Transcript Slide 1
The importance of knowing the primary mass – and how little we really know
Alan Watson University of Leeds [email protected]
Pylos: 7 September 2004
Key Questions about UHECR
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Energy Spectrum above 10 19 eV?
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Arrival Direction distribution?
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Mass Composition?
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Aim of talk is to show where I think that we have got to in trying to answer the fundamental question of what is the mass at the highest energies.
Life may be less simple than some theorists seem to think!
Question of Mass Composition
“We remain with the dilemma: protons versus heavy
nuclei. A clear cut decision cannot be reached yet. I believe that up to the highest energies the protons are the most abundant in the primary cosmic rays. However, I must confess that a leak proof test of the problem. Experimentally it is quite a difficult
problem.” G Cocconi: Fifth International Cosmic Ray Conference, Guanajuato, Mexico, 1955
Corrections necessary to determine energy from fluorescence ~ 5% The energy estimates are
HIGHER
assumed if Fe is Song et al Astroparticle Physics 2000
For S(600), the energy estimates are
LOWER
if iron is assumed S 0 = 50 vem
1.04
1.13
1.09
1.13
From Takeda et al Astroparticle Physics 2003
Mass Composition (i): X max with energy Elongation Rate (Linsley 1977, Linsley and Watson 1981) dX max / dlog E < 2.3X
0 g cm -2 /decade from Heitler model X max =
ln (E o /
c )/ ln 2 extended to baryonic primaries: dX max / dlog E = 2.3X
0 (1 - B n - B
) where B n = d ln(n)/ d ln E and B
= (-
N /X 0 )(d ln
N /d ln E)
Composition from depth of maximum (i)
Model dependent AND < 10 19.25
eV Abbasi et al: astro-ph/0407622
Some personal comments on the recent HiRes Composition Paper Abbasi et al (astro-ph/0407622)
Selection of events: χ 2 per dof < 20 2 measures of X max within 500 g cm -2 Measurements within 400 g cm -2 for global fit to 2 eyes But resolution of X max claimed as 30 g cm -2 from Monte Carlo
-
BUT surely the resolution will depend on the distance from the Eyes (apparently not considered) Periods of calibrated and uncalibrated atmosphere (419 and 134 events) put together
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would have been interesting to have seen these groups apart
HiRes Composition from X max fluctuations (ii) p
BUT diurnal and seasonal atmospheric changes
Solid lines: data
likely to be very important
Fe Models are Sibyll and QGSjet
Astroparticle Physics in press; also data shown at ICRC2003
“Standard” Atmospheres can bias composition inferences
M. Risse et al ICRC03
From L Perrone (Auger group): Catania CRIS meeting
Mass Composition (iii): muons
Muon Content of Showers: N
(>1 GeV) = AB(E/A
) p ( depends on mass/nucleon ) N
(>1 GeV) = 2.8A(E/A
) 0.86 ~ A 0.14
So, more muons in Fe showers Muons are about 10% of total number of particles Used successfully at lower energies (KASCADE) VERY expensive - especially at high energies - conclusions derived are rather model dependent
Results from the AGASA array Claim: Consistent with proton dominant component
Kenji Shinosaki: 129 events > 10 19 eV 1 0 − 1 − 2 19 19.5
20 Log(Energy [eV]) 20.5
Model dependence of muon signals Sibyll 1.7: Sibyll 2.1: QGSjet98 1: 1.17:1:45 Important to recall that we do not know the correct model to use.
LHC CMS energy corresponds to ~ 10 17 eV
From Ralph Engel’s presentation in Leeds, July 2004
(i) QGSjet (ii) AGASA data: a second look (ii) (i) Plots by Maria Marchesini
Mass Composition (iv): Using the lateral distribution
(r)~ r –(
+ r/4000)
circa 1978: Feynman Scaling Primary Uranium?!
Sample LDF compared with new model: QGSjet’98
Distribution of lateral distribution
Haverah Park data: Ave et al. 2003
T h
Estimate of Mass Composition
QGSjet models (’98, dotted line and ’01, solid line).
First 3 points: trigger bias
Lateral distribution data from Volcano Ranch interpreted by Dova et al (2004) Astropart Phys (in press)
Comparisons from Dova et al (2004) Astropart Phys
Are results consistent between different methods applied by same experimental group? An extreme situation HiRes/MIA data: Abu-Zayyad et al: PRL 84 4276 2000
Ideas to explain the Enigma
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Decay of super heavy relics from early Universe (or top down mechanisms) Wimpzillas/Cryptons/Vortons
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New properties of old particles?
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Breakdown of Lorentz Invariance?
or is it ‘simple’?
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Are the UHE cosmic rays iron nuclei?
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Are magnetic field strengths really well known?
Potential of the Auger Observatory
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Directions
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Energy
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Mass
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photons
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neutrinos
protons or iron?
K-H Kampert’s talk
HARDER:
will use X max , LDF, FADC traces, Radius of curvature…
Mass information from study of Inclined Showers
M. Ave: 80°, proton at 10 19 eV Details in Ave, Vazquez and Zas, Astroparticle Physics
Ave et al. PRL 85 2244 2000
Haverah Park: Photon limit at 10 19 eV < 40% (@95% CL) AGASA: muon poor events Gamma-ray fraction upper limits (@90%CL) 34% (>10 19 eV)
( g /p<0.45)
56% (>10 19.5
eV
) ( g /p<1.27) 60 ° < θ < 80° Ave, Hinton, Vazquez, aaw, and Zas PRL 85 244 2000
An Elegant Mass Determination Method
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Zatsepin Effect
Zatsepin 1951 Zatsepin and Gerasimova 1960 Solar Magnetic Field Important Medina Tanco and Watson (1998) “..events from this very beautiful idea are too infrequent to be of use in any real experiment…”
Typical scale is ~ 1000 km
Conclusions
Beware
: the experimentalists are still some way from AGREED statements about the mass composition above 10 17 eV - after one studies the differences between different experiments - and even
the different conclusions
from within the same experiment.
From Auger,
we will get neutrino and photon limits (signals?) more readily than baryonic masses - but we have many tools in our armoury and should succeed in getting the latter, when we fully understand the showers and our hybrid detector. (
Recall: ground breaking was only 5 years ago)
.
Personal view
: assume 100% protons above 10 19 eV at your own risk!