衍射深虚拟康普顿散射
193 浏览量
2020-05-04
01:59:59
上传
评论
收藏 279KB PDF 举报
Diffractive deeply virtual Compton scattering
B. Pire ,
1
L. Szymanowski ,
2
and S. Wallon
3
1
CPHT, CNRS, École Polytechnique, I. P. Paris, 91128 Palaiseau, France
2
National Centre for Nuclear Research (NCBJ), Pasteura 7, 02-093 Warsaw, Poland
3
LPT, CNRS, Univ. Paris-Sud, Universit´e Paris-Saclay, 91405 Orsay, France and Sorbonne Universit´e,
Facult´e de Physique, 4 place Jussieu, 75252 Paris Cedex 05, France
(Received 20 December 2019; accepted 19 March 2020; published 6 April 2020)
Diffractive deeply virtual Compton scattering (DiDVCS) is the process γ
ð−Q
2
ÞþN→ ρ
0
þγ
ðQ
02
ÞþN
0
,
where N is a nucleon or light nucleus, in the kinematical regime of large rapidity gap between the ρ
0
and the
final photon-nucleus system, and in the generalized Bjorken regime where both photon virtualities Q
2
and
Q
02
are large. We show that this process has the unique virtue of combining the large diffractive cross
sections at high energy with the tomographic ability of deeply virtual Compton scattering to scrutinize the
quark and gluon content of nucleons and light nuclei. Its study at an electron-ion collider will enlighten the
internal structure of hadrons.
DOI: 10.1103/PhysRevD.101.074005
I. INTRODUCTION
It is now common wisdom that the dominant mechanism
of a diffractive electroproduction process in the hard regime
is the scattering of a small transverse-size (Oð
1
Q
Þ) colorless
dipole on a nuclear target, where Q is the virtuality of the
exchanged hard photon. This justifies the use of perturbative
QCD methods for the description of the process. In the
Regge inspired k
T
-factorization approach which is known
to be applicable at high energy, W ≫ Q ≫ Λ
QCD
, one writes
the scattering amplitude in terms of two impact factors with,
at leading order, a two Reggeized gluon exchange in the
t-channel. The Balitsky-Fadin-Kuraev-Lipatov (BFKL)
evolution [1–3] can then be applied to account for specific
large energy QCD resummation effects.
On the other hand, the unique features of nearly forward
exclusive hard scattering amplitudes in the generalized
Bjorken regime allowed to construct a vast program aiming
at the tomography of nucleons and light nuclei. The
theoretical framework is collinear factorization [4–6] of
the scattering amplitude into generalized parton distribu-
tions [7,8] and hard perturbatively calculable coefficient
functions. Deeply virtual Compton scattering (γ
N → γN
0
)
(DVCS) and the timelike Compton scattering (TCS) related
process (γN → γ
N
0
) have been much discussed both
theoretically and experimentally [9], and shown to provide
the best tool available for a 3-dimensional imaging [12–15]
of the quark and gluon structure of the proton and light
nuclei.
The process we study here—called DiDVCS for dif-
fractive deeply virtual Compton scattering—adds the mer-
its of these two classes of reactions, with a large cross
section at large energy and an excellent resolution of the
nucleon’s interior. It is particularly well suited for future
experiments at an electron-ion collider which is under
active study recently [16–18].
II. KINEMATICS
We study the process, see Fig. 1
γ
ðq; εÞþNðp
1
; λ
1
Þ
→ ρ
0
ðp
ρ
; ε
ρ
Þþγ
ðq
0
; ε
0
ÞþN
0
ðp
2
; λ
2
Þ; ð1Þ
at large squared energy s
γN
¼ðq þ p
1
Þ
2
, in the forward
limit where the ρ meson flies in the same direction as the
virtual initial photon and in the kinematical regime of large
rapidity gap between the ρ
0
and the photon, i.e., s
1
¼
ðq
ρ
þ q
0
Þ
2
≫ s
2
¼ðq
0
þ p
2
Þ
2
.
We define
P
μ
¼
p
μ
1
þ p
μ
2
2
; Δ
μ
¼ p
μ
2
− p
μ
1
; ð2Þ
and decompose momenta on a Sudakov basis as
v
μ
¼ γn
μ
þ δp
μ
þ v
μ
⊥
; ð3Þ
with p and n the light-cone vectors (2p:n ¼ s)
Published by the American Physical Society under the terms of
the Creative Commons Attri bution 4.0 International license.
Further distribution of this work must maintain attribution to
the author(s) and the published article’s title, journal citation,
and DOI. Funded by SCOAP
3
.
PHYSICAL REVIEW D 101, 074005 (2020)
2470-0010=2020=101(7)=074005(5) 074005-1 Published by the American Physical Society
资源评论
