Arnold, O.

Fabbietti, L.

GSI Repository

Investigation of two-particle correlations in p+93Nb collisions atEkin = 3.5GeV∗O. Arnold1,2, L. Fabbietti1,2 for the HADES collaboration1Physik Department E12, Technische Universita¨t Mu¨nchen, James-Franck-Str. 1, 85748 Garching, Germany;2Excellence Cluster ’Origin and Structure of the Universe’, Boltzmannstr. 2, 85748 Garching, GermanyWith the HADES setup the reaction p+93Nb was mea-sured in September 2008, where the proton had a kineticenergy of 3.5 GeV (√sNN = 3.18 GeV). This rather mod-erate energy gives us the possibility to study the productionand interaction of particles at small excess energies.Studying two-particle correlation functions at small rel-ative momenta provide information about the spatio-temporal extent of the particle emitting source. Originally,the formalism of intensity interferometry was developedfor astrophysical investigations to measure the angular sizeof stars [1]. Nowadays, the technique is mainly applied inthe field of heavy-ion physics to gain information about thehighly excited matter state and its properties created duringthe collision of the two nuclei.The basic idea of femtoscopy is to deduce effects of fi-nal state interactions (FSI) from phase-space correlationsof emitted particles. In low energy p+A systems we ex-pect no contributions from collective effects to the particleemission like flow or energetic jets. Because of this reason,we are in the position to study only FSI of different particlespecies and do not have to consider effects from physicalnon-femtoscopic sources.FSI can be studied with correlation functions, which aredefined as the ratio of the two-particle probability dividedby the uncorrelated probabilities:C(p1,p2) =P (p1,p2)P (p1)P (p2), (1)where pi is the single-particle momentum of the particle i.Whenever this ratio deviates from unity one measures par-ticle correlations.We started to study the correlation function between iden-tical particles to have a benchmark for more complex cor-relation functions like p-Λ [2]. This would enable a studyof the YN interaction in terms of scattering lengths. Forprotons, three correlation classes enter in Eq. (1): quan-tum statistics, Coulomb and strong interaction. The Pauliexclusion principle and Coulomb interaction both act re-pulsively between protons which shows up in the correla-tion function as a suppression of the correlation signal atvery low relative momenta (k < 10 MeV/c). The attrac-tive strong interaction acts mainly via the s-wave channeland leads to an enhancement of the correlation signal ataround k ≈ 20 MeV/c. The height of the correlation peak(C(k = 20 MeV/c)) is inversely proportional to the lengthof homogeneity RG (often called source size) which will∗Work supported by Helmholtz funds VH-NG-330 and ExcellenceCluster ’Universe’be deduced in future work. Fig. 1 displays the preliminaryresult of proton-proton correlations measured in the p+Nbsystem, which shows the characteristic functional shape asdiscussed above.For identical negative pions one expects a positive correla-tion signal at small relative momenta due to Bose-Einsteinstatistics, which leads to an attraction as is seen in Fig. 1where the correlation function shows an increase at low kand stays positive. However, this signal is still distorted bythe repulsive Coulomb interaction. For pions, one can cor-rect this effect by folding the Coulomb wave function witha source parametrization. This correction will be part ofour future work.To summarize, we have reconstructed the correlation func-tion for protons and negative pions. In the next step, wehave to correct this functions for certain detector deficien-cies and will then compare them to theoretical models. Forthe p-Λ correlation function we determined the number ofΛs which can be used for the correlation study to about5× 105 with a signal-to-background ratio of 1.23.Figure 1: Proton-proton (upper) and π−π− (lower) corre-lation function.References[1] R. Hanbury Brown and R. Q. Twiss, Nature 178, 1046 (1956).[2] F. Wang and S. Pratt, Phys. Rev. Lett. 83, 3138 (1999).GSI SCIENTIFIC REPORT 2013 NQM-HADES-01doi:10.15120/GR-2014-1-NQM-HADES-01 1

Investigations on two-particle correlations in $p+^{93}Nb$ collisions at $E_{kin} = 3.5$ GeV

http://repository.gsi.de/record/67734/files/NQM-HADES-01.pdf

Investigations on two-particle correlations in $p+^{93}Nb$ collisions at $E_{kin} = 3.5$ GeV

Abstract

Similar works

Full text

Available Versions

GSI Repository

Investigations on two-particle correlations in p+93Nbp+^{93}Nbp+93Nb collisions at Ekin=3.5E_{kin} = 3.5Ekin​=3.5 GeV

Abstract

Similar works

Full text

Available Versions

GSI Repository

Investigations on two-particle correlations in $p+^{93}Nb$ collisions at $E_{kin} = 3.5$ GeV