Laser cooling of TeV muons Page: 1 of 5
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t Fermilab
FERMILAB-Conf-00/162 August 2000
1
Laser Cooling of TeV Muons*
Fermilab-Conf-00/ 162
Fritz DeJongha
aFermi National Accelerator Laboratory, fritzd@fnal.gov
We show that Compton scattering can be used to cool TeV-scale muon beams, and derive analytical expressions
for the equilibrium transverse angular spread, longitudinal energy spread, and power requirements. We find that
a factor of a few thousand reduction in emittance is possible for a 3 TeV muon collider.1. Introduction
Muon colliders are a possible future tool for
the exploration of physics at the TeV scale and
beyond. The current status of the developent of
the muon collider concept is described in Ref. [1],
which includes a description of a 3 TeV center-of-
mass (COM) machine.
One of the major challenges to realizing a high-
luminosity muon collider is to cool the diffuse
bunches of muons produced in pion decays. Much
effort is being put into the problem of quickly
cooling these bunches at the front-end of a muon-
collider and maintaining the low emittance while
bunches are being accelerated and brought into
collision.
For the 3 TeV COM machine, the problems of
neutrino radiation [2] and power consumption are
already becoming prohibitive. Additional cooling
of the bunches after acceleration would mitigate
these problems by allowing a given luminosity to
be attained with fewer stored muons and a low-
er repitition rate, and allow consideration of even
higher energy muon colliders. For example, the
tunnels and high-field magnets being discussed
for future hadron colliders [3] could ultimately be
used for a 100 TeV-scale muon collider. Post-
acceleration cooling would also reduce detector
backgrounds from muon decay.
The possibility of using Compton scattering
for cooling of electron bunches for 'y'y collider-
s has been previously considered [4]. The lu-
minosity for e+e- collisions is already limited
by beamstrahlung effects, but additional cooling
may greatly improve the yy luminosity.
*Contributed to the NuFAct'00 International Workshop.We propose herein the possibility of post-
acceleration cooling of muons beams using Comp-
ton scattering.
2. Compton Scattering
The Compton Scattering cross-section, in the
rest frame of the muon, is:da _ c& (k'N z
dQ 2m2 k )
where+ + - -sin2 9 ,
kc k' /k 1+ (k/m)(1 -cosB)
(1)
(2)
and k is the incoming photon energy, k' is the
outgoing photon energy, and 9 is the photon s-
cattering angle. For k m, k' I k and the
scattering is roughly isotropic:d-a
oc (1 + cos2 9), (3and the total cross-section is given by:
8ir c&
ac = 82
3 m23 2
(4)
where r is the classical muon radius. Thus, com-
pared to electrons, the cross-section is reduced by
4 x 104.
As an example, to expect 1 collision with a 0.1
eV photon, the light energy density would need
to be 10 J/(m)2.
Consider a beam of muons, with energy and
momentum defined by , 'y, E , and p , colliding
head-on with a mono-energetic beam of photons(3)
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DeJongh, Fritz. Laser cooling of TeV muons, article, August 8, 2000; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc711935/m1/1/: accessed April 26, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.