Alan Watson University of Leeds, UK a.a.watson@leeds.ac.uk - - PowerPoint PPT Presentation

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Alan Watson University of Leeds, UK a.a.watson@leeds.ac.uk - - PowerPoint PPT Presentation

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High Energy Physics Group: Imperial College 6 March 2019 Recent results on Astrophysics and Particle Physics from studies of cosmic rays with the Pierre Auger Observatory Alan Watson University of Leeds, UK a.a.watson@leeds.ac.uk Outline:

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Recent results on Astrophysics and Particle Physics from studies of cosmic rays with the Pierre Auger Observatory

Alan Watson University of Leeds, UK a.a.watson@leeds.ac.uk

High Energy Physics Group: Imperial College

6 March 2019

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Outline:

  • Goals of UHECR (> 1018 eV, or 1 EeV) research
  • Pierre Auger Observatory
  • Energy Spectrum
  • Arrival Directions – to show that we too get 5 σ results
  • Hadronic models needed to get Mass Composition – limitation
  • f conclusions so far

(no discussion of photon, neutrino or monopole searches: best limits available)

  • p-p cross-section up to 57 TeV centre-of-mass
  • Anomalies between muon data and predictions
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Astrophysical Questions at the highest energies

  • What are the sources?
  • How are the particles accelerated?
  • Does the energy spectrum terminate?

γ2.7 K + p à Δ+ à n + π+ or p + πo and γIR/2.7 K + A à (A – 1) + n Prediction of steepening (GZK effect) around 50 EeV

  • What is the mass of the particles?

Lack of knowledge of hadronic physics is main limitation here

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S Swordy (Univ. Chicago)

32 decades in intensity 11 Decades in Energy

1 particle m-2 s-1 ‘Knee’ 1 particle m-2 per year Ankle 1 particle km-2 per year

Flux of Cosmic Rays Air-showers

LHC AMS PAMELA (ISS-) CREAM Auger Telescope Array

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Shower initiated by proton in lead plates

  • f cloud chamber

1.3 cm Pb Fretter: Echo Lake, 1949 Detectors can find particle number and arrival times

10 GeV proton

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Engel et al. Ann Rev NPS 2011

Shower components as a function of distance and depth

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‘Fast timing’ gives the direction: This is crucial when trying to establish the origin of the particles which travel across magnetic fields

Accuracy of finding direction ~ 1° Water-Cherenkov detectors

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A tank was opened at the ‘end of project’ party on 31 July 1987. The water shown had been in the tank for 25 years but was quite drinkable!

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250 300 350 400 450 nm 5 W blue light bulb moving at speed of light ~ 15 km away at ~ 3 x 1018 eV Auroral Light

Visible

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A Fluorescence Detector of the Utah University Group

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x 1010

3 x 1020 eV (?)

ApJ 441 144 1995

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~1990: different techniques gave different results –

  • but agreed that rate is low:

~ 1 per km2 per century at 1020 eV (~ 10/min on earth’s atmosphere)

  • 1990: Need larger areas > 1000 km2
  • 1991: Started working with Jim Cronin (Chicago)

to form a collaboration to design and build such an instrument, and to raise the money

  • Our efforts helped create the Pierre Auger Observatory

~ 400 scientists from 17 countries

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Array of water- Cherenkov detectors → Fluorescence →

The Design of the Pierre Auger Observatory marries the two techniques the ‘HYBRID’ technique

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AND

Enrique Zas, Santiago de Compostela

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LH C LHC

The Pierre Auger Observatory: Malargüe, Argentina

  • 1600 water-Cherenkov

detectors: 10 m2 x 1.2 m

  • 3000 km2
  • Fluorescence detectors

at 4 locations

  • Two laser facilities for

monitoring atmosphere and checking reconstruction

  • Lidars at each FD site

CLF XLF .

. .

CLF XLF

..

.

Glasgow Edinburgh

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2004: Data taking started with about 200 water- Cherenkov detectors and two fluorescence telescopes - 13 years after first discussions Soon surpassed the exposure at Haverah Park accrued in 20 years – now over 67,000 km2 sr years

HP

After Michael Unger 2017

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The Auger Observatory Campus in Malargüe

The Office and Assembly Buildings in Malargüe

  • funded by the University of Chicago ($1M)
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GPS Receiver and radio transmission

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Fluorescence detector at Los Leones

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Fall-off of signal with distance

A large event: 7 x 1019 eV Signal at 1000 m from densest part of shower is chosen to define the ‘size’ of the shower

Footprint ~ 25 km2

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Energy from fluorescence measurements

Correction for invisible energy

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A Hybrid Event Energy Estimate

  • from area under

curve (2.1 ± 0.5) x 1019 eV must account for ‘invisible energy’

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Getting the Energy and Xmax

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839 events 7.1 x 1019 eV

Auger Energy Calibration S(1000)38 VEM

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67 000 km2 sr yr 290 000 events

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What might the steepening mean?

Rigidity-limited Photo-disintegration effects

p He N Fe

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Cosmic rays with energies above 8 EeV come from outside of our Galaxy: Science 22 September 2018

Significance ~ 5.2 sigma

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Auger/TA all sky survey at high energies

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photons protons Fe Data log (Energy) Xmax The variation of mass with energy Energy per nucleon is crucial Need to assume a model

< 0.5 % above 10 EeV dXmax/log E = elongation rate

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Given the necessity of using models, an important question is “Are the cosmic-ray models adopted sensible?” Here, the LHC results have proved an excellent test-bed

  • to evaluate three different models -All within Gribov’s

Reggeon Field Theory framework

  • EPOS: parton-based Gribov-Regge Theory
  • QGS: quark-gluon string model – multi-pomeron amplitudes

calculated to all orders

  • Sibyll: based on Dual-parton model – mini-jet model
  • Each model has a different but self-consistent assumptions to

describe hadronic interactions. This is ALL I really can tell you about the details of the models!

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More later

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Some Longitudinal Profiles measured with Auger

rms uncertainty in Xmax < 20 g cm-2 from stereo-measurements

1000 g cm-2 = 1 Atmosphere ~ 1000 mb

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Fraction of p, He, N and Fe as function of energy

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Many models have been devised to explain data Appealing ones have acceleration of ‘normal’ range of masses which are photo- disintegrated close to source. Neutrons escape and their decay gives protons around 1 EeV Unger et al. arXiv 1505.02153 Globus et al. arXiv 1505.01377

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Some success

  • and of some problems

Hadronic Interactions

Auger Design Study (1995): virtually no mention Rather, argued how well we would do without detailed knowledge of hadronic physics!

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Bristol: Conference on Very High Energy Interactions, January 1963

J G Wilson Trying to get information about particle interactions from studying Extensive Air Showers is like trying to get information about the workings

  • f the British Cabinet by reading the

Daily Mirror AGS 33 GeV CERN PS 28 GeV

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Distribution of Xmax for two energy ranges ICRC 2015

Λη , the attenuation length, is found from the 20% most penetrating events

1196/1809 1384/21270

Measure Λη

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Relationship between Λη and proton-air cross-section 25% Helium contamination: σ reduced by -17 and – 16 mb

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Proton-air cross-section as function of energy Impact of 25% He is included as systematic uncertainty (- 16 mb) Photons have been shown to be < 0.5% at energies of interest: contamination would raise σ by ~ 4.5 mb

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arXiv: 1902.09505

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For very forward particles all models need retuning though CR models slightly better arXiv:1902.09505

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β = 0.9 εc = energy at which pion interaction becomes less probable than decay (~10 GeV) Nμ increases with energy increases with A at given energy

‘The Muon Problem’

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37 stations 71° 3200 g cm-2 54 EeV Fit made to density distribution Energy measured with ~20 % accuracy

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Inclined showers are useful to test models – muons dominate

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Maps such as these are compared and fitted to the observations so that the number of muons, Nµ, can be obtained Average muon density profile

  • f simulated-proton of 1019eV
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Predicted muon numbers are under-estimated by 30 to 80% (20% systematic)

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ρ0 → π+ + π-

Thus there is a channel to enhance muon production Taking energy out of electromagnetic channel will raise depth of shower maximum - slightly lighter primaries

NA62/SHINE

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Was a similar muon problem seen with LEP detectors?

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CERN Courier December 2015 ALICE

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JCAP 01 032 2016

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Conclusion in ALICE paper makes assumption about mass composition, in contradiction with cosmic ray data

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Summary:

  • Energy spectrum shows two features:

Flattening at ~ 4 x 1018 eV Steepening at about 4 x 1019 eV

  • Mass is proton-dominated near 1018 eV and then gets heavier

as energy rises (details are model-dependent)

  • Arrival direction data show evidence of anisotropies
  • While cosmic-ray models fit some data reasonably well, there

are problems in fitting the muon features: too many muons?

  • p-p cross-section at 57 TeV
  • May be excess of production of ρ0 in p-C collisions
  • Need data on pion-A collisions and p-A collisions