Very forward measurement at LHC
for Ultra-High Energy Cosmic-Ray physics
SAKO Takashi for the LHCf collaboration
(Solar-Terrestrial Environment Laboratory &
Kobayashi-Maskawa Institute, Nagoya University)
RIKEN seminar, 21-Jul-2011
1
Outline
• Current UHECR observations
• Forward emission in hadronic interaction
• LHCf
– Experiment overview
– Analysis of single photon at √s=7TeV pp collisions
– Impact on UHECR (on going work)
• Future
2
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
3
Observations (10 years ago and now)
GZK Cutoff mechanism
100MeV photon
3K CMB
Proton at rest
1020eV proton
 GZK cutoff prediction at 1020eV
 Debate in AGASA, HiRes results in 10 years ago
4
Observations (10 years ago and now)
 Auger, HiRes (final), TA indicate GZK-like cutoff
 Absolute values differ between experiments and between
methods
5
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
6
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 at
accelerators are indispensable.
7
① Inelastic cross section
④ 2ndary interactions
If large s
rapid development
If small s
deep penetrating
② Forward energy spectrum
If softer
shallow development
If harder
deep penetrating
③ Inelasticity k
(1-Eleading)/E0
If large k
rapid development
If small k
deep penetrating
8
What should 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
9
The LHCf experiment
10
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
A-L.Perrot CERN, Switzerland
11
Detector Location
√s=14TeV
]
LHCf Detector(Arm#1)
ATLAS
Elab=1017eV
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)
12
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
13
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
14
BABY SIZE DETECTOR!
64cm
62cm
*photo: two years ago.
She is now larger than LHCf and difficult to control
Calorimeters viewed from IP
η
θ
0 crossing angle
[μrad]
310
8.7
0 ∞
Projected edge
of beam pipe
 Geometrical acceptance of Arm1 and Arm2
16
Expected Results at 14 TeV Collisions
(MC assuming 0.1nb-1 statistics)
Detector response
not considered
Operation at LHC 2009-2010
18
Summary of Operations in 2009 and 2010
With Stable Beam at 900 GeV
Total of 42 hours for physics
About 105 showers events in Arm1+Arm2
With Stable Beam at 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+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
2009-2010 run summary (7TeV)
High luminosity (L=3~20e29cm2s-1)
(1e11ppb, b*=3.5m,Nb=1~8)
Low luminosity (L=2~10e28cm2s-1)
(1~2.5e10ppb, b*=2m,Nb=1~4)
No crossing angle
100mrad crossing
Integrated showers at 7TeV
108
Detector removed
# of showers
900GeV
107
106
4/1
# of p0
1000K
5/27
7/22
Arm1 p0 stat.
500K
4/4
5/30
7/25
20
arXiv:1104.5294v2
PLB Received
Analysis for single photon spectra
(Photons are mostly decay products of π0 and η)
21
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
22
Event Sample (π0 candidate)
Event sample in Arm2
Longitudinal development
Small
calorimeter
Lateral development
Silicon X
Large
calorimeter
Note :
• A Pi0 candidate event
• 599GeV gamma-ray
and 419GeV gammaray in 25mm and 32mm
tower respectively.
Silicon Y
23
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
24
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 non-uniformity
Shower leakage-out
Shower leakage-in
25
Analysis Step.2
 Single event selection (multi-hit cut)
– Single-hit detection efficiency
– Multi-hit identification efficiency (using superimposed
single photon-like events)
Small tower
Large tower
Arm1
Double hit in a single calorimeter
Arm2
Single hit detection
efficiency
Double hit detection efficiency
26
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.
photon
hadron
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
1(E1)
R
=
Arm2
Measurement
Arm2 MC
R
140 m
140m
2(E2)

I.P.1
M = θ√(E1xE2)
28
Analysis Step.5
 Spectra in Arm1, Arm2 common rapidity
 Energy scale error not included in plot (maybe correlated)
 Nine = σine ∫Ldt
(σine = 71.5mb assumed)
29
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
Systematic errors
Major sources of
systematic error
• Absolute energy
• PID
• Multi-hit detection
efficiency
• Beam position
31
Comparison with Models
32
Comparison with Models
DPMJET 3.04 QGSJET II-03 SIBYLL 2.1 EPOS 1.99 PYTHIA 8.145
33
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.
DPMJET3, PYTHIA8: good agreement in 0.5-1.5TeV at η>10.94 but large difference
>2TeV.
QGSJET-II gives overall lower photon yield, especially in small η.
SIBYLL2 shows good spectral shape >0.5TeV at η>10.94 but only half yield
34
Impact on CR physics
35
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?
 What happens at LHC energy?
=> On-going
30g/cm2
36
Future
37
Next step
 Analysis
– π0 energy spectrum
• Fundamental in EM component of air shower
– PT spectrum for photon and π0
• Extrapolation to the non-observable phase space
– Hadron (neutron) analysis
• Elasticity in the air shower development
– Analysis for 900GeV collision data
• Energy dependence of the interaction
 Measurements
–
–
–
–
14 TeV p-p collisions at LHC after 2014
Study for p-Pb data taking at LHC (2012)?
Detector upgrade for 14TeV run
Measurements at other accelerators?
38
Measurements at other colliders?
-hadron collider is not only LHC Systematic forward measurements for different
types of collision using the LHCf detectors
 p-p collision at lower energy
– No dedicated forward measurement since UA7 at
SppS (√s=630GeV)
– Lower energy but wide acceptance required (LHC
900GeV is not appropriate)
 Ion collisions to understand p-p to A-A
– In CRs, p-N, N-N, Fe-N are important (N; Nitrogen)
– p-Pb collisions at LHC
39
LHCf stands for
Long-island Hadron Collider forward??
Potential Advantages
– Having ZDC installation slots close to IP
• possible wide rapidity coverage
• π0->2γ pair detectable
– √s=500GeV p-p collision. Equivalent to UA7, but
more data available with LHCf detectors.
– Ion collisions; essential for CR physics
• excellent if light ions are available
η = -ln(tan(θ/2))
When θ = (415mm/2)/(9.8m+14.3m) = 8.6 mrad
=> η = 5.44
40
π0 energy and photon opening angle
 Feasibility to test the existing models is under study by MC
 Detail input of the geometry (crucial to know the rapidity
41
coverage) is necessary
Summary
 LHCf has successfully finished first measurements
at LHC for √s=0.9 and 7 TeV p-p collisions.
 First analysis result of single photon spectra is
published.
 Impact of LHCf results on CR physics is in
investigation.
 Further measurements at LHC 14TeV p-p
collisions is programmed after 2014.
 LHC p-Pb run in study.
 Measurements at other accelerators in study.
42
Backup
43
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 44
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
45
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
46
Where is zero degree?
Beam center LHCf vs BPMSW
LHCf online hit-map monitor
Effect of 1mm shift in the final spectrum
47
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
48
Last forward experiment at hadron
collider – UA7 -
 No sizable violation of Feynman scaling in forward
 √s = 630GeV, Elab = 2x1014 eV
49
π0 energy flow at 500GeV p-p
collisions predicted by PYTHIA8
Geometrical acceptance and rapidity coverage
50mm/20m (2.5mrad acceptance)
200mm/25m (8mrad acceptance)
400mm/20m (20mrad acceptance)
50