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Recent Results from the new Tibet hybrid experiment

Get insights into the sharp knee of the spectrum and possible explanations from the new hybrid experiment by J. Huang at HESZ 2015 in Japan. Discover the primary cosmic-ray spectra measured, models explored, and future experiments planned.

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Recent Results from the new Tibet hybrid experiment

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  1. Recent Results from the new Tibet hybrid experiment J. Huang for the Tibet ASγCollaborationaaInstitute of high energy physics, Chinese Academy of Sciences China, Beijing 100049a International Conference ( HESZ2015 ) , Nagoya University, Japan

  2. Knee of the spectrum. • Two Possible explanations for the sharp knee. • New hybrid experiment (YAC+Tibet-III). • Test of hadronic interaction models and compositions models. • Primary proton, helium spectra obtained by (YAC-I + Tibet-III). • Expected primary P, He and iron spectra by YAC-II • Summary Contents J. Huang (HESZ 2015, Japan)

  3. All-particle spectrum measured by Tibet-III array　 from 1014 ~1017eV (ApJ 678, 1165-1179 (2008)) 3 J. Huang (HESZ 2015, Japan) 5/ 31

  4. Energy spectrum around the knee measured by many experiments TibetKASCADEHEGRA CASA/MIABASJEAkeno DICE J. Huang (HESZ 2015, Japan)

  5. Normalized spectrum J. Huang (HESZ 2015, Japan)

  6. A sharp knee is clearly seen ( see the paper: M.Shibata, J. Huang et al. APJ 716 (2010) 1076 ) What is the origin of the sharp knee? There were many models: nearby source, new interaction threshold, etc. In the following, I would introduce our two analyses for the origin of the sharp knee. 6 J. Huang (ISVHECRI2012, Berlin, Germany) 6/ 31

  7. Two possible explanations for the sharp knee ( see the paper: M.Shibata, J. Huang et al. APJ 716 (2010) 1076 ) 2) Model B: Sharp knee is due to nonlinear effects in the diffusive shock acceleration (DSA) 1) Model A: Sharp knee is due to nearby sources All-particle knee = CNO? All-particle knee =Fe knee? J. Huang (HESZ 2015, Japan)

  8. In order to distinguish betweenModel AandModel Band many other models, measurements of the chemical composition around the knee, especially measurements of the spectra of individual component till their knee will be essentially important. Therefore, we planed a new experiment: 1) to lower down the energy measurement of individual component spectra to *10TeV and make connection with direct measurements; 2) to make a high precision measurement of primary p, He, …, Fe till 100 PeV region to see the rigidity cutoff effect. These aims will be realized by our new experiments YAC (Yangbajing AS Core array) ! J. Huang (HESZ 2015, Japan) 15/ 31

  9. Proton Helium Knee of the spectrum • The early works doing the research of the chemical composition • of the knee region were the Tibet emulsion chamber (Tibet-EC) • experiment and the KASCADE experiment. The results of the • Tibet-EC suggest that the main component responsible for making • the knee structure is composed of nuclei heavier than helium, • however, the KASCADE claims that the knee is due to the • steepening of the spectra of light elements with an exponential • type cutoff as shown in this Figure. • It is also noted that the experimental data points are still poor • in the energy range between the direct measurements and • the indirect measurements waiting us to study. J. Huang (HESZ 2015, Japan)

  10. Proton Helium Knee of the spectrum YAC • The YAC-II aims to observe the energy • spectrum of proton , helium, iron whose • energy range will overlap with direct observations • at lower energies such as CREAM, ATIC and • TRACER, and Tibet-EC experiment at higher • energies. J. Huang (HESZ 2015, Japan)

  11. New hybrid experiment (YAC-II+Tibet-III+MD) 7 r.l. Pb Iron Scint. AS YAC2 MD This hybrid experiment consists of low threshold Air shower core array (YAC-II) and Air Shower array ( Tibet-III ) and Muon Detector ( MD ) . YAC-II aims to measure the primary energy spectrum of 4 mass groups of Proton, Helium, iron and 4<A<56,at 50 TeV – 1016 eV range covering the knee. • Tibet-III (50000 m2) : Primary energy and incident direction. • YAC-II ( 500 m2 ): High energy AS core within several x 10m from the axis. • Tibet-MD ( 4500 m2) : Number of muon. J. Huang (HESZ 2015, Japan)

  12. - Full M.C. Simulation - • Hadronic interaction model • CORSIKA (Ver. 7.3500 ) • – EPOS -LHC– • – QGSJETII-04– • – SIBYLL 2.1 – • = Air Shower simulation = • CORSIKA 7.3500 (EPOS –LHC, QGSJETII-04, • SIBYLL2.1) • ( 1 ) Primary energy: E0 >1 TeV • ( 2 ) All secondary particles are traced until their energies become 300 MeV in the atmosphere. • ( 3 ) Observation Site : Yangbajing (606 g/cm2 ) • =Detector simulation= • Geant 4 ( Ver. 9.5) • Simulated air-shower events are reconstructed with the same detector configurationand structure as the Tibet-III YAC and Muon detector array. • Primary composition model • Helium poor model [1] • Helium rich model [1] • Gaisser’s fit model [1] • see [1] J. Huang et al. Astropart. Phy 66 (2015) 18 J. Huang (HESZ 2015, Japan) 20/ 28

  13. Primary cosmic-ray composition models ( see the paper: J. Huang et al. Astropart. Phy. 66 (2015) 18) • The main differences between “He-poor model” , “He-rich model” • and “Gaisser’s fit model” are as follows: • The He spectrum of “He-poor model” coincides with the • results from RUNJOB, • The He spectrum of “He-rich model” coincides with the • results from CREAM, ATIC2 and JACEE. • The “Gaisser-fit model” fits to a higher He model (almost • same as our “He-rich model”)at the low energy range • and to the KASCADE-QGSJET data at high energy range • in which light components dominate in the chemical • composition. • In all models mentioned above, each component is summed • up so as to match with the all-particle spectrum with • a sharp knee, which was obtained with the Tibet-III AS array. J. Huang (HESZ 2015, Japan)

  14. Tests of hadronic interaction models by ( YAC-I + Tibet-III ) J. Huang (HESZ 2015, Japan)

  15. Prototype experiment (YAC-I+Tibet-III) ( data taking started from 2009.04.01) YAC1 Total : 16 YAC detectors Effective area: 10 m2 J. Huang (HESZ 2015, Japan) 19/ 31

  16. Tests of hadronic interaction models and composition models(Some preliminary results from YAC-I data samples, primary energy: 100TeV -1PeV • Observable parameters of high energy cores as sumNb , • Nb_top, <R> and <Nb*R> are calculated for various • combination of interaction and primary models and are • compared each others as shown in Figure. The area of all • distributions are normalized as their total area =1. The • shape of each parameter distribution is almost same since • these cores are mainly multiple EM cascade processes • originated by decayed gamma rays from neutral pions. • The experimental data are consistent with those, which • mean that there exist no detection bias. • Note that the shape shows a (cascade) scaling behavior, • while its intensity depends on the primary model. J. Huang (HESZ 2015, Japan)

  17. Some discrepancies in the absolute intensities are seen: • First, note that the three interaction models give same intensity when the primary is the “He-poor” model. This result suggest that the difference among three interaction models are very small, say at most 10% since almost all high energy cores are produced by same primary protons (He contribution is very small). • Experimental Data are very close to SIBYLL2.1, EPOS-LHC and QGSJETII-04, if we assumed “He-rich” primary composition. It means that YAC-experimental data have the same primary composition with the “ He-rich” model. • However, the “Gaisser’s fit” primary model always gives a higher flux by a factor 1.4 - 2.0 than the experimental result and other primary models. It means that there are too many primary light components (P,He) in “Gaisser’s fit” model than experimental data. • These results well show that YAC is very sensitive to observe light components and well reflet the structure of primary spectrum of light components as seen in this figure. Comparison of event absolute intensities between Expt. and MC preliminary Expt.data For details, please see the following paper: L.M.Zhai, J.Huang et al., J.Phys. G: Nucl. Part. Phys. 42 (2015), 045201 preliminary Fig. 2 : The intensity ratios of (SumNb) to that obtained by the Expt. Data. The red dash line (Ratio =1) is Expt.data. Fig. 1: Intergral burst-size spectra (SumNb) J. Huang (HESZ 2015, Japan)

  18. Comparison of event mean lateral spreads (<NbR>) between Expt. and MC • Some discrepancies in the mean lateral spreads are seen: • This conclusion is same as the above Fig.1 and Fig.2’s • conclusion, that is, YAC-experimental data are very close • to “EPOS-LHC + He-rich” and “QGSJETII-04 + He-poor ” • model. However, the “Gaisser’s fit” primary composition • model always gives a lower distribution. It means that • there are too many primary light components (P,He) in • “Gaisser’s fit” than experimental data. preliminary Fig. 3. Mean lateral spread of AS-cores J. Huang (HESZ 2015, Japan)

  19. Primary proton, helium spectra analysis J. Huang (HESZ 2015, Japan)

  20. Primary proton, He spectra analysis Identification of proton events ANN (a feed-forward artificial neural network) is used. Input event features: Ne, ΣNb, Nbtop, Nhit, <Rb>, < NbRb>, θ Classification: proton/others Primary (proton+He) energy determination E0=f(Ne,s) based on (p+He)-like MC events J. Huang (HESZ 2015, Japan)

  21. Air shower size to primary energy The primary energy (E0 ) of each AS event is determined by the air-shower size (Ne) which is calculated by fitting the lateral particle density distribution to the modified NKG function. Modified NKG function J. Huang (HESZ 2015, Japan)

  22. Air shower size to primary energy E0=1.88*( Ne/1000.0)0.92 ) (TeV) Energy resolution ~ 20% ( at 200 TeV ) J. Huang (HESZ 2015, Japan)

  23. Primary (P+He) separation by ANN for MC events QGSJET Purity – 95.2% Efficiency – 62% P+He Other Nuclei SIBYLL Purity – 94.5% Efficiency – 63% P+He Other Nuclei J. Huang (HESZ 2015, Japan)

  24. Results and discussions preliminary J. Huang (HESZ 2015, Japan)

  25. (YAC-II +Tibet-III+MD) is well running now( data taking started from 2014. 2) YAC-II Pb 50cm 80cm Total : 124 YAC detectors Cover area: ~ 500 m2 J. Huang (HESZ 2015, Japan) 16/ 28

  26. Expected results by (YAC-II+Tibet-III +MD) • MC simulation shows that (YAC-II+Tibet-III +MD) is powerful enough to obtain proton, helium, iron and 4<A<56 spectra of primary CRs in the range of • 50 TeV -1016 eV with an energy resolution better than 12% at 1015eV. • Expected primary P, He spectra • Expected primary Iron spectra Iron 26 J. Huang (HESZ 2015, Japan)

  27. Summary 1. YAC-I shows the ability and sensitivity in checking the hadronic interaction models. Based on the “He-poor” primary model, we estimate that the difference of EPOS-LHC, QGSJETII-04, SIBYLL2.1 is within 10 % in our concerned energy region. High core events are very sensitive to the light components in CRs and the core parameters of sum Nb, Nb_top, <R> and <Nb*R> are very useful to separate the light components from all the observed events using a ANN technique. The flux of high energy core events are sensitive to the light components, since the interaction model seems to depend strongly on the production of high energy core events, we can obtain the energy spectrum of light components in primary CRs with sufficient accuracy as discussed in the YAC-I experiment. Simultaneous observation of core events with YAC and MD array may allow us to obtain the spectrum of each of primary components separately. Actually, the full MC simulation shows that the (YAC-II+Tibet-III +MD) array is powerful enough to obtain the energy spectra of proton, helium, medium nuclei and iron spectra of primary CRs in the range of 50 TeV -10 PeV with sufficient accuracy. It is estimated that the energy resolution of primary particles of 1 PeV is better than 12%。

  28. Summary 4. We obtained the primary energy spectrum of proton, helium and (P+He) spectra between 50 TeV and 1 PeV , and found that the knee of the (P+He) spectra is located around 400 TeV. 5. The interaction model dependence in deriving the primary proton, helium and (P+He) spectra are found to be small (less than 25% in absolute intensity, 10% in position of the knee ), and the composition model dependence is less than 10% in absolute intensity, and various systematic errors are under study now ! 6. Next phase experiment YAC2 will measure the primary energy spectrum of 4 mass groups of P, He, 4<A<40, A>40 at 1014 – 1016 eV range covering the knee.

  29. Thank you for your attention !!

  30. Core event selection Event selection condition for AS core event was studied by MC and following criteria were adopted to reject non core events whose shower axis is far from the YAC array. Nb>200, Nhit≧4, Nbtop ≧1500, Ne>80000 | AS axis by LDF – burst center| < 5 m Statistics of core events in MC simulation and experiment Live Time is 106.05 days. J. Huang (ISVHECRI2012, Berlin, Germany)

  31. Sensitivity of (YAC-II+Tibet-III+MD) to measure the P,He and iron component at the knee Other like Iron like Purity – 83.5% Efficiency – 65.3%

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