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Limites supérieures au flux de photons UHE avec lobservatoire Pierre Auger Cécile Roucelle Pour la collaboration Auger LPNHE-Paris.

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Présentation au sujet: "Limites supérieures au flux de photons UHE avec lobservatoire Pierre Auger Cécile Roucelle Pour la collaboration Auger LPNHE-Paris."— Transcription de la présentation:

1 Limites supérieures au flux de photons UHE avec lobservatoire Pierre Auger Cécile Roucelle Pour la collaboration Auger LPNHE-Paris

2 Bottom up Top down Bottom up Top down Baryons (3/10%) Large fraction de γ attendue

3 Prédictions et limites actuelles pour les fractions de photons HP: Ave et al. (2000, 2002) A1: Shinozaki et al. (2002) A2: Risse et al. (2005) SHDM: Aloisio et al. (2004) ZB, TD: Sigl (2001)

4 Possible développement dune pré-gerbe avant lentrée dans latmosphère par interaction avec le champ magnétique terrestre. Signatures de photons UHE Baisse de la section efficace γ/air Effet LPM pour les γ E > γ Conversion de γ Modulation de leffet LPM Signature sur la direction darrivée (coord locales) Gerbes peu développées Billoir et al. ICRC 2001 Asymétrie NS pour E> Max de dvlp de la gerbe=

5 Observation devenements hybrides Xmax

6 Sélection des événements Restriction (temporaire) aux zones ou lefficacité du détecteur est totale Restriction (temporaire) aux zones ou lefficacité du détecteur est totale Angle azimuthal > 35° Angle azimuthal > 35° Gerbes de très haute énergie (> 10 EeV) Gerbes de très haute énergie (> 10 EeV) Critères de qualité de reconstruction FD Critères de qualité de reconstruction FD Conséquence: Statistique relativement faible pour cette première analyse basée sur 17 événements Conséquence: Statistique relativement faible pour cette première analyse basée sur 17 événements Choix très conservateur !

7 Un exemple de traitement: evt # Simulations de photons: = 1020 g cm -2, rms = 80 g cm -2 Simulations de photons: = 1020 g cm -2, rms = 80 g cm -2 Le Xmax observe est bien en deça des valeurs attendues pour Le Xmax observe est bien en deça des valeurs attendues pour des photons Pour cet evenement Xmax = 744 ± 40 g cm -2 Pour cet evenement Xmax = 744 ± 40 g cm -2 θ=49°,1.1*10 19 eV Combinaison des probabilités Pour les 17 evts

8 Limite supérieure sur la fraction de γ UHE Limite supérieure de 23% a 95% CL pour E eV Limite supérieure de 23% a 95% CL pour E eV Confirme et même améliore les estimations précédentes de limites supérieures a eV Confirme et même améliore les estimations précédentes de limites supérieures a eV Markus Risse

9 Utilisation du détecteur de surface Une analyse sur une statistique beaucoup plus large Une analyse sur une statistique beaucoup plus large Possibilité dune limite supérieure sur le flux de γ très contraignante et à plus hautes énergies Possibilité dune limite supérieure sur le flux de γ très contraignante et à plus hautes énergies ? Analyse très puissante mais plus complexe Janvier Juin 2005 Limite sur la fraction α 1/N

10 Variables SD pour la recherche de photons Courbure du front de gerbe Temps de montée du signal Proton Photon Développement tardif Composition en muons signal temps μ

11 Premières observations SD Même méthode danalyse que pour les événements hybrides Même méthode danalyse que pour les événements hybrides Possibilité de traitement evt par evt soutenant qualitativement lanalyse précédente pour 7 des événements hybrides selectionnés Possibilité de traitement evt par evt soutenant qualitativement lanalyse précédente pour 7 des événements hybrides selectionnés

12 Reconstruction de lenergie dun photon par le detecteur de surface Sous-estimation systématique et fluctuations importantes de lenergie des photons par des reconstructions « classiques » Rappel : une gerbe de photons est plus compacte au sol du fait de son développement tardif Rappel : une gerbe de photons est plus compacte au sol du fait de son développement tardif La distribution latérale de la densité de particules est différente pour une gerbe de photon et varie plus de gerbe à gerbe La distribution latérale de la densité de particules est différente pour une gerbe de photon et varie plus de gerbe à gerbe

13 Distortion de lénergie des γ avec SD

14 Des solutions à létude: Corriger... Déconvolution SVD Résultat MC Appui sur un spectre supposé Sen passer...

15 Conclusions : L observatoire Pierre Auger semblerait défavoriser la présence de γ UHE au vu dune analyse préliminaire L observatoire Pierre Auger semblerait défavoriser la présence de γ UHE au vu dune analyse préliminaire Une analyse mettant en jeu le détecteur de surface uniquement est en cours qui permettra dutiliser une plus large statistique conduisant à un résultat plus ferme et à plus hautes énergies... Une analyse mettant en jeu le détecteur de surface uniquement est en cours qui permettra dutiliser une plus large statistique conduisant à un résultat plus ferme et à plus hautes énergies......Mais soyons prudents :...Mais soyons prudents : Etude approfondie de la réponse du détecteur a de telles gerbes Etude approfondie de la réponse du détecteur a de telles gerbes Extrapolations des sections efficaces γ/air à eV hasardeuses ? Extrapolations des sections efficaces γ/air à eV hasardeuses ?

16 En plus...

17 2-Ne pas reposer sur la mesure de E ! En ont des temps de montée > 200ns P.Billoir Même coupure appliquée aux photons simulés en supposant des spectres en 1/E a (a = 1.7 à 3 par pas de 0.1) On teste une forme de spectre donnée

18 Extraction de la limite supérieure sur la fraction de photons Traitement statistique developpé dans Traitement statistique developpé dans astro-ph/ (Risse et al.) probabilité que les événements considérés soient des γ. (PDF de χ 2 utilisant des distributions de photons simulées pour les caractéristiques de chaque événement) probabilité que les événements considérés soient des γ. (PDF de χ 2 utilisant des distributions de photons simulées pour les caractéristiques de chaque événement) = 0

19 Utilisation du détecteur Auger pour lidentification de photons Observation directe du maximum de développement de gerbe (Xmax) Observation directe du maximum de développement de gerbe (Xmax) Détection dévénements FD ou hybrides Détection dévénements FD ou hybrides Observation indirecte en étudiant des variables qui lui sont corrélées Observation indirecte en étudiant des variables qui lui sont corrélées Détection de surface Détection de surface

20 Impact théorique dune faible fraction de photons : Défavoriserait certains modèles TD restant en lice, SHDM notamment, constituant un indice fort. Défavoriserait certains modèles TD restant en lice, SHDM notamment, constituant un indice fort. Reste lincertitude sur le comportement de ces UHECR au travers de leur section efficace Reste lincertitude sur le comportement de ces UHECR au travers de leur section efficace La non observation dans les années à venir dun excès dUHECR en provenance du centre galactique sy ajoutant pourrait conduire a la mort de ces modèles. La non observation dans les années à venir dun excès dUHECR en provenance du centre galactique sy ajoutant pourrait conduire a la mort de ces modèles.

21 Autre ecueil : lacceptance du détecteur Lacceptance nest pas saturée en deçà de eV Lacceptance nest pas saturée en deçà de eV Lutilisation dune très large statistique à «basse» énergie sera encore plus complexe... Lutilisation dune très large statistique à «basse» énergie sera encore plus complexe...

22 Statistiques pour la recherche dévénements rares Toy MC

23 Matrice donnant la distortion Pour les énergies reconstruites Matrice inversée SINGULIERE !!! utilisation SVD Déconvolution des énergies

24 Angle de vue initial initial 15°, i.e. Contribution Cerenkov directe importante Reconstruit pas une procedure iterative convergeante en 4 etapes. Energie estimee: 2 EeV raw directe diffusee Gaisser-Hillas form Hans Bluemer Reconstruction des profils longitudinaux avec FD

25 Markus ICRC

26 Discrimination power of SD observables in some events, standard SD reconstruction possible; e.g.: in some events, standard SD reconstruction possible; e.g.: rise time of detector signal at 1000 m core distance rise time of detector signal at 1000 m core distance curvature of shower front curvature of shower front observed values below photon prediction observed values below photon prediction independent confirmation: photon primary unlikely independent confirmation: photon primary unlikely 10

27 Upper limit on the primary photon fraction from the Pierre Auger Observatory introduction, some details, to do (10-15 min) introduction, some details, to do (10-15 min) ICRC talk (10 min ?!) ICRC talk (10 min ?!) comments... comments... (if time: beyond the ICRC (5 min) ) (if time: beyond the ICRC (5 min) )

28 Towards Auger photon fraction November 2004: prelim. studies November 2004: prelim. studies end of March 2005: go for it! end of March 2005: go for it! April 19-22: Leeds photon meeting April 19-22: Leeds photon meeting May : draft manuscript May : draft manuscript June 30: ICRC paper deadline June 30: ICRC paper deadline until June 30: finalizing; num. value might change until June 30: finalizing; num. value might change collaborative & hybrid effort! collaborative & hybrid effort! mailing list mailing list talks, papers... at: -> photon group talks, papers... at: -> photon group Cecile, Dave, Bruce, Michael, Analisa, Jean-Christophe, Chris, Katsushi, Pierre, Jose, Ralph, Henryk, Alan, Miguel, Gilles, Serguei, Dmitri, Paul, Markus, Piotrek, Arun, Sylvie, Ralf, Min, Dave, Johannes, Fabian, Paul...

29 SD & primary photons (Leeds workshop) SD-only upper limit? Beyond ICRC / towards paper SD-only upper limit? Beyond ICRC / towards paper differences between (detector, shower) simulations differences between (detector, shower) simulations photon acceptance; S(1000) -> energy mismatch photon acceptance; S(1000) -> energy mismatch ICRC: ICRC: discrimination power of SD observables discrimination power of SD observables support for hybrid-X max limit support for hybrid-X max limit Sub-tasks: Sub-tasks: SD data (A. Mariazzi, P. Billoir) SD data (A. Mariazzi, P. Billoir) SD simulation (D. Barnhill) SD simulation (D. Barnhill) Energy mismatch, statistical method (C. Roucelle, J.-C. Hamilton) Energy mismatch, statistical method (C. Roucelle, J.-C. Hamilton)

30 Energy mismatch and derivation of limit re-binning of photons vs hadrons required to avoid underestimation of photon fraction ?! re-binning of photons vs hadrons required to avoid underestimation of photon fraction ?! mismatch factor depends on energy, zenith, (preshower: direction) mismatch factor depends on energy, zenith, (preshower: direction) assume: fraction=50%=const; spectrum index -3; bins of lgE=0.3: true: factor p 32 8 p 8 2 p 2 dN/dlgE lgE lgErec dN/dlgEr reconstructed : now reconstruct photon energy factor 2 smaller than proton energy 2 32 p 8 2p2p 8 p => fraction=20% ?!

31 Photon limit with hybrid X max Offline v1r2 list (Bruce & Jose) of reconstructed hybrid events: -> geometry (better with hybrid), energy, X max, X max Offline v1r2 list (Bruce & Jose) of reconstructed hybrid events: -> geometry (better with hybrid), energy, X max, X max for each event: simulated X max distribution for photons for each event: simulated X max distribution for photons statistical treatment => limit on primary fraction statistical treatment => limit on primary fraction caveat: selection bias (e.g. near-vertical photons, X max below ground) : -> restrict to phase space (E, geometry) with photon eff. ~1 caveat: selection bias (e.g. near-vertical photons, X max below ground) : -> restrict to phase space (E, geometry) with photon eff. ~1 problem: limited event statistics -> compromise: statistics phase space with eff. efficiency correction to be applied -> to do: re-check compromise & apply correction; include new data problem: limited event statistics -> compromise: statistics phase space with eff. efficiency correction to be applied -> to do: re-check compromise & apply correction; include new data simulation uncertainty: extrapolation of photonucl. cross- section simulation uncertainty: extrapolation of photonucl. cross- section statistical method given in astro-ph/ statistical method given in astro-ph/

32 Acceptance of photon to nuclear primaries small statistics => phase space with smaller photon efficiency included small statistics => phase space with smaller photon efficiency included ~10% efficiency correction would bring upper limit from 23% to 25% ~10% efficiency correction would bring upper limit from 23% to 25% (Michael Unger) simulation study in progress !

33 Uncertainty from hadronic interactions this uncertainty exists also for previous upper limits this uncertainty exists also for previous upper limits now (ICRC) OK: compare to existing limits now (ICRC) OK: compare to existing limits later (if very small limits / ruling-out of models attempted later (if very small limits / ruling-out of models attempted detailed study required; quantify systematics detailed study required; quantify systematics (i.e. photonuclear cross-section (we use PDG); hadronic models) this affects X max and muons! QGSJET01 seems conservative choice note: predictions will slightly change -> update by Dmitri Semikoz

34 Small statistics -> minimum value for limit Account for limited statistics when ``picking´´ events from primary flux: Account for limited statistics when ``picking´´ events from primary flux: For hypothetical photon fraction F g, a data set of n m events contains n g photons with probability For hypothetical photon fraction F g, a data set of n m events contains n g photons with probability Example : n m = 17, F g = 17% => q(n g =0) ~ 5% Example : n m = 17, F g = 17% => q(n g =0) ~ 5% 5% probability, that set of 17 events contains no photon at all for F g =17% 5% probability, that set of 17 events contains no photon at all for F g =17% minimum possible value for photon upper limit at 95% CL: 17% minimum possible value for photon upper limit at 95% CL: 17% In general, we have to sum over all possibilities of having n g = 0...n m photons in the data set In general, we have to sum over all possibilities of having n g = 0...n m photons in the data set

35 17 profiles from hybrid reconstruction (Bruce, Jose) 17 profiles from hybrid reconstruction (Bruce, Jose)

36 ICRC talk: already now: compete well with (improve) existing limits already now: compete well with (improve) existing limits demonstrate discrimination power of SD observables demonstrate discrimination power of SD observables this is only the very beginning! this is only the very beginning! title motivation Xmax as observable data selection Xmax uncertainty simulation Xmax: individual event Xmax: data sample upper limit discrim. power SD summary & outlook

37 Upper limit on the primary photon fraction from the Pierre Auger Observatory The Pierre Auger Collaboration presented by Markus Risse Forschungszentrum Karlsruhe, Germany Institute of Nuclear Physics PAN, Kraków, Poland Data & simulation Data & simulation Upper limit from X max in hybrid events Upper limit from X max in hybrid events Discrimination power of surface detector observables Discrimination power of surface detector observables 1

38 Motivation cosmic-ray photon fraction: check non-acceleration models cosmic-ray photon fraction: check non-acceleration models current upper limits: surface detector experiments current upper limits: surface detector experiments this work: X max (fluorescence) in hybrid events this work: X max (fluorescence) in hybrid events HP: Ave et al. (2000, 2002) A1: Shinozaki et al. (2002) A2: Risse et al. (2005) SHDM: Aloisio et al. (2004) ZB, TD: Sigl (2001) 2

39 Photon discrimination with X max at eV: D (photon, hadron) > 200 g cm -2 at eV: D (photon, hadron) > 200 g cm -2 primary energy 3

40 Data selection & reconstruction January April 2005 January April 2005 hybrid events (=> improved geometry fit) hybrid events (=> improved geometry fit) Selection criteria: Selection criteria: E g >10 19 eV, q >35° E g >10 19 eV, q >35° X max observed, track length >400 g cm -2 X max observed, track length >400 g cm -2 distance < 30 km+f(E), f(E)=10km*(lgE/eV-19.0) distance < 30 km+f(E), f(E)=10km*(lgE/eV-19.0) minimum viewing angle >18° minimum viewing angle >18° high quality high quality comparable efficiencies for photon and nuclear primaries comparable efficiencies for photon and nuclear primaries large zenith angles due to deep X max of photon primaries large zenith angles due to deep X max of photon primaries 17 events after cuts 17 events after cuts reconstruction based on end-to-end telescope calibration and monitoring of local atmosphere (!here efficiency corr. would be stated!) 4

41 X max uncertainty main contributions (vary from event to event): main contributions (vary from event to event): profile fit profile fit atmospheric conditions atmospheric conditions Cherenkov subtraction Cherenkov subtraction uncertainty in reconstructed geometry and energy uncertainty in reconstructed geometry and energy each in general <15 g cm -2 each in general <15 g cm -2 total X max uncertainty ~40 g cm -2 (conservative) total X max uncertainty ~40 g cm -2 (conservative) well below typical photon shower fluctuations well below typical photon shower fluctuations analysis not limited by measurement uncertainty analysis not limited by measurement uncertainty 5

42 Primary photon simulation CORSIKA PRESHOWER CORSIKA PRESHOWER photonuclear cross-section: Part. Data Group extrapolation photonuclear cross-section: Part. Data Group extrapolation QGSJET 01 QGSJET 01 for each measured event, 100 primary photon simulations for each measured event, 100 primary photon simulations X max distribution expected for photons vs observed X max X max distribution expected for photons vs observed X max 6

43 Example event: X max = 744 ± 40 g cm -2 event: X max = 744 ± 40 g cm -2 photons: = 1020 g cm -2, rms = 80 g cm -2 photons: = 1020 g cm -2, rms = 80 g cm -2 observed X max well below photon expectation observed X max well below photon expectation Event: 49°, 1.1*10 19 eV 7

44 Data sample: Expected vs observed X max if (part of) events were photons, they should fluctuate around the plotted line if (part of) events were photons, they should fluctuate around the plotted line photon X max values 2-3 stand. dev. larger than observed photon X max values 2-3 stand. dev. larger than observed derivation of upper limit on photon fraction derivation of upper limit on photon fraction stat. method: Risse et al., astro-ph/ ; also poster ICRC-xxx stat. method: Risse et al., astro-ph/ ; also poster ICRC-xxx 8

45 Upper limit 23% upper limit (95% CL) on cosmic-ray photon fraction 23% upper limit (95% CL) on cosmic-ray photon fraction confirms and improves previous limits above eV confirms and improves previous limits above eV 9

46 Discrimination power of SD observables in some events, standard SD reconstruction possible; e.g.: in some events, standard SD reconstruction possible; e.g.: rise time of detector signal at 1000 m core distance rise time of detector signal at 1000 m core distance curvature of shower front curvature of shower front observed values below photon prediction observed values below photon prediction independent confirmation: photon primary unlikely independent confirmation: photon primary unlikely 10

47 Summary & Outlook 23% upper limit (95% CL) on photon fraction >10 19 eV 23% upper limit (95% CL) on photon fraction >10 19 eV based on X max in hybrid events based on X max in hybrid events improving previous upper limits improving previous upper limits future: hybrid statistics factor ~10 larger within ~2 years future: hybrid statistics factor ~10 larger within ~2 years discrimination power from SD observables discrimination power from SD observables independent check on photon primaries independent check on photon primaries SD-only upper limit: SD-only upper limit: factor ~10 more events than hybrid factor ~10 more events than hybrid caveat: photon acceptance caveat: photon acceptance Photonuclear cross-section extrapolation: Photonuclear cross-section extrapolation: systematic uncertainty to all existing photon limits systematic uncertainty to all existing photon limits 1

48 Beyond the ICRC in September: groups provide written summary of their analysis status in September: groups provide written summary of their analysis status sections for lengthy GAP note sections for lengthy GAP note basis for journal publication basis for journal publication last Tuesday: photon analysis update (C. Roucelle, P.Billoir, D. Barnhill, S. Dagoret-Campange, V. de Souza, D. Badagnani, D. Semikoz) last Tuesday: photon analysis update (C. Roucelle, P.Billoir, D. Barnhill, S. Dagoret-Campange, V. de Souza, D. Badagnani, D. Semikoz) refinement of statist. tools, exploit further SD obs., simulation comparisons: differences vanish / start being understood; GZK photons refinement of statist. tools, exploit further SD obs., simulation comparisons: differences vanish / start being understood; GZK photons energy mismatch photon/hadron: analyses that... energy mismatch photon/hadron: analyses that... (i) need correction (ii) avoid problem (iii) make use of it (i) need correction (ii) avoid problem (iii) make use of it statistical tools for large event statistics statistical tools for large event statistics studies on photonuclear cross-section studies on photonuclear cross-section toy analysis: simulated data sample with unkown photon fraction toy analysis: simulated data sample with unkown photon fraction

49 Statistical treatment Analysis of each individual event: Analysis of each individual event: Simulation of 100 photon showers for particular event geometry and energy (CORSIKA + PRESHOWER) => simulated X max distribution Simulation of 100 photon showers for particular event geometry and energy (CORSIKA + PRESHOWER) => simulated X max distribution Calculation of chi2 quantity for each event j: Calculation of chi2 quantity for each event j: : probability that photon-initiated showers yield chi2- values larger/equal to measured one : probability that photon-initiated showers yield chi2- values larger/equal to measured one Aim: derivation of limit on photon fraction by combining individual showers Aim: derivation of limit on photon fraction by combining individual showers

50 Statistical treatment (2) Account for limited statistics when ``picking´´ events from primary flux: Account for limited statistics when ``picking´´ events from primary flux: For hypothetical photon fraction F g, a data set of n m events contains n g photons with probability For hypothetical photon fraction F g, a data set of n m events contains n g photons with probability Example : n m = 30, F g = 10% => q(n g =0) ~ 5% Example : n m = 30, F g = 10% => q(n g =0) ~ 5% 5% probability, that set of 30 events contains no photon at all for F g =10% 5% probability, that set of 30 events contains no photon at all for F g =10% minimum possible value for photon upper limit at 95% CL: 10% minimum possible value for photon upper limit at 95% CL: 10% In general, we have to sum over all possibilities of having n g = 0...n m photons in the data set In general, we have to sum over all possibilities of having n g = 0...n m photons in the data set

51 Statistical treatment (3) chance probability for hypothetical F g to get c 2 values than found in data: chance probability for hypothetical F g to get c 2 values than found in data: probability that... with confidence 1- P(F g ), photon fractions F g can be rejected with confidence 1- P(F g ), photon fractions F g can be rejected... data set contains n g photons... n g ``photons´´ yield c 2 values than in data... n g -n m ``non- photons´´ yield c 2 values than in data : are set to unity (no test on ``non-photons´´) : take n g most photon-like looking events => is minimal; determine with MC technique (non-Gaussian fluct.!) astro-ph/


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