Depth of maximum of air-shower profiles at the Pierre Auger - - PowerPoint PPT Presentation

1

Depth of maximum of air-shower profiles at the Pierre Auger Observatory: Measurements above 10 17.2 eV and Composition Implications

1The University of Adelaide, School of Physical Sciences, South Australia, 5005, Australia 2Observatorio Pierre Auger, Av. San Martín Norte 304, 5613 Malargüe, Argentina

Email: auger_spokespersons@fnal.gov Full author list: http://www.auger.org/archive/authors_icrc_2017.html

Jose Bellido The University of Adelaide1 for the Pierre Auger Collaboration2

2

FD standard telescopes

(one of four FD buildings) Credit: Steven Saffi University of Adelaide

3

HEAT telescopes

(in upward mode)

4

FD-standard

(FOV 0º to 30º elevation)

HeCo (HEAT + Coihueco)

(FOV 0º to 60º elevation)

5

CO HEAT FD-standard HeCo (HEAT + Coihueco)

E = 1.07 x 1020 eV

E = 4.75 x 1017 eV

6

Event Selection Criteria

• exclude events during cloudy or aerosol rich nights.
• Xmax needs to be within expected field of view.
• exclude events with large χ2 in the profile fit.
• observed profile track length > 200 g/cm2 (applied only in FD-standard).
• (proton) trigger probability of SD station > 0.9
• difference of proton and Iron trigger probabilities < 0.05
• fluorescence detector FOV cuts

1.Good data taking periods 2.Quality selection: 3.Fiducial selection:

7

fluorescence detector FOV cuts Three types of event geometries (A, B and C) Detector location FoV limit

Observed Xmax distribution for each type of geometry Sum of the Xmax distributions

8

Resolution and Systematics in the Xmax measurements Resolution Systematic error

9

Xmax moments

10

Xmax moments

(combining HeCo and FD-standard)

11

Elongation rate

Preliminary

12

lnA moments

(estimated using Xmax moments, for the method see JCAP 1302 (026), 2013)

13

Xmax distributions (HeCo)

14

Xmax distributions (HeCo)

Interpreting Xmax distributions with EPOS-LHC

four components composition model

Proton, Helium, Nitrogen and Iron Sum of four components

15

Xmax distributions (HeCo)

Interpreting Xmax distributions with Sibyll2.3

four components composition model

Proton, Helium, Nitrogen and Iron Sum of four components

16

Xmax distributions (HeCo)

Interpreting Xmax distributions with QGSJETII-04

four components composition model

Proton, Helium, Nitrogen and Iron Sum of four components

17

Xmax distributions (FD)

17

18

Xmax distributions (FD)

18

four components composition model

Proton, Helium, Nitrogen and Iron Sum of four components Interpreting Xmax distributions with EPOS-LHC

19

Xmax distributions (FD)

19

four components composition model

Proton, Helium, Nitrogen and Iron Sum of four components Interpreting Xmax distributions with Sibyll2.3

20

Xmax distributions (FD)

20

four components composition model

Proton, Helium, Nitrogen and Iron Sum of four components Interpreting Xmax distributions with QGSJETII-04

21

Composition fractions

(obtained from fits to the Xmax distributions)

21

22

Summary

• Xmax moments (free of detector effects) 1017.2 eV - 1019.6 eV
• D10 = 79 ± 1 g/cm2 / decade , E < 1018.33± 0.02 eV
• D10 = 26 ± 2 g/cm2 / decade , E > 1018.33± 0.02 eV
• Confirmation (with more statistics) of narrowing of σ(Xmax), E > 1018.3 eV

Interpretation (model dependent)

• Moments of lnA: The absolute values depend on the model, but the trends with energy are consistent

among the three models. The lightest composition is observed at around 1018.3 eV.

• Fits to the Xmax distributions:
• The largest proton abundance is around 1018.3 eV. Above this energy EPOS-LHC and SIBYLL 2.3 suggest

an increasing presence of Nitrogen and QGSJETII04 suggests an increasing presence of Helium.

• Absence of Iron between 1018 and 1019.4 eV.
• Small p-values observed in several energy bins.

23

Backup

24

fluorescence detector FOV cuts Xlow Xup We select events with geometries such that: Xlow < Xlow-limit Xup > Xup-limit

Xlow-limit and Xup-limit are estimated using real data:

PHYSICAL REVIEW D 90, 122005 (2014)

Xlow Xlow Three types of event geometries (A, B and C) Detector location Xup Xlow

25

Xmax acceptance

• The acceptance is estimated for each energy bin using simulations.
• The FOV cuts guarantee a homogeneous acceptance between the Xlow-limit and the Xup-limit.
• Simulations estimate the acceptance in the outer regions of the tails of the Xmax distribution for more

precise Xmax moments.

17.5 < lgE eV < 17.6 19.0 < lgE eV < 19.1

26

Effects of the improvements in the VAOD calculation (with respect ICRC15)

27

ICRC15 - statistics ICRC17 - statistics

28

29