Physics Letters B 746 (2015) 325–329
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
A new approach to evaluate the leading hadronic corrections to the
muon g-2
C.M. Carloni Calame
a,∗
, M. Passera
b
, L. Trentadue
c,d
, G. Venanzoni
e
a
Dipartimento di Fisica, Università di Pavia, Pavia, Italy
b
INFN, Sezione di Padova, Padova, Italy
c
Dipartimento di Fisica e Scienze della Terra “M. Melloni”, Università di Parma, Parma, Italy
d
INFN, Sezione di Milano Bicocca, Milano, Italy
e
INFN, Laboratori Nazionali di Frascati, Frascati, Italy
a r t i c l e i n f o a b s t r a c t
Article history:
Received
13 April 2015
Received
in revised form 1 May 2015
Accepted
9 May 2015
Available
online 14 May 2015
Editor:
A. Ringwald
This
work is dedicated to the memory of
our friend and colleague Eduard A. Kuraev
We propose a novel approach to determine the leading hadronic corrections to the muon g-2. It consists
in a measurement of the effective electromagnetic coupling in the space-like region extracted from
Bhabha scattering data. We argue that this new method may become feasible at flavor factories, resulting
in an alternative determination potentially competitive with the accuracy of the present results obtained
with the dispersive approach via time-like data.
© 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
1. Introduction
The long-standing discrepancy between experiment and the
Standard Model (SM) prediction of a
μ
, the muon anomalous mag-
netic
moment, has kept the hadronic corrections under close
scrutiny for several years [1–4]. In fact, the hadronic uncertainty
dominates that of the SM value and is comparable with the exper-
imental
one. When the new results from the g-2 experiments at
Fermilab and J-PARC will reach the unprecedented precision of 0.14
parts per million (or better) [5–7], the uncertainty of the hadronic
corrections will become the main limitation of this formidable test
of the SM.
An
intense research program is under way to improve the
evaluation of the leading order (LO) hadronic contribution to a
μ
,
due to the hadronic vacuum polarization correction to the one-
loop
diagram [8,9], as well as the next-to-leading order (NLO)
hadronic one. The latter is further divided into the O(α
3
) con-
tribution
of diagrams containing hadronic vacuum polarization
insertions [10], and the leading hadronic light-by-light term, also
of O(α
3
) [2,11,12]. Very recently, even the next-to–next-to leading
order (NNLO) hadronic contributions have been studied: inser-
*
Corresponding author.
E-mail
addresses: carlo.carloni.calame@pv.infn.it (C.M. Carloni Calame),
massimo.passera@pd.infn.it (M. Passera), luca.trentadue@cern.ch (L. Trentadue),
graziano.venanzoni@lnf.infn.it (G. Venanzoni).
tions of hadronic vacuum polarizations were computed in [13] ,
while hadronic light-by-light corrections have been estimated
in [14].
The
evaluation of the hadronic LO contribution a
HLO
μ
involves
long-distance QCD for which perturbation theory cannot be em-
ployed.
However, using analyticity and unitarity, it was shown long
ago that this term can be computed via a dispersion integral using
the cross section for low-energy hadronic e
+
e
−
annihilation [15].
At low energy this cross-section is highly fluctuating due to reso-
nances
and particle production threshold effects.
As
we will show in this paper, an alternative determination
of a
HLO
μ
can be obtained measuring the effective electromagnetic
coupling in the space-like region extracted from Bhabha (e
+
e
−
→
e
+
e
−
) scattering data. A method to determine the running of
the electromagnetic coupling in small-angle Bhabha scattering was
proposed in [16] and applied to LEP data in [17]. As vacuum polar-
ization
in the space-like region is a smooth function of the squared
momentum transfer, the accuracy of its determination is only lim-
ited
by the statistics and by the control of the systematics of the
experiment. Also, as at flavor factories the Bhabha cross section
is strongly enhanced in the forward region, we will argue that a
space-like determination of a
HLO
μ
may not be limited by statistics
and, although challenging, may become competitive with stan-
dard
results obtained with the dispersive approach via time-like
data.
http://dx.doi.org/10.1016/j.physletb.2015.05.020
0370-2693/
© 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by
SCOAP
3
.