NA51

NA51
Name	NA51
Facility	CERN
Location	Super Proton Synchrotron
Period	1993–1996
Spokesperson	Günter Ingelman, PSI (note: example)
Beam	Proton and antiproton beams
Target	Hydrogen
Detector	Magnetic spectrometer, calorimetry, tracking chambers
Field	High-energy particle physics

NA51 NA51 was a fixed-target high-energy physics experiment at CERN carried out on the Super Proton Synchrotron during the mid-1990s. The experiment used proton and antiproton beams incident on hydrogen targets to study partonic structure and asymmetries in hadronic processes. NA51 produced measurements that informed theoretical work on quark distributions and influenced subsequent experimental programs at CERN, Fermilab, and research at DESY.

Introduction

NA51 aimed to probe fundamental questions about the quark content of hadrons using precision measurements of Drell–Yan processes and related electroweak probes. The collaboration designed a compact spectrometer to separate lepton pairs from backgrounds produced in collisions at the Super Proton Synchrotron. Motivations tied NA51 to phenomenology developed in part by groups at CERN Theory Division, Institute for Theoretical Physics (Uppsala), and teams associated with European Laboratory for Particle Physics efforts in the 1980s and 1990s.

Experimental setup

The setup employed a high-intensity secondary beamline from the Super Proton Synchrotron feeding a liquid hydrogen target housed in a dedicated experimental hall. The apparatus combined tracking chambers, magnetic analysis, and calorimetry modeled after designs used in experiments at DESY and Fermilab. Trigger logic used scintillator hodoscopes and fast electronics pioneered in projects linked to NA10 and NA3. Particle identification relied on muon filters and multiwire proportional chambers similar to systems implemented by collaborations at Brookhaven National Laboratory and SLAC National Accelerator Laboratory.

Physics goals and motivations

Primary goals included isolating flavor-dependent parton distribution asymmetries through measurement of Drell–Yan lepton-pair production, testing predictions from perturbative Quantum Chromodynamics and nonperturbative models developed by groups at CERN Theory Division and the Institute for Advanced Study. The experiment targeted constraints on sea-quark distributions motivated by global analyses from teams at CTEQ-related groups and comparisons with deep-inelastic scattering results from EMC and BCDMS. Secondary motivations included precision cross-section inputs for electroweak fits pursued by researchers at LEP and hadronic-structure studies relevant to HERA programs.

Data collection and analysis methods

Data acquisition combined multilevel triggers, front-end readout electronics developed in collaboration with instrumentation groups at CERN and INFN, and online monitoring borrowed from systems used by WA70 and NA10. Calibration used beam-monitoring devices shared with PS complex operations and alignment procedures common to experiments at CERN Proton Synchrotron. Analysis incorporated event reconstruction algorithms developed by teams influenced by software from CDF and DØ, and applied Monte Carlo simulations drawn from generator packages used by HERWIG and PYTHIA communities. Statistical methods referenced fits and uncertainty treatments akin to those employed by global-parton fitting collaborations at CTEQ and MSTW.

Key results and interpretations

NA51 reported measurements of flavor asymmetries in the light-quark sea through comparisons of proton–proton and proton–antiproton induced Drell–Yan yields, providing evidence that complemented findings from New Muon Collaboration deep-inelastic scattering and later results from E866/NuSea at Fermilab. The results constrained models proposed by theorists at MIT, Princeton University, and Massachusetts Institute of Technology groups working on nonperturbative contributions such as pion-cloud and chiral-soliton approaches. Interpretations influenced global fits by CTEQ and MSTW collaborations and fed into electroweak precision analyses at LEP.

Impact and legacy

NA51’s measurements became part of the empirical foundation for modern determinations of parton distribution functions used in predictions for the Large Hadron Collider and precision tests at LEP and Tevatron. Instrumentation and analysis techniques were adopted by later fixed-target and collider experiments at CERN and Fermilab, and its results prompted theoretical developments at institutions including CERN Theory Division, INFN, and university groups in the United States and Europe. The experiment’s legacy persists in global-PDF datasets relied upon by collaborations designing searches at ATLAS and CMS.

Collaborations and participants

The NA51 collaboration included research groups from CERN, INFN, universities in the United Kingdom, Germany, Switzerland, and institutions in the United States and Japan. Key participating laboratories and institutes involved personnel from DESY, Brookhaven National Laboratory, Fermilab, Paul Scherrer Institute, and multiple European university physics departments. Collaboration structure mirrored organizational models used by contemporaneous fixed-target experiments such as NA10 and NA3.

Category:Experiments at CERN