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Title: Measurement of the cosmic-ray energy spectrum above 2.5 × 10 18     eV using the Pierre Auger Observatory

Journal Article · · Physical Review. D.
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We report a measurement of the energy spectrum of cosmic rays for energies above $$2.5 {\times} 10^{18}~$$eV based on 215,030 events recorded with zenith angles below $$60^\circ$$. A key feature of the work is that the estimates of the energies are independent of assumptions about the unknown hadronic physics or of the primary mass composition. The measurement is the most precise made hitherto with the accumulated exposure being so large that the measurements of the flux are dominated by systematic uncertainties except at energies above $$5 {\times} 10^{19}~$$eV. The principal conclusions are: (1) The flattening of the spectrum near $$5 {\times} 10^{18}~$$eV, the so-called "ankle", is confirmed. (2) The steepening of the spectrum at around $$5 {\times} 10^{19}~$$eV is confirmed. (3) A new feature has been identified in the spectrum: in the region above the ankle the spectral index $$\gamma$$ of the particle flux ($$\propto E^{-\gamma}$$) changes from $$2.51 \pm 0.03~{\rm (stat.)} \pm 0.05~{\rm (sys.)}$$ to $$3.05 \pm 0.05~{\rm (stat.)} \pm 0.10~{\rm (sys.)}$$ before changing sharply to $$5.1 \pm 0.3~{\rm (stat.)} \pm 0.1~{\rm (sys.)}$$ above $$5 {\times} 10^{19}~$$eV. (4) No evidence for any dependence of the spectrum on declination has been found other than a mild excess from the Southern Hemisphere that is consistent with the anisotropy observed above $$8 {\times} 10^{18}~$$eV.

Research Organization:
Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
Sponsoring Organization:
USDOE Office of Science (SC), High Energy Physics (HEP); São Paulo Research Foundation (FAPESP); Czech Republic; Institut Lagrange de Paris (ILP); Consejo Nacional de Ciencia y Tecnología (CONACYT); Ministry of Science and Higher Education; National Science Centre; Romanian Ministry of Education and Research; Slovenian Research Agency; Ministerio de Economía, Industria y Competitividad; Xunta de Galicia; Junta de Andalucía; RENATA Red Nacional Temática de Astropartículas; María de Maeztu Unit of Excellence
Contributing Organization:
Pierre Auger Collaboration
Grant/Contract Number:
AC02-07CH11359; FR02-04ER41300; FG02-99ER41107; SC0011689; 0450696; 2019/10151-2; 2010/07359-6; 1999/05404-3; MSMT CR LTT18004; LM2015038; LM2018102; CZ.02.1.01/0.0/0.0/16_013/0001402; CZ.02.1.01/0.0/0.0/18_046/0016010; CZ.02.1.01/0.0/0.0/17_049/0008422; LABEX ANR-10-LABX-63; ANR-11-IDEX-0004-02; 167733; DIR/WK/2018/11; 2013/08/M/ST9/00322; 2016/23/B/ST9/01635; HARMONIA 5–2013/10/M/ST9/00062; UMO-2016/22/M/ST9/00198; PN19150201/16N/2019; PN19060102; PN-III-P1-1.2-PCCDI-2017-0839/19PCCDI/2018; P1-0031; P1-0385; I0-0033; N1-0111; FPA2017-85114-P; FPA2017-85197-P; ED431C 2017/07; SOMM17/6104/UGR; FPA2015-68783-REDT; MDM-2016-0692
OSTI ID:
1661742
Alternate ID(s):
OSTI ID: 1668400
Report Number(s):
arXiv:2008.06486; FERMILAB-PUB-20-432-E-TD; PRVDAQ; 062005
Journal Information:
Physical Review. D., Journal Name: Physical Review. D. Vol. 102 Journal Issue: 6; ISSN 2470-0010
Publisher:
American Physical Society (APS)Copyright Statement
Country of Publication:
United States
Language:
English

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Figures / Tables (22)

FIG. 1(p. 7)figure FIG. 1
FIG. 2(p. 7)figure FIG. 2
FIG. 3(p. 8)figure FIG. 3
TABLE I(p. 8)table TABLE I
TABLE II(p. 9)table TABLE II
FIG. 4(p. 10)figure FIG. 4
FIG. 5(p. 10)figure FIG. 5
FIG. 6(p. 11)figure FIG. 6
FIG. 7(p. 12)figure FIG. 7
FIG. 8(p. 14)figure FIG. 8
FIG. 9(p. 14)figure FIG. 9
TABLE III(p. 14)table TABLE III
FIG. 10(p. 15)figure FIG. 10
FIG. 11(p. 16)figure FIG. 11
FIG. 12(p. 16)figure FIG. 12
FIG. 13(p. 17)figure FIG. 13
TABLE IV(p. 17)table TABLE IV
FIG. 14(p. 18)figure FIG. 14
FIG. 15(p. 21)figure FIG. 15
TABLE V(p. 23)table TABLE V
FIG. 16(p. 24)figure FIG. 16
TABLE VI(p. 24)table TABLE VI

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