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Workshop Agenda, IHEP, CAS, Beijing, October 17 - 18, (2012)

CR spectrum and composition measured by Tibet hybrid experiment (YAC+Tibet-III) J. Huang for the Tibet AS γ Collaboration Institute of high energy physics, Chinese Academy of Sciences China, Beijing 100049. Workshop Agenda, IHEP, CAS, Beijing, October 17 - 18, (2012).

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Workshop Agenda, IHEP, CAS, Beijing, October 17 - 18, (2012)

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  1. CR spectrum and composition measured by Tibet hybrid experiment (YAC+Tibet-III)J. Huang for the Tibet ASγ Collaboration Institute of high energy physics, Chinese Academy of Sciences China, Beijing 100049 Workshop Agenda, IHEP, CAS, Beijing, October 17 - 18, (2012)

  2. Knee of the spectrum. • Two Possible explanations for the sharp knee. • New hybrid experiment (YAC+Tibet-III). • Primary proton, helium spectra obtained by (YAC-I + Tibet-III). • Expected results by (YAC-II + Tibet-III). • Summary Contents J. Huang (Workshop Agenda, Beijing, China, (2012))

  3. Tibet experiment1014-1017 eV The merit of the Tibet experiment is that the atmospheric depth of the experimental site (4300 m above sea level) is close to the maximum development of the air showers, with energies around the knee almost independent of the masses of primary cosmic rays as shown in this figure. 7 r.l. Pb Iron Scint. Box Merit of high altitude • AS array at high altitude (4300m a.s.l.) • Tibet-III array:37000m2 with 789 scint. • YAC array: 500m2 with 124 scint. • MD array: 5000m2 with 5 pools of water Cherenkov muon D.s . • Measure:energy spectrum around the knee • and chemical composition using sensitivity of air showers to the primary nuclei through detection of high energy AS core. YAC J. Huang (Workshop Agenda, Beijing, China, (2012))

  4. Cosmic ray(P,He,Fe…) Particle density & spread Separation of particles Tibet-III: Energy and direction of air shower Tibet YACarray(Yangbajing Air shower Core arary) J. Huang (Workshop Agenda, Beijing, China, (2012))

  5. All-particle spectrum measured by Tibet-III array　 from 1014 ~1017eV (ApJ 678, 1165-1179 (2008)) 5 J. Huang (Workshop Agenda, Beijing, China, (2012)) 5/ 31

  6. Energy spectrum around the knee measured by many experiments TibetKASCADEHEGRA CASA/MIABASJEAkeno DICE J. Huang (Workshop Agenda, Beijing, China, (2012))

  7. Normalized spectrum J. Huang (Workshop Agenda, Beijing, China, (2012))

  8. A sharp knee is clearly seen (ApJ 678, 1165-1179 (2008)) 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. 8 J. Huang (Workshop Agenda, Beijing, China, (2012)) 6/ 31

  9. Two possible explanations for the sharp knee ( M. Shibata, J. Huang et al. APJ 716 (2010) 1076 ) For explaining the sharp knee we proposed two composition models (called Model A and Model B) that are based on: 1) the up-to-now available experimental results; 2) some physics (or theoretical) assumptions. 9 J. Huang (Workshop Agenda, Beijing, China, (2012)) 7/ 31

  10. For ‘the up-to-now available experimental results’, we request: a) In the enery region lower than 100 TeV the directly measured p, He, …, ironspectra by CREAM, ATIC, JACEE, RUNJOB etc should be smoothly connected by the modeling spectra; b) In the energy region higher than 100 TeV the modeling p and He spectra should be consistent with our indirectly measuredp and He spectra; c) The superposed spectrum of all elemental spectra in the modeling should be consistent with our measuredall-particle spectrum. J. Huang (Workshop Agenda, Beijing, China, (2012))

  11. Some physics (or theoretical ) assumptions for both Model A and Model B • Diffusive shock acceleration in SNRs is assumed; • Multiple galactic sources were considered. • For each source there is an ‘acceleration limit’ ε(Z) which • --- is proportional to the charge Z of accelerated nuclei, --- denotes the energy the accelerated particles start to deviate from the power law; • εmax is introduced that denotes the ‘Maximum acceleration limit’ among multiple sources. J. Huang (Workshop Agenda, Beijing, China, (2012)) 8/ 28

  12. In this physics picture the knee is caused by the‘minimum accelerationlimit’ε(Z), (see details in the paper). Taking different ε(Z)andεmaxthe obtained all particle spectrum shows a smooth structure (see the figure below). The sharp knee cannot be produced. To explain the sharp knee we proposed two approaches, called Model Aand Model B. (ApJ ,716:1076-1083(2010)) J. Huang (Workshop Agenda, Beijing, China, (2012))

  13. Model A: Sharp knee is due to nearby sources (ApJ ,716:1076-1083(2010)) Substracting the smooth spectrum from the measured all particle spectrum, a power-law spectrum with index -2 is obtained (see the dotted line in the figure).This is very consistent with the assumption of CR particles coming fromnearby source(s). Extra component can be approximated by: J. Huang (Workshop Agenda, Beijing, China, (2012)) 9/ 28

  14. Model B: Sharp knee is due to nonlinear effectsin the defuse shock acceleration It was suggested (Malkov & Drury 2001; Ptuskin & Zirakashvili 2006) that: In the diffuse shock acceleration mechanism, the nonliner effect at supernova shock fronts is present that may produce a harder cosmic ray spectrum in the source. We included this effect by introducing an additional term in our formalism that showed to produce a dip below the ‘minimum accelerationlimit’ of the spectrum of each element (see the figure). J. Huang (Workshop Agenda, Beijing, China, (2012)) 10/ 28

  15. Their superposition can well produce the all-particle spectrum including the sharp knee. (Model B) (ApJ ,716:1076-1083(2010)) J. Huang (Workshop Agenda, Beijing, China, (2012))

  16. Two possible explanations for the sharp knee ( 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 (Workshop Agenda, Beijing, China, (2012))

  17. Short summary Two scenarios (model A and model B) are proposed to explain the sharpness of the knee. In model A, an excess component is assumed to overlap the global component, and its spectrum shape suggests that it can be attributed to nearby source(s)because it is surprisingly close to the expected source spectrum of the diffuse shock acceleration. CNO dominant composition is predicted by this model at the knee. In model B, a hard observed energy spectrum of each element from a given source is assumed. The sharp knee can be explained by a rigidity-dependent acceleration limit and hard spectrum due tononlinear effects. Iron-dominant composition is predicted by this model at the knee and beyond. J. Huang (Workshop Agenda, Beijing, China, (2012)) 11/ 28

  18. 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 (Workshop Agenda, Beijing, China, (2012)) 15/ 31

  19. ＹＡＣ YAC project(*10TeV -100 PeV) J. Huang (Workshop Agenda, Beijing, China, (2012))

  20. New hybrid experiment (YAC+Tibet-III+MD) 7 r.l. Pb Iron Iron Scint. Proton AS YAC2 MD This hybrid experiment consists of low threshold Air shower core array (YAC) and Air Shower (AS ) array and Muon Detector ( MD ) . YAC2 will measure the primary energy spectrum of 4 mass groups of P, He, 4<A<40, A>40 at 50 TeV – 1016 eV range covering the knee. • Tibet-III (37000 m2) : Primary energy and incident direction. • YAC2 ( 500 m2 ): High energy AS core within several x 10m from the axis. • Tibet-MD ( 5000 m2) : Number of muon. J. Huang (Workshop Agenda, Beijing, China, (2012)) 16/ 31

  21. 7 r.l. Pb Iron Scint. Box YAC Detector • Observe shower electron size • under lead plate (burst size Nb) • induced by high energy E.M. • particles at air-shower core. • WLSF (wave length shifting fibers) is used to collect the scintillation light for the purpose of good uniformity. • Two PMTs are used to cover wide dynamic range (1MIP is calibrated by single muon). • For High gain PMT , Nb: 1 – 3000 MIPs • For Low gain PMT , Nb: 1000- 106 MIPs 50cm Plastic scintillaors (4cm×50×1cm, 20pcs) 80cm WLSf Low gain PMT R5325 High gain PMT R4125 J. Huang (Workshop Agenda, Beijing, China, (2012))

  22. YAC1is well running now( data taking started from 2009.04.01) YAC1 Total : 16 YAC detectors Effective area: 10 m2 J. Huang (Workshop Agenda, Beijing, China, (2012)) 19/ 31

  23. Detector Calibration • PMT linearity, • use of LED light source; • 2. Linearity of PMT+scintillator, • a. probe calibration; • b. accelerator beam calibration. J. Huang (Workshop Agenda, Beijing, China, (2012))

  24. Probe Calibration ( The determination of the burst size is calibrated using single muon peak ) Single muon calibration 1 MIP Using a probe detector, we can obtain the single particle peak for each YAC detector. 24 J. Huang (Workshop Agenda, Beijing, China, (2012))

  25. PMT linearity In order to record the electromagnetic showers of burst size from 1 to 10^6 particles, a wide dynamic range of PMT is required. For each PMT (high gain and low gain) used in YAC-I the linearity has been measured by using LED light source and optical filters. In the test we fixed the positions of LED, filter and PMT. By using different filters we can get light of different intensity, and then, we can check the Linearity of PMTs. Dynamic range and linearity High gain PMT R4125 106 Proton PMT output charge[pC×0.25] 1MIP Iron Nb_top 106MIPs Low gain PMT R5325 Input light Primary Energy (GeV) 1017 eV 25 J. Huang (Workshop Agenda, Beijing, China, (2012))

  26. Electron beam calibration of YAC to get ADC count vs number of particles YAC YAC Thick IC Thin IC The Beam 106 MIPs BEPC:Beijing Electron-Positron Collider 17/ 28

  27. Calibration using BEPC The experimental sketch Saturation of PMT & Saturation of scintillator • The accelerator-beam experiment shows a good linearity between the incident particle flux and YAC-ADC output below 5×106 MIPs. • the saturation effect of the plastic scintillator satisfies YAC detector’s requirement. Thin IC Thick IC Number of particles (Beam) 18/ 28

  28. Primary proton, helium spectra analysis J. Huang (Workshop Agenda, Beijing, China, (2012))

  29. - Full M.C. Simulation - • Hadronic interaction model • CORSIKA (Ver. 6.204 ) • – QGSJET2– • – SIBYLL2.1– • = Air Shower simulation = • CORSIKA 6.204 (QGSJET2, 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= • Simulated air-shower events are reconstructed with the same detector configurationand structure as the YAC array using Epics (uv8.64) • Primary composition model • NLA (above-mentioned • Nonlinear effects model ). • HD model • (Heavy Dominant model: • seeM. Shibata, J. Huang et al. APJ 716 (2010) 1076) 29 J. Huang (Workshop Agenda, Beijing, China, (2012)) 20/ 28

  30. Primary cosmic-ray composition spectrum assumed in MC ( M. Shibata, J. Huang et al. APJ 716 (2010) 1076 ) J. Huang (Workshop Agenda, Beijing, China, (2012))

  31. The difference between NLA and HD model NLA: ‘He rich’ model HD : ‘He poor’ model • The proton spectrum of the two models is connected with the direct experiment in the low energy and consistent with the spectrum obtained from the Tibet (EC+AS) experiment in the high energy. • The He spectrum of HD model coincides with the results from RUNJOB and ATIC-I, we called ‘He poor’ model. • However, the He spectrum of NLA coincides with the results from JACEE, ATIC-II, CREAM, we called ‘ He rich’ model. • The sum of all single-component spectra can reproduce the sharp knee in all particle spectrum. J. Huang (Workshop Agenda, Beijing, China, (2012)) 16/ 31

  32. 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 (Workshop Agenda, Beijing, China, (2012))

  33. Core event selection Base on the above core event selection condition, we found the AS axis estimated by LDF is within 5 m from our YAC detector array. 105 <= Ne <= 106 R <= 5 m 3464/3483=99.5% R< 5m J. Huang (Workshop Agenda, Beijing, China, (2012))

  34. Interaction model dependence in (YAC1+Tibet-III) experiment These figures shows that QGSJET and SIBYLL, both models produce distribution shapes consistent with our experimental data. Air shower size (Ne) spectra Total burst size (sum Nb) spectra Top burst size (Nb_top)spectra Mean lateral spread (NbR)spectra

  35. 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 energy determination E0=f(Ne,s) based on proton-like MC events J. Huang (Workshop Agenda, Beijing, China, (2012))

  36. Primary (P+He) separation by ANN QGSJET Purity – 95.2% Efficiency – 62% P+He Other Nuclei SIBYLL Purity – 94.5% Efficiency – 63% P+He Other Nuclei J. Huang (Workshop Agenda, Beijing, China, (2012))

  37. Primary proton separation by ANN for MC events QGSJET Purity – 79% Efficiency – 46% Other P roton SIBYLL Purity – 78% Efficiency – 40% Other P roton J. Huang (Workshop Agenda, Beijing, China, (2012))

  38. 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 (Workshop Agenda, Beijing, China, (2012))

  39. Size resolution (MC Data) (based on QGSJET+HD model )(1.0 ≦ sec(Θzenith) < 1.1) QGSJET＋HD Ne resoultion: ~7% (Ne>105 ) QGSJET+HD

  40. Primary energy determination (1.) Energy Resolution – Proton like events ( for T<=0.4& sec(theta) <=1.1 ) 1e+05 < Ne < 1e+06 Energy Resolution : 22% @ 500TeV

  41. Check the systematic errors by ANN P+He Proton Helium The primary energy of (P+He)-like or P-like or Helium-like events is in a good agreement with the true primary energy spectrum. J. Huang (ISVHECRI2012, Berlin, Germany)

  42. (SΩ)effcalculated by MC (1) Nb >= 200 Nhit >= 4 Nbtop >= 1500 Ne >= 80000

  43. Primary (P+He) spectra obtained by (YAC1+Tibet-III) preliminary J. Huang (Workshop Agenda, Beijing, China, (2012))

  44. Primary proton , helium spectra obtained by (YAC1+Tibet-III) preliminary preliminary J. Huang (Workshop Agenda, Beijing, China, (2012))

  45. YAC2 is also well running now( data taking started from 2011.8.1) YAC-II Pb 50cm 80cm Total : 124 YAC detectors Cover area: ~ 500 m2 J. Huang (Workshop Agenda, Beijing, China, (2012)) 16/ 28

  46. Expected results by (YAC2+Tibet-III) 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. • Solid lines:input • Symbols:reconstructed • Expected primary energy spectra 46 J. Huang (Workshop Agenda, Beijing, China, (2012))

  47. Summary YAC1 shows the ability and sensitivity in checking the hadronic interaction models. (2) The experimental distribution, sumNb has the shape very close to the MC predictions of QGSJET+NLA, QGSJET+HD , SIBYLL+NLA and SIBYLL+HD. Some other quantities, such as Ne, Nb_top, <R> have the same behavior as well. (3) Some discrepancies in the absolute intensities are seen. Data normally shows a higher intensity than MC. Taking a more hard He spectrum as given by CREAM can improve this situation. A further study is going on. (YAC1+Tibet-III ) could measure protons and heliums spectra at > 50 TeV which is shown to be smoothly connected with direct observation data at lower energies and also with our previously reported results at higher energies. J. Huang (Workshop Agenda, Beijing, China, (2012))

  48. 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. (6) 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 ! (7) 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. J. Huang (Workshop Agenda, Beijing, China, (2012))

  49. Thank you for your attention !!

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