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Groping for the (Cosmic Ray) Knee
Frank Jones, Robert Streitmatter and Demos Kazanas
Physics at the End of the Galactic Cosmic Ray SpectrumAspen, April 25 – May 1, 2005
If Simon Swordy didn’t
exist we would have to invent him.
Two Component CR Spectrum
Log E (eV)
10 11 12 13 14 15 16 17 18 19 20 21
Flu
x X
E2.
7
-1
0
1
2nd Tooth Fairy
1st Tooth Fairy
<ln(A)>
Energy (GeV)
104 105 106 107 108
<ln
(A)>
0
1
2
3
4
CASA - BLANCA
JACEE
Baloon Data
RUNJOB
JACEE2
SPASE
KASCADE e*
KASCADE hadron
KASCADE nn
HiRes
HEGRA crt
HEGRA airobic
Havera Park
Fly's Eye
DICE
Chacaltaya
CASA - MIA
BLANCA
KASCADE max
<ln(A)>
Energy (GeV)
104 105 106 107 108
<ln
(A)>
0
1
2
3
4
CASA - BLANCAFly's EyeDICEBLANCAKASCADE max
One Knee Scenario:
There is another proton component that would
explain the drop in <lnA> just below the knee.
Energy (GeV)
102 103 104 105 106 107 108
Flu
x X
E2.
5 (
m2
s sr
/Gev
1.5 )
-1
102
103
104
105
HePother
Ptotal
All Particle
Fe
CNONe-S
PSN
<ln(A)>
Energy (GeV)
104 105 106 107 108
<ln
(A)>
0
1
2
3
4
Theory: Toy ModelCASA - BLANCAFly's EyeDICEKASCADE maxKASCADE max
•Vernov, Zatsepin, Khristiansen, and Chudakov, Report to the All Union Conference on Cosmic Rays, Tbilisi, 1956
•Kulikov and Khristiansen, JETP 35, 635, 1958
Why was the knee discovered? – New Physics?
The Idea!
•A new production channel opens up in the particle collision cross section.
•Some products are “invisible” resulting in “lost” energy.
•Produces apparent steepening of the cosmic-ray spectrum.
•We follow the approach of Kazanas and Nicolaidas
Toy Model
To obtain the bend in the observed spectrum it turns out that we require:
Toy Model: Spectrum at Knee
Energy (GeV)
105 106 107 108
Dif
fere
nti
al F
lux
X E
2.8
(Arb
itra
ry U
nit
s)
10
100
<ln(A)>
Energy (GeV)
104 105 106 107 108
<ln
(A)>
0
1
2
3
4
To make the mass appear to become heavier we need to make the hadronic cross sections increase at the same energy that the new channel opens up.
Typically, the mass of a primary particle is determined by the depth in the atmosphere of the shower maximum.
What could make the mass look heavier?
Toy Model: Shower Maximum
• In an air shower that involves the new process there are two effects that can raise the position of the shower maximum.– If the cross section increases for energies > Ec
then each leg of the cascade in this energy region will be shorter.
– If the multiplicity increases there is an additional raising of the maximum because the energy is diluted quicker.
<ln(A)>
Energy (GeV)
104 105 106 107 108
<ln
(A)>
0
1
2
3
4
Shower ElongationToy Model
log(Energy) (eV)10 11 12 13 14 15 16 17 18 19 20
Xm
ax (
g/cm
2 )
200
400
600
800
1000
Shower ElongationToy Model
log(Energy) (eV)10 11 12 13 14 15 16 17 18 19 20
Xm
ax (
g/cm
2 )
200
400
600
800
1000