Transcript First LHCf measurement of photon spectra at pseudorapidity

arXiv:1104.5294
CERN-PH-EP-2011-061
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, 503-1-001 Council Chamber
1
Thanks to…
CERN, especially LHC crew
ATLAS collaboration
Michelangelo and LHCC referees
Financial support mainly from Japan and Italy
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Plan of the talk
1. Motivation
– History and recent progress in the UHECR observation
– Hadron interaction models and forward measurements
2. The LHCf Experiment
3. Single photon spectra at 7TeV pp collisions
4. 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
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1. Motivation
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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
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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
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Estimate of Particle Type (Xmax)
0g/cm2
Xmax
Auger
TA
Proton and nuclear showers
of same total energy
HiRes
 Xmax gives information of the
primary particle
 Results are different between
experiments
 Interpretation relies on the MC
prediction and has model
dependence
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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.
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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
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2. The LHCf Experiment
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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
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Detector Location
LHCf Detector(Arm#1)
ATLAS
140m
Two independent detectors at
either side of IP1 ( Arm#1, Arm#2 )
Protons
Charged particles (+)
Neutral particles
Beam pipe
Charged particles (-)
96mm
TAN -Neutral Particle Absorbertransition from one common beam pipe to two pipes
Slot : 100mm(w) x 607mm(H) x 1000mm(T)
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ATLAS & LHCf
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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
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Calorimeters viewed from IP
η
θ
[μrad]
310
8.7
0 ∞
0 crossing angle
100urad crossing angle
η
8.5
∞
Projected edge
of beam pipe
 Geometrical acceptance of Arm1 and Arm2
 Crossing angle operation enhances the acceptance
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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
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Front Counter
 Fixed scintillation
counter
 L=CxRFC ; conversion
coefficient calibrated
during VdM scans
17
3. Single photon spectra
at LHC 7TeV pp collisions
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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
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Event Sample (π0 candidate)
Event sample in Arm2
Longitudinal development
Lateral development
Note :
• A Pi0 candidate event
• 599GeV gamma-ray
and 419GeV gammaray in 25mm and 32mm
tower respectively.
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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
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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
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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
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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 24
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.
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Uncertainty in Step.3
Imperfection in L90% distribution
Template fitting A
Original method
ε/P from two methods
(Small tower, single & gamma-like)
Artificial modification in
peak position (<0.7 r.l.)
and width (<20%)
Template fitting B
(ε/P)B/ (ε/P)A
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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
1(E1)
R
=
Arm2
Measurement
Arm2 MC
R
140 m
140m
2(E2)

I.P.1
M = θ√(E1xE2)
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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)
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Combined spectra
Weighted average of Arm1 and Arm2 according to the errors
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Spectral deformation
TRUE
MEASURED
True: photon energy spectrum
at the entrance of calorimeter
TRUE/MEASURED
 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
Beam Related Effects
Pile-up (7% pileup at collision)
Beam-gas BG
Beam pipe BG
Beam position (next slide)
Crossing vs non-crossing bunches
MC w/ pileup vs w/o pileup
Direct vs beam-pipe photons
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Where is zero degree?
Beam center LHCf vs BPMSW
LHCf online hit-map monitor
Effect of 1mm shift in the final spectrum
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Comparison with Models
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Comparison with Models
DPMJET 3.04 QGSJET II-03 SIBYLL 2.1 EPOS 1.99 PYTHIA 8.145
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DPMJET 3.04 QGSJET II-03 SIBYLL 2.1 EPOS 1.99 PYTHIA 8.145
1.
2.
3.
4.
None of the models perfectly agree with data.
QGSJET II, DPMJET3, PYTHIA8: good agreement in 0.5-1.5TeV 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
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and PYTHIA8
4. Impact on the CR physics
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π0 spectrum and air shower
QGSJET II original
Artificial modification
X=E/E0
Ignoring X>0.1 meson
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
37
Model uncertainty at LHC energy
Very similar!?
π0 energy at √s = 7TeV
Forward concentration of x>0.1 π0
 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
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…
SIBYLL
QGSJET2
7 TeV
10 TeV
14 TeV (1017eV@lab.)
7 TeV
10 TeV
14 TeV
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
40
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
41
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
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Backup
43
CR Acceleration limit
44
Surface Detectors (SD) to
sample particles on ground
Telescopes to image the
fluorescence light (FD)
45
E0
Key measurements
EM
shower
E leading baryon
Cross section
Elasticity / inelasticity
Forward spectra
(Multiplicity) 46
CMS/TOTEM
Nagoya University
ALICE
ATLAS
LHCf Arm2
LHCf Arm1
LHCb/MoEDAL
47
 Detectors are installed in
TAN attached to the
vertical manipulators
 Neutral particles
(predominantly photons,
neutrons) enter in the
LHCf calorimeters
48
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Luminosity Estimation
• Luminosity for the analysis is calculated from Front Counter
rates:
L = CF ´ RFC
•The conversion factor CF is estimated from luminosity measured
during Van der Meer scan
LVDM = n b f rev
I1I2
2ps xs y
Beam sizes sx and sy measured
directly by LHCf
BCNWG paper
https://lpc-afs.web.cern.ch/lpcafs/tmp/note1_v4_lines.pdf
VDM scan
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
51
Beam
test
at
SPS
Energy Resolution
Detector
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
σ=40μm
for 200GeV
electrons
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%)
±3.5% Gaussian probability
±7.8% flat probability
135MeV
Quadratic sum of two errors
is given as energy error
145.8MeV
(to allow both 135MeV and
(Arm1 observed) observed mass peak)
53
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…
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Summary of systematic errors
55
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