Recent results from the cosmic ray program of the NA61/SHINE experiment
RRecent results from the cosmic ray program of the NA61/SHINE experiment
Raul R.
Prado , , , ∗ for the NA61 / SHINE Collaboration ∗∗ Deutsches Elektronen-Synchrotron (DESY), Platanenallee 6, D-15738 Zeuthen, Germany IKP, Karlsruhe Institute of Technology (KIT), Postfach 3640, D-76021 Karlsruhe, Germany Instituto de Física de São Carlos (IFSC / USP), Av. Trabalhador São-carlense 400, 13566-590, São Carlos, Brazil
Abstract.
NA61 / SHINE is a fixed target experiment designed to study hadron-proton, hadron-nucleus andnucleus-nucleus interactions at the CERN Super-Proton-Synchrotron. In this paper we summarize the resultsfrom pion-carbon collisions recorded at beam momenta of 158 and 350 GeV / c . Hadron production measure-ments in this type of interactions is of fundamental importance for the understanding of the muon production inextensive air showers. In particular, production of (anti)baryons and ρ are mechanisms responsible for increasingthe number of muons which reaches the ground. The underestimation of the (anti)baryons or ρ production ratesin current hadronic interaction models could be one of the sources of the excess of muons observed by cosmicray experiments. The results on the production spectra of π ± , K ± , p, ¯p, Λ , ¯ Λ , K , ρ , ω and K ∗ are presented, aswell as their comparison to predictions of hadronic interaction models currently used in air shower simulations. Measurements of ultrahigh energy cosmic rays are onlypossible through the detection of secondary particles pro-duced in extensive air showers (EAS). The inference ofsome of the properties of the primary cosmic ray par-ticles like their nuclear mass, relies on the comparisonof measured EAS observables to predictions from simu-lations [1]. These simulations are performed by MonteCarlo codes that make use of hadronic interaction mod-els to describe the nucleus-air and hadron-air collisionsalong the shower development [2]. Although simulationsusing recent hadronic models can provide a good overalldescription of EAS, it has been observed by cosmic rayexperiments that the hadronic models fail on describingthe muon production in EAS. Measurements by HiRes-MIA [3], Pierre Auger Observatory [4–7], Telescope Ar-ray [8], KASCADE-Grande [9], IceTop / IceCube [10] andSugar [11] show that there is an inconsistency between dataand simulations for observables related to the muonic com-ponent of air showers. In particular, the number of muons( N µ ) obtained from simulations is observed to be signifi-cantly smaller than the measured ones, which is known asthe “muon deficit problem”.The majority of muons in EAS are produced by thedecay of charged mesons, which in turn, are produced inmeson-air and nucleon-air interactions. Depending on theprimary energy and detection distance, the relevant meson-air and nucleon-air interaction energies are between 10 and1000 GeV [12, 13]. Therefore, measurements of particleproduction in this energy range are of great value for un-derstanding muon production in EAS and consequently forimproving its modeling. Of particular interest are the pro- ∗ e-mail: [email protected] ∗∗ Full author list: http: // shine.web.cern.ch / content / author-list duction spectra of (anti-)baryons and ρ in meson-air andnucleon-air. It is well known [14, 15] that the productionof (anti-)baryons and ρ mesons in hadronic interactionsis important to predict the muon content of air showers.Therefore the production cross sections of these particlesneeds to be known accurately for a precise modeling of airshowersNA61 / SHINE experiment [16] (see Sec. 2) has pro-vided a number of particle production and cross sectionmeasurements which are relevant for the modeling ofhadronic interaction in EAS (e.g. Refs [17, 18]). In thispaper, however, the focus will be on the results of the 2009run with negatively charged pion beam colliding against athin carbon target ( π − + C data) at 158 and 350 GeV / c . Since π -air is the most abundant hadronic interaction occurring inan EAS, our π − + C data is of high relevance for the tuningof hadronic interaction models dedicated to EAS simula-tions. The results are presented in three parts: the spectra ofcharged hadrons ( π ± , K ± , p and ¯p) are presented in Sec. 3,the spectra of V mesons ( Λ , ¯ Λ and K ) in Sec. 4 and thespectra of resonance mesons ( ρ , K ∗ and ω ) in Sec. 5. NA61 / SHINE (SHINE = SPS Heavy Ion and Neutrino Ex-periment) is a fixed target experiment at the CERN SPSdesigned to study hadron production in nucleus-nucleusand hadron-nucleus collisions. Its physics goals comprisea) the strong interaction program, which investigates theproperties of the onset of deconfinement and search for thecritical point of strongly interacting matter, b) the neutrinoprogram, to precisely measure the hadron production im-portant to calculate the neutrinos and antineutrino fluxes inthe T2K neutrino experiment [19], and c) the cosmic raysprogram, focused on the measurements of the hadron and a r X i v : . [ h e p - e x ] O c t igure 1: Schematic layout of the NA61 / SHINE experiment [16]. meson production which are most relevant for the model-ing of extensive air showers. The full description of theNA61 / SHINE experiment and its science program can befound in Ref. [16]The NA61 / SHINE detector measures charged particlesproduced by the collision of the beam particles with the tar-get through a set of five Time Projection Chambers (TPC).Since two of the TPCs are placed in the magnetic fieldproduced by superconducting dipole magnets, the chargeand the momenta of the particles can be measured and theachieved resolution on p is of the order of σ ( p ) / p = − (GeV / c ) − . Additionally, the energy loss per unit of length(d E / d x ) in the TPCs is used in this work for particle iden-tification. The experimental layout of the NA61 / SHINEdetector is shown in Fig. 1.A beam detector system composed of scintillation andCherenkov counters is placed upstream of the detector toidentify and measure the beam particles. The position ofthe beam is measured by a set of three beam position de-tectors, which are also placed upstream of the target. π ± , K ± , p and ¯ p Charged particles are identified in NA61 / SHINE bythe track-by-track measurement of the deposited energy,d E / d x , performed by the TPCs. After splitting the datainto bins of total and transverse momentum ( p and p T ), ad E / d x model is fitted to the measured d E / d x distributionsby accounting for contributions of 5 particle types ( e , π , K , p and deuterons). From the results of the fit, the par-ticle yields of π ± , K ± and p(¯p) are determined. Examplesof measured d E / d x distributions and of the results of thed E / d x fit are shown in Fig. 2. After performing the parti-cle identification through the d E / d x fit, the detector e ff ects(e.g. acceptance, e ffi ciency) are corrected by using a setof Monte Carlo simulations and the spectra are derived. Amore detailed description of the analysis procedure can befound in Ref. [20].The single-di ff erential spectra as a function of p (inte-grated over p T ) for π ± , K ± and p(¯p) are shown in Figs. 5 - - log e p Kpd = 0.35 GeV/c æ T p Æ = 2.19 GeV/c, æ p Æ RST, q=-, - - (dE/dX) log - - s / D - - log e p Kpd = 0.35 GeV/c æ T p Æ = 2.19 GeV/c, æ p Æ RST, q=+, - - (dE/dX) log - - s / D Figure 2: Example of the d E / d x distributions for one phase spacebin ( (cid:104) p (cid:105) = . / c and (cid:104) p T (cid:105) = . / c ) of the 158 GeV / c data set. The black markers show the measured distributions andthe colored distributions show the result of the d E / d x fit. Nega-tively charged particles are shown on the top and positively oneson the bottom. and 6, where the measurements are compared to the pre-dictions of E pos ibyll ibyll et II-04 [23] and E pos
LHC [24]. The double-di ff erential spectra as a function of p and p T can be foundin Ref. [25] for the π ± spectra and in Ref. [20] for the K ± and p(¯p) spectra. Λ , ¯ Λ and K S Since Λ ( ¯ Λ ) and K are neutral weakly decaying particles,they can be measured by NA61 / SHINE through the detec-tion of the charged particles which are produced in theirdecays. The invariant mass ( m inv ) spectra for a given de-cay channel can then be used to extract their signal. Thedecay channels used here are Λ → p + π − , ¯ Λ → ¯ p + π + , ) [GeV/c - p (p, inv m N = 4371/ndf = 0.8 c – S = 855.3 =0.13 GeV/c æ T p Æ =31.53 GeV/c, æ p Æ ] ) [GeV/c - p (p, inv m s / D - - Λ ] ) [GeV/cp, + p ( inv m N = 5301/ndf = 1 c – S = 597.4 =0.13 GeV/c æ T p Æ =31.5 GeV/c, æ p Æ ] ) [GeV/cp, + p ( inv m s / D - - ¯ Λ ] ) [GeV/c - p , + p ( inv m N = 49610/ndf = 1.8 c – S = 9812.8 =0.29 GeV/c æ T p Æ =24.98 GeV/c, æ p Æ ] ) [GeV/c - p , + p ( inv m s / D - - K Figure 3: Example of the m inv distributions for one phase space bin ( (cid:104) p (cid:105) and (cid:104) p T (cid:105) are indicated on the top of each plot) of the 158 GeV / c data set. The black markers show the measured distributions and the colored lines show the result of the signal extraction fit, where thesignal is shown in blue and the background in red. K → π + + π − . To extract the signal, the m inv distributionswere fitted by considering a signal contribution, modeledby using Monte Carlo templates, and the background, mod-eled by a 2nd-degree polynomial function. Examples of thefitted m inv distributions are shown in Fig. 3.This analysis was performed in 2-dimensional phasespace bins of p and p T . For each phase space bin, the de-tector e ff ects were corrected by using Monte Carlo simula-tions. The full double-di ff erential spectra as a function of p and p T for Λ ( ¯ Λ ) and K at 158 and 350 GeV / c can befound in Ref. [26]. In Figs. 7 and 8 we show the measuredsingle-di ff erential spectra as function of p (integrated over p T ) together with predictions of the hadronic models. ρ , K ∗ and ω ) [GeV] - p + p ( inv m C o m b i na t i on s / . G e V · Data r *0 K w f f h S0 K = 1.01 df /n c Figure 4: Example of the m inv ( π + π − ) distribution for one x F bin(0 . < x F < .
4) of the 158 GeV / c data set. The black mark-ers show the measured distributions and the colored distributionsshow the results of the template fit. By using the NA61 / SHINE apparatus, the yields of ρ ,K ∗ and ω can be measured through the π + π − invariantmass ( m inv ( π + π − )) spectra. The signal extraction is per-formed by fitting Monte Carlo templates to the measured m inv ( π + π − ) distribution. The Monte Carlo events were gen-erated using E pos / SHINE detectorsimulation and reconstruction chain. The estimation of thecombinatorial background were done by two methods: thecharge mixing method, in which the π + π + and π − π − aretreated as the background, and the Monte Carlo method,in which the background mass distribution is obtained di-rectly from simulations. One example of the m inv ( π + π − )distributions with the results of the template fit is shownin Fig. 4. After the signal extraction, the particle yieldswere corrected by the detector e ff ects and the productionspectra were derived. The full description of the analysisprocedure and the results can be found in Ref. [27].We show in Fig. 9 the obtained ρ , K ∗ and ω spectra to-gether with predictions from simulations with the hadronicmodels. The ρ spectra are shown for both beam energies,158 and 350 GeV / c , and the ω and K ∗ spectra are limitedto the 158 GeV / c data set because of the large uncertaintiesobtained at 350 GeV / c . The NA61 / SHINE experiment, within its very rich pro-gram, has provided a large number of measurements whichhave been used for testing and tuning of hadronic interac-tion models used by the cosmic ray community. In this pa-per, we have summarized the results of the special cosmicray runs for π − + C interactions.First, we have shown the identified spectra of chargedhadrons obtained by using the d E / d x measurements. Ofparticular interest here is the production spectra of p(¯p),which are relevant to study the (anti)baryon productionsin hadron-air interactions and its implications on the muonroduction in EAS. From the ¯p spectra shown in Figs. 5and 6, one can see that the (anti)baryon production is notunderestimated in general by the models. In particular, theE pos model shows to describe very well the ¯p production.As a conclusion, the underproduction of (anti)baryons in π -air interactions by the hadronic models is unlikely to be themost relevant source of the lack of muons in simulations.Secondly, we have shown the results of the V analy-sis, aiming the Λ ( ¯ Λ ) and K spectra. Although these mea-surements are surely relevant for model testing and tuning,our main motivation here is to reduce the systematic un-certainties on the π ± and p(¯p) spectra due to the feed-downcontributions from weak decays. Since a significant frac-tion of π ± and p(¯p) detected are produced by the decay of Λ , ¯ Λ and K , this e ff ect has to be corrected. In the resultsshown in Sec. 3 (and in Ref.[20]) this correction is done byusing Monte Carlo simulations and the model dependenceof this procedure is added to the systematic uncertainties.By measuring the spectra of Λ , ¯ Λ and K , we are able toavoid this model dependence and consequently reduce thesystematic uncertainties. Updated π ± and p(¯p) spectra withimproved systematic uncertainties will be presented in thefuture in another publication.Finally, we have shown the final results of the mesonresonance analysis which have already been published inRef. [27]. From the ρ production spectra shown in Fig. 9,one can see that none of the hadronic models can describewell the measurements. The small excess of ρ observedwith relation to the predictions from simulations can be rel-evant to explain the muon deficit in simulations. We would like to thank the CERN EP, BE and EN Depart-ments for the strong support of NA61 / SHINE.This work was supported by the Hungarian Scien-tific Research Fund (Grants NKFIH 123842–123959),the János Bolyai Research Scholarship of the Hungar-ian Academy of Sciences, the Polish Ministry of Scienceand Higher Education (grants 667 / N-CERN / /
0, NN202 48 4339 and NN 202 23 1837), the Polish NationalCenter for Science (grants 2011 / / N / ST2 / / / N / ST2 / / / N / ST2 / / / E / ST2 / / / B / ST2 / / / M / ST2 / / / N / ST2 / / / B / ST2 / / / / / / References [1] K.H. Kampert, M. Unger, Astroparticle Physics ,660 (2012), [2] R. Engel, D. Heck, T. Pierog, Annual Review of Nu-clear and Particle Science , 467 (2011)[3] T. Abu-Zayyad et al. (HiRes / MIA Collabora-tion), Physical Review Letters , 4276 (2000), astro-ph/9911144 [4] A. Aab et al. (Pierre Auger Collaboration), PhysicalReview D91 , 032003 (2015), [5] A. Aab et al. (Pierre Auger Collaboration), PhysicalReview Letters , 192001 (2016), [6] A. Aab et al. (Pierre Auger Collaboration), PhysicalReview
D90 , 012012 (2014), [7] A. Aab et al. (Pierre Auger Collaboration), PhysicalReview
D96 , 122003 (2017), [8] R.U. Abbasi et al. (Telescope Array Collaboration),Phys. Rev.
D98 , 022002 (2018), [9] W.D. Apel et al. (KASCADE-Grande Collaboration),Astroparticle Physics , 25 (2017)[10] H. Dembinski (IceCube Collaboration), EPJ Web ofConferences , 01003 (2017)[11] J.A. Bellido, R.W. Clay, N.N. Kalmykov, I.S.Karpikov, G.I. Rubtsov, S.V. Troitsky, J. Ulrichs,Phys. Rev. D98 , 023014 (2018), [12] C. Meurer, J. Bluemer, R. Engel, A. Haungs, M. Roth,Czechoslovak Journal of Physics , A211 (2006), astro-ph/0512536 [13] I. C. Maris (for the NA61 / SHINE Collaboration),Proc. of 31st ICRC (2009)[14] T. Pierog, K. Werner, Physical Review Letters ,171101 (2008), astro-ph/0611311 [15] H.J. Drescher, Physical Review
D77 , 056003 (2008), [16] N. Abgrall et al. (NA61 / SHINE Collaboration),Journal of Instrumentation , P06005 (2014), arXiv:1401.4699 [17] N. Abgrall et al. (NA61 / SHINE Collaboration), Eu-ropean Physics Journal
C76 , 84 (2016), [18] A. Aduszkiewicz et al. (NA61 / SHINE Collabora-tion), European Physics Journal
C77 , 671 (2017), [19] K. Abe et al. (T2K Collaboration), Nuclear Instru-ments and Methods in Physics.
A659 , 106 (2011), [20] R. R. Prado (for the NA61 / SHINE Collaboration),Proc. of 35th ICRC (2017), [21] E.J. Ahn, R. Engel, T.K. Gaisser, P. Lipari, T. Stanev,Physical Review
D80 , 094003 (2009), [22] R. Engel, F. Riehn, A. Fedynitch, T.K. Gaisser,T. Stanev, Proc. of 35th ICRC (2017)[23] S. Ostapchenko, Physical Review
D83 , 014018(2011), [GeV/c] dpdnp NA61/SHINE preliminary + X + π→ + C - π at 158 GeV/c NA61 / SHINEPRELIMINARY p [GeV/c] dpdnp NA61/SHINE preliminary + X - π→ + C - π at 158 GeV/c p [GeV/c] dpdnp NA61/SHINE preliminary + X + K → + C - π at 158 GeV/c p [GeV/c] dpdnp NA61/SHINE preliminary + X - K → + C - π at 158 GeV/c p [GeV/c] dpdnp NA61/SHINE preliminary + X + p → + C - π at 158 GeV/c EPOS1.99Sibyll2.1Sibyll2.3cQGSJetII-04EPOS-LHC p [GeV/c] dpdnp NA61/SHINE preliminary + X - p → + C - π at 158 GeV/c Figure 5: Spectra of π ± , K ± and p(¯p) as a function of p (integrated over p T ), for the 158 GeV / c data set. The statistical uncertainties areshown as black bars and the systematic ones as gray bands. [24] T. Pierog, I. Karpenko, J.M. Katzy, E. Yatsenko,K. Werner, Physical Review C92 , 034906 (2015), [25] A. Herve (for the NA61 / SHINE Collaboration), Proc.of 34th ICRC (2015), [26] R. R. Prado (for the NA61 / SHINE Collaboration), in (Valparaiso, Chile, 2018)[27] A. Aduszkiewicz et al. (NA61 / SHINE Collabora-tion), European Physics Journal
C77 , 626 (2017), [GeV/c] dpdnp NA61/SHINE preliminary + X + π→ + C - π at 350 GeV/c NA61 / SHINEPRELIMINARY p [GeV/c] dpdnp NA61/SHINE preliminary + X - π→ + C - π at 350 GeV/c p [GeV/c] dpdnp NA61/SHINE preliminary + X + K → + C - π at 350 GeV/c p [GeV/c] dpdnp NA61/SHINE preliminary + X - K → + C - π at 350 GeV/c p [GeV/c] dpdnp NA61/SHINE preliminary + X + p → + C - π at 350 GeV/c EPOS1.99Sibyll2.1Sibyll2.3cQGSJetII-04EPOS-LHC p [GeV/c] dpdnp NA61/SHINE preliminary + X - p → + C - π at 350 GeV/c Figure 6: Spectra of π ± , K ± and p(¯p) as a function of p (integrated over p T ), for the 350 GeV / c data set. The statistical uncertainties areshown as black bars and the systematic ones as gray bands. p [GeV/c] dpdnp − × EPOS1.99Sibyll2.1Sibyll2.3cQGSJetII-04EPOS-LHC
NA61 / SHINE PRELIMINARY π − + C → K + Xat 158 GeV / c p [GeV/c] dpdnp − × π − + C → K + Xat 350 GeV / c Figure 7: Spectra of K as a function of p (integrated over p T ), for the 158 and 350 GeV / c data set. The statistical uncertainties are shownas black bars and the systematic ones as gray bands. [GeV/c] dpdnp − × EPOS1.99Sibyll2.1Sibyll2.3cQGSJetII-04EPOS-LHC
NA61 / SHINE PRELIMINARY π − + C → Λ +
Xat 158 GeV / c p [GeV/c] dpdnp − × π − + C → Λ +
Xat 350 GeV / c p [GeV/c] dpdnp − × π − + C → ¯ Λ +
Xat 158 GeV / c p [GeV/c] dpdnp − × π − + C → ¯ Λ +
Xat 350 GeV / c Figure 8: Spectra of Λ ( ¯ Λ ) as a function of p (integrated over p T ), for the 158 and 350 GeV / c data set. The statistical uncertainties areshown as black bars and the systematic ones as gray bands. x F d x dn F x EPOS1.99DPMJet3.06Sibyll2.1Sibyll2.3QGSJetII-04EPOSLHC +C at 158 GeV/c - p in r NA61/SHINE F x F d x dn F x EPOS1.99DPMJet3.06Sibyll2.1Sibyll2.3QGSJetII-04EPOSLHC +C at 350 GeV/c - p in r NA61/SHINE F x F d x dn F x EPOS1.99DPMJet3.06Sibyll2.1Sibyll2.3EPOSLHC +C at 158 GeV/c - p in KNA61/SHINE F x F d x dn F x DPMJet3.06Sibyll2.1Sibyll2.3EPOSLHCEPOS1.99 +C at 158 GeV/c - p in w NA61/SHINE