Introduction tothe cosmic-ray air shower
observations and LHCf
Takashi Sako
(ISEE/KMI, Nagoya University)

2016/10/29

France-Japan SAKURA Workshop on small-x
physics at the LHC

1

2016/10/29

France-Japan SAKURA Workshop on small-x
physics at the LHC

2

Cosmic-ray spectrum and collider energy（D’Enterria et al., APP, 35,98-113, 2011 ）

RHIC

LHC

FCC
End of galactic CR andtransition to extra-gal CRAnkle

Knee: end of galactic proton CR(GZK) cutoff:
end of CR spectrum

Indirect observation through air shower

3
Because of low flux, high-energy CRs are observed through atmospheric air showers

Air shower observation technic

Surface detectors = single layer sampling calorimeter
Fluorescence detectors = total absorption calorimeter4

3 key observables in air showerobservations• Energy (spectrum)• Acceleration mechanism at source• Propagation in the interstellar or intergalactic space (photopion production, photo-disintegration)• Mass (chemical composition)• Environment of the source• Photo-disintegration in the propagation• Direction• Source direction (astronomy)• Bending and diffusion in the magnetic field• Rigidity (E/Z) dependence

Not independent each other=> source and propagation scenario to explain all observations is required

5How can we measure energy (E) and mass (A)?
ex) 1017 eV proton

14x1017 eV proton

0g/cm2 ; top of the atmosphere
Xmax

Xmax

observation altitude# of electrons
1 (norm.)# of muons
1 (norm.)Xmaxlog(1) (norm.)
Intensity of Fluor. 1 (norm.)>14~14log(14)146How can we measure energy (E) and mass (A)?
ex) 1017 eV proton

14x1017 eV proton

0g/cm2 ; top of the atmosphere
Xmax

14x1017 eV Nitrogen= 14 superposition of1017eV proton (nucleon)

Xmax

Xmax

observation altitude# of electrons
1 (norm.)# of muons
1 (norm.)Xmaxlog(1) (norm.)
Intensity of Fluor. 1 (norm.)>14~14log(14)14

14~14log(1)14(E,A) degeneracy are usually solved by (Ifluor, <Xmax>) or (Ne, Nmu) observables

7

number onumber o

A comparison of the predictions of the moments fromelongation
simulations for proton- and iron-induced air showers toto a chang
the data is shown in Fig. 13. The simulations have been
performed 1 using the three contemporary hadronic inter1
action models that were either tuned to recent LHC data
-0.3
-0.2
-0.1
00.1
0.2
0.3(QGSJetII-04-0.2[95,96],-0.1Epos-LHC
00.1[97,98])
or0.2
foundtru in0.3goodbias
rectrurecbias
deviation after correction log (N )-C -log (N )deviation after correction log (Nµ )-Cµ -log (Nµ )10 chch
10 ch
1010A single
agreement with these measurements(Sibyll2.1[81], see[99]). andIt isnotingthatthe energyof exemplarily
the first fordata
not describ
Fig. 4. The distribution of the deviations between the reconstructed (bias corrected)
trueworthshower sizes
in caseof charged
particles (left,the interval

Cosmic-ray measurements andhadronic interactiontru
6:6 < log10 ðN tru
ch Þ < 6:7) and of muons (right, exemplarily for the interval 5:7 < log10 ðN l Þ < 5:8), as well as the determined parametrization (curves). To increase the available
simulation statistics, a mixed composition is used.

PAO, PRD, 90, 122005 (2014)98.58KASCADE-Grande data (full efficiency)
0°-18°c. 78000 events
isolines according to
response matrix for:
pFe

i5%

9.22-9.36

102

8.80-8.94

7.5
8.38-8.52

76.5
65

0.01%

5%

7.96-8.10
intervals of true energy
in log (E/GeV):
10
7.54-7.68

7.12-7.26
5.5
66.5
7
reconstructed number of muons log (Nµrec)of the data plane with constant probability (from the inner13 to

103

0.01%

10%

ations as well as that of the properties of the experiment. Shown!
"recare some isolines representing the cells log10 ðN recÞ;log
ðNÞ10chl

7.5

10

number of showers

10chrec. number of charged particles log (Nrec)

KASCADE Grande, Astropart. Phys., 47 (2013) 54-66

10#4 , represent the smallest probability value just considered in
the response matrix after its conditioning. As can be seen, these outer isolines cover almost all measured data; hence, the minimal probability is not set too large.
4. Error propagation

1

10Response (color contours) was calculated using
QGSJET II-02 + FLUKA 2002.4

the outermost isoline: 0:1; 0:05 and 10#4 probability density). For
reasons of clarity, only the results for two exemplary primaries areillustrated: protons and iron nuclei. The isolines, which correspondrecto the log10 ðNrecch Þ-log10 ðN l Þ combinations with a probability ofFig. 5. A comparison between the measured shower size distribution (greyrechistogram) and some isolines with log10 ðN recl Þ-log10 ðN ch Þ combinations of constantprobability according to the parametrizations (from the inner to the outermost line
10%, 5% and 0.01%). This is illustrated exemplarily for protons as well as iron nuclei,
FIG. 13.
and in case of six energy bins (labelled below each isoline set).

The determination of the elemental energy spectra will be subjected to influences of different error sources. They can roughly beclassified in four categories (cf. [17] for details):(i) Statistical uncertainties due to the limited measurement time:
Due to the limited exposure, the measured data sample will
suffer from unpreventable statistical uncertainties, which
Energy evolution of the first two central moments of the X max distributio
are expected to be Poisson distributed. These uncertainties
iron primaries will
[80,81,95–98].
be propagated through the applied unfolding algorithm
In order to parametrize the dependence of the resolution of theand are usually amplified thereby. The statistical uncertainexperiment on the true sizes, a possible bias in the charged particle
ties can be determined by means of a frequentist approach:and muon number reconstruction must first be corrected by using
8bias
bias
The measured two-dimensional shower size plane is considappropriate correction functions C ch and C l , respectively, deter122005-19ered as probability distribution. Based on a random
generamined based on the simulations. The correction is typically in theInterpretations rely on the MC predictions with an assumed hadronic interaction modelEffect to <Xmax>(R.Ulrich et al., PRD, 83 (2011) 054026)

Artificial modification of parametersbase model : SIBYLL 2.1
no modification E<1015eV
f19 parameter defines smooth
modification E>1015eVex) f19 =0.8, 80% at 1019eV
f19=1.2 120% at 1019eV
9

Effect to <Xmax>(R.Ulrich et al., PRD, 83 (2011) 054026)
Cross section
Multiplicity
ElasticityCharge ratio

10Effect to <Xmax>(R.Ulrich et al., PRD, 83 (2011) 054026)
Cross section
Multiplicity
Elasticity
Charge ratio

Reasonable range of f19 is unknown
Effects of spectra, nuclear effect are unknown(difficult to modify a single parameter like f19)
Experimental data by accelerators as much as possible are important11

What should be measured at colliders
multiplicity and energy flux at LHC 14TeV collisions
pseudo-rapidity; η= -ln(tan(θ/2))

Multiplicity

Energy FluxAll particles
neutralMost of the particles are produced in the central regionMost of the energy flows into very forward = relevant to CR air shower

12The LHC forward experiment
LHCf Arm#1ATLAS
140m

Two independent detectors at either sideof IP1 (Arm#1, Arm#2 )Beam96mm

Beam pipe
Charged particles (+)

Neutralparticles

LHCf Arm#2

Charged particles (-)ü All charged particles are swept by dipole magnet
ü Neutral particles (photons and neutrons) arrive at LHCfü η>8.4 (to infinity) is covered13

LHCf Detectors
ü Imaging sampling shower calorimeters
ü Two calorimeter towers in each of Arm1 and Arm2ü Each tower has 44 r.l. of Tungsten,16 sampling scintillator and 4 position
sensitive layers
ü Plastic scintillators => GSO scintillators, SciFi => GSO bars in Run2
LHCf Arm#1 Detector
20mmx20mm+40mmx40mm
4 XY SciFi+MAPMT

LHCf Arm#2 Detector
25mmx25mm+32mmx32mm
4 XY Silicon strip detectors

14

Event categories of LHCf
Leading baryon(neutron)

LHCf calorimeters

Single hadron
event

Multi meson production

photonπ0π0photonSingle photonevent

Pi-zero event(photon pair)15

photon (predominantly π0 decay) cross section at 7TeV p-p collision
EPOS 7TeV p-p photon

5.3

6.6

7.2
7.6

8.2
8.9〜pz16

LHCf (RHICf) History
ü2004 LOI submitted to CERN
ü2006 TDR approved by CERN
ü2009 First data taking at √s=900GeV p-p collisionü2010 √s=7TeV p-p collisionü2013 √s=2.76TeV p-p & √sNN=5TeV p-Pb collisions
ü2015 √s=13TeV p-p collisionü2016 √sNN=8.1TeV p-Pb collisionü2017 √s=510GeV p-p collision as RHICf
17

Publications

physics results
performance results

Photon(EM shower)

Neutron(hadronshower)

Beam test

NIM, A671(2012) 129136

JINST, 9 (2014)
P03016

0.9TeV p-p

PLB, 715(2012) 298303

7TeV p-p

PLB, 703(2011) 128134

2.76TeV p-p

PRD, 86(2012) 092001
PRC, 89 (2014)065209

5.02TeV p-Pb
13TeV p-p

PLB, 750(2015) 360366

π0 (limitedacceptance)

Preliminary

π0 (fullacceptance)

Performance

IJMPA, 28(2013) 1330036
PRD, 94 (2016)
032007

Analysis in progress18π0 pz spectra in 7TeV p-p collisions
10− 1
10− 210− 3LHCf s=7TeV

10− 4∫ Ldt=2.64+2.85nb-1

10− 51(d) 0.6 < p [GeV] < 0.8T
pz [GeV]

10−110−2
10−3−41010−51000 2000
pz [GeV]

3000(b) 0.2 < p [GeV] < 0.4
T

1/σinel Ed3σ/dp3 [GeV-2]

T

1/σinel Ed3σ/dp3 [GeV-2]

1(a) 0.0 < p [GeV] < 0.2

1/σinel Ed3σ/dp3 [GeV-2]

1/σinel Ed3σ/dp3 [GeV-2]

1/σinel Ed3σ/dp3 [GeV-2](PRD, 94 (2016) 032007)(e) 0.8 < p [GeV] < 1.0
Tpz [GeV]11(c) 0.4 < p [GeV] < 0.6T

pz [GeV]
LHCf (stat.+syst.)
DPMJET 3.06
QGSJET II-04
SIBYLL 2.1
PYTHIA 8.185
EPOS LHC

1000 2000
pz [GeV]

3000p
FIG. 5: (coloronline). Experimental
combined pdeveloped
LHCf(filledcircles) inp + p collisions at s =19
7 TeV.
z spectra of thefor
Comparison
with models
CRdetector
physics
exceptPYTHIA
Shaded rectangles indicate the total statistical and systematic uncertainties. The predictions of hadronic interaction models

𝜋0 in 7TeV p-p collision
LHCf and models

20𝜋0 in 7TeV p-p collision

LHCf and models (ratio to data)
EPOS-LHC/LHCf dataPTratio1GeV2.0
1.50.5GeV

1.00.50GeVQGSHET II-04/LHCf data

01TeV

2TeV

3TeV

SIBYLL 2.1/LHCf dataPz

210√s scaling ; πü Scaling is essential to extrapolate beyond LHC
ü (630GeV −) 2.76TeV – 7TeV
good scaling within uncertainties
ü Wider coverage in y and pT with 13TeV dataü Wider √s coverage with RHICf experiment in2017 at √s=510GeV

22

0.9s =200 GeV : PHENIX exponential p form

7%–22%

16%–39%T0.8s =200 GeV : PHENIX gaussian p form
T0.7s =30.6 GeV : ISR

0.6

s =44.9 GeV : ISR

0.5

s =52.8 GeV : ISR
s =62.7 GeV : ISR

0.4
0.3
0.20.1section meaincluded innty was estifor the BBC

Gaussian pTform

Fig. 6. Unfolded energy spectra of the small towers (η > 10.76) and the larsystematic errors, and the bars represent the Arm2 systematic errors except
the reader is referred to the web version of this article.)√s scaling; Neutron @ zero degreedσ /dx (mb)inties evalross section
included into be 9.7%on).
red neutron
GeV for thethe simularound fromulation. The
a was deteriscussed inch collision.
d the beamsystematicwere calcuhe result ofm, and theainty.

affected by the energy cutoff before the unfolding. ThepT range in each xF bin is 0 < pT < 0:11xF GeV=c from
Eq. (2) with the acceptance cut of r < 2 cm. The absolutenormalization uncertainty for the PHENIX measurement,
9.7%, is not included.

00

0.1

0.2

0.3

0.4

0.5xF

0.6

0.7

0.8

0.9

1

PRD,
032006(2013)
FIG. 13 PHENIX,(color online).
The88,
crosssection presultsfor forward
ﬃﬃﬃ
neutron productioninpþ
pcollisions
ats¼
200
GeV arepT < 0.11x GeV/cshown. Two different
forms, Fexponential (squares) and Gaussian= 30-60@ISRStatistical uncertaindistribution.
(circles), were√s
used
for the pTGeV
ties are shown as error bars for each point, and systematic√s = 200 GeV @RHIC
uncertainties are shown as brackets. The integrated pT region
for each bin is 0 < pT < 0:11xF GeV=c. Shapes of ISR results
are also shown. Absolute normalization errors for the PHENIXand ISR are 9.7% and 20%, respectively.

032006-10

LHCf

Fig. 7. Comparison of the LHCf results with model predictions at the small tow
pT < 0.15
xF GeV/cgray shaded areas
show thecombined results of the LHCf Arm1 and Arm2 d= 7000
GeV@LHC
the reader is√sreferredto theweb
version of this article.)dN ("η, " E ) is the number of neutrons observed inü PHENIX explains the result bywhere1pion
exchangeeach rapidity range, "η , and each energy bin, " E. L is the iü More complicated exchangesgrated
at >TeV?
luminosity corresponding to the data set. The cross sectareandsummarized
5. Fig. 7 shows the combined Arm1
ü LHCf data at 900GeV, 2.76TeV
13TeV intoTablebe analyzed
Arm2 spectra together with the model predictions.
23 The experim
ü RHICf data at 510GeV will betaladdedin
2017
results indicate the highest neutron production rate comp

uncertainty in the parameter aðxF Þ in the Gaussian form
evaluated by HERA. There is no significant difference inthe result in case of using the ISR (exponential) pT
distribution.
The mean values of the simulated pT distributions ineach energy region are also listed in Table I. The crosssection was obtained after the correction of the energy
unfolding and the cut efficiency.
Table II summarizes all systematic uncertainties evaluated as the ratio of the variation to the final cross section
values. The absolute normalization error is not included inthese errors. It was estimated by BBC counts to be 9.7%
(22:9 # 2:2 mb for the BBC trigger cross section).
The background contamination in the measured neutronenergy with the ZDC energy from 20 to 140 GeV for theacceptance cut of r < 2 cm was estimated by the simulation with the PYTHIA event generator. The background fromprotons was estimated to be 2.4% in the simulation. The
systematic uncertainty in the experimental data was determined to be 1.5 times larger than this as discussed inSec. II B 3. Multiple particle detection in each collision
was estimated to be 7% with the r < 2 cm cut.
In the cross section analysis, we evaluated the beam
center shift described in Appendix A as a systematicuncertainty. For the evaluation, cross sections were calculated in the different acceptances according to the result ofthe beam center shift while requiring r < 2 cm, and thevariations were applied as a systematic uncertainty.

Only highest energy?

PHENIX and ISR neutrons
PHENIX, PRD, 88, 032006 (2013)s =200 GeV : PHENIX exponential p form

Gaussian pTform

T0.8s =200 GeV : PHENIX gaussian p form
T0.7s =30.6 GeV : ISR

0.6s =44.9 GeV : ISR0.5

s =52.8 GeV : ISR
s =62.7 GeV : ISR

0.4
0.3
0.2
0.1

TABLE II. Systematic uncertainties for the cross section measurement. The absolute normalization error is not included inthese errors. The absolute normalization uncertainty was estimated by BBC counts to be 9.7% (22:9 # 2:2 mb for the BBCtrigger cross section).
Exponential pT
form

LHCf neutrons
PLB 750 (2015) 360-366

Fig. 6. Unfolded energy spectra of the small towers (η > 10.76) and tsystematic errors, and the bars represent the Arm2 systematic errors ex
the reader is referred to the web version of this article.)

0.9

dσ /dx (mb)

LHCf 𝜋0, PRD (2016)

The differential cross section, d!=dxp
F ,ﬃﬃﬃ for forward
neutron production in p þ p collisions at s ¼ 200 GeV
was determined using two pT distributions: a Gaussianform, as used in HERA analysis, and an exponential
form, used for ISR data analysis. The results are listed inTable III and plotted in Fig. 13. We show the results for xF
above 0.45 since the data below 0.45 are significantly
affected by the energy cutoff before the unfolding. ThepT range in each xF bin is 0 < pT < 0:11xF GeV=c fromEq. (2) with the acceptance cut of r < 2 cm. The absolutenormalization uncertainty for the PHENIX measurement,9.7%, is not included.

000.1

0.2

0.3

0.4

0.5xF

0.6

0.7

0.8

0.9

1FIG. 13 (color online). The cross section presults
for forward
ﬃﬃﬃ
neutron production in p þ p collisions at s ¼ 200 GeV areshown. Two different forms, exponential (squares) and Gaussian(circles), were used for the pT distribution. Statistical uncertainties are shown as error bars for each point, and systematic
uncertainties are shown as brackets. The integrated pT region
for each bin is 0 < pT < 0:11xF GeV=c. Shapes of ISR results
are also shown. Absolute normalization errors for the PHENIXand ISR are 9.7% and 20%, respectively.

Fig. 7. Comparison of the LHCf results with model predictions at the sma
gray shaded areas show the combined results of the LHCf Arm1 and Ar
the reader is referred to the web version of this article.)

Movingup/down
detectors“scaling” is a key to extrapolate
beyondthe LHC
energypT distribution
Beam center shift
Proton background
Multiple hit
Total

3%–10%

7%–22%

3%–31%
3.6%
7%

11%–33%

16%–39%032006-10••

where dN ("η, " E ) is the number of neutrons observe
each rapidity range, "η , and each energy bin, " E. L isgrated luminosity corresponding to the data set. The crossare summarized in Table 5. Fig. 7 shows the combined A
Arm2 spectra together with the model predictions. The exp
tal results indicate the highest neutron production rate cControlled by the withhandle
the MC models at the most forward rapidity. The
II-03 model
located on the upperside.predicts a neutron production rate similar toperimental results in the largest rapidity range. However
The movement is MJET
very3.04
slow
model predicts neutron production rates bettesmaller
rapidity ranges. These tendencies were alreadyand stable.
the spectra before unfolding, and they are not artifacts oThe detector was ing.
well fixed
The neutron-to-photon ratios (N n / N γ ) in three differeeven in the middle position.
ity regions were extracted after unfolding and are summ
The position was Table
kept4.without
Here, N n and N γ are the number of neutrons aber of photons, respectively, with energies greater than 1
any support.
The numbers of photons were obtained from the previo
The movable range[9] theand the same analysis for the pseudo-rapidity
ysis of
8.99–9.22
detector was about
16.5 defined
cm in this study. The experimental data inmore abundant neutron production rate relative to the pho
duction than any model predictions studied here.

ü RHICfusing one of the LHCf•
detectors is approved for
operation in 2017 at 510GeV p+p•collisions
at RHICü Installation and commissioning
are on going24

Summary• Cosmic-ray source and propagation are still key topic ofastrophysics• Air shower observations developed, but uncertainty inthe hadronic interaction limits the interpretation• Forward production (soft interaction) is key• LHCf and RHICf measure forward particle production• Hadron physics can make a significant contribution to
the astrophysics• (Air shower observations may contribute hadronphysics, or new physics)
25