Physics Letters B 750 (2015) 360–366
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Measurement of very forward neutron energy spectra for 7TeV
proton–proton collisions at the Large Hadron Collider
O. Adriani
a,b
, E. Berti
a,b
, L. Bonechi
a
, M. Bongi
a,b
, G. Castellini
a,c
, R. D’Alessandro
a,b
,
M. Del Prete
a,b
, M. Haguenauer
d
, Y. Itow
e,f
, K. Kasahara
g
, K. Kawade
e,∗
, Y. Makino
e
,
K. Masuda
e
, E. Matsubayashi
e
, H. Menjo
h
, G. Mitsuka
b
, Y. Muraki
e
, Y. Okuno
e
, P. Papini
a
,
A.-L. Perrot
i
, S. Ricciarini
a,c
, T. Sako
e,f
, N. Sakurai
f
, Y. Sugiura
e
, T. Suzuki
g
, T. Tamura
j
,
A. Tiberio
a,b
, S. Torii
g
, A. Tricomi
k,l
, W.C. Turner
m
, Q.D. Zhou
e
a
INFN Section of Florence, Italy
b
University of Florence, Italy
c
IFAC-CNR, Italy
d
Ecole-Polytechnique, France
e
Solar-Terrestrial Environment Laboratory, Nagoya University, Japan
f
Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University, Japan
g
RISE, Waseda University, Japan
h
Graduate School of Science, Nagoya University, Japan
i
CERN, Switzerland
j
Kanagawa University, Japan
k
INFN Section of Catania, Italy
l
University of Catania, Italy
m
LBNL, Berkeley, USA
a r t i c l e i n f o a b s t r a c t
Article history:
Received
13 March 2015
Received
in revised form 15 September
2015
Accepted
16 September 2015
Available
online 25 September 2015
Editor:
M. Doser
Keywords:
LHC
Forward
neutron production
Hadronic-interaction
model
The Large Hadron Collider forward (LHCf) experiment is designed to use the LHC to verify the hadronic-
interaction
models used in cosmic-ray physics. Forward baryon production is one of the crucial points
to understand the development of cosmic-ray showers. We report the neutron-energy spectra for LHC
√
s = 7TeVproton–proton collisions with the pseudo-rapidity η ranging from 8.81 to 8.99, from 8.99
to 9.22, and from 10.76 to infinity. The measured energy spectra obtained from the two independent
calorimeters of Arm1 and Arm2 show the same characteristic feature before unfolding the detector
responses. We unfolded the measured spectra by using the multidimensional unfolding method based on
Bayesian theory, and the unfolded spectra were compared with current hadronic-interaction models. The
QGSJET II-03 model predicts a high neutron production rate at the highest pseudo-rapidity range similar
to our results, and the DPMJET 3.04 model describes our results well at the lower pseudo-rapidity ranges.
However, no model perfectly explains the experimental results over the entire pseudo-rapidity range. The
experimental data indicate a more abundant neutron production rate relative to the photon production
than any model predictions studied here.
© 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 forward particle production process induced by collisions
of high-energy particles is a poorly understood phenomenon in
high-energy physics. Though it is important to understand the de-
velopment
of cosmic-ray showers in the atmosphere, the validity
of hadronic-interaction models has not been sufficiently verified
*
Corresponding author.
E-mail
address: kawade@stelab.nagoya-u.ac.jp (K. Kawade).
at energies for ultra-high-energy cosmic rays (UHECRs, > 10
18
eV)
because of the lack of experimental data in this energy range. This
lack of data results in a large uncertainty in the interpretation of
the energy and chemical composition of UHECRs. Forward baryons
play a very important role in the development of cosmic-ray show-
ers.
If forward baryons carry more collision energy, cosmic-ray
showers develop much deeper in the atmosphere, and vice versa.
However, in the energy range of UHECRs, the predictions by cur-
rent
models differ significantly among themselves.
http://dx.doi.org/10.1016/j.physletb.2015.09.041
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
.