Pion Production Cross-section Measurements in p+C Collisions at the CERN SPS for Understanding Extensive Air Showers
XXVI International Symposium on Very High Energy Cosmic Ray InteractionsISVHECRI 2010, Batavia, IL, USA (28 June – 2 July 2010) Pion Production Cross-section Measurements in p+C Collisions at the CERNSPS for Understanding Extensive Air Showers
Marek Szuba for the NA61/SHINE Collaboration
Karlsruhe Institute of Technology, Germany
An important approach to studying high-energy cosmic rays is the investigation of the propertiesof extensive air showers; however, the lateral distribution of particles in simulations of such showersstrongly depends on the applied model of low-energy hadronic interactions. It has been shownthat many constraints to be applied to these models can be obtained by studying identified-particlespectra from accelerator collisions, in the energy range of the CERN Super Proton Synchrotron.Here we present measurements of the pion production cross-section obtained by the NA61/SHINEexperiment at the SPS, in proton-carbon collisions at the beam energy of 31 GeV from the year2007. Further analyses of identified-particle yields in SHINE, in particular with a pion beam, are inpreparation.
I. INTRODUCTION
The most common way employed nowadays tostudy high-energy cosmic rays is to examine the prop-erties of extensive air showers (EAS) they induce inthe atmosphere, using several different observablesand detection techniques. The latter include measure-ments of shower size and composition at ground levelusing surface arrays of scintillation or Cherenkov-lightdetectors, observation of energy losses of shower parti-cles as they traverse the atmosphere using fluorescencedetectors, detection of radio emission from the showerusing appropriate antennae, and others. Examples ofexperiments measuring EAS include the surface ar-rays KASCADE and KASCADE-Grande as well asthe hybrid surface-and-fluorescence Pierre Auger Ob-servatory [1–3].Unfortunately, determination of properties of theinitial particle from such observables strongly dependson models, especially those of hadronic interactionsoccurring during shower development. Many suchmodels exist yet they frequently fail to consistentlyand accurately reproduce experimental data, for in-stance underestimating the yield of shower muons atground level or showing non-smooth transition fromlow- to high-energy hadronic interactions [4–7].In light of the above, additional data is required inorder to appropriately tune models of hadronic inter-actions in EAS. Such data can be provided by acceler-ator experiments observing collisions of hadrons suchas protons or pions with light ions such as carbon nu-clei. In particular, it has been demonstrated that theenergy range of the Super Proton Synchrotron (SPS)at CERN makes it highly suitable for reproducing finalhadronic interactions[15] in showers of energies stud-ied by KASCADE, KASCADE-Grande and the PierreAuger Observatory [5].This article presents the first results by theNA61/SHINE experiment at the SPS obtained for thepurpose of measuring the particle yield in the long-baseline neutrino experiment T2K and tuning EASmodels — pion spectra from p+C collisions at 31 GeV.
II. THE NA61/SHINE EXPERIMENT
NA61/SHINE is an experiment at the CERN SPSusing the upgraded NA49 hadron spectrometer toaccomplish a number of physics goals. In addi-tion to providing reference data for cosmic-ray ex-periments it shall also provide model-tuning infor-mation for the neutrino experiment T2K, producefor the first time in the SPS energy range large-statistics proton-proton data sets for high- p T stud-ies and, last but not least, perform a comprehensiveenergy and system-size scan in search for the QCDcritical point. Its large acceptance (around 50 %for p T ≤ σ ( p ) /p ≈ − ( GeV /c ) − ) and tracking efficiency(over 95 %), and excellent particle-identification ca-pabilities ( σ ( d E d x ) / d E d x ≈ , σ ( t T oF ) ≈ ps ) makeit an excellent tool for investigating hadron spectra.Moreover, its kinematic range covers well that of KAS-CADE, KASCADE-Grande and the Pierre Auger Ob-servatory (see Figure 1).The following are the main features of the NA61detector as shown in Figure 2 [9, 10]: • tracking plus momentum, charge and d E/ d x measurement with five Time-Projection Cham-bers; • three Time-of-Flight walls for additional identi-fication information; • high-precision downstream Projectile SpectatorDetector; • a number of beam and triggering detectors.For the purpose of cosmic-ray studies, SHINE ac-quired in the years 2007 and 2009 5.4 million p+C events at 31 GeV, 3.6 million π − +C events at158 GeV and 4.7 million π − +C events at 350 GeV.The analysis of these data sets is currently in progress.The results presented here have been produced fromthe 0.6 million p+C -at-31 GeV events registered dur-ing the 2007 pilot run. C35 a r X i v : . [ a s t r o - ph . H E ] S e p XVI International Symposium on Very High Energy Cosmic Ray InteractionsISVHECRI 2010, Batavia, IL, USA (28 June – 2 July 2010) (E/GeV) log / d ( l n E ) µ d N QGSJET/FLUKA (80 GeV)QGSJET/FLUKA (500 GeV)SIBYLL/FLUKA (80 GeV)SIBYLL/FLUKA (500 GeV) pionsnucleonskaons
NA61 (pion+C)NA61 (p+C)
FIG. 1:
Left : Energy distributions, simulated using several models, of the “grandfather” particles in extensive air showerswith E = 10 eV, with vertical lines indicating the beam energy in relevant NA61/SHINE runs. Middle and right :coverage of NA61 in pion–carbon collisions at 158 (middle) and 300 (right) GeV vs that of KASCADE and Auger, withcontours indicating the 66-percent level for each [8]. VTPC−1 ToF−LToF−RTarget ToF−F PSDVTPC−2VTPC−2GTPC
BEAM
BPD−1/2/3 13 m
MTPC−RMTPC−L
FIG. 2: A view of an NA61/SHINE p+C collision, superimposed on the layout of the apparatus.
III. THE METHOD
The pion spectra presented here have been obtainedusing three independent analysis techniques: • The h − method, in which all negative hadronsproduced in a collision are assumed to be pionsand the contribution of other species is correctedfor using simulations. Pros: simple, high statis-tics. Cons: stronger model dependence, doesn’twork for positive pions; • d E/ d x identification of π ± . Pros: explicit iden- tification, still high statistics thanks to NA61design. Cons: only works in the momentum re-gions where Bethe-Bloch bands do not overlap; • d E/ d x -plus-ToF identification of π ± . Pros:explicit identification over a wide momentumrange. Cons: limited acceptance.For all three approaches, particles passing all the cutsare divided into ( p, θ ) bins, where p is the total mo-mentum and θ is the polar angle, to account for chang-ing detection and identification properties. C35
VI International Symposium on Very High Energy Cosmic Ray InteractionsISVHECRI 2010, Batavia, IL, USA (28 June – 2 July 2010)
IV. RESULTS
Figures 3 and 4 show the production cross-section( σ prod = σ inel − σ qel , where σ inel and σ qel are in-elastic and quasi-elastic cross-section, respectively) ofnegative and positive pions in different θ bins, com-pared to air-shower simulations based on the COR-SIKA package, using three different interaction mod-els: GHEISHA, FLUKA and UrQMD [11–14]. Pleasesee the summary for a discussion of these results. V. SUMMARY AND OUTLOOK
NA61/SHINE has produced its first results relevantto tuning models of hadron production in extensive airshowers: preliminary π ± spectra from p+C collisionsat 31 GeV. The spectra were obtained using three dif-ferent methods, with very good agreement observedbetween them. Systematic uncertainties are at the moment no greater than 20 %, with work ongoing toreduce them further. Last but not least, preliminarycomparisons with simulations show good agreementwith FLUKA for polar angles below 180 mrad andwith UrQMD above that threshold.We are now working on finalising and publishingthese results, as well getting ready to analyse thelarge-statistics p+C and π +C runs from 2009. Acknowledgments
This work has been supported by the HungarianScientific Research Fund (OTKA 68506), the PolishMinistry of Science and Higher Education (N N2023956 33), the Federal Agency of Education of theMinistry of Education and Science of the RussianFederation (grant RNP 2.2.2.2.1547) and the RussianFoundation for Basic Research (grants 08-02-00018and 09-02-00664), the Ministry of Education, Cul-ture, Sports, Science and Technology, Japan, Grant-in-Aid for Scientific Research (18071005, 19034011,19740162), Swiss Nationalfonds Foundation 200020-117913/1 and ETH Research Grant TH-01 07-3. [1] T. Antoni et al. (KASCADE), Nucl. Instrum. Meth.
A513 , 490 (2003).[2] G. Navarra et al., Nucl. Instrum. Meth.
A518 , 207(2004).[3] J. Abraham et al. (Pierre Auger), Nucl. Instrum.Meth.
A523 , 50 (2004).[4] Bl¨umer, J. and Engel, R. and H¨orandel, J. R., Prog.Part. Nucl. Phys. , 293 (2009), 0904.0725.[5] C. Meurer et al., Czech. J. Phys. , A211 (2006),astro-ph/0512536.[6] T. Antoni et al. (KASCADE), Astropart. Phys. ,245 (2002), astro-ph/0102443.[7] J. Abraham et al. (Pierre Auger), Proc of 31th Int.Cosmic Ray Conf., Lodz (2009), 0906.2319.[8] I. Maris et al. (NA61/SHINE), Proc of 31th Int. Cos-mic Ray Conf., Lodz (2009).[9] S. Afanasev et al. (NA49), Nucl. Instrum. Meth. A430 , 210 (1999).[10] N. Antoniou et al. (NA61/SHINE) (2006), cERN-SPSC-2006-034.[11] D. Heck et al. (1998), report Forschungszentrum Karl-sruhe FZKA 6019.[12] H. Fesefeldt (1985), report Aachen PITHA-85-02.[13] A. Fasso, A. Ferrari, P. R. Sala, and J. Ranft (2000),prepared for International Conference on AdvancedMonte Carlo for Radiation Physics, Particle Trans-port Simulation and Applications (MC 2000), Lisbon,Portugal, 23-26 Oct 2000.[14] S. A. Bass et al., Prog. Part. Nucl. Phys. , 255(1998), nucl-th/9803035.[15] That is, interactions producing hadrons which do notinteract further but decay into leptons instead. C35
XVI International Symposium on Very High Energy Cosmic Ray InteractionsISVHECRI 2010, Batavia, IL, USA (28 June – 2 July 2010)
FIG. 3: Momentum dependence of π − production cross-section in p+C collisions at 31 GeV/c. Circles: h − analysis;squares: pions identified using d E/ d x ; triangles: pions identified using combined d E/ d x and ToF information. Verticalbars and boxes indicate statistical and systematic uncertainties, respectively. Lines indicate model calculations.FIG. 4: Momentum dependence of π + production cross-section in p+C collisions at 31 GeV/c. Squares: pions identifiedusing d E/ d x ; triangles: pions identified using combined d E/ d x and ToF information. Vertical bars and boxes indicatestatistical and systematic uncertainties, respectively. Lines indicate model calculations.and ToF information. Vertical bars and boxes indicatestatistical and systematic uncertainties, respectively. Lines indicate model calculations.