References - Bogoliubov Laboratory of Theoretical Physics - JINR

POLARIZATION AT PHOTON COLLIDER. USING FOR PHYSICAL
STUDIES
I.F. Ginzburg †
Sobolev Institute of Mathematics and Novosibirk State University, Novosibirsk, Russia
† E-mail: ginzburg@math.nsc.ru
Abstract
Photon Colliders will have photon beams with high and easily variable polarization
(mainly circular). It offer opportunity for new experimental studies in the
problems of hadron physics and QCD in a new energy and transfer regions, in the
Standard Model physics and in the physics beyond Standard Model.
• Photon Collider. (PLC) is specific option of Linear Collider (LC). The focused laser
flash meet the electron bunch of LC in the conversion point C. Here a laser photon scatters
on high–energy electron taking from it a large portion of energy. Scattered photons travel
along the direction of the initial electron, they are focused in the interaction point. Here
they collide with opposite electron (eγ collider) or photon (γγ collider) [1–3]. The PLC
will start after 10 years of work of LHC and few years of work of e + e − ILC.
With two different laser photon energies two types of PLC are possible, the first one
is most suitable for ILC-1 Ee =0.25 TeV, the second one can be realized only for high
energy PLC with Ee =0.5 ÷ 1.5 TeV (ILC-2, CLIC) [2]. The typical expected parameters
of PLC in these two variants are enumerated below. In the cases when parameters for
second variant differ from those for the first variant they are shown in curly brackets.
The total additional cost is estimated as ∼ 10% from that of LC [3].
The conversion coefficient e → γ is 0.7 {0.15}.
Characteristic photon energy Eγmax ≈ 0.8 {0.95}Ee.
For high energy peak (Eγ1,2 > 0.7Eγmax), separated well from low energy part of spectrum
Luminosity Lγγ ≈ 0.35 {0.01 ÷ 0.05}Lee and Leγ ≈ 0.25 {0.2}Lee.
with � Lγγdt, � Leγdt ≈ 200 ÷ 150 {50 ÷ 100} fb −1 /year.
Mean energy spread < ΔEγ >≈ 0.07 {0.03}Eγmax.
Mean photon helicity ≈ 0.95, with easily variable sign.
• QCD and hadron physics. Photon structure function is unique object of QCD,
calculable at large enough Q2 without additional phenomenological parameters [4]. It can
be measured here in eγ mode with high accuracy, since photon target with its energy and
polarization here are practically known. In this case the range of accessible virtualities of
photon is limited from below by the details of detector set-up.
The region of electron transverse momenta above 50 GeV (MZ/2) can be studied well,
providing opportunity to study effect of Z-boson exchange and γ∗ γ − Z ∗ γ − Z ∗ − Z interference.
The manipulation with beam polarizations will be important instrument here.
The other studies like those at HERA are possible here.
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