News from the NA61/SHINE experiment - EPJ Web of Conferences

EPJ Web of Conferences 171, 01002 (2018) https://doi.org/10.1051/epjconf/201817101002 SQM 2017

News from the NA61/SHINE experiment Tatjana Šuša for the NA61/SHINE Collaboration1 , 1

Institute Ruder ¯ Bošković

Abstract. The main goals of the NA61/SHINE experiment at the CERN SPS are the search for the critical point of strongly interacting matter and the study of the properties of the onset of deconfinement. These aims are pursued by performing a two-dimensional scan of the phase diagram of strongly interacting matter by varying the momentum and size of the colliding nuclei. This contribution summarises the latest results from the NA61/SHINE experiment, in particular, new results on spectra and yields of φ meson in p+p interactions at 40, 80 and 158 GeV/c and K + and K − production in central Be+Be collisions at mid-rapidity. In addition, results on system size dependence of particle yield ratios and fluctuations are presented.

1 Introduction NA61/SHINE [1] is a fixed-target experiment located in the H2 beam line of the CERN SPS accelerator complex. The main detector system is a set of five Time Projection Chambers (TPCs) which allows a precise measurement of the particle momenta and provides particle identification via the measurement of the specific energy loss, dE/dx. Two time-of-flight walls improve the kaon identification capabilities. The geometrical layout of the TPCs allows particle detection down to pT = 0 GeV/c in a broad interval of forward rapidities. A high resolution hadron calorimeter, the Projectile Spectator Detector, measures forward going energy E F and is used to select centrality in nuclear collisions. The main goal of the strong interactions programme of the NA61/SHINE experiment is to discover the critical point of strongly interacting matter and study the properties of the onset of deconfinement. The programme is motivated by the discovery of the onset of deconfinement in Pb+Pb collisions at 30A GeV/c by the NA49 experiment [2, 3]. To achieve this goal a two-dimensional scan of the phase diagram of strongly interactiong matter is performed by varying the beam momentum (13A-150/158A GeV/c) and the size of the colliding nuclei (p+p, p+Pb, Be+Be, Ar+Sc, Xe+La, Pb+Pb).

2 Recent results from NA61 2.1 φ meson production in p+p interactions

The production of φ meson is measured in p+p interactions at 40, 80 and 158 GeV/c. φ mesons were identified by their charged kaon decays φ → K + K − using the invariant mass method. The statistics e-mail: [email protected]

© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/).

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1. Examples of transverse momentum of φ mesons inand p+p80 interactions at beam momenta of First measurement of production in distributions p+p interactions at GeV/c, more detailed and ‣ Figure Rapidity spectra y ∈φ [0.9, 1.5) y ∈40 [1.5, 2.1) 158 (left),measurement 80 (middle) andat 40158 (right) GeV/c. precise GeV/c 6 6 ‣ d2n/dpTdy spectra Þtted with the mT exponential function −3 −3 −3 ×10 ×by 10 a blue ×10error bars indicate the uncertainty is shown shaded box, horizontal ‣ The6 systematic −3 −3 6 6 ×10 4 4×10 width ofNA61 the pPreliminary NA61 Preliminary NA61 Preliminary T bins y ∈ [0.0, 0.3) y ∈ [0.3, 0.6)

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‣ Large coverage in rapidity Figure 2. Rapidity distributions of φ mesons in p+p interactions at beam momenta od 158 (left), 80 (middle) and 0 describe the shape 0 0 of 0 0.5 1 1.50 0.5the spectra 1 1.50 0.5 1 1.5 40 (right) GeV/c. ‣ The models approximately p [GeV] T - the models normalised to the integral of the data ‣ Shape approximately described by Gaussian (black curve) ‣ The is shown by a blue shaded box,pT spectra in one wide of 40 GeV/c dataset onlysystematic allowed touncertainty extract single differential dn/dy and dn/d 8 horizontal error indicate of rapidity 1.4]bars GeV/c) and the onewidth rapidity (y ∈ [0,bins 1.5]) bin, respectively, while at transverse momentum (pT ∈ [0,

80 and 158 GeV/c a double-differential analysis in bins of rapidity and transverse momentum could be performed. These are the first measurements of φ production at 40 and 80 GeV/c and the first double-differential measurements at 158 GeV/c. Examples of pT spectra are presented in Fig. 1. The systematic uncertainties are shown by the blue shaded boxes while horizontal error bars indicate the width of the pT bins. The spectra are fitted with an exponential function in mT shown by the blue curve. The extracted values of the inverse slope parameter T at 80 and 158 GeV/c are in the range 120 - 160 MeV and decrease with increasing rapidity (see conference slides). The rapidity spectra of φ mesons are presented in Fig. 2. The systematic uncertainties are shown by the blue shaded boxes while horizontal error bars indicate the width of the rapidity bins. Shown are also predictions for the shape of rapidity spectra from the Epos1.99 [4, 5] (version in CRMC1.6.0 package [6]), Pythia6.4.28 [7] and Urqmd3.4 [8, 9] models which are normalised to the integral of the data. All models approximately describe the shape of the spectra. The result of the fit with a single Gaussian to the experimental points is shown by the black curve. The width of the rapidity spectra

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in p+p and Pb+Pb exhibit different slopes derived from the fit ‣isφ compared to the width of the rapidity spectra of π− , K + and K − in p+p [10] 8 collisions in Fig. 3 (left) and to the width of the rapidity spectra of φ meson in Pb+Pb [11] collisions p+p in Fig. interactions 3 (right). While in p+p collisions the φ follows the trend of the other hadrons, the widths of the rapidity distributions of φ mesons in p+p and Pb+Pb exhibit different behavior.

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‣ Results consistent with world data ‣ EPOS close to data, Pythia underestimates experimental data, UrQMD underestimates ~2x mean φV.multiplicity, is derived by summing the064906) measured rapidity spectra and by ex‣ HRG (V.The Vovchenko, V. Begun, M. I.φ, Gorenstein, Phys.Rev. C93 (2016) to the unmeasured high rapidity region the fitted single Gaussian. The obtained ‣ trapolation Canonical ensamble, π±, Κ±, antiprotons used in the Þt, γS using included ‣ values Overestimates yield ~2x are doubled to take into account the contribution from the backward hemisphere. The NA61 9

results on mean φ multiplicity are compared in Fig. 4 to the world data [12–15] and to the predictions of the Epos, Pythia6, Urqmd and hadron resonance gas (HRG [16]) models. The NA61/SHINE results on mean φ multiplicity are consistent with the world data and are much more accurate. The Epos model describes the data quite well, Pythia6 underestimates the experimental data, while Urqmd underestimates and HRG overestimates NA61/SHINE results approximately by a factor two. The ratio of mean multiplicity of φ mesons and pions in p+p and central Pb+Pb collisions as a function of center of mass energy per nucleon pair is shown in Fig. 5 (left), while the double ratio (Pb+Pb)/(p+p) of the ratios φ/π and K ± /π± is presented in Fig. 5 (right). Pb+Pb data are from NA49 [2, 3, 11], while p+p kaon and pion data are taken from Ref. [10]. As seen from Fig. 5 (left) the √ φ/π ratio increases with sNN . In Pb+Pb collisions it is approximately three times larger than in p+p collisions, independently of the interaction energy. Figure 5 (right) shows that the enhancement between pp and PbPb of the double ratio φ/π is close to that of K + /π+ and systematically larger than that of K − /π− .

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y≈0 y≈0 p+p NA61 (prelim.) 0.1 0.10.1 Be+Be NA610.1(prelim.) p+p RHIC p+p LHC 0 0 0 2 p+p world (4π1)0 1 10210 104104 102102 1 1 200 200 sNNsNN [GeV] [GeV] Au+Au AGS Au+Au RHIC ++ + /fi Pb+Pb SPS • •HORN structure in in K+K/fi in in Pb+Pb collisions was predicted (SMES) asas a si HORN structure Pb+Pb collisions was predicted (SMES) a onset of of deconfinement Pb+Pb LHC onset deconfinement + + + /fi + 2 2 4SPS • •K K/fi dependence in p+p reaches a plateau at at energies (onset p+p rapidly a plateau SPS energies (onseo 10dependence 104rapidly 10reaches 10 1 1 in deconfinement in in p+p?) deconfinement p+p?) sNN [GeV] sNN [GeV] • •Surprisingly thethe Be+Be points areare very close toto p+p! will bebe Ar+Sc an Surprisingly Be+Be points very close p+p!(where (where will Ar+Sc

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Step-like structure• visible Step-like in p+p structure for K≠ visible in p+p for K≠ Fig. 6 and Fig. 7 present the energy dependence of the inverse slope parameter of mT spectra • Stepabove Step in Be+Be slightly in Be+Be p+p above p+p of charged kaons and theslightly multiplicity ratio of charged kaons to pions at mid-rapidity, respectively. Results for Be+Be interactions are compared with NA61/SHINE p+p results and with results from central Pb+Pb collisions from NA49 [2, 3] and other experiments [17–24]. A plateau in the energy alena Kuich (University of Magdalena Warsaw) Kuich (University News of from Warsaw) NA61/SHINE experiment. NA61/SHINE experiment. June 20-23 2017 13 /BNL, 23 June 20-23 2017 dependence of the inverse slope parameterNews andfrom a peak observedBNL, in the energy dependence of the multiplicity ratio of charged kaons to pions in Pb+Pb collisions were predicted by the SMES [25] model as signatures of the onset of deconfinement. The NA61/SHINE results on the energy dependence of the inverse slope parameter in p+p and Be+Be interactions are also consistent with the plateau in the SPS energy range, while a step structure with plateau is observed in the energy dependence of the K + /π+ ratio, suggesting that some properties of hadron production previously attributed to onset of deconfinement in heavy ion collisions might be present also in p+p and Be+Be interactions. 12

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closepion to p+p independently of collision energy ‣ Be+Be results Figure 8.•Ratio of positively Significant jump charged betweenkaon light to systemsyield andata mid-rapidity heavy systemas a function of mean number of wounded difference between ‣ SigniÞcant nucleons W at 30A (left) and 150/158A (right) GeV/c.the light and medium/heavy systems 14 • Waiting on the edge of my sit for Ar+Sc results!

on spectra from NA61/SHINE experiment. EPS-HEP, July in 5-12 p+p 2017 10 / 15 In Magdalena Fig. 8Kuich the (University ratios ofofWarsaw) positivelyNewscharged kaon to pion yield at mid-rapidity and Be+Be collision at 30A and 150/158A GeV/c are shown, together with the C+C, Si+Si and Pb+Pb data from the NA49 experiment. Mid-rapidity K + /π+ ratios in p+p and Be+Be collisions are very close, independently of the collison energy and differ significanty from those in medium and heavy system. NA61/SHINE uses the scaled variance of the multiplicity distribution ω[N] ≡ Var(N)/N to characterize the strength of multiplicity fluctuations. It is an intensive variable, insensitive to the volume of the system, but sensitive to fluctuations of the volume. In Fig. 9 the scaled variance of the multiplicity distribution of negatively charged hadrons in p+p, Be+Be and Ar+Sc collisions at 30A and 150/158 AGeV/c is shown as a function of the mean number of wounded nucleons W.

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‣ Be+Be with results to p+p signiÞcantly higher than Ar+Sc • Ê[N] decreases theclose system size and what is not expected in Ideal Boltzmann Grand expected in Ideal Boltzmann gas, in decreases with theorsystem size ⟶ not ‣ ω[N] Canonical Ensemble (Poisson) the Wounded Nucleon Model (p+p)

The multiplicity fluctuations in p+p and Be+Be collisions are similar significantly higher than in Grand close Canonical Ensamble (Poisson) or the Wounded Nucleon Model and (p+p) • Be+Be results to p+p and significantly higher than Ar+Sc 17 Ar+Sc collisions. The observed suppression of the scaled variance in Ar+Sc collisions is not expected for an Ideal Boltzmann gas in the Grand Canonical Ensamble treatment nor in the Wounded Nucleon Model [26]. Magdalena Kuich (University of Warsaw) News from NA61/SHINE experiment. BNL, June 20-23 2017 17 / 23

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