study global observables and two particle correlations with respect to symmetries of the event. Flow excitation functions are examined and discussed in the context of the Nuclear Equation of State.

We have measured the proton elliptic flow excitation function for the Au + Au system spanning the beam energy range 2 -- 8 AGeV. The excitation function shows a transition from negative to positive elliptic flow at a beam energy, $E_{tr} \sim$ 4 AGeV. Detailed comparisons with calculations from a relativistic Boltzmann-equation are presented. The comparisons suggest a softening of the nuclear equation of state (EOS) from a stiff form (K \sim 380 MeV) at low beam energies (E_{Beam} \le 2 AGeV) to a softer form (K \sim 210 MeV) at higher energies (E_{Beam} \ge $ 4 AGeV) where the calculated baryon density $ \rho \sim 4 \rho_0$.

A sample of Lambda's produced in 2 A*GeV Ni + Cu collisions has been obtained with the EOS Time Projection Chamber at the Bevalac. Low background in the invariant mass distribution allows for the unambiguous demonstration of Lambda directed flow. The transverse mass spectrum at mid-rapidity has the characteristic shoulder-arm shape of particles undergoing radial transverse expansion. A linear dependence of Lambda multiplicity on impact parameter is observed, from which a total Lambda + Sigma^0 production cross section of $112 +/- 24 mb is deduced. Detailed comparisons with the ARC and RVUU models are made.

Transverse kinetic energies of individual fragments have been measured over a broad range of emitter excitation energies for the reaction 1AGeV Au+C. For excitation energies leading to large intermediate mass fragment multiplicities, these transverse energies require large collective radial expansion of the emitting systems. However, the traditional decomposition of the transverse energy into a thermal component and a Coulomb and collective component proportional to the fragment mass cannot account for this expansion. Expansion velocities show an increase with decreasing fragment Z and thus indicate fractionation of the collective energy for the expanding system. This collective energy increases with emitter excitation up to about 50{percent} of the energy deposited for a nuclear system with total energy {approximately}12AMeV. The bulk of the collective energy is carried away by ejectiles of Z{le}3. {copyright} {ital 1998} {ital The American Physical Society}

A high-statistics exclusive study of the multifragmentation of 1A GeV gold on carbon has been performed. Particles with Z{le}2 show evidence of emission in a first prompt stage as well as in a second equilibrium stage whereas fragments with Z{ge}3 appear to be emitted essentially only in the second stage. Two methods for the separation of the Z{le}2 particles into the two stages are given and they are in agreement. The yields for each stage are determined as a function of the event charged particle multiplicity m. The mass, nuclear charge, excitation energy per nucleon, and temperature of the remnant left after the first stage and their fluctuations have been determined as a function of m. The expansion of the remnant to fragment freeze-out is examined. The freeze-out temperature is determined from double isotope ratios as a function of m and isentropic trajectories are obtained in the temperature-density plane. The caloric curve shows a monotonic increase with excitation energy. Some of the energy is in the form of radial flow. Overall, the results are consistent with a previous statistical analysis of the data which suggests that, over a certain range of excitation energies, multifragmentation involves a continuous phase transition. {copyright}more » {ital 1998} {ital The American Physical Society}« less

The E895 experiment has undertaken a systematic and exclusive study of Au+Au collisions between 2–8 A GeV. Complete event-by-event data were obtained using the EOS time projection chamber (TPC) which provided good particle identification and continuous tracking over almost 4π solid angle. In central Au+Au collisions at 6 A GeV, the proton rapidity distribution indicates almost complete stopping, hence high baryon density. We present preliminary results on collective flow observables as a function of beam energy. Data are compared with theoretical predictions.

Invariant mass analyses of (p,{pi}{sup {plus_minus}}) pairs in {sup 58}Ni+Cu collisions at 1.97A GeV have been performed and show correlations resulting from the decays of the {Delta} resonance, the {Lambda} baryon, and possibly the N{sup {asterisk}}(1440) resonance. A reduction in the {Delta} mass is observed and the mass reduction increases with collision centrality. Events generated by the relativistic cascade model (ARC) also reveal a mass reduction. The mass reduction is related to the size of the reaction volume and the details of {Delta} production mechanisms in heavy ion collisions. {copyright} {ital 1997} {ital The American Physical Society}

Transverse flow has been studied as a function of impact parameter for pions and protons from the reaction 1.15A GeV {sup 197}Au+{sup 197}Au. We observe an {open_quotes}antiflow{close_quotes} behavior for both {pi}{sup +} and {pi}{sup -} in peripheral collisions. {copyright} {ital 1997} {ital The American Physical Society}

We study the energy dependence of collective (hydrodynamic-like) nuclear matter flow in (400{endash}1970){ital A} MeV Ni+Au and (1000{endash}1970){ital A} MeV Ni+Cu reactions. The flow increases with energy, appears to reach a maximum, and then to decrease at higher energies. A way of comparing the energy dependence of flow values for different projectile-target mass combinations is introduced, which demonstrates a more-or-less common scaling behavior among flow values from different systems. {copyright} {ital 1997} {ital The American Physical Society}

Author(s): Lisa, M.A.; Albergo, S.; Bieser, F.; Brady, F.P.; Caccia, Z.; Cebra, D.A.; Chacon, A.D.; Chance, J.L.; Choi, Y.; Costa, S.; Elliott, J.B.; Gilkes, M.L.; Huager, J.A.; Hirsch, A.S.; Hjort, E.L.; Insolia, A.; Justice, M.; Keane, D.; Kintner, J.; Matis, H.S.; McMahan, M.; McParland, C.; Olson, D.L.; Partlan, M.D.; Porile, N.T.; Potenza, R.; Rai, G.; Rasmussen, J.O.; Ritter, Hans G.; Romanski, J.; Romero, J.L.; Russo, G.V.; Scharenberg, R.P.; Scott, A.; Shao, Y.; Srivastava, B.K.; Symons, T.J.M.; Tincknell, M.L.; Tuve, C.; Wang, S.; Warren, P.; Westfall, G.D.; Wieman, H.H.; Wolf, K.

Measurements of the transverse momenta ([ital p][sub [ital T]]) of medium and heavy mass projectile fragments for a range of projectile nuclei ([sup 40]Ar, [sup 93]Nb, [sup 139]La, [sup 197]Au) have been carried out. It is found that the width of the transverse momentum distributions increases more rapidly with projectile and fragment mass than predicted by models based on nucleon momenta in the projectile nuclei. The distributions can be fit by including an additional transverse momentum, [ital p][sub [ital B]] (for Bounce). The extracted values of [ital p][sub [ital B]]/[ital A][sub [ital F]] increase with decreasing [ital A][sub [ital F]], and extrapolations to small [ital A][sub [ital F]] appear to be consistent with the mean values of reaction-plane-projected [ital p][sub [ital T]] per nucleon for light particle (e.g., nucleon) bounce-off.''

Brookhaven-AGS. Measuerment of the spectra of charged pions over nearly full rapidity coverage from target to beam rapidity in the centrality range 0-5pct in AU-AU collisions at beam energies from 2 to 8 A GeV/nucleon. The rapidity densities are extracted using a thermal paramatrization model to fit the transverse mass spectra.. Numerical values supplied by J Klay.. This part (1) covers the data at 2 GeV/nucleon. Brookhaven-AGS. Measuerment of the spectra of charged pions over nearly full rapidity coverage from target to beam rapidity in the centrality range 0-5pct in AU-AU collisions at beam energies from 2 to 8 A GeV/nucleon. The rapidity densities are extracted using a thermal paramatrization model to fit the transverse mass spectra.. Numerical values supplied by J Klay.. This part (2) covers the data at 4 GeV/nucleon. Brookhaven-AGS. Measuerment of the spectra of charged pions over nearly full rapidity coverage from target to beam rapidity in the centrality range 0-5pct in AU-AU collisions at beam energies from 2 to 8 A GeV/nucleon. The rapidity densities are extracted using a thermal paramatrization model to fit the transverse mass spectra.. Numerical values supplied by J Klay.. This part (3) covers the data at 6.0 GeV/nucleon. Brookhaven-AGS. Measuerment of the spectra of charged pions over nearly full rapidity coverage from target to beam rapidity in the centrality range 0-5pct in AU-AU collisions at beam energies from 2 to 8 A GeV/nucleon. The rapidity densities are extracted using a thermal paramatrization model to fit the transverse mass spectra.. Numerical values supplied by J Klay.. This part (4) covers the data at 8.0 GeV/nucleon. Brookhaven-AGS. Measurement of the spectra of charged pions over nearly full rapidity coverage from target to beam rapidity in the centrality range 0-5pct in AU-AU collisions at beam energies from 2 to 8 A GeV/nucleon. The rapidity densities are extracted using a thermal paramatrization model to fit the transverse mass spectra.. Numerical values supplied by J Klay.. This part (5) covers the data Rapidiy density data.

Source images are extracted from two-particle correlations constructed from strange and nonstrange hadrons produced in 6A GeV Au+Au collisions. Very different source images result from pp vs p Lambda vs pi(-)pi(-) correlations. Scaling by transverse mass can describe the apparent source size ratio for p/pi(-) but not for Lambda/pi(-) or Lambda/p. These observations suggest important differences in the space-time emission histories for protons, pions, and neutral strange baryons produced in the same events.

The yield for the multi-strange $\Xi^{-}$ hyperon has been measured in 6 AGeV Au+Au collisions via reconstruction of its decay products $\pi^{-}$ and $\Lambda$, the latter also being reconstructed from its daughter tracks of $\pi^{-}$ and p. The measurement is rather close to the threshold for $\Xi^{-}$ production and therefore provides an important test of model predictions. The measured yield for $\Xi^{-}$ and $\Lambda$ are compared for several centralities. In central collisions the $\Xi^{-}$ yield is found to be in excellent agreement with statistical and transport model predictions, suggesting that multi-strange hadron production approaches chemical equilibrium in high baryon density nuclear matter., Comment: Submitted to PRL

Source images are extracted from two-particle correlations constructed from strange and nonstrange hadrons produced in 6A GeV Au+Au collisions. Very different source images result from pp vs p Lambda vs pi(-)pi(-) correlations. Scaling by transverse mass can describe the apparent source size ratio for p/pi(-) but not for Lambda/pi(-) or Lambda/p. These observations suggest important differences in the space-time emission histories for protons, pions, and neutral strange baryons produced in the same events.

Proton elliptic flow is studied as a function of impact-parameter $b$, for two transverse momentum cuts in 2 - 6 AGeV Au + Au collisions. The elliptic flow shows an essentially linear dependence on b (for $1.5 < b < 8$ fm) with a negative slope at 2 AGeV, a positive slope at 6 AGeV and a near zero slope at 4 AGeV. These dependencies serve as an important constraint for discriminating between various equations of state (EOS) for high density nuclear matter, and they provide important insights on the interplay between collision geometry and the expansion dynamics. Extensive comparisons of the measured and calculated differential flows provide further evidence for a softening of the EOS between 2 and 6 GeV/nucleon.

A systematic analysis of the multifragmentation (MF) in fully reconstructed events from 1A GeV Au, La and Kr collisions with C has been performed. This data is used to provide a definitive test of the variable volume version of the statistical multifragmentation model (SMM). A single set of SMM parameters directly determined by the data and the semi-empiricalmass formula are used after the adjustable inverse level density parameter, $\epsilon_{o}$ is determined by the fragment distributions. The results from SMM for second stage multiplicity, size of the biggest fragment and the intermediate mass fragments are in excellent agreement with the data. Multifragmentation thresholds have been obtained for all three systems using SMM prior to secondary decay. The data indicate that both thermal excitation energy $E_{th}^{*}$ and the isotope ratio temperature $T_{He-DT}$ decrease with increase in system size at the critical point. The breakup temperature obtained from SMM also shows the same trend as seen in the data. The SMM model is used to study the nature of the MF phase transition. The caloric curve for Kr exhibits back-bending (finite latent heat) while the caloric curves for Au and La are consistent with a continuous phase transition (nearly zero latent heat) and the values of the critical exponents $\tau$, $\beta$ and $\gamma$, both from data and SMM, are close to those for a 'liquid-gas' system for Au and La. We conclude that the larger Coulomb expansion energy in Au and La reduces the latent heat required for MF and changes the nature of the phase transition. Thus the Coulomb energy plays a major role in nuclear MF.

Rapidity distributions of protons from central ${}^{197}\mathrm{Au}{+}^{197}\mathrm{Au}$ collisions measured by the E895 Collaboration in the energy range from $(2--8)A\mathrm{GeV}$ at the Brookhaven AGS are presented. Longitudinal flow parameters derived using a thermal model including collective longitudinal expansion are extracted from these distributions. The results show an approximately linear increase in the longitudinal flow velocity, $〈\ensuremath{\beta}\ensuremath{\gamma}{〉}_{L}$, as a function of the logarithm of beam energy.

The fragment yields from the multifragmentation of gold, lanthanum and krypton nuclei obtained by the EOS Collaboration are examined in terms of Fisher's droplet formalism modifed to account for Coulomb energy. The critical exponents sigma and tau and the surface energy coefficient c0 are obtained. Estimates are made of the pressure-temperature and temperature-density coexistence curves of finite neutral nuclear matter as well as the location of the critical point., Comment: 14 pages, 13 figures, 6 tables, submitted to Phys. Rev. C

The multifragmentation data of the ISiS Collaboration and the EOS Collaboration are examined. Fisher's droplet formalism, modified to account for Coulomb energy, is used to determine the critical exponents {tau} and {sigma}, the surface energy coefficient c{sub 0}, the pressure-temperature-density coexistence curve of finite nuclear matter and the location of the critical point.

Rapidity distributions of protons from central 197Au+197Au collisions measured by the E895 Collaboration in the energy range from (2-8)A GeV at the Brookhaven AGS are presented. Longitudinal flow parameters derived using a thermal model including collective longitudinal expansion are extracted from these distributions. The results show an approximately linear increase in the longitudinal flow velocity,betagamma(L), as a function of the logarithm of beam energy.

Multifragmentation MF results from 1A GeV Au on C have been compared with the Copenhagen statistical multifragmentation model ~SMM!. The complete charge, mass, and momentum reconstruction of the Au projectile was used to identify high momentum ejectiles leaving an excited remnant of mass A, charge Z, and excitation energy E* which subsequently multifragments. Measurement of the magnitude and multiplicity ~energy! dependence of the initial free volume and the breakup volume determines the variable volume parametrization of SMM. Very good agreement is obtained using SMM with the standard values of the SMM parameters. A large number of observables, including the fragment charge yield distributions, fragment multiplicity distributions, caloric curve, critical exponents, and the critical scaling function are explored in this comparison. The two stage structure of SMM is used to determine the effect of cooling of the primary hot fragments. Average fragment yields with Z>3 are essentially unaffected when the excitation energy is 170 the effective latent heat approaches zero. Thus for heavier systems this transition can be identified as a continuous thermal phase transition where a large nucleus breaks up into a number of smaller nuclei with only a minimal release of constituent nucleons. Z

J. L. Chance, F. P. Brady, J. L. Romero, S. Albergo, F. Bieser, Z. Caccia, D. Cebra, A. D. Chacon, Y. Choi,* S. Costa, J. B. Elliott, M. L. Gilkes, J. A. Hauger, A. S. Hirsch, E. L. Hjort, A. Insolia, M. Justice, D. Keane, J. C. Kintner, V. Lindenstruth, M. A. Lisa, H. S. Matis, M. McMahan, C. McParland, W. F. J. Muller, D. L. Olson, M. D. Partlan, N. T. Porile, R. Potenza, G. Rai, J. O. Rasmussen, H. G. Ritter, J. Romanski, G. V. Russo, H. Sann, R. Scharenberg, A. Scott, Y. Shao, B. K. Srivastava, T. J. M. Symons, M. Tincknell, C. Tuve, S. Wang, P. G. Warren, H. H. Wieman, T. Wienold, and K. Wolf

A systematic analysis of the moments of the fragment size distribution has been carried out for the multifragmentation of $1A\mathrm{GeV}$ Au, La, and Kr on carbon. The breakup of Au and La is consistent with a continuous thermal phase transition. The data indicate that the excitation energy per nucleon and isotopic temperature at the critical point decrease with increasing system size. This trend is attributed primarily to the increasing Coulomb energy with finite size effects playing a smaller role.

The inclusive light fragment (Z⩽7) yield data in Au+Au reactions, measured by the EOS Collaboration at the LBNL Bevalac, are presented and discussed. For peripheral collisions the measured charge distributions develop progressively according to a power law which can be fitted by a single τ exponent independently of the bombarding energy in the range 250–1200 A MeV. In addition to this universal feature, we observe that the location of the maximum in the individual yields of different charged fragments shift towards lower multiplicity as the fragment charge increases from Z=3 to Z=7. This trend is common to all six measured beam energies. Moments of charge distributions and correlations among different moments are reported. Finally, the THe,DT thermometer has been constructed for central and peripheral collisions using the double yield ratios of He and D, T projectile fragments. The measured nuclear temperatures are in agreement with experimental findings in other fragmentation reactions.

Source imaging analysis was performed on two-pion correlations in central Au + Au collisions at beam energies between 2 and 8$A$ GeV. We apply the imaging technique by Brown and Danielewicz, which allows a model-independent extraction of source functions with useful accuracy out to relative pion separations of about 20 fm. We found that extracted source functions have Gaussian shapes. Values of source functions at zero separation are almost constant across the energy range under study. Imaging results are found to be consistent with conventional source parameters obtained from a multidimensional HBT analysis., Talk given at Bologna 2000 - Structure of the Nucleus at the Dawn of the Century, Bologna, Italia, May 29 - June 3, 2000

Directed flow measurements for Lambda hyperons are presented and compared to those for protons produced in the same Au+Au collisions (2A, 4A, and 6A GeV; b5-6 fm). The measurements indicate that Lambda hyperons flow consistently in the same direction but with smaller magnitudes. A strong positive flow [for Lambdas] has been predicted in calculations which include the influence of the Lambda-nucleon potential. The experimental flow ratio Lambda/p is in qualitative agreement with expectations (approximately 2/3) from the quark counting rule at 2A GeV but is found to decrease with increasing beam energy.

Multifragmentation in fully reconstructed events from 1A GeV Kr and La collisions with C has been studied. Results are compared with similar data for 1A GeV Au+C. The emitted charged particles and fragments are identified with emission from either a prompt first stage or a second stage in which the remnant resulting from the first stage breaks up. The nuclear charge, mass, and excitation energy distributions of the remnant are determined. The total charged multiplicity, as well as those of the first and second stages are obtained. Freeze-out temperatures and thermal excitation energy permit the determination of the caloric curve. The fragment charge distribution as well as the IMF multiplicity distribution and those of individual fragments are obtained. The various results are examined as to the extent of universal behavior when scaled for varying system size. Comparisons are made with intranuclear cascade and statistical multifragmentation model calculations. (c) 2000 The American Physical Society.

The properties of the remnant resulting from the emission of prompt particles in the interaction of 1A GeV {sup 197}Au+C interactions have been compared with intranuclear cascade and Boltzmann-Uehling-Uhlenback transport calculations. The number of first-stage particles and the energy spectra of first-stage protons are also compared. Both models can fit the general but not the detailed features of the data. (c) 1999 The American Physical Society.

We present a preliminary excitation function of π - intensity inteferometry at AGS energies (2-8 AGeV). The sensitivity of the multidimensional correlation functions to both the geometry and dynamics of the hot pionemitting system provide a stringent test of transport models of heavy ion collisions. Detailed comparisons are performed with the RQMD transport model, both with and without an explicit nuclear meanfield. These comparisons suggest that the evolution in the reaction dynamics with beam energy is different in the model and the data. A suggested signal of the onset of the transition to quark-gluon plasma in the inteferometry excitation function is not observed.

A primary goal of high-enery heavy ion physics is to create and study the quark-gluon plasma (QGP), a phase of matter in which partonic- instead of hadronic- degrees of freedom describe the system. Several transport, hydrodynamic, and nucleation theories1,2,3,4 suggest that energy densities achieved in central collisions between heavy ions at AGS energies may be sufficient to create the QGP.

It is shown that thermodynamic scaling when applied to systems with few (∼150) constituents, in accordance with the theory of critical phenomena, is observed in nuclear multifragmentation. Yields of different nuclear fragments, obtained over a wide range of excitation energies, collapse with some scatter onto a universal curve. This curve is the nuclear scaling function, which is intimately related to the free energy of the system. The determination of the scaling function forms the basis for quantitatively predicting the critical behavior in nuclei.

The mimimum requirement for a meaningful comparison of the 1 GeV Au on C data with the SMM1 predications is that the mass AR the charge Z R , and the excitation energy E x of the multifragmenting system be determined on an event by event basis. This can only be done if a full reconstruction of the collision is possible for each event. The EOS data2–4 provides a complete charge and momentum reconstruction for every event. Average fragment masses are determined. The basic remnant information A R (ZR, EX) is also used as input information for the SMM calculation. Thus a fragmentation event produced by SMM consists of M2s fragments with masses A F and charge Z F. A data fragmentation event consists of M2D fragments with mass A F and charge Z F . Since the remnant mass A R = A AU - M1 where M1 is the collisional particle multiplicity, it is convenient to introduce the total charged particle multiplicity M T for both the SMM predictions and the data. M T = M 2s + M1 for the SMM events and M T = M 2D + M1 for the Au on C events.

We supplement a recent study of the dynamics of the multifragmentation of the remnant of 1A GeV Au + C collisions by (1) providing a more complete characterization of the remnant and (2) performing a more detailed analysis of collective radial flow and exploring its consequences for the caloric curve.

A progress report is given for the various components of the STAR detector system. We report on the recent developments in the detector proto-typing and construction, with an emphasis on the main TPC, recent TPC cosmic ray testing and shipping to Brookhaven National Laboratory

We discuss the experimental situation of nucleon-induced reactions. Motivated by important current technological applications such as single event upsets (SEU) in microelectronic devices and particle-beam radiotherapy, we focus on light elements and beam energies below 250 MeV. We review the data from proton- and neutron-induced reactions obtained at UC Davis and elsewhere in the last 2 decades. Despite the large compilation of data (mainly inclusive spectra of light ions), we point out the scarcity of recoil data. We emphasize the fact that recoil nuclei contribute a significant part of the secondary radiation which is a major source of SEUs in devices, and of importance for radiation-related calculations. We discuss a new program under development, in which we measure recoil spectra using reverse kinematics. We discuss results from a recent experiment of 1H(28Si,A)x at 80 MeV/nucleon performed at the NSCL at Michigan State University. The preliminary data are compared well with a cascade-statistical reaction model (NUSPA).

Multifragmentation (MF) is the break-up of colliding nuclei into many species of lighter nuclei, particularly intermediate mass fragments (IMF’s) with 3 ≤ Z IMF ≤ 30 [1]. MF occurs in many different kinds of nuclear reactions when the excitation energy per nucleon is comparable to the nucleon binding energy. At lower excitation energy, a compound nucleus is formed, which decays by evaporation of a few light particles (primarily neutrons, protons, and alphas), leaving a large residual nucleus that contains most of the original mass. At higher energy, the excited system decomposes entirely into light particles. As excitation energy increases, the final mass yields start at low excitation with a double structure peaked at the lowest and highest masses, progress through a power law mass distribution of IMF’s at intermediate excitation, and end at high excitation with an exponential distribution of only light particles. This evolution strongly resembles the progression of a heated fluid from the liquid state through the critical point into the gaseous phase. Since pioneering studies in the early 1980’s [2], intense experimental and theoretical effort has focused on this behavior, attempting to understand the mechanism of MF. Although it is not universally accepted, the idea of a nuclear liquid-gas phase transition has become the leading paradigm used to interpret MF phenomena. Many important questions remain unresolved, including: does MF exhibited by different nuclear reactions have a common underlying physical mechanism? do the excited systems equilibrate sufficiently to apply thermal concepts? is the phase transition first order or continuous, and does this vary for different reactions? what are the thermodynamic properties (e.g. temperature, density, entropy) of these systems? what are the trajectories in the temperature-density plane for various reactions? can the physical properties of nuclear matter, including the equation of state, be extracted from MF data?

We have studied the yield of individual fragments formed in the projectile fragmentation of gold nuclei at 1 AGeV incident on a carbon target as a function of the total charge multiplicity. The yields of fragments of different nuclear charge peak at different multiplicities. We show that this behavior can be used to determine the critical exponent σ. We obtain σ = 0.68±0.05, consistent with the liquid-gas value.

The breakup of 1A GeV gold nuclei incident on carbon has been studied with a detector system that permitted exclusive event reconstruction of nearly all charged reaction products. The moments of the resulting charged fragment distribution and fluctuations therein provide strong evidence that nuclear matter possesses a critical point observable in finite nuclei. Values of the critical exponents γ, β, and τ have been determined. These values are close to those for liquid-gas systems but differ significantly from those for other 3-dimensional systems. Assumptions in our analysis have been examined and confirmed by dynamical information.

In two recent publications [1, 2], the EOS Collaboration has presented the first model independent determination of four critical exponents for nuclear matter based on the analysis of exclusive nuclear multifragmentation data obtained in 1 GeV/nucleon collisions of gold on a carbon target at the Lawrence Berkeley Bevalac. These studies were motivated in part by the striking resemblance nuclear multifragmentation data has with many aspects of critical phenomena [3, 4, 5]. In reference [2], the critical exponent σ was determined assuming that the multifragmentation data would exhibit the type of scaling expected for systems possessing critical behavior. In this paper, we demonstrate that this is indeed the case, and we determine for the first time the scaling function of nuclear matter.

Exclusive measurements have been made of Au+Au reactions with beam energies ranging from 0.25{ital A} to 1.15{ital A} GeV. We present measurements of directed collective flow averaged over all light fragments with masses up to alphas, as well as separate measurements for protons, deuterons, tritons, {sup 3}He, {sup 4}He, and Li. The results show a strong increase of the directed flow with fragment mass at all energies measured. Experimental results are compared with a quantum molecular dynamics model. We find that neither the ``soft`` nor the ``hard`` equation of state can describe the data over the entire range of beam energies.

Energy spectra of hydrogen and helium isotopes emitted in Au+Au collisions at 0.25, 0.40, 0.60, 0.80, 1.0, and 1.15 A GeV have been measured. A systematic study of the shapes of the spectra reveals a significant non-thermal component consistent with collective radial flow. The strength of this component is evaluated as a function of bombarding energy. Comparisons of the flow signal to predictions of QMD and BUU models are made. Using reverse kinematics, the breakup of gold nuclei has been studied in Au+C reactions at 1.0 A GeV. The moments of the resulting charged fragment distribution provide evidence that nuclear matter possesses a critical point observable in finite nuclei. Values for the critical exponents γ, β, and τ have been determined. These values are close to those for liquid-gas systems and different from those for 3D percolation.

Using charged-particle-exclusive measurements of Au+Au collisions in the LBL Bevalac`s EOS time projection chamber, we investigate momentum-space densities of fragments up to {sup 4}He as a function of fragment transverse momentum, azimuth relative to the reaction plane, rapidity, multiplicity, and beam energy. Most features of these densities above a transverse momentum threshold are consistent with momentum-space coalescence, and, in particular, the increase in sideward flow with fragment mass is generally well described by a momentum-space power law.