1. arXiv:
CERN-PH-EP
Submitted to PLB
First LHCf measurement of photon spectra at pseudorapidity >8.8 in LHC 7TeV pp collisions
Takashi SAKO
(Solar-Terrestrial Environment Laboratory,
Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University)
For the LHCf Collaboration
CERN Joint EP/PP/LPCC seminar, 17-May2011, Council Chamber

2. Thanks to… CERN, especially LHC crew ATLAS collaboration
Michelangelo and LHCC referees
Financial support mainly from Japan and Italy

3. Plan of the talk Motivation The LHCf Experiment
History and recent progress in the UHECR observation
Hadron interaction models and forward measurements
The LHCf Experiment
Single photon spectra at 7TeV pp collisions
Impact on the CR physics
Introduction to on-going works
Next plan
Further analysis of 0.9 and 7 TeV collision data
14TeV pp / pA, AA collisions
Summary

4. 1. Motivation

5. Frontier in UHECR Observation
What limits the maximum observed energy of Cosmic-Rays?
Time?
Technology?
Cost?
Physics?
GZK cutoff (interaction with CMB photons) >1020eV was predicted in 1966
Acceleration limit

6. Observations (10 years ago and now)
Debate in AGASA, HiRes results in 10 years ago
Now Auger, HiRes (final), TA indicate cutoff
Absolute values differ between experiments and between methods

7. Estimate of Particle Type (Xmax)
0g/cm2
Xmax
Proton and nuclear showers of same total energy
Auger TA
Xmax gives information of the primary particle
Results are different between experiments
Interpretation relies on the MC prediction and has model dependence
HiRes

8. Summary of Current CR Observations
Cutoff around 1020 eV seems exist.
Absolute energy of cutoff, sensitive to particle type, is still in debate.
Particle type is measured using Xmax, but different interpretation between experiments.
(Anisotropy of arrival direction also gives information of particle type; not presented today)
Still open question : Is the cutoff due to GZK process of protons or heavy nuclei, or acceleration limit in the source?
Both in the energy determination and Xmax prediction MC simulation is used and they are one of the considerable sources of uncertainty. Experimental tests of hadron interaction models are indispensable.

9. What to be measured at colliders multiplicity and energy flux at LHC 14TeV collisions pseudo-rapidity; η= -ln(tan(θ/2))
Multiplicity
Energy Flux
All particles
neutral
Most of the energy flows into very forward

10. 2. The LHCf Experiment

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

12. Detector Location ATLAS 96mm LHCf Detector(Arm#1)
Two independent detectors at either side of IP1 ( Arm#1, Arm#2 )
96mm
Charged particles (+)
Neutral particles
Beam pipe
Protons
Charged particles (-)
TAN -Neutral Particle Absorber-
transition from one common beam pipe to two pipes
　　Slot : 100mm(w) x 607mm(H) x 1000mm(T)

13. ATLAS & LHCf

14. LHCf Detectors Imaging sampling shower calorimeters
Two independent calorimeters in each detector (Tungsten 44r.l., 1.6λ, sample with plastic scintillators)
Arm#1 Detector
20mmx20mm+40mmx40mm
4 XY SciFi+MAPMT
Arm#2 Detector
25mmx25mm+32mmx32mm
4 XY Silicon strip detectors

15. Calorimeters viewed from IP
0 crossing angle
100urad crossing angle η ∞
8.7 θ
[μrad]
310
8.5
Projected edge of beam pipe
Geometrical acceptance of Arm1 and Arm2
Crossing angle operation enhances the acceptance

16. LHCf as EM shower calorimeter
EM shower is well contained longitudinally
Lateral leakage-out is not negligible
Simple correction using incident position
Identification of multi-shower event using position detectors

17. Front Counter Fixed scintillation counter
L=CxRFC ; conversion coefficient calibrated during VdM scans

18. 3. Single photon spectra at LHC 7TeV pp collisions

19. Data Set for this analysis
Date : 15 May :45-21:23 (Fill Number : 1104) except runs during the luminosity scan.
Luminosity : ( )x1028cm-2s-1
(not too high for pile-up, not too low for beam-gas BG)
DAQ Live Time : 85.7% for Arm1, 67.0% for Arm2
Integral Luminosity (livetime corrected):
0.68 nb-1 for Arm1, 0.53nb-1 for Arm2
Number of triggers : 2,916,496 events for Arm ,072,691 events for Arm2
With Normal Detector Position and Normal Gain MC
About 107 pp inelastic collisions with each hadron interaction model, QGSJET II-03, DPMJET 3.04, SYBILL 2.1, EPOS 1.99 and PYTHIA Only PYTHIA has tuning parameters. The default parameters were used

20. Event Sample (π0 candidate)
Event sample in Arm2
Longitudinal development
Note :
A Pi0 candidate event
599GeV gamma-ray and 419GeV gamma-ray in 25mm and 32mm tower respectively.
Lateral development

21. Analysis Step.1 : Energy reconstruction Step.2 : Single-hit selection
Step.3 : PID (EM shower selection)
Step.4 : π0 reconstruction and energy scale
Step.5 : Spectra reconstruction

22. Analysis Step.1
Energy reconstruction : Ephoton = f(Σ(dEi)) (i=2,3,…,13)
( dEi = AQi determined at SPS. f() determined by MC. E : EM equivalent energy)
Impact position from lateral distribution
Position dependent corrections
Light collection non-uniformity
Shower leakage-out
Shower leakage-in (in case of two calorimeter event)
Light collection nonuniformity
Shower leakage-out
Shower leakage-in

23. Analysis Step.2 Single event selection Single-hit detection efficiency
Multi-hit identification efficiency (using superimposed single photon-like events)
Effect of multi-hit ‘cut’ (next slide)
Small tower
Large tower
Arm1
Double hit in a single calorimeter
Arm2
Single hit detection efficiency
Double hit detection efficiency

24. Uncertainty in Step.2 Fraction of multi-hit and Δεmulti, data-MC
Effect of multi-hit ‘cut’ : difference between Arm1 and Arm2
Effect of Δεmulti to single photon spectra
Single / (single+multi), Arm1 vs Arm2

25. Analysis Step.3 PID (EM shower selection)
Select events <L90% threshold and multiply P/ε
ε (photon detection efficiency) and P (photon purity)
By normalizing MC template L90% to data, ε and P for certain L90% threshold are determined.

26. Uncertainty in Step.3 Imperfection in L90% distribution
Template fitting A
Template fitting B
Original method
ε/P from two methods
(Small tower, single & gamma-like)
Artificial modification in peak position　(<0.7 r.l.) and width (<20%)
(ε/P)B/ (ε/P)A

27. Analysis Step.4
π0 identification from two tower events to check absolute energy
Mass shift observed both in Arm1 (+7.8%) and Arm2 (+3.7%)
No energy scaling applied, but assigned the shifts in the systematic error in energy
Arm2
Measurement
Arm2 MC
I.P.1 
1(E1)
2(E2)
140m R
M = θ√(E1xE2)

28. Analysis Step.5 Spectra in Arm1, Arm2 common rapidity
Enegy scale error not included in plot (maybe correlated)
Nine = σine ∫Ldt
(σine = 71.5mb assumed)

29. Combined spectra
Weighted average of Arm1 and Arm2 according to the errors

30. Spectral deformation Suppression due to multi-hit cut at medium energy
Overestimate due to multi-hit detection inefficiency at high energy (mis-identify multi photons as single)
No correction applied, but same bias included in MC to be compared
TRUE/MEASURED
TRUE
MEASURED
True: photon energy spectrum at the entrance of calorimeter

31. Beam Related Effects Pile-up (7% pileup at collision) Beam-gas BG
Beam pipe BG
Beam position (next slide)
MC w/ pileup vs w/o pileup
Crossing vs non-crossing bunches
Direct vs beam-pipe photons

32. Where is zero degree? Beam center LHCf vs BPMSW
LHCf online hit-map monitor
Effect of 1mm shift in the final spectrum

33. Comparison with Models

34. Comparison with Models
DPMJET QGSJET II-03 SIBYLL 2.1 EPOS PYTHIA 8.145

35. DPMJET 3.04 QGSJET II-03 SIBYLL 2.1 EPOS 1.99 PYTHIA 8.145
None of the models perfectly agree with data.
QGSJET II, DPMJET3, PYTHIA8: good agreement in TeV at η>10.94 but large difference >2TeV.
SIBYLL2 shows good spectral shape >0.5TeV at η>10.94 but only half yield
Less deviation at 8.81<η<8.99 but still big difference >2TeV in DPMJET3 and PYTHIA8

36. 4. Impact on the CR physics

37. π0 spectrum and air shower
QGSJET II original
Artificial modification
Ignoring X>0.1 meson
X=E/E0
π0 spectrum at Elab = 1019eV
Longitudinal AS development
Artificial modification of meson spectra and its effect to air shower
Importance of E/E0>0.1 mesons
Is this modification reasonable?
30g/cm2

38. Model uncertainty at LHC energy
Very similar!?
Forward concentration of x>0.1 π0
π0 energy at √s = 7TeV
On going works
Air shower simulations with modified π0 spectra at LHC energy
Try&Error to find artificial π0 spectra to explain LHCf photon measurements
Analysis of π0 events

39. 5. Next Plan Analysis Experiment Energy scale problem to be improved
Correction for multi-hit cut / reconstruction for multi-hit event
π0 spectrum
Hadron
900GeV
PT dependence
Experiment
14TeV pp collisions
pA, AA collisions (only ideas)

40. 14TeV: Not only highest energy, but energy dependence…
SIBYLL
7 TeV
10 TeV
14 TeV
QGSJET2
7 TeV
10 TeV 14
Note: LHCf detector taken into account (biased)
Secondary gamma-ray spectra in p-p collisions at different collision energies (normalized to the maximum energy)
SIBYLL predicts perfect scaling while QGSJET2 predicts softening at higher energy
Qualitatively consistent with Xmax prediction

41. LHC-COSMIC ? p-Pb relevant to CR physics?
CR-Air interaction is not p-p, but A1-A2 (A1:p, He,…,Fe, A2:N,O)
Total
Neutron
Photon
LHC Nitrogen-Nitrogen collisions
Top: energy flow at 140m from IP
Left : photon energy spectra at 0 degree

42. 6. Summary
LHCf has measured photon spectra at η>8.8 during LHC 7TeV p-p collisions.
Measured spectra are compared with the prediction from various models.
None of the models perfectly agree with data
Large suppression in data at >2TeV w.r.t. to DPM3, QGS-II, PYTHIA predictions
Study on the effect of LHCf measurements to the CR air shower is on-going
Further analysis and preparation for next observations are on-going

43. Backup

44. CR Acceleration limit

45. Telescopes to image the fluorescence light (FD)
Surface Detectors (SD) to sample particles on ground

46. Key measurements E0 EM shower E leading baryon Forward spectra
(Multiplicity)
Cross section
Elasticity / inelasticity

47. Nagoya University
LHCf Arm LHCf Arm1
ATLAS
ALICE
LHCb/MoEDAL
CMS/TOTEM

48. Detectors are installed in TAN attached to the vertical manipulators
Neutral particles (predominantly photons, neutrons) enter in the LHCf calorimeters
Neutral particles

50. Luminosity Estimation
Luminosity for the analysis is calculated from Front Counter rates:
The conversion factor CF is estimated from luminosity measured during Van der Meer scan
VDM scan
Beam sizes sx and sy measured directly by LHCf
BCNWG paper

51. Operation 2009-2010 With Stable Beam at √s = 900 GeV
Total of 42 hours for physics
About 105 showers events in Arm1+Arm2
With Stable Beam at √s = 7 TeV
Total of 150 hours for physics with different setups
Different vertical position to increase the accessible kinematical range
Runs with or without beam crossing angle
~ 4·108 shower events in Arm1+Arm2
~ 106 p0 events in Arm1 and Arm2
Status
Completed program for 900 GeV and 7 TeV
Removed detectors from tunnel in July 2010
Post-calibration beam test in October 2010
Upgrade to more rad-hard detectors to operate at 14TeV in 2014

52. 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)
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=172μm
for 200GeV
electrons
σ=40μm
for 200GeV
electrons

53. Effect of mass shift
Energy rescaling NOT applied but included in energy error
Minv = θ √(E1 x E2)
(ΔE/E)calib = 3.5%
Δθ/θ = 1%
(ΔE/E)leak-in = 2%
=> ΔM/M = 4.2% ; not sufficient for Arm1 (+7.8%)
145.8MeV
(Arm1 observed)
135MeV
±3.5% Gaussian probability
±7.8% flat probability
Quadratic sum of two errors is given as energy error
(to allow both 135MeV and observed mass peak)

54. π0 mass shift in study
Reanalysis of SPS calibration data in 2007 and 2010 (post LHC) <200GeV
Reevaluation of systematic errors
Reevaluation of EM shower using different MC codes (EPICS, FLUKA, GEANT4)
Cable attenuation recalibration(1-2% improve expected)
Re-check all 1-2% effects…

55. Summary of systematic errors