1. on behalf for the LHCf collaboration
Comparison of hadron interaction models with measurement of forward spectra by the LHCf apparatus
Hiroaki MENJO
INFN Firenze, Italy
on behalf for the LHCf collaboration
WISH2010, Catania September 2010

2. LHCf = LHC forward Outline LHCf Introduction and physics motivation
Overview of the LHCf experiment
Operation in 2009 and 2010
First results at 900GeV and 7TeV
Summary
ATLAS
LHCb
CMS/TOTEM
ALICE
LHCf

3. The LHCf collaboration
Y.Itow, K.Kawade, T.Mase, K.Masuda, Y.Matsubara, G.Mitsuka, K.Noda, T.Sako, K.Taki
Solar-Terrestrial Environment Laboratory, Nagoya University, Japan
K.Yoshida Shibaura Institute of Technology, Japan
K.Kasahara, M.Nakai, Y.Shimizu, T.Suzuki, S.Torii
Waseda University, Japan
T.Tamura Kanagawa University, Japan
Y.Muraki Konan University, Japan
M.Haguenauer Ecole Polytechnique, France
W.C.Turner LBNL, Berkeley, USA
O.Adriani, L.Bonechi, M.Bongi, R.D’Alessandro, M.Grandi, H.Menjo, P.Papini, S.Ricciarini, G.Castellini
INFN, Univ. di Firenze, Italy
A.Tricomi INFN, Univ. di Catania, Italy
J.Velasco, A.Faus IFIC, Centro Mixto CSIC-UVEG, Spain
D.Macina, A-L.Perrot CERN, Switzerland 3

4. -Neutral particle absorber-
Experimental set-up
LHCf Detector(Arm#1)
ATLAS
140m
LHCf Detector (Arm#2)
Inside of TAN
-Neutral particle absorber-
!! Detectors at zero degree of collisions !!
96mm
Charged particles
Neutral particles
Beam pipe
Protons
In the long straight sections, there are big absorbers call TAN to protect the super conducting magnets.
at IP1 TAN are located 140m far from IP. Inside TAN beam pipe makes transition from one big pipe
to two small pipes. The gaps between the two pipes allow to see collisions at zero degrees.
TAN has an experimental slot to insert forward detectors inside the gap.
LHCf detectors had been installed in the first slot.
In secondary particles produced at collisions, charged particles are bended by dipole magnet installed between TAN and
interaction point. but we can see neutral particles at zero degree.
The detector has been installed in 96mm gap of the beam pipes.

5. Arm2 Arm1 The LHCf detectors Sampling and Positioning Calorimeters
25mm
32mm
W (44 r.l , 1.7λI ) and Scintillator x 16 Layers
4 positioning layers XY-SciFi(Arm1) and XY-Silicon strip(Arm#2)
Each detector has two calorimeter towers, which allow to reconstruct p0
Expected Performance
Energy resolution (> 100GeV)
< 5% for photons
30% for neutrons
Position resolution < 200μm (Arm#1)
40μm (Arm#2)
Arm2
The Arm#1 and Arm#2 , each detector has two sampling and imaging calorimeters.
The each calorimeter are made of 44 r.l. tungsten layer and 16 scintillator layers and 4 position sensitive layers.
The position sensitive layers of Arm#1 are made of XY pair of scintillating fiber bundles.
The position sensitive layers of Arm#2 are made of XY silicon strip detectors.
Two independent calorimeters allow to reconstruct neutral pion from pair photons.
The energy resolution is less than 5% for photons with more than 100GeV and about 30 % for neutrons.
The position resolution of Scintillating fibers in Arm1 is less than 200 um.
And position resolution of silicon detectors in Arm2 is about 40um.
Front Counter
thin scintillators with 80x80mm2
To monitor beam condition.
For background rejection of beam-residual gas collisions by coincidence analysis
40mm
Arm1
20mm

6. Arm#1 Arm#2 620mm 620mm 280mm 92mm 90mm 280mm
These are photos of the real LHCf detectors.
The LHCf detectors are really compact to insert to inside of narrow experimental slot of TAN.
There are calorimeter towers inside of light green materials on bottom of the detectors.
280mm
92mm
90mm
280mm

7. Transverse projection of Arm#1
IP1,ATLAS
Arm2 η ∞
8.7
Shadow of beam pipes
between IP and TAN
8.4 ∞
This is photos of our detectors installed in the LHC ring.
The red one is the surface of TAN located 140m far from IP1. we can see our electronics boxes on TAN but detector were completely in experimental slots of TAN.
Behind of our detectors, Luminosity monitor BRAN and ATLAS ZDC has been installed.
@ 140mrad crossing angle
neutral beam axis
Transverse projection of Arm#1
@ zero crossing angle

8. Energy spectra and Transverse momentum distribution of
LHCf can measure
ATLAS
Energy spectra and Transverse momentum distribution of
Gamma-rays (E>100GeV,dE/E<5%)
Neutral Hadrons (E>a few 100 GeV, dE/E~30%)
Neutral Pions (E>700GeV, dE/E<3%)
LHCf
at psudo-rapidity range >8.4
Energy
Next, I present what we can measure.
We can measure energy spectra and transverse momentum distribution of gamma-ray with more than 100GeV
and neutral hadrons it’s mainly neutrons with more than a few hundreds GeV, and neutral pions with more than 700GeV
at rapidity range from 8.4 to infinity.
because we don’t have own central detectors and LHCf trigger is completely independent on ATLAS trigger,
so LHCf can measure only inclusive spectra . However we are recording ATLAS event ID number event by event,
so it is possible to identify coincidence events with ATLAS event and to analyze with ATALS in future.
High energy flux !!
Low multiplicity !!
simulated by DPMJET3

9. Why the forward region ?
Ultra High energy cosmic rays

10. Ultra High Energy Cosmic rays
Extensive air shower observation
HECRs
= Air shower developments =
longitudinal distribution
lateral distribution
Arrival direction g p Fe
Air shower development
Astrophysical parameters
Spectrum
Composition
Source distribution
Xmax distribution measured by AUGER
PROTON
The hadron interaction models used in air shower simulations have an uncertainty due to the lack of experimental data in the energy range over 1015eV
IRON

11. LHC gives us unique opportunities to measure at 1017eV
7TeV+7TeV → Elab = 1017eV
　3.5TeV+3.5TeV → Elab = 2.6x1016eV
450GeV+450GeV → Elab = 2x1014eV
Cosmic ray spectrum
Key parameters
for air shower developments
Total cross section ↔ TOTEM, ATLAS(ALFA)
Multiplicity ↔ Central detectors
Inelasticity/Secondary spectra ↔ Forward calorimeters LHCf, ZDCs
SPS
Tevatron
LHC
AUGER

12. p0 LHCf can Neutron Gamma-rays Expected spectra
by hadron interaction models
at 7TeV+7TeV
LHCf can
Neutron
Gamma-rays
Different interaction model gives different production spectra
in the forward region.
It means the LHCf can discriminate
the interaction models.
Next, I present what we can measure.
We can measure energy spectra and transverse momentum distribution of gamma-ray with more than 100GeV
and neutral hadrons it’s mainly neutrons with more than a few hundreds GeV, and neutral pions with more than 700GeV
at rapidity range from 8.4 to infinity.
because we don’t have own central detectors and LHCf trigger is completely independent on ATLAS trigger,
so LHCf can measure only inclusive spectra . However we are recording ATLAS event ID number event by event,
so it is possible to identify coincidence events with ATLAS event and to analyze with ATALS in future. p0

13. Operation & Results
Dec in the LHCf control room

14. We completed operation at 900GeV and 7TeV successfully !!
Operation in
At 450GeV+450GeV
06 Dec. –15 Dec. in 2009
27.7 hours for physics, 2.6 hours for commissioning
~2,800 and ~3,700 shower events in Arm1 and Arm2
02-03, and 27 May in 2010
~15 hours for physics
~44,000 and ~63,000 shower events in Arm1 and Arm2
At 3.5TeV+3.5TeV
30 Mar. – 19 Jul. in 2010
~ 150 hours for physics with several setup
~2x108 and ~2x108 shower events in Arm1 and Arm2
30 Mar.-06 Jun. with zero crossing angle, Jun.-19 Jul with 100mrad crossing angle
We completed operation at 900GeV and 7TeV successfully !!
The detectors were removed from the LHC tunnel on 20 July 2010.
The detectors will be re-installed for operation at 7TeV+7TeV in 2013 after the upgrade of the detector.

15. Event sample
@ Arm1
Results at 900GeV
Event sample
@ Arm2

16. Some results at 900GeV 2009 2010 Arm1 Arm2 Hit map of Gamma-rays
shadow
of beam pipes
Hit map of Gamma-rays
Arm1
Background due to beam-residual gas collisions
about 10% @ 2009 Data
about 1% @ 2010 Data
2009
2010
Arm2
I shows preliminary resutls in last year operation.
in last year, in total LHC had about 10 to 6th collisions at all IPs.
We took about 6000 shower events by Arm1 and Arm2 calorimeters.
The left figure show the hit map of gamma-ray events. black open circles show events at colliding bunches and
red marks shows events at non-colliding bunches. beam and residual gas collisions made these non-colliding bunch events.
Black markers have clear cut because of the beam pipe shadow.
Left figure show distribution of energy deposit in Arm1 detectors.
Red dots shows events at colliding beams and Blue shows events at non-colliding beam events.
By subtract with non-colliding beam events, we can see clear collision events.
Red: colliding bunch Blue: single bunch = collision + BG = BG only

17. Particle Identification
A transition curve for Gamma-ray
A transition curve for Hadron
Thick for E.M. interaction (44X0)
Thin for hadronic interaction(1.7l)
40mm cal. of Arm1
Definition of L90%
MC (QGSJET2)
Preliminary
Data
Gamma-ray like
Hadron like
L90% is defined as the longitudinal position containing 90% of the sum of the shower particles.
PID study is still ongoing
Criteria for gamma-rays
16 r.l x SdE

18. Arm1 Arm2 Energy Spectra at 900GeV Gamma-ray like Hadron like
Hadron response
under study
Gamma-ray like
Hadron like
preliminary
preliminary
Only statistical
errors are shown
Arm2
Hadron like
Gamma-ray like
preliminary
preliminary
The spectra are normalized by number of gamma-ray and hadron like events
The detector response for hadrons and the systematic error are under study.

19. Results at 7TeV TeV gamma-ray !!
Event sample measured by Arm2 at 30 March 2010
TeV gamma-ray !!

20. Measured Spectra at 7TeV
preliminary
Gamma-ray like
Hadron like
Arm1
preliminary
Gamma-ray like
Hadron like
Arm2
Very high statistics !! only 2% of all data
Comparisons with MC are ongoing.

21. p0 reconstruction An example of p0 events
measured energy Arm2
25mm
32mm
preliminary
Silicon strip-X view
Reconstructed Arm2
ΔM/M=2.3%
Pi0’s are a main source of electromagnetic secondaries in high energy collisions.
The mass peak is very useful to confirm the detector performances and to estimate the systematic error of energy scale.
preliminary

22. h Candidate h search p0 Candidate
preliminary
h/p0 ratio vary a lot among different interaction models.
A good handle to probe the hadron interaction models
Another calibration point for more robust energy scale

23. Future Plan + We are thinking
2010, July
Completed operation at 7TeV
=> Removed the detectors from the tunnel
2010, Oct
The beam test at SPS to confirm the radiation damage and the performance.
2011
Upgrade the detector to radiation harder one with GSO scintillators.
2013
Install the detectors to the LHC tunnel again
for the operation at 14TeV.
+ We are thinking
- Operation at LHC light ion collisions (not Pb-Pb).
Finally I present our operation plan. We will take data in beginning of LHC commissioning phases with very low luminosity
at every collision energy.
In this year, we will take data at 900GeV and 7TeV collisions until the integral luminosity of 2pb-1, then we will remove the
detectors and upgrade them for next operation. In 2013, LHC will finish to upgrade for 14TeV, we will install the detectors again to take data at 14 TeV collisions.
And also we want to take data at intermediate collision energy and light lions collisions if LHC has.

24. Summary
The LHCf experiment is a forward experiment of LHC with calorimeters at zero degree. The aim is to measure energy spectra and transverse momentum distributions of very energetic neutral secondaries at the very forward region of IP1 (h>8.4).
LHCf successfully completed data taking at 900GeV and 7TeV. The LHCf detectors has been removed from LHC the tunnel and will be re-installed for data taking at 7TeV+7TeV in 2013.
900 GeV analysis is almost final and ready to be submitted for publication while 7 TeV analysis is progressing quickly.

25. Back up

26. Sub detectors -Front Counter-
Thin scintillators with 8x8cm2 acceptance, which have been installed in front of each main detector.
Schematic view of
Front counter
To monitor beam condition.
For background rejection of beam-residual gas collisions by coincidence analysis
We have a sub-detector with thin scintillator layers, we call Front Counter.
Front Counter has much larger acceptance than calorimeters.
It’s useful to monitor collisions and for background rejection of beam and residual gas collisions by coincidence analysis of both size.

27. Beam test at SPS p,e-,mu σ=172μm σ=40μm Detector Energy Resolution
for electrons with 20mm cal.
- Electrons 50GeV/c – 200GeV/c
Muons 150GeV/c
Protons 150GeV/c, 350GeV/c
Position Resolution (Silicon)
Position Resolution (Scifi)
σ=172μm
for 200GeV
electrons
The detector performance was checked by beam tests at SPS.
We had exposed the detectors in electron, muon and protons beams with a few hundreds GeV.
This is energy resolution of one of the calorimeters as a function of gamma-ray energy.
It is in a very good agreement with simulation results and good resolution of 5% for more than 100GeV.
And bottom figures show position resolution of scintillating fibers of Arm1 and silicon detectors of Arm2 for 200GeV electrons.
σ=40μm
for 200GeV
electrons

28. Eγ – PTγ Correlation plot
140
Beam crossing angle
Detectable events 28