NA35

NA35
Name	NA35
Facility	Super Proton Synchrotron
Location	CERN
Country	Switzerland
Operation period	1985–1995
Collaboration	CERN NA35 Collaboration
Primary beam	Sulfur ions, proton beams
Energy	60–200 GeV/nucleon
Detector type	streamer chamber, time projection chamber
Spokesperson	Günter Kern

NA35 NA35 was a fixed-target heavy-ion experiment at the Super Proton Synchrotron designed to study particle production, strangeness enhancement, and collective phenomena in nucleus–nucleus collisions. The experiment operated at CERN during the late 1980s and early 1990s and produced influential measurements that shaped understanding at the onset of relativistic heavy-ion physics. NA35 results informed later programs at the Relativistic Heavy Ion Collider and the Large Hadron Collider heavy-ion experiments, and contributed to theoretical development by groups associated with Statistical Model of Hadronization, Hydrodynamics (physics), and Quark–Gluon Plasma studies.

Background and Development

NA35 originated within the context of escalating interest in high-energy nucleus–nucleus collisions after pioneering campaigns at Bevalac and proposals circulated by teams at Brookhaven National Laboratory and CERN. The collaboration assembled experimentalists from institutions including CERN, Universität Frankfurt, Universität Heidelberg, University of Bergen, Orsay, and Warsaw University to build instrumentation suited for multiparticle final states. NA35 leveraged technological advances from streamer and time projection chamber techniques developed in experiments such as NA22 and NA34/3 and drew on theoretical motivation articulated in workshops like the Quark Matter series and reports from CERN SPS Heavy Ion Committee. Funding and governance involved national agencies including Bundesministerium für Bildung und Forschung and national research councils of participating countries.

Experimental Setup and Detector

The NA35 detector system combined a large-volume streamer chamber with external tracking and particle-identification subsystems to reconstruct charged-particle multiplicities and strange particle decays. The central tracking was complemented by a Time Projection Chamber module, scintillator hodoscopes, and a series of magnetic elements derived from CERN PS hardware for momentum analysis. Particle identification exploited ionization and decay topology to reconstruct Lambda baryon and K-short signals, while calorimetric modules provided transverse-energy measurements similar in function to devices later used in WA98 and PHENIX. The data acquisition and trigger logic incorporated electronics advances pioneered by collaborations such as NA35 Collaboration partners and shared firmware concepts with experiments like NA44.

Beam, Targets, and Collision Systems

NA35 ran beams of sulfur ions and proton beams delivered by the Super Proton Synchrotron onto targets composed of nuclei such as gold, lead, uranium, and lighter elements including Tantalum and carbon foils. Collision energies spanned center-of-mass regimes accessed by the SPS heavy-ion program, enabling comparisons across system size and centrality that mirrored later comparisons at RHIC and LHC. The experiment investigated symmetric systems such as S + S and asymmetric systems like S + Au, varying impact parameter selections using upstream multiplicity and zero-degree calorimeters, approaches later echoed by NA49 and NA50.

Data Analysis and Results

NA35 produced systematic measurements of charged-particle multiplicity distributions, transverse mass spectra, and rapidity densities for pions, kaons, and strange baryons. Analysis techniques combined topological reconstruction of V0 decays, combinatorial background subtraction methods used in WA85, and acceptance corrections developed alongside simulation tools influenced by GEANT. Key results included observation of enhanced strangeness production in nucleus–nucleus relative to proton–nucleus collisions, quantified through K/π and Λ/π ratios, and transverse mass slope parameters indicative of collective transverse flow comparable to predictions from Hydrodynamics (physics) and blast-wave parameterizations later applied by STAR and ALICE. NA35 also reported on event-by-event fluctuations and intermittency signals that stimulated theoretical work by authors associated with Statistical Model of Hadronization and percolation theory.

Physics Interpretations and Impact

The NA35 findings on strangeness enhancement and collective spectral shapes provided early empirical support for the hypothesis that high-energy nucleus–nucleus collisions create a medium with properties distinct from superposed nucleon–nucleon interactions. Interpretations invoked concepts from Quark–Gluon Plasma phenomenology, equilibration scenarios modeled by the Hadron Resonance Gas model, and transport approaches such as UrQMD and HSD (Hadron–String Dynamics). NA35 stimulated renewed theoretical attention in the Quark Matter conference series and influenced the experimental agendas of NA49, NA50, PHENIX, and ALICE. Its legacy includes methodological standards for strange-particle reconstruction and centrality selection, and its data serve as benchmarks in meta-analyses comparing SPS-era results with those at RHIC and LHC energies.

Collaborations and Timeline

The NA35 collaboration comprised research groups from multiple European universities and national laboratories, coordinated through working groups that paralleled structures in contemporaneous experiments such as NA34/3 and WA80. Operational milestones included first runs in the mid-1980s, systematic sulfur-beam campaigns in the late 1980s, and final analyses and publications in the early 1990s, overlapping with the commissioning of NA49. Key collaboration meetings and presentations were held at venues associated with CERN and at Quark Matter conferences where NA35 results were first disseminated to the international heavy-ion community. The experiment's data and publications remain cited in reviews and retrospective studies by authors affiliated with European Physical Journal C and proceedings of the International Conference on High Energy Physics.

Category:Experiments at CERN