SPS Experiments Research Articles

Sequential charmonium dissociation

Finite temperature lattice QCD indicates that the charmonium ground state J/ψ can survive in a quark–gluon plasma up to 1.5Tc or more, while the excited states χc and ψ′ are dissociated just above Tc. We assume that the χc suffers the same form of suppression as that observed for the ψ′ in SPS experiments, and that the directly produced J/ψ is unaffected at presently available energy densities. This provides a parameter-free description of J/ψ and ψ′ suppression which agrees quite well with that observed in SPS and RHIC data.

On the Discrepancy of pp, Formulap Total Cross Sections at s = 1.8 TeV between E710, E811 and CDF

Based on the previous approach, we have investigated a possibility to resolve the discrepancy between the E710, E811 and CDF at sqrt s =1.8TeV, using the experimental data of the pp, pbar p total cross sections sigma tot(+) and rho(+)$ ratio up to the SPS experiments (sqrt s = 0.9TeV) as inputs. We predict sigma tot(pbar p) and rho(pbar p) at the Tevatron energy(sqrt s=1.8TeV) as sigma tot(pbar p)=75.9+- 1.0mb, rho(pbar p)=0.136+- 0.005. It turns out that only the data of E710 is consistent with the prediction in the one standard deviation. So we can conclude that E710 is preferable but we can exclude neither CDF nor E811 results.

The SPS heavy ion programme

After reviewing the states of matter and the critical behaviour provided by statistical QCD, I review the proposed experimental probes of different features and then summarize the corresponding results obtained in SPS experiments. In the final section, I try to assess what conclusions can be drawn from the presently available data.

Physics with hadron and photon beams at the SPS

This report attempts to cover the physics results obtained in the last 25 years by some 70 SPS experiments. A variety of beams, pion, kaon, proton, antiproton, hyperon and photon were used in these experiments, and, in one case (UA6), the p and p¯ beams stored in the SPS Collider were made to hit an internal gas jet target. The panoply of detection techniques employed was also very large, from bubble chambers to silicon microdetectors, and the physics issues addressed ranged from hard to ultrasoft processes. The available space however, will only allow to touch briefly a few amongst the many interesting results which have been published since 1979.In what follows, we shall try to group the experiments under four headings:(1) Hard scattering, (2) Heavy flavours, (3) Spectroscopy, (4) Soft processes.

Direct photon production in heavy-ion reactions at SPS and RHIC

A review on experimental results for direct photon production in heavy ion reactions is given. A brief survey of early direct photon limits from SPS experiments is presented. The first measurement of direct photons in heavy ion reactions from the WA98 collaboration is discussed and compared to theoretical calculations. An outlook on the perspective of photon measurements at RHIC is given.

J/ψsuppression in heavy ion collisions by quark momentum diffusion

The momentum diffusion effect of the quark pair due to the multiple scattering in a nuclear medium is studied to explain the observed J/psi yields in SPS experiments. The resulting suppression is found to be insufficient to reproduce the J/psi yield in Pb-Pb collisions at SPS energy.

SPS experiments with the lead beam

SPS experiments with the lead beam

Long-range charge fluctuations and search for a quark-gluon plasma signal

We critically discuss recent suggestion to use long-range modes of charge (electric or baryon) fluctuations as a signal for the presence of Quark-Gluon Plasma at the early stages of a heavy ion collision. We evaluate the rate of diffusion in rapidity for different secondaries, and argue that for conditions of the SPS experiments, it is strong enough to relax the magnitude of those fluctuations almost to its equilibrium values, given by hadronic ``resonance gas''. We further argue that experimental data from SPS agree with this conclusion. We evaluate the detector acceptance needed to measure such ``primordial'' long-range fluctuations at RHIC conditions. We conclude with an application of the charge fluctuation analysis to the search for the QCD critical point.

Critical baryonic effects in heavy-ion physics

In the vicinity of the quark-hadron critical point, in the phase diagram, simple power-law relations constrain the mid-rapidity net-baryon density, for different heavy-ion processes, in a unifying scheme. These relations reveal a characteristic trend of the SPS experiments ( S + S, S + Ag, S + Au, Pb + Pb) supporting the hypothesis of a critical point of second order, at nonzero baryon density. However, the central events in these experiments stay outside the critical area, especially in Pb + Pb collisions, suggesting the absence of strong critical fluctuations in these processes. The role of noncentral events and the possibility to reach the QCD critical point at RHIC and LHC, is also discussed.

Recent results from CERN SPS experiments and the future heavy ion programme

We describe the important results from the recent experiments using lead beams at the CERN SPS. The results of the WA98 experiment, which has substantial Indian participation along with the photon multiplicity detector is described in some detail. Combining the preliminary results from various experiments looking at different signals of phase transition, one finds enough evidences to suggest that phase transition has taken place in nuclear collisions at the SPS. Future programme of heavy ion physics at the LHC is being greared around the ALICE experiment. This will comprise of detector subsystems capable of studying almost all the signals in the same event. The photon multiplicity detector will be an important component of the ALICE experiment, being a totally Indian contribution to ALICE.

Where Is the Jet Quenching inPb+PbCollisions at158AGeV?

Because of the rapidly falling particle spectrum at large ${p}_{T}$ from jet fragmentation at CERN SPS energy, the high- ${p}_{T}$ hadron distribution should be highly sensitive to parton energy loss inside a dense medium as predicted by recent perturbative QCD (PQCD) studies. A careful analysis of recent data from CERN SPS experiments via PQCD calculation shows little evidence of energy loss. This implies that either the lifetime of the dense partonic matter is very short or one has to rethink parton energy loss in dense matter. The hadronic matter does not seem to cause jet quenching in $\mathrm{Pb}+\mathrm{Pb}$ collisions at the CERN SPS. High- ${p}_{T}$ two particle correlation in the azimuthal angle is proposed to further clarify this issue.

From Tsukuba into the future

An exciting week of intense physics discussions comes to an end. This Quark Matter 1997 meeting at Tsukuba could be called the meeting where the Quark Gluon Plasma was discovered in the Pb+Pb data from the various SPS experiments, if...!. Some of us think there is no “if” in one's own data but most of us think it is clearly not the QGP signal what the other experiment claims. On the other side we seem to be stuck in an eternal dilemma not to be able to call a dog a dog even if it smells like adog, barks like a dog, walks on 4 legs most of the time and hates cats. Furthermore, impatience is plaguing some of us and the need to reach the goal we started out in 1986 (or even earlier!) is a mighty pressure barely tolerable for some. This, however, should not be an excuse to overlook some facts in our data that tell us that nature may not be what we thought.

Recent results from the CERN lead beam experiments: How close have we come to the quark-gluon plasma?

Recent results from various heavy-ion SPS experiments are briefly discussed. Various observables, possibly affected by a quark-gluon plasma phase, are presented. Those data indicate strong interacting matter at the parton level and a thermalized system at the hadronic level. A short introduction into the future programs at RHIC and LHC is given.

Multiparticle production in p-nucleus and nucleus-nucleus collisions.

Kinematic properties of inclusive $p+A\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}$ and ${A}_{1}+{A}_{2}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}$ at 200 GeV/nucleon are compared with $p+p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}$ at 200 GeV/c using data of CERN SPS experiments. The partition temperature is found to be practically the same for all the reactions analyzed, suggesting an approximate scaling. The peak shift of pseudorapidity $\ensuremath{\eta}$ distributions of these nuclear reactions with respect to the peak of $\mathrm{pp}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}$ follows a geometrical law: ${\ensuremath{\eta}}^{*}\ensuremath{\simeq}\frac{({A}_{1}^{\frac{1}{3}}\ensuremath{-}{A}_{2}^{\frac{1}{3}})}{8}$, independent of energy. The mean free path $l$ characteristic of the energy loss suffered by the projectile fireball passing through the nuclear target is $l\ensuremath{\simeq}6.21$ fm. Semiempirical formulas for $〈{n}_{\ensuremath{-}}〉$ of $p+A$ and ${A}_{1}+{A}_{2}$ reactions are proposed and tested using available data.