LHCf Report Takashi SAKO for the LHCf Collaboration 18-Dec-2009 CERN Main Auditorium.
Recent results on neutral particles spectra from the LHCf experiment Massimo Bongi - INFN (Florence,...
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Transcript of Recent results on neutral particles spectra from the LHCf experiment Massimo Bongi - INFN (Florence,...
Recent results on neutral particles spectra from the
LHCf experiment
Massimo Bongi - INFN (Florence, Italy)
LHCf Collaboration
13th ICATPP Conference onAstroparticle, Particle, Space Physics and Detectors for Physics
ApplicationsVilla Olmo - Como, Oct 3rd – 7th, 2011
Massimo Bongi – ICATPP – 3rd October 2011 – Como
High-energy cosmic rays
LHC
SPS
AUGER
Tevatron
E [eV]
Recent excellent observations (e.g. Auger, HiRes, TA) but the
origin and composition of HE CR is still unclear
2
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Development of atmospheric showers
LHC forward (LHCf) experiment
1019 eV proton
The dominant contribution to the shower development comes from particles emitted at low angles (forward region).
Experimental tests of hadron interaction models are necessary
LHC gives us the unique opportunity to study hadronic interactions at 1017eV
7 TeV + 7 TeV→ Elab ≈ 1 x 1017 eV
3.5 TeV + 3.5 TeV → Elab ≈ 3 x 1016 eV
450 GeV + 450 GeV → Elab ≈ 4 x 1014 eV
The depth of the maximum of the shower Xmax in the atmosphere depends on energy and type of the primary particle
Several Monte Carlo simulations (different hadronic interaction models) are used and they give different answers about composition
3
Massimo Bongi – ICATPP – 3rd October 2011 – Como
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, JapanH.Menjo Kobayashi-Maskawa Institute, Nagoya University, JapanK.Yoshida Shibaura Institute of Technology, Japan
K.Kasahara, T.Suzuki, S.Torii Waseda University, JapanY.Shimizu JAXA, 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 and Universita’ di Firenze, ItalyK.Noda, A.Tricomi INFN and Universita’ di Catania, Italy
J.Velasco, A.Faus IFIC, Centro Mixto CSIC-UVEG, Spain
A-L.Perrot CERN, Switzerland
The LHCf collaboration
4
Massimo Bongi – ICATPP – 3rd October 2011 – Como
LHCf experimental set-up
96mm
ATLAS
140m
LHCf Detector (Arm1)
ATLASLHCb
CMS
ALICELHCf
Beam pipe
Protons Charged particles (+)
Charged particles (-)
Neutral particlesTAN
5
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Arm1 detectorScintillating Fibers + MAPMT:
4 pairs of layers (at 6, 10, 30, 42 X0),tracking measurements (resolution <
200 μm)
Plastic Scintillator: 16 layers, 3 mm thick,
trigger and energy profile measurement
40mm
20mm
Absorber: 22 tungsten
layers, 44 X0, 1.55
• Sampling e.m.
calorimeters:
each detector has two
calorimeter towers
which allow to reconstruct 0
• Front counters:
thin plastic scintillators, 80x80 mm2
monitor beam condition
estimate luminosity
reject background due to beam -
residual gas collisions by coincidence
analysis
6
Massimo Bongi – ICATPP – 3rd October 2011 – Como
25mm
32mm
Arm2 detector
Plastic Scintillator: 16 layers, 3 mm thick,
trigger and energy profile measurement
Absorber: 22 tungsten
layers, 44 X0, 1.55
• Sampling e.m.
calorimeters:
each detector has two
calorimeter towers
which allow to reconstruct 0
• Front counters:
thin plastic scintillators, 80x80 mm2
monitor beam condition
estimate luminosity
reject background due to beam -
residual gas collisions by coincidence
analysis
Silicon Microstrip:4 pairs of layers (at 6, 12, 30, 42 X0),
tracking measurements (resolution ~ 40 μm)
7
Massimo Bongi – ICATPP – 3rd October 2011 – Como
What LHCf can measureEnergy spectra and transverse momentumdistribution of: gamma rays (E>100 GeV,
dE/E<5%) neutral hadrons (E>few 100 GeV,
dE/E~30%) π0 (E>600 GeV,
dE/E<3%)in the pseudo-rapidity range η>8.4
Multiplicity @ 14TeV Energy Flux @ 14TeV
Low multiplicity
High energy flux
(simulated by DPMJET3)
η
∞
8.5
Front view of calorimeters,
@100μrad crossing angle
Projected edge of beam pipe
mm
10
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Event categoriesleading baryon
(neutron)
multi meson production
π0 photon
hadron event
π0 event
photon event
LHCf calorimeters
11
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Summary of operations in 2009 and 2010
With stable beams at 450GeV+450GeVTotal of 42 hours for physics (6th–15th Dec. 2009, 2nd-3rd,27thMay 2010)
~ 105 showers events in Arm1+Arm2
With stable beams at 3.5TeV+3.5TeVTotal of 150 hours for physics (30th Mar.-19th Jul. 2010)
Different vertical positions to increase the accessible kinematical range
Runs with or without beam crossing angle
~ 4·108 shower events in Arm1+Arm2
~ 106 0 events in Arm1+Arm2
StatusCompleted program for 450GeV+450GeV and 3.5TeV+3.5TeV
Removed detectors from tunnel in July 2010 (luminosity >1030 cm-2s-1)
Post-calibration beam test in October 2010
Upgrade to more rad-hard detectors to operate at 7TeV+7TeV in 2014
12
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Photon energy spectra analysisE X P E R I M E N TA L D ATA
• p-p collisions at √s=7 TeV, no crossing angle (Fill# 1104, 15th May 2010 17:45-21:23)
• Luminosity: (6.3÷6.5) x 1028 cm-2s-1 (3 crossing bunches)
• Negligible pile-up (~0.2%)
• DAQ Live Time: 85.7% (Arm1), 67.0% (Arm2)
• Integrated luminosity: 0.68 nb-1 (Arm1), 0.53 nb-1 (Arm2)
M O N T E C A R LO D ATA
• 107 inelastic p-p collisions at √s=7 TeV simulated by several MC codes:
DPMJET 3.04, QGSJET II-03, SYBILL 2.1, EPOS 1.99, PYTHIA 8.145
• Propagation of collision products in the beam pipe and detector response simulated by EPICS/COSMOS
A N A LY S I S P R O C E D U R E
1. Energy Reconstruction: total energy deposition in a tower (corrections for light yield, shower leakage, energy calibration, etc.)
2. Rejection of multi-hit events: transverse energy deposit
3. Particle identification (PID): longitudinal development of the shower
4. Selection of two pseudo-rapidity regions: 8.81 < η < 8.99 and η > 10.94
5. Combine spectra of Arm1 and Arm2 and compare with MC expectations 13
Massimo Bongi – ICATPP – 3rd October 2011 – Como
1 TeV π0 candidate event
25mmtower
32mmtower
scintillator layers – longitudinal development
silicon layers – transverse energy
Y view
X view
600 GeVphoton
420 GeVphoton
Energy reconstruction
PID
Hit position Multi-hit
identification
π0 mass reconstruction
14
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Energy reconstruction Energy reconstruction: Ephoton = f( Σ Ei ) (i = layer index)
(Ei = A x Qi determined at SPS; f() determined by MC and checked at
SPS) Impact position from lateral distribution Position dependent corrections:
• light collection non-uniformity• shower leakage-out (and 2 mm edge cut)• shower leakage-in
Light collection non-uniformity Shower leakage-in
correction
2 mm
Shower leakage-out
25mmtower
32mmtower
15
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Multi-hit rejection Rejection of multi-hit events is mandatory especially at high energy (> 2.5 TeV)
Multi-hit events are identified thanks to position sensitive layers in Arm1 (SciFi) and Arm2 (Si-mstrip)
Arm1
Arm2
Small tower Large towerArm2
Multi-hit detection efficiency
Single-hit detection efficiency
16
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Particle identification
500 GeV < EREC < 1 TeV
photon
hadron
44 X0
1.55 λ
L90%: longitudinal position containing 90% of the shower energy
Photon selection based on L90% cut Energy dependent threshold in order to
keep constant efficiency εPID = 90%
Purity P = Nphot/(Nphot+Nhad) estimated by
comparison with MC Event number in each bin corrected by P/εPID
MC photon and hadron events are
independently normalized to data
Comparison done in each energy
bin
LPM effects are switched on17
Massimo Bongi – ICATPP – 3rd October 2011 – Como
π0 mass reconstruction
m 140
R
I.P.1
1(E1)
2(E2)
140 mR
m ≈ θ√(E1xE2)
Energy scale can be checked by π0 identification
Mass shift observed both in Arm1 (+7.8%) and Arm2 (+3.7%)
Many checks have been done to understand the energy scale difference: the estimated systematic uncertainty on π0 reconstruction is 4.2%
Conservative approach: no correction is applied to the energy scale, but an asymmetric systematic error is assigned
Arm2MC
Peak :135.0 ± 0.2MeV
18
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Comparison between the two detectors
R1 = 5 mmR2-1 = 35 mmR2-2 = 42 mm
We define two common pseudo-rapidity and azimuthal regions for
the
two detectors: 8.81 < η < 8.99, Δφ = 20˚ (large tower)
η > 10.94, Δφ = 360˚ (small tower)
Normalized by the number of inelastic collisions
(assuming σine = 71.5 mb)
General agreement between the two detectors
(deviation in small tower within the error)
Δφ
Red points: Arm1 detector Blue points: Arm2 detectorFilled area: uncorrelated systematic uncertainties 19
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Combined photon spectragray hatch: systematic error error bars: statistical error
20
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Comparison with MCgray hatch: systematic error magenta hatch: MC statistical
error
DPMJET 3.04 QGSJET II-03 SYBILL 2.1 EPOS 1.99 PYTHIA 8.14521
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Preliminary π0 spectra Mass range selection: +/- 10 MeV
around the measured peak
Acceptance depends on energy and
transverse momentum (lowest energy is
limited by maximum angle between
photons)
Comparison with MC is on-going
Extend the analysis
to events with two
photons in the same
towerm ≈ θ√(E1xE2)Eπ = E1+E2
22
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Summary and outlook Single photon analysis at 3.5 TeV + 3.5 TeV:
• first comparison of various hadronic interaction models with experimental data in a challenging phase space region
• very safe estimation of systematics• no model perfectly reproduces LHCf data, especially at high
energynew input data for model developersimplications for HE CR physics under study
Neutral pion analysis at 3.5 TeV + 3.5 TeV is in progress:• compare pion spectra with MC• include events with two gammas hitting the same tower• the same analysis can be extended to η and K0 particles
Other analysis: complete the analysis at 450 GeV + 450 GeV, neutrons, transverse momentum distributions, extend pseudo-rapidity range,…
We are upgrading the detectors to improve their radiation hardness (GSO scintillators):• we will come back on the LHC beam for the 7 TeV + 7 TeV runs• discussion is under way to come back for possible p-Pb runs in
2013
23
Massimo Bongi – ICATPP – 3rd October 2011 – Como
AGASA SystematicsTotal ±18%
Hadr Model ~10% (Takeda et al., 2003)
Open Issues on UHECR spectrum
M NaganoNew Journal of Physics 11 (2009) 065012
Depth of the max of the shower Xmax in the atmosphere
AUGERHiRes
25
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Front counters• Thin scintillators with 8x8cm2 acceptance,
which have been installed in front of each main detector.
• To monitor beam condition. • For background rejection of
beam-residual gas collisions by coincidence analysis
Schematic view of Front counter
26
Detector vertical position and acceptance Remotely changed by a manipulator( with accuracy of 50 mm)
Distance from neutral center Beam pipe aperture
Data taking modewith different positionto cover PT gap
N
L
G
All g from IP
Viewed from IP
Neutral flux center
N
L
7TeV collisions
Collisions with a crossing angle lower the neutral flux center thus enlarging Pt acceptance
27
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Expected results @ 14 TeV collisions
n0
Energy spectra and transverse momentum distribution of:
• photons (E > 100 GeV): E/E < 5%
• neutral pions (E > 500 GeV): E/E < 3%
• neutrons (E > few 100 GeV): E/E ~ 30%
in the pseudo-rapidity range > 8.4
28
Massimo Bongi – ICATPP – 3rd October 2011 – Como
LHCf energy resolution
2.5 x 2.5 cm2 tower 2.0 x 2.0 cm2 tower
Energy resolution < 5% at high energy, even for the smallest tower
29
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Arm1 position resolutionN
um
ber
of
even
tN
um
ber
of
even
t
x-pos[mm]
y-pos[mm]
200 GeV electrons
E[GeV]
E[GeV]
σX=172µm
σY=159µmσ X
[mm
]σ Y
[mm
]
30
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Arm2 position resolutionPosition Resolution X Side
0
20
40
60
80
100
120
0 50 100 150 200 250
Energy (GeV)
Re
so
luti
on
(m
icro
ns
)
Data
Simulation Spread Out
Position Resolution Y Side
0
20
40
60
80
100
120
140
160
0 50 100 150 200 250
Energy (GeV)
Re
so
luti
on
(m
icro
ns
)
Data
Simulation Spread Out
x-pos[mm]
y-pos[mm]
Alignment has been taken into account
200 GeV electrons
E[GeV]
E[GeV]
σX=40µm
σY=64µmσ X
[µm
]σ Y
[µm
]
31
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Estimation of pile-up
!)(
N
eNP
N
• When the circulated bunch is 1x1, the probability of N collisions per crossing is:
• The ratio of the pile-up event is:
• The maximum luminosity per bunch during runs used for the analysis is
2.3x1028cm-2s-1
• So the probability of pile-up is estimated to be 7.2%, with σ=71.5mb and
frev = 11.2 kHz
• Taking into account our calorimeter acceptance for an inelastic collision
(~0.03) only 0.2% of events have multi-hit due to pile-up
32
Massimo Bongi – ICATPP – 3rd October 2011 – Como
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
33
Massimo Bongi – ICATPP – 3rd October 2011 – Como
p0 mass vs p0 energy
Arm2 data
No strong energy dependence of reconstructed
mass
34
Massimo Bongi – ICATPP – 3rd October 2011 – Como
2g invariant mass spectrum @ 7 TeV
Arm2 detector, all runs with zero crossing angleTrue η mass: 547.9 MeVMC reconstructed η mass peak: 548.5 ± 1.0 MeVData reconstructed η mass peak: 562.2 ± 1.8 MeV (2.6% shift)
35
Massimo Bongi – ICATPP – 3rd October 2011 – Como
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
±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)
36
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Systematic uncertainties• Energy reconstruction (detector response, from beam test at SPS): 3.5%
• Multi-hit rejection (estimated by comparing true MC and reconstructed MC
spectra after MH cut): from 1% for E < 1.5 TeV to 20% at E = 3 TeV
• PID (by comparing 2 different approaches): 5% for E < 1.7 TeV, 20% for E > 1.7
TeV
• Beam center position (by comparing position measured by LHCf and by Beam
Position Monitors): 5÷20 % varying with energy and pseudo-rapidity
• Luminosity (Front Counter measurement during Van der Meer scans): 6.1%, it
causes an energy independent shift of spectra, not included in photon spectra
• Energy shift (π0 mass shift, asymmetric): 7.8% Arm1, 3.7% Arm2
Total energy scale systematic: -9.8% / +1.8% for Arm1
-6.6% / +2.2% for Arm2
Systematic uncertainty on spectra is estimated from the difference
between normal spectra and energy scaled spectra37
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Background
Beam-Gas backgroundsSecondary-beam pipe backgrounds
1. Pile-up of collisions in one beam crossing Low Luminosity fill, L=2.3x1028cm-2s-1
7.2% pile-up at collisions, 0.2% at the detectors.
2. Collisions between secondary's and beam pipes Very low energy particles reach the detector (few % at 100GeV)
3. Collisions between beams and residual gas Estimated from data with non-crossing bunches. ~0.1%
38
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Arm1
Arm2
gamma-ray like hadron like
Acceptance is different for the two arms.Spectra are normalized by # of -ray and hadron like events.
Energy spectra at 900 GeV
PRELIMINARY
PRELIMINARY
Only statistical errors are
shown
39
Massimo Bongi – ICATPP – 3rd October 2011 – Como
Radiation damage studies
30 kGy
Dose evaluation on the
basis of LHC reports on
radiation environment at
IP1
~ 100 Gy/day @ 1030 cm-
2s-1 luminosity are
expected
~ 10 kGy during few
months operation lead to
~ 50% light output
decrease
continuous laser
calibration to monitor
scintillators and correct
for the decrease of light
output
test of Scintillating fibers and
scintillators
40