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