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Measurement of the proton-air inelastic cross section with ARGO-YBJ

21° European Cosmic Ray Symposium 9-12 September 2008 – Kosice, Slovakia. Measurement of the proton-air inelastic cross section with ARGO-YBJ. A. Surdo Istituto Nazionale di Fisica Nucleare Lecce – Italy on behalf of ARGO-YBJ Collaboration. Introduction.

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Measurement of the proton-air inelastic cross section with ARGO-YBJ

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  1. 21° European Cosmic Ray Symposium 9-12 September 2008 – Kosice, Slovakia Measurement of the proton-air inelastic cross section with ARGO-YBJ A. Surdo Istituto Nazionale di Fisica Nucleare Lecce – Italy on behalf of ARGO-YBJ Collaboration A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  2. Introduction • Inelastic proton-air (and total p-p) cross section can be derived from • cosmic ray measurements through several methods • Direct method: • measure the distribution of X1, the 1st interaction point of p-air • collisions, to directly measure the mean free path lp-air •  feasible (in principle) at relatively low energies only • Indirect methods: • (a) for fixed primary energy and zenith angle, measure the exponential • tail of the shower maximum depth (Xmax)distribution (b) for fixed primary energies, measure the exponential zenith angle distribution of the shower intensity  slope parameter (L) connected to lp-air ARGO-YBJ approach A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  3. The ARGO-YBJ experiment • Collaboration between: • Istituto Nazionale di Fisica Nucleare (INFN) – Italy • Chinese Academy of Science (CAS) • Site:Cosmic Ray Observatory @ Yangbajing (Tibet), China High Altitude Cosmic Ray Laboratory @ YangBaJing Site Altitude: 4,300 m a.s.l. , ~ 600 g/cm2 Site Coordinates: longitude 90° 31’ 50” E, latitude 30° 06’ 38” N A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  4. Search for GRB’s(full GeV / TeV energy range)  Talk by T. Di Girolamo ARGO-YBJ is a full-coverage Extensive Air Shower detector with several main goals: • VHE g-Ray Astronomy: search for point-like (and diffuse) galactic and extra-galactic sources at few hundreds GeV energy threshold  Poster by D. Martello • Sun and Heliosphere physics(Eth 10 GeV) • Cosmic ray physics: • anti-p / p ratio at TeV energy • spectrum and composition (Eth few TeV) • study of the shower space-time structure • fundamental physics issues (p-air cross section, ...) ARGO-YBJ physics objects A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  5. 12 RPC =1 Cluster ( 5.7 ´ 7.6 m2 ) ARGO-YBJ detector 8 Strips = 1 Pad (56 ´ 62 cm2) Central carpet: 130 Clusters 1,560 RPCs 124,800 Strips (5,600m2 active area) 99 m 74 m 10 Pads = 1 RPC (2.80 ´ 1.25 m2) 78 m 111 m RPC Strip = spatial pixel (6.5 x 62 cm2) Pad = time pixel Time resolution ~1 ns + Analog RPC charge read-out +0.5 cm lead converter (2009) A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  6. ARGO-YBJ detector Currently completed and in data taking Inclusive trigger Npad > 20 (“shower mode” trigger) on the central carpet. Trigger rate 4 kHz and data flow 7 MB/s. A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  7. h0 q Measurement of the Flux attenuation Use the shower frequency vs (secq -1) for fixed energy and shower age (h0=vert. depth). The absorption length L is connected to lint through:  sp-Air (mb) = 2.41·104 / lint(g/cm2) L = k lint • The parameter k takes into accounts how the primary energy is dissipated in the shower • kdetermined by simulations, depends on: • interaction model • shower fluctuations • actual set of experimental observables • …….. • Warning • Constrain XDO = Xdet – X0 or • better XDM = Xdet – Xmax • Select deep showers (large • Xmax, i.e. small XD0 or XDM) A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  8. 3-D view of a detectedshower Top view of the sameshower Analysis general criteria • Exploit peculiar detector features: • space/time granularity, • full-coverage technique, • high altitude (h0600 g/cm2) detailed space-time pattern for unique EAS reconstruction • Select deep showers (large XMax, i.e. small XD0 or XDM) in order to • minimize the impact of shower development fluctuations A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  9. Event selection • Basic cuts: • Shower fully reconstructed (0<qzen<40°) through conical fit • Shower “detected size” (Nstrip) > 400 • Core reconstructed inside a fiducial area (64 x 64 m2) • + • more specific cuts, based on extension of the detected shower, • hit density near the reconstructed core and lateral profile, • in order to: • reduce the contamination of external core events • put a constraint on the maximum XDM value • Finally: • strip multiplicity (Nstrip) used to set primary energy intervals A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  10. Monte Carlo simulation • CORSIKA showers, by p and He primaries • Energy ranges: p (0.3-3000)TeV • He (1-3000)TeV • Zenith angle range: 0<q<45° • QGSJET interaction model • Use of information on the longitudinal shower profile (Xmax,…) • Full detector response simulation based on GEANT package • Proper choice of the sampling area including the detector • Same analysis chain as for real data A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  11. Cuts in-dependence on the zenith angle Energy XDM = XDet –XMax No significant zenith angle dependence below 30 degrees. A slight shift might be seen above 40 degrees. In this analysis we stop at 40 degrees A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  12. The energy scale Use of the strip multiplicity (Nstrip) for the estimation of shower size  up to 100 TeV primary energy > For DNstrip fold the MC energy distribution with parametrized sp-air distribution of lint. > Get the energy corresponding to <lint>(ELog). Log(E/TeV) lint (g/cm2) l(MC)int Average lint also used to evaluate k factor: k = L(MC)obs/l(MC)int A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  13. Analysis of MC data: secq distributions (L(MC)obs=h0/|Slope|) and k factors k = L(MC)obs/l(MC)int A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  14. Analysis of real data: secq distributions from MC sCR-air (mb) = 2.41·104/l(exp)int (g/cm2) A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  15. proton Heavy primaries contribution Hoerandel AP 19 (2003) 193 taken as reference. JACEE and RUNJOB for the evaluation of systematic error helium A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  16. Heavy primaries contribution Correction on reconstructed s at 80 TeV Above 1 TeV: primary Helium fraction ≈ 40% After analysis cuts: ≈ 15-20% Heavier primaries can be neglected A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  17. Inelastic p-air cross section (statistical errors only in the plot) A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  18. From p-air to p-p cross section Several available models to obtain stotp-p from sinelp-air: • Glauber – Matthiae theory • Durand – Pi • Wibig – Sobczynska • …. Models agree within few % in our energy range systematic error: 5% A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  19. Systematic uncertainties • Variations of the atmospheric depth (pressure) • h0MC = 606.7 g/cm2 (4300m a.s.l. standard atm.), • h0MC / <h0> = 0.988 ± 0.007 impact on cross section analysis: 1% • Uncertainty on l(MC)int: RMS of MC distribution 2÷3 % • Uncertainty on the contribution of heavy neclei: comparing slopes from different (p+He) fluxes (Hoerandel, Jacee, RunJob)  1÷4 % • Uncertainty on “sp-air to sp-p”: comparing different models  5 % Statistical and systematic errors independently propagated A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  20. Total p-p cross section A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  21. Total p-pbar cross section A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

  22. Summary and outlook • The flux attenuation technique has been successfully used in ARGO-YBJ experiment, by exploiting the detector features and location. • The inelastic proton-air (and the total p-p) cross section has been measured in a scarcely explored energy region and results are in agreement with previous ARGO results. • More checks on systematics are in progress (shower fluctuations, interaction models, heavy primaries contribution, …). • Shower age and energy determinations will be improved by the use of timing (rise time, front curvature,..) and topological information • In the future, the analysis will be extended to higher energies (up to 1PeV), thus covering a region with few experimental data, by exploiting the analog RPC readout. A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ

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