First results with the Au-beam at the AGS

NUCLEAR PHYSICS A

Nuclear Physics A$53 (1993) 799c-812c North-Holland, Amsterdam

First R e s u l t s W i t h T h e A u - B e a m A t T h e A G S Michel GON1N (E-802/E-866 Collaboration) Physics Departmeut Brookhaven National Laboratory, Upton, NY 11973, U.S.A.

Abstract Tile first measurements using it.6 A.GeV/c ISTAu beam have been made in April 1992 at the Tandem-Boostcr-AGS accelerator facilities. Preliminary results from different experiments are presented for An + Au collisions. Experiment E-877 shows large increase of the total transverse energy between Si + A! and Au -F Au reactions. Experiment E-866 observes an increase of the K+/~r+ ratio (0.25 + 0.02) with respect the Si + Au ratio.

1. Introduction The world's highest energy gold beam (11.6 A.GeV/c, Au 79+) was delivered to experinleuts at I]rookbavea's Tandcm-AGS facilities on April 24, 1992. This has provided an unique opportunity to achieve in a nuclear reaction the highest baryon densities ever obtained in ally experiment. Because of the large number of collisions involved in the Au-I-Au reaction, one mlgllt expect a complete thermalization of the system. The hope is that by using a "truly" heavy ion beam a "new" klnd of physics :'Jch as the formation of dense nnclear matter or tile quark-ghlon plasma can be achieved. • .A.brief description of the AGS exl~eriments using the gold beam is shown in table 1. ~1Ins include a large number of "small experiments (short exposure) and two major experlments E-866 (E-802 collaboration) and E-877 (E-814 collaboration). A fair amount of data was collected during the running permd of roughly two weeks. ~1he typical beam intensit.y on the target was of the order of ~- 5.10 ~ gohl ions/see. Tile data reported in this ilaper concern tile two majors experiments and the E-878 collaboration.

2. E - 8 7 7

Experiment (E-814 collaboration)

This experiloent is designed to study tile ultra-relativistlc nuclear collisions using tile E-814 calorimetry and a forward spectrometer. Energy flow is measured in the target (TCAL) and participant (PCAL) calorimeters {1]. Fig. l shows the total transverse energy produced in Si + AI and Au + Au reactions for PCAL. These data which are corrected for acceptaace and resolutioa show a large Elsevier Science Publishers B.V.

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M. Gonia / Fir,*t resuhs with the Au-beam at the AGS

increase of the total transverse etlergy with the mass of the collhliug ions. The E-877 experhnent has assumed that the total transverse energy production is proportional to A% They found the same value of ~= 1.11 =]=0.03 by scaling the transverse energy, locating the "knee" of the curves or by evahmtiug the transverse energy scale at the upper 30 mb cross section. This result is a strong indication for a high degree of "nuclear stopping" in Au+Au central collisions. It should be noted however first that the precise value of ¢x has to take with some caution because the two measurements have been done at different incident l~lomenta attd second that the total transverse energy is generated by pions and baryons. Figure 2 show similar results for the backward hemisphere calorimeter TCAL. The correlation of the transverse energy (or multiplicity) measured by PCAL with the transverse energy measured by TCAL is shown in ligure 3. The correlations look much narrower for the Au+Au case than for the Si+Al case. This may be related to an increase of the fluctuations in the Si ¢-AI reaction reflecting the geometry of the smaller size system. The dependence of the collishm's impact parameter may be viewed as a source of fluctuations more important in the Si+AI case than in the Au+Au case.

3. F -878 F,xperiment The goal of thls experiment is to search for antideuterons and other rare particles h'. '.he Au+Au reaction. This collMmration is a continuation of the E-858 beam line spectrometer co[[ahoratiou [2] (see figure 4). The bottom part of the figure 4 shows the iuvarisut cross section for *r- detected at zero degree beyond the beam rapidity. Due to the preliminary nature of the data, E-878 has applied a 50~ systematic error.

4. E-866 F

xperiment (F -802 Collaboration)

The program of E-866 is to continue tile iuvestigathm of semi-inclusive hadron spectra initiated by tile E-802 experiment wlth the proton, oxygen and silicon beams. First measurements with tile new beam were made with the existing E-802 magnetic spectrometer [3]. An upgraded forward calorimeter (ZCAL) provided a centrality trigger corresponding to roughly 4~0 of the total interaction cross section. Figure 5 shows the charge of beam particles measured by beam counters placed before and after the gohl target. We conclude from the top spectra that the beam (Z=79) purity is better than 1/300. T~Je bottom part of lignre 5 illustrates the effect of the 4% centrality cut of the zero degree calorimeter trigger, the residual charge of the beam projectile being reduced to very light particles. The large particle multiplicities expected in Au ~ A u collisions cause serious difficulties for the spectrometer tracking analysis. The data reported here have been takeu with Ihe spectrometer poslthmed at backward angles 34 deg. and 44 deg. where the mulip[icities are compatible with the capabilities of the spectrometer. Figure 6 shows the resulting acceptances for 7r~ and K +. Because of the target-projectile symmetry of the Au~-Au reactiou, results can be extrapolated to Ifigher vapidities by reflection, the missing part remaining the told-rapidity (y-~l.6). For baryon spectra some selected 21 deg. runs have also been iucluded. Before discussing data one should note that beside the statistical errors shown iu the f,dlowing figures, a systematic error o f 1 5 ~ has to be applied for each preliminary dN/dy point. The systematic error is 5 ~ for the inverse slopes.

M. Gonin / First results with the Au-beam at the AGS

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lnvarlant cross section versus transverse kinetic energy for protons and deuterons in the rapidity interval 0.50<_y_<0.70 are shown in figure 7. The full llne represents an exponential fit to tbe invarlant cross section. The multiplicity density dN/dy is obtained by integration of the exponential fit. The inverse slope parameter for protons is comparable with the Si-t-Au results. The higher inverse slope parameter for deuterons (T -~ 250 MeV) with respect to the protons inverse slope (T -~ 201 MeV) is not consistent with the prediction of the coab.~ceuce model. The d / p ratio reaches 8.4% +1.0% which is smaller by a factor of ~-2 than tire ratio in Si 4-An [4] in the same rapidity interval This is due to the fact that the peak of the dN/dy distribution for protons shifts from Iow*rapldity ill the Si ~-Au toward mid-rapidity in An+An. In figure 8 is plotted dN/dy distributions for central collisions ill Au+Au and Si+AI reactions [4] where rellected points about the center of mass rapidity are filled symbols. The dN/dy distribution for Au+Au does not exhibit a maximum at y ~-1.0 as does the Si FAI distribution. This suggests that a fairly large amount of stopping has been achieved in the central An+An collisions. In addition, we see in figure 9 that the distribution of the inverse slope parameter (shifted by ~y=+0.12 for An+An due to tile lower incident momentum ) is broader for the heavier system. The incident energy is more thermallzed in the An+An reaction than in tile Si FA! reaction, probably due to the larger number of collisions. This could be further evidence of the formation of matter with a high baryon density and a large lifetime in the central Au+Au collisions. Strangeness enhancement has been considered one of the signatures for the quark gluon plasma formation. E-802 results [5] indicated larger K+/Tr+ ratio in AA coillslons than in pp collisions. W~ plot in fgure 10 the K ~ and lr ~ spectra produced in central collisions in the rapidity interval 0.55 _
802¢

M, Gonin / First resuhs with the Au-beam at the AGS

7r- ( , ~ ) data have been multiplied by 1.15 (1.10). The low mt enhancement for ~r- is reproduced by the calculath~ns. No difl'erence is predicted between 7r- and ~r+ by ARC ca[culations which do not include Coulomb effects. As a conchlsimt for this comparison, the excellent agreement between E-866 and ARC suggest that low-lying haryons and mesons resonances play a leading role in the dynamics of the A u + A u collision at AGS cnerglcs.

5. Summary The recent AGS experiments with the gold beam have allowed the study of properties o[ nuclear matter under e×treme conditions. E-877 prelindnary data show that {.he total transverse energy is proportional to A~' with c~= 1.11 ±0.tl3 for symmetric systems. E-866 preliminary data indicate that a high amount of stopping and high degree o[ thermalization are achieved in the central Au+Au collision at 11.6 A.GeV/c. The ratio for K ~/~r ~ reaches 25% =i:2% and f~)r K - / K + about 16% 4-2%. Low mt enhancement (r,-) has been observed for the central collisions. Excellent agreement is found between E-866 preliminary data and the ARC predictions. These preliminary data need to be confirmed and extended by the upgraded experiments which are planned for 1993 and 1994. ACKNOWLEDGEMENTS Vtre are pleased to acknowledge the expertise of the AGS-Tandem staff for having dellvered the gold beam on time. It is my pleasure to thank C. Chasman and O. Hansen for the cri|ical reading of this mauuscript, P. Brauu-Munzinger a ud il. Crawford for providing the results of E-877 and E-878. The author also thanks T.J. Schlagel, S.H. Kahana and Y. Pang for allowing him to show the AR.C predictions. F,xperlments 8{12/866 are supported in part by the U.S. Department of Energy contracts and grants with ANL, BNL, UC-Berkeley, UC-Riverslde, Columbia, LLNL, and M|T, ia part by NASA nmler contract with UC-Berkeley, and by the US-Japan High Energy Physics Collaboration Treaty.

REFEH~.NCES [I] E-81,t Collaboration, P. Braun-Munzinger, Proc. of QM'91. [2] M. Aoki et al., submitted to Phys. Rev. Lett. ['~I T. Ahbott et al., N|M, A290 (1990) 4[-60 [-1] T. Abbott et al., E-802 collaboration, to he published. [5] T. Abhott et al., Phys. Rev. Left. 64, 847 (1990) [6] C. Parsons, Doctoral thesis, MIT (1992) [71 K. Kurita, Doctoral thesis, Colmnbia University (1992) [8] A. Wrol,lewski, Proc. Int. Syrup. on Multiparticle Dynamics, Kayserber(1977) I9] lt.R. Schmidt and J. Shukraft, to be published in Int. Journ. of Modern Phys. [1O] E.V. Shuryak, Nucl. Phys. A533, 761-788(1991) [11] Y. Pang et al., Phys. Rev. Lett. 68, 2743 (1992), T.J. Scldagel et al., to be published in Phys. Rev. Lett.

M. Gonin / First results with the Au-beam at the AGS

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List of current AGS experiments with the Au.beam E-862

Hill

Electromagnetic dissociation of Co and Au

E-863

Otter|und. Wilkes

Particle production and nuclear fragmentation

E-868

Waddington

Interactions of nuclei in light and heavy targets

E-869

Waddington

Measurement of fragment yields

E-875

Jain

Study of particle o, oduction and nuclear fragmentation

E-882

Price

Search for particles with large A/Z

E-883

Heinrich

Fragmentation of Au-pmjectiles

E-886

Imai, Pile

Search for new particles

E-878

Craw ford

Investigation of antinucleus and new particleproduction

E-866

Chasman, Steadman E-802 collaboration. Studies of particle production

E-877

Braun-Munzinger

E-814 collaboration. Study of relativistic nuclear collisions

Table 2: S u m m a r y of the K+/~ + and K ' / r ratios for E-866 and E-802

K+/~ + (y = [0.55-0.85])

Si+AI Si+Au Au+Au

Mininum Bias

Central

0.10 + 0.01 0.12 + 0.01

0.18+0.03 0.19 + 0.02

0.14 + 0.01

0.25 + 0.02

K ' / K + (y = [0.55 - 0.85])

Central Si+AI Si+Au Au+Au

0.35+0.11 0.28 + 0.10 0.16 + 0.02

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M. Gonin / First results with the Au-bemn at the AGS

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805c

M. Gonin I First results with the Au-beam at the AGS

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M. Gonin I First resuhs with the Au-heam at the AGS

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808C

M. Gonin l First results with tile Au-beam at the AGS

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M. Gonin I First results with the Au-beam at the AGS

1 1.6 GeV/c Au+Au

809c

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M. Gonin / First results with the Au-beam at the AGS

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M. Goni. / First results with the Au-beam at the AGS

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M. Go~,in / First results with the A~-bcmn at the AGS

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