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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
1CERN Joint EP/PP/LPCC seminar, 17-May2011, 503-1-001 Council Chamber
arXiv:1104.5294
CERN-PH-EP-2011-061
Submitted to PLB
Thanks to…
CERN, especially LHC crew
ATLAS collaboration
Michelangelo and LHCC referees
Financial support mainly from Japan and Italy
2
Plan of the talk
1. Motivation– History and recent progress in the UHECR observation– Hadron interaction models and forward measurements
2. The LHCf Experiment3. Single photon spectra at 7TeV pp collisions4. Impact on the CR physics
– Introduction to on-going works
5. Next plan– Further analysis of 0.9 and 7 TeV collision data– 14TeV pp / pA, AA collisions
6. Summary
3
1. Motivation
4
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 limit5
Observations (10 years ago and now)
6
Debate in AGASA, HiRes results in 10 years agoNow Auger, HiRes (final), TA indicate cutoffAbsolute values differ between experiments and between
methods
Estimate of Particle Type (Xmax)
Xmax gives information of the primary particle
Results are different between experiments
Interpretation relies on the MC prediction and has model dependence
7
0g/cm2
Xmax
Proton and nuclear showers of same total energy
AugerTA
HiRes
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.
8
What to be measured at collidersmultiplicity 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 forward9
2. The LHCf Experiment
10
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
The LHCf Collaboration
11
Detector Location
96mmTAN -Neutral Particle Absorber-
transition from one common beam pipe to two pipesSlot : 100mm(w) x 607mm(H) x 1000mm(T)
ATLAS
140m
LHCf Detector(Arm#1)
Two independent detectors at either side of IP1 ( Arm#1, Arm#2 )
12
Charged particlesCharged particles (+)(+)
Neutral particlesNeutral particles
Beam pipeBeam pipe
ProtonsProtons
Charged particlesCharged particles ((--))
ATLAS & LHCf
13
LHCf Detectors
Arm#1 Detector20mmx20mm+40mmx40mm4 XY SciFi+MAPMT
Arm#2 Detector25mmx25mm+32mmx32mm4 XY Silicon strip detectors
Imaging sampling shower calorimeters Two independent calorimeters in each detector (Tungsten 44r.l.,
1.6λ, sample with plastic scintillators)
14
Calorimeters viewed from IP
Geometrical acceptance of Arm1 and Arm2
Crossing angle operation enhances the acceptance
η
∞
8.7
θ[μrad]
0
310
η
∞
8.5
15
0 crossing angle 100urad crossing angle
Projected edge of beam pipe
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 16
Front Counter
17
Fixed scintillation counter
L=CxRFC ; conversion coefficient calibrated during VdM scans
3. Single photon spectra at LHC 7TeV pp collisions
18
Data Set for this analysis
Data– Date : 15 May 2010 17:45-21:23 (Fill Number : 1104)
except runs during the luminosity scan. – Luminosity : (6.3-6.5)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 Arm1
3,072,691 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 PYTHIA8.145
Only PYTHIA has tuning parameters. The default parameters were used
19
Event Sample (π0 candidate)Event sample in Arm2
Note :
• A Pi0 candidate event• 599GeV gamma-ray
and 419GeV gamma-ray in 25mm and 32mm tower respectively.
20
Longitudinal development
Lateral development
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
21
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)
22Light collection nonuniformity Shower leakage-out Shower leakage-in
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)
23
Double hit in a single calorimeter
Single hit detection efficiency
Small tower Large tower
Double hit detection efficiency
Arm1
Arm2
Uncertainty in Step.2 Fraction of multi-hit and Δεmulti, data-MC
Effect of multi-hit ‘cut’ : difference between Arm1 and Arm2
24Single / (single+multi), Arm1 vs Arm2Effect of Δεmulti to single photon spectra
Analysis Step.3
PID (EM shower selection)
– Select events <L90% threshold and multiply P/εε (photon detection efficiency) and P (photon purity)
– By normalizing MC template L90% to data, ε and P for certain L90% threshold are determined.
25
Uncertainty in Step.3
Imperfection in L90% distribution
26
Template fitting A
Template fitting B
(Small tower, single & gamma-like)
Artificial modification in peak position (<0.7 r.l.) and width (<20%)
Original method
ε/P from two methods
(ε/P)B/ (ε/P)A
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
27
m 140=
R
I.P.1
1(E1)
2(E2)
140mR
Arm2 Measurement
Arm2 MC
M = θ√(E1xE2)
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)
28
Combined spectra
29
Weighted average of Arm1 and Arm2 according to the errors
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
30
TRUEMEASURED TRU
E/M
EASU
RED
True: photon energy spectrum at the entrance of calorimeter
Beam Related Effects
Pile-up (7% pileup at collision)
Beam-gas BG
Beam pipe BG
Beam position (next slide)
31
MC w/ pileup vs w/o pileup
Crossing vs non-crossing bunches Direct vs beam-pipe photons
Where is zero degree?
32Effect of 1mm shift in the final spectrum
Beam center LHCf vs BPMSW
LHCf online hit-map monitor
33
Comparison with Models
34
Comparison with Models
DPMJET 3.04 QGSJET II-03 SIBYLL 2.1 EPOS 1.99 PYTHIA 8.145
35
1. None of the models perfectly agree with data.
2. QGSJET II, DPMJET3, PYTHIA8: good agreement in 0.5-1.5TeV at η>10.94 but large difference >2TeV.
3. SIBYLL2 shows good spectral shape >0.5TeV at η>10.94 but only half yield
4. Less deviation at 8.81<η<8.99 but still big difference >2TeV in DPMJET3 and PYTHIA8
DPMJET 3.04 QGSJET II-03 SIBYLL 2.1 EPOS 1.99 PYTHIA 8.145
4. Impact on the CR physics
36
π0 spectrum and air shower
Artificial modification of meson spectra and its effect to air shower
Importance of E/E0>0.1 mesons
Is this modification reasonable?
37
π0 spectrum at Elab = 1019eV
QGSJET II originalArtificial modification
Longitudinal AS development
Ignoring X>0.1 meson
X=E/E0
30g/cm2
Model uncertainty at LHC energy
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 38
Very similar!?
π0 energy at √s = 7TeV Forward concentration of x>0.1 π0
5. Next Plan Analysis
– 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)
39
14TeV: Not only highest energy, but energy dependence…
7 TeV10 TeV14 TeV (1017eV@lab.)
SIBYLL
7 TeV10 TeV14 TeV
QGSJET2
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 prediction40
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)
LHC Nitrogen-Nitrogen collisionsTop: energy flow at 140m from IPLeft : photon energy spectra at 0 degree
41
TotalNeutronPhoton
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
42
Backup
43
CR Acceleration limit
44
45
Surface Detectors (SD) to sample particles on ground
Telescopes to image the fluorescence light (FD)
Key measurements
E leading baryon
Elasticity / inelasticityForward spectra
(Multiplicity)Cross section
EM shower
E0
46
Nagoya University
LHCf Arm2 LHCf Arm1
ATLASALICELHCb/MoEDAL
CMS/TOTEM
47
48
Detectors are installed in TAN attached to the vertical manipulators
Neutral particles (predominantly photons, neutrons) enter in the LHCf calorimeters
49
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
LVDM = nb f revI1I2
2ps xs y
VDM scan
BCNWG paperhttps://lpc-afs.web.cern.ch/lpc-
afs/tmp/note1_v4_lines.pdf
L =CF ´ RFC
Beam sizes sx and sy measured directly by LHCf
Operation 2009-2010With Stable Beam at √s = 900 GeV
Total of 42 hours for physicsAbout 105 showers events in Arm1+Arm2
With Stable Beam at √s = 7 TeVTotal 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
StatusCompleted 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 201451
Beam test at SPS Energy Resolution
for electrons with 20mm cal.
Position Resolution (Scifi)
Position Resolution (Silicon)
Detector
σ=172μmfor 200GeV
electrons σ=40μmfor 200GeV
electrons
- Electrons 50GeV/c – 200GeV/c
- Muons 150GeV/c
- Protons 150GeV/c, 350GeV/c
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%)
53
145.8MeV(Arm1 observed)
135MeV
±7.8% flat probability
±3.5% Gaussian probability
Quadratic sum of two errors is given as energy error(to allow both 135MeV and observed mass peak)
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…
54
Summary of systematic errors
55
56