/ 15 1/ 31 Cosmic ray data and their interpretation: the Tibet hybrid EAS experiment -- Primary energy spectra of Cosmic Rays at the knee and tests of hadronic interaction models -- J. Huang for the Tibet AS γ Collaboration Institute of high energy physics, Chinese Academy of Sciences China, Beijing ISVHECRI2010, Fermilab, U.S.A, June 28- July 2, (2010)

/ 15 Outline (1) Hybrid experiment using AS core detector to measure proton and helium spectra; (2) All particle spectrum measured by Tibet-III air shower array ; (3) Two possible explanations for the structure of the knee; (4) Tibet new hybrid EAS experiment: aimed at the measurement of p, He, iron, other nuclei spectra up to eV; (5) Some preliminary results of the checking of hadronic interaction models at 100 – 300 TeV region using (Tibet-III+ YAC-I) data. Jing Huang (ISVH2010-Fermilab) 2/ 31

/ 15 3 Take a look at the CR spectrum again ‘Knee’ ： 3-5 PeV dJ/dE ∝ E -γ γ=2.65  3.1 3/ 31 Jing Huang (ISVH2010-Fermilab) The steepening of the knee around PeV range is thought to relate with the change of the chemical composition, because it can be explained as the acceleration limit by SNRs and an effect of rigidity dependent cutoff for different chemical component.

/ 15 4 P, He spectra by Tibet hybrid Experiment (Phys. Lett. B, 632, 58 (2006)) 4 Primary Proton spectrumPrimary Helium spectrum (All - (P+He)) /All 1) Our results shows that the main component responsible for the knee of the all particle spectrum is heavier than helium nuclei. 2) The absolute fluxes of protons and helium nuclei are derived within 30% systematic errors depending on the hadronic interaction models. 4/ 31 Jing Huang (ISVH2010-Fermilab)

/ 15 5 ModelKnee Position (PeV) Index of spectrum QGS.+ HD 4.0 ± 0.1R1= ± 0.01 R2= ± 0.01 QGS.+ PD 3.8 ± 0.1R1= ± 0.01 R2= ± 0.01 SIB.+ HD 4.0 ± 0.1R1= ± 0.01 R2= ± / 31 Jing Huang (ISVH2010-Fermilab) All-particle spectrum measured by Tibet-III array from ~10 17 eV (ApJ 678, (2008))

/ 15 6 (ApJ 678, (2008)) A sharp knee is clearly seen (ApJ 678, (2008)) 6/ 31 Jing Huang (ISVH2010-Fermilab) What is the origin of the sharp knee? There were many models: nearby source, new interaction threhold, etc. In the following, we would introduce our two analyses for the origin of the sharp knee.

/ 15 7 Two possible explanations for the sharp knee 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. (ApJ,716: (2010)) 7/ 31 Jing Huang (ISVH2010-Fermilab)

/ 15 8 For ‘the up-to-now available experimental results’, we request: a) In the enery region lower than 100 TeV the directly measured p, He, …, iron spectra 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 measured p and He spectra; c) The superposed spectrum of all elemental spectra in the modeling should be consistent with our measured all-particle spectrum. Jing Huang (ISVH2010-Fermilab) 8/ 31

/ 15 9 Diffuse shock wave acceleration in SNRs is assumed; For each source, there is a ‘minimum 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; For each source a ‘maximum acceleration limit’ εmax is introduced that denotes the maximun acceleration ability of the source. For the cosmic ray propogation in the Galaxy the ragidity cutoff effects is taken into account. Multiple galactic sources were considered. Some physics (or theoretical) assumptions for both Model A and Model B Jing Huang (ISVH2010-Fermilab) 9/ 31

/ (ApJ,716: (2010)) In this physics picture the knee is caused by the‘minimum acceleration limit’ ε (Z), (see details in the paper). Taking different ε (Z) and ε max the 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 A and Model B. 10/ 31

/ Model A: Sharp knee is due to nearby sources 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 from nearby source(s). (ApJ,716: (2010)) Extra component can be approximated by: Jing Huang (ISVH2010-Fermilab) 11/ 31

/ Model B: Sharp knee is due to nonlinear effects in the defuse shock wave acceleration It was suggested (Malkov & Drury 2001; Ptuskin & Zirakashvili 2006) that: In the diffuse shock wave 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 acceleration limit’ of the spectrum of each element (see the figure). Jing Huang (ISVH2010-Fermilab) 12/ 31

/ Their superposition can well produce the all- particle spectrum including the sharp knee. (ApJ,716: (2010)) 13/ 31 Jing Huang (ISVH2010-Fermilab)

/ 15 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. Middle 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 to nonlinear effects. Iron-dominant composition is predicted by this model at the knee and beyond. Jing Huang (ISVH2010-Fermilab) 14/ 31

/ 15 In order to distinguish between Model A and Model B and many other models, measurements of the chemical composition around the knee, especially measurements of the spectra of individual component till their knee region 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 next phase experiments YAC (Yangbajing AS Core array) ! Jing Huang (ISVH2010-Fermilab) 15/ 31

/ YAC AS MD New hybrid experiment (Tibet-AS+YAC+MD ) Pb 7 r.l. Scint. Iron Tibet-AS (existd) : Primary energy and direction of an air shower. YAC-II (Yangbajing Air shower Core array) (will be setup this September) Core information  Separation of primary nuclei. Tibet-MD (will be set up this July) : Number of muon. This hybrid experiment consists of low threshold Burst Dector grid (YAC) and Air Shower (AS ) array and Muon Detector ( MD ) without Emulsion Chamber, which observe AS core within several x 10m from the axis. Jing Huang (ISVH2010-Fermilab) 16/ 31

/ YAC array Tibet-AS Three steps of new hybrid expt. Total detectors: 16 Spacing : 0.5 m Total area ： 10 m 2 Total detectors : 100 Spacing : 1.5 m Total area ： 200 m 2 Total detector : 400 Spacing ： 3.75 m Total area ： 5000 m 2 0.5m YAC AS 1.5m YAC AS 3.75m YAC AS YAC -IYAC -IIYAC -III Pb Iron Scint. Box 7 r.l. 17/ 31

/ 15 Three physical targets of YAC (1) Step-1: ( Tibet-AS+YAC-I ) hybrid experiments Target (1): Check of hardronic interaction models. (2) Step-2: (Tibet-AS+YAC-II+ MD) hybrid experiments Target (2) : Measurement of primary proton spectrum and helium spectrum covering three decades of energy range around the knee. (3) Step-3: (Tibet-AS+YAC-III+MD) hybrid experiments Target(3) : Measurement of primary iron spectrum and other nuclei spectrum covering three decades of energy range around the knee. Jing Huang (ISVH2010-Fermilab) 18/ 31

/ 15 YAC-I is well running now data taking started from Iron Box 7 r.l. Pb Scint. Main aim is to check hadronic interaction models YAC 19/ 31

/ 15 Thin IC Thick IC YAC The Beam YAC BEPC: Beijing Electron-Positron Collider Calibration using BEPC (1) 20/ 31

/ 15 Thin IC Thick IC The result shows good linearity in the range from few MIPs to ~5X10 6 MIPs. Calibration using BEPC(2) Jing Huang (ISVH2010-Fermilab) 21/ 31

/ 15 Burst size spectrum ( High + Low gain PMT ) after the gain compensation of each PMT trigger condition : Nb>12(~10mV) (high gainPMT) any 1 YAC trigger rate : 30 Hz PMT dynamic range: high gain PMT: MIPs low gain PMT: MIPs Jing Huang (ISVH2010-Fermilab) 22/ 31

/ = Air Shower simulation = CORSIKA (QGSJET01c, SIBYLL2.1) ( 1 ) Primary energy: E0 >1 TeV, 2.5×10 10 events ( 2 ) All secondary particles are traced until their energies become 300 MeV in the atmosphere. ( 3 ) Observation Site : Yangbajing (606 g/cm 2 ) = Detector simulation = Simulated air-shower events are reconstructed with the same detector configuration and structure as the YAC array using Epics (uv8.64) - M.C. Simulation - Primary composition model Model B (above-mentioned Nonlinear effects model ). HD model (Heavy Dominant model: see ApJ, 678: , 2008 ) Hadronic interaction model CORSIKA (Ver ) – QGSJET01c– – SIBYLL2.1– Jing Huang (ISVH2010-Fermilab) 23/ 31

/ 15 For YAC detectors, the following parameters are used in this analysis. N b : number of shower particles hitting a detector unit; N hit : number of ‘fired’ detector units each with Nb >= 100; N b _ top : the maximum burst size among fired detectors; Sum(N b ): total burst size of all fired detector units; : the mean lateral distance from the air shower core to a detector unit. ( = Sum(R i ) / N hit ) : energy weighted mean lateral distance ( = Sum (Nb i x R i ) / N hit ) Jing Huang (ISVH2010-Fermilab) Some parameters 24/ 28

/ 15 a ) Distribution of primary energy b) Distribution of core position error. Some preliminary results from two YAC-I data samples 1) Selection condition 1: Nb>100 && 6 ~ 100 TeV; core resolution < 3m; ~80% selected events are induced by p and He. 2) Selection condition 2: Nb>100 && 7 ~ 270 TeV; core resolution < 3m; ~75% selected events are induced by p and He. c ) Distribution of primary energy d) Distribution of core position error. 25/ 31

/ 15 Comparison of YAC-I data with MC model prediction (1) interaction model:QGSJET, SIBYLL composition model: ModelB Nb>100 Nhit=6,7 Nb>100 7<Nhit<13 Preliminary data Nb>100 Nhit=6,7 Nb>100 7<Nhit<13 The total burst size ( sumNb ) spectra and the top burst size ( Nbtop ) spectra of YAC-I high-energy core events are compared with the simulation results:  QGSJET+Model B results are compatible with experimental data.  SIBYLL+Model B gives a 30% higher flux than experimental data.  Both models produce distribution shapes consistent with experimental data. E

/ 15 Comparison of YAC-I data with MC model prediction (2) interaction model:QGSJET,SIBYLL composition model: ModelB Preliminary data The mean lateral distance (Rw) and energy weighted mean lateral distance (Nb X Rw) are shown in these figures.  both QGSJET and SIBYLL models are consistent with our experimental data, Nb>100 Nhit=6,7 Nb>100 Nhit=6,7 Nb>100 7<Nhit<13 Nb>100 7<Nhit<13 E 27/ 31

/ 15 Comparison of YAC-I data with MC model prediction (3) interaction model: QGSJET, composition model: HD,ModelB Preliminary data Jing Huang (ISVH2010-Fermilab) Nb>100 Nhit=6,7 Nb>100 Nhit=6,7 Nb>100 Nhit=6,7 Nb>100 Nhit=6,7  It shows that when QGSJET is combined with Model B or a heavy-enriched primary composition model (HD ), the gross features of observed core events around TeV can well be reproduced. 28/ 31

/ 15 Comparison of YAC-I data with MC model prediction (4) interaction model: SIBYLL, composition model: HD, ModelB Preliminary data Jing Huang (ISVH2010-Fermilab) Nb>100 Nhit=6,7 Nb>100 Nhit=6,7 Nb>100 Nhit=6,7 Nb>100 Nhit=6,7  It shows that SIBYLL+Model B results in a 30% higher flux than experimental data, and SIBYLL+HD gives a higher flux by 10% than experimental data at energy region around TeV. 29/ 31

/ Summary The preliminary results show that, at around TeV energy region, QGSJET model can well reproduce the gross features of observed core events when combined with composition Model B or a heavy-enriched primary composition model (HD ). SIBYLL+Model B gives a 30% higher flux than experimental data, and SIBYLL+HD results gives a 8 % higher flux than experimental data. QGSJET and SIBYLL models produce distribution shapes consistent with our experimental data. In energy regions higher than 300 TeV our data is under analysis. Next phase of Tibet experiment, (Tibet-III+YAC+MD), will measure the individual component spectra at the knee towards to clearify the “Origin of the knee.” We also plan to build a ground based large and complexγ/CR observatory at high altitude (4300m a.s.l.) within 10 years.  Complementary to CTA in γ astronomy  Unique in CR measurements at the knee. Jing Huang (ISVH2010-Fermilab) 30/ 31

/ 15 Large High Altitude Air Shower Observatory You are invited to Lhaaso at Tibet ! Jing Huang (ISVH2008-PARIS) 31/ 31

/ 15 END Thank you!