Observation of an ABC effect in proton-proton collisions

Dymov, S. ; Hartmann, M. ; Kacharava, A. ; et al.
Phys.Rev.Lett. 102 (2009) 192301, 2009.
Inspire Record 812534 DOI 10.17182/hepdata.51593

The cross section for inclusive multipion production in the pp->ppX reaction was measured at COSY-ANKE at four beam energies, 0.8, 1.1, 1.4, and 2.0 GeV, for low excitation energy in the final pp system, such that the diproton quasi-particle is in the 1S0 state. At the three higher energies the missing mass Mx spectra show a strong enhancement at low Mx, corresponding to an ABC effect that moves steadily to larger values as the energy is increased. Despite the missing-mass structure looking very different at 0.8 GeV, the variation with Mx and beam energy are consistent with two-pion production being mediated through the excitation of two Delta(1232) isobars, coupled to S-- and D-- states of the initial pp system.

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The Near-threshold production of phi mesons in pp collisions

Hartmann, M. ; Maeda, Y. ; Keshelashvilli, I. ; et al.
Phys.Rev.Lett. 96 (2006) 242301, 2006.
Inspire Record 713863 DOI 10.17182/hepdata.41806

The pp->pp phi reaction has been studied at the Cooler Synchrotron COSY-Juelich, using the internal beam and ANKE facility. Total cross sections have been determined at three excess energies epsilon near the production threshold. The differential cross section closest to threshold at epsilon=18.5 MeV exhibits a clear S-wave dominance as well as a noticeable effect due to the proton-proton final state interaction. Taken together with data for pp omega-production, a significant enhancement of the phi/omega ratio of a factor 8 is found compared to predictions based on the Okubo-Zweig-Iizuka rule.

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Forward K+ production in subthreshold pA collisions at 1.0-GeV

The ANKE collaboration Koptev, V. ; Buescher, Markus ; Junghans, H. ; et al.
Phys.Rev.Lett. 87 (2001) 022301, 2001.
Inspire Record 556676 DOI 10.17182/hepdata.31765

K+ meson production in pA (A = C, Cu, Au) collisions has been studied using the ANKE spectrometer at an internal target position of the COSY-Juelich accelerator. The complete momentum spectrum of kaons emitted at forward angles, theta < 12 degrees, has been measured for a beam energy of T(p)=1.0 GeV, far below the free NN threshold of 1.58 GeV. The spectrum does not follow a thermal distribution at low kaon momenta and the larger momenta reflect a high degree of collectivity in the target nucleus.

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(Anti-)deuteron production in pp collisions at $\sqrt{s}=13 \ \text {TeV}$

The ALICE collaboration Acharya, S. ; Adamova, Dagmar ; Adler, Alexander ; et al.
Eur.Phys.J.C 80 (2020) 889, 2020.
Inspire Record 1784203 DOI 10.17182/hepdata.97183

The study of (anti-)deuteron production in pp collisions has proven to be a powerful tool to investigate the formation mechanism of loosely bound states in high energy hadronic collisions. In this paper the production of (anti-)deuterons is studied as a function of the charged particle multiplicity in inelastic pp collisions at $\sqrt{s}=13$ TeV using the ALICE experiment. Thanks to the large number of accumulated minimum bias events, it has been possible to measure (anti-)deuteron production in pp collisions up to the same charged particle multiplicity ($\rm{d} N_{ch}/\rm{d}\eta\sim26$) as measured in p-Pb collisions at similar centre-of-mass energies. Within the uncertainties, the deuteron yield in pp collisions resembles the one in p-Pb interactions, suggesting a common formation mechanism behind the production of light nuclei in hadronic interactions. In this context the measurements are compared with the expectations of coalescence and Statistical Hadronisation Models (SHM).

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Transverse momentum distributions of deuterons in the INEL>0 pp collisions

Transverse momentum distributions of deuterons in the INEL pp collisions

Transverse momentum distributions of anti-deuterons in the INEL>0 pp collisions

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Version 2
Dihadron azimuthal correlations in Au$+$Au collisions at $\sqrt{s_{NN}}=$ 200 GeV

The PHENIX collaboration Adare, A. ; Afanasiev, S. ; Aidala, C. ; et al.
Phys.Rev.C 78 (2008) 014901, 2008.
Inspire Record 778396 DOI 10.17182/hepdata.96764

Azimuthal angle (Delta phi) correlations are presented for a broad range of transverse momentum (0.4 < pT < 10 GeV/c) and centrality (0-92%) selections for charged hadrons from di-jets in Au+Au collisions at sqrt(s_NN) = 200 GeV. With increasing pT, the away-side Delta phi distribution evolves from a broad and relatively flat shape to a concave shape, then to a convex shape. Comparisons to p+p data suggest that the away-side distribution can be divided into a partially suppressed head region centered at Delta phi ~ \pi, and an enhanced shoulder region centered at Delta phi ~ \pi \pm 1:1. The pT spectrum for the associated hadrons in the head region softens toward central collisions. The spectral slope for the shoulder region is independent of centrality and trigger pT . The properties of the near-side distributions are also modified relative to those in p + p collisions, reflected by the broadening of the jet shape in Delta phi and Delta eta, and an enhancement of the per-trigger yield. However, these modifications seem to be limited to pT < 4 GeV/c, above which both the dihadron pair shape and per-trigger yield become similar to p + p collisions. These observations suggest that both the away- and near-side distributions contain a jet fragmentation component which dominates for pT \ge 5GeV and a medium-induced component which is important for pT \le 4 GeV/c. We also quantify the role of jets at intermediate and low pT through the yield of jet-induced pairs in comparison to binary scaled p + p pair yield. The yield of jet-induced pairs is suppressed at high pair proxy energy (sum of the pT magnitudes of the two hadrons) and is enhanced at low pair proxy energy. The former is consistent with jet quenching/ the latter is consistent with the enhancement of soft hadron pairs due to transport of lost energy to lower pT.

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RHS versus $p^b_T$ for p + p collisions for four trigger selections.

RHS versus $p^b_T$ for Au + Au collisions for four trigger selections.


Strange meson enhancement in Pb Pb collisions

The NA44 collaboration Bearden, I. ; Bøggild, H. ; Boissevain, J. ; et al.
Phys.Lett.B 471 (1999) 6-12, 1999.
Inspire Record 504074 DOI 10.17182/hepdata.31360

The NA44 Collaboration has measured yields and differential distributions of K+, K-, pi+, pi- in transverse kinetic energy and rapidity, around the center-of-mass rapidity in 158 A GeV/c Pb+Pb collisions at the CERN SPS. A considerable enhancement of K+ production per pi is observed, as compared to p+p collisions at this energy. To illustrate the importance of secondary hadron rescattering as an enhancement mechanism, we compare strangeness production at the SPS and AGS with predictions of the transport model RQMD.

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Kaon Pair Production in Proton--Proton Collisions

The ANKE collaboration Maeda, Y. ; Hartmann, M. ; Keshelashvili, I. ; et al.
Phys.Rev.C 77 (2008) 015204, 2008.
Inspire Record 763646 DOI 10.17182/hepdata.25173

The differential and total cross sections for kaon pair production in the pp->ppK+K- reaction have been measured at three beam energies of 2.65, 2.70, and 2.83 GeV using the ANKE magnetic spectrometer at the COSY-Juelich accelerator. These near-threshold data are separated into pairs arising from the decay of the phi-meson and the remainder. For the non-phi selection, the ratio of the differential cross sections in terms of the K-p and K+p invariant masses is strongly peaked towards low masses. This effect can be described quantitatively by using a simple ansatz for the K-p final state interaction, where it is seen that the data are sensitive to the magnitude of an effective K-p scattering length. When allowance is made for a small number of phi events where the K- rescatters from the proton, the phi region is equally well described at all three energies. A very similar phenomenon is discovered in the ratio of the cross sections as functions of the K-pp and K+pp invariant masses and the identical final state interaction model is also very successful here. The world data on the energy dependence of the non-phi total cross section is also reproduced, except possibly for the results closest to threshold.

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Version 2
Global polarization measurement in Au+Au collisions

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Rev.C 76 (2007) 024915, 2007.
Inspire Record 750410 DOI 10.17182/hepdata.98581

The system created in non-central relativistic nucleus-nucleus collisions possesses large orbital angular momentum. Due to spin-orbit coupling, particles produced in such a system could become globally polarized along the direction of the system angular momentum. We present the results of Lambda and anti-Lambda hyperon global polarization measurements in Au+Au collisions at sqrt{s_NN}=62.4 GeV and 200 GeV performed with the STAR detector at RHIC. The observed global polarization of Lambda and anti-Lambda hyperons in the STAR acceptance is consistent with zero within the precision of the measurements. The obtained upper limit, |P_{Lambda,anti-Lambda}| <= 0.02, is compared to the theoretical values discussed recently in the literature.

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Strangeness Enhancement in Cu+Cu and Au+Au Collisions at $\sqrt{s_{NN}} = 200$ GeV

The STAR collaboration Agakishiev, G. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Rev.Lett. 108 (2012) 072301, 2012.
Inspire Record 918779 DOI 10.17182/hepdata.95886

We report new STAR measurements of mid-rapidity yields for the $\Lambda$, $\bar{\Lambda}$, $K^{0}_{S}$, $\Xi^{-}$, $\bar{\Xi}^{+}$, $\Omega^{-}$, $\bar{\Omega}^{+}$ particles in Cu+Cu collisions at \sNN{200}, and mid-rapidity yields for the $\Lambda$, $\bar{\Lambda}$, $K^{0}_{S}$ particles in Au+Au at \sNN{200}. We show that at a given number of participating nucleons, the production of strange hadrons is higher in Cu+Cu collisions than in Au+Au collisions at the same center-of-mass energy. We find that aspects of the enhancement factors for all particles can be described by a parameterization based on the fraction of participants that undergo multiple collisions.

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$K^0_S$ invariant mass spectra from Au+Au $\sqrt{s_{NN}} = 200$ GeV collisions, where $|y| < 0.5$. The uncertainties on the spectra points are statistical and systematic combined.

$\Lambda$ and $\bar{\Lambda}$ invariant mass spectra from Au+Au $\sqrt{s_{NN}} = 200$ GeV collisions, where $|y| < 0.5$. The $\Lambda$ and $\bar{\Lambda}$ yields have not been feed down subtracted from weak decays. The uncertainties on the spectra points are statistical and systematic combined.


Muon pair production in ep collisions at HERA

The H1 collaboration Aktas, A. ; Andreev, V. ; Anthonis, T. ; et al.
Phys.Lett.B 583 (2004) 28-40, 2004.
Inspire Record 632638 DOI 10.17182/hepdata.46338

Cross sections for the production of two isolated muons up to high di-muon masses are measured in ep collisions at HERA with the H1 detector in a data sample corresponding to an integrated luminosity of 71 pb^-1 at a centre of mass energy of sqrt{s} = 319 GeV. The results are in good agreement with Standard Model predictions, the dominant process being photon-photon interactions. Additional muons or electrons are searched for in events with two high transverse momentum muons using the full data sample corresponding to 114 pb^-1, where data at sqrt{s} = 301 GeV and sqrt{s} = 319 GeV are combined. Both the di-lepton sample and the tri-lepton sample agree well with the predictions.

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