Transcript Document

Status and Physics Programme of
LHCf experiment
Sergio Ricciarini
for the LHCf collaboration
Istituto Nazionale di Fisica Nucleare (INFN)
Structure of Florence, Italy
Workshop on “Diffractive and electromagnetic processes at LHC”
ECT Trento - 5 January 2010
Summary
• 1. Physics motivations
• 2. LHCf experimental setup
• 3. LHCf physics performances
• 4. Preliminary results for 2009 operation
• 5. Future programme
S. Ricciarini 2010-01-05
1.
Physics motivations
The LHCf Collaboration
USA
LBNL Berkeley:
W.C. Turner
CERN:
D. Macina, A.L. Perrot
FRANCE
Ecole Polytechnique Paris:
M. Haguenauer
SPAIN
IFIC Valencia:
A.Faus, J.Velasco
ITALY
Firenze University and INFN: O.Adriani,
L.Bonechi, M.Bongi, G.Castellini,
R.D’Alessandro, H. Menjo, P.Papini,
S.Ricciarini, A.Viciani
Catania University and INFN: A.Tricomi
JAPAN
STE Laboratory Nagoya University:
K. Fukui, Y.Itow, T.Mase, K.Masuda,
Y.Matsubara, H.Matsumoto, T.Sako, K.Taki
Konan University Kobe: Y.Muraki
University of Tokyo: Y.Shimizu
Kanagawa University Yokohama: T.Tamura
Waseda University: K.Kasahara, M.Mizuishi,
S.Torii
Shibaura Institute of Technology Saitama:
K.Yoshida
S. Ricciarini 2010-01-05
LHCf: LHC “forward” experiment
• The smallest of the six LHC
experiments.
LHCf:
Calibration of hadronic Monte Carlo
used in HECR Physics with data
collected at LHC
• LHCf is fully dedicated to High
Energy Cosmic Rays (HECR)
Physics.
• Experimental observation of HECR
(E > 1014 eV) achieved only through
Extensive Air Showers (EAS).
• LHCf will provide useful data to
calibrate the hadronic interaction
models used in Monte Carlo
simulations of EAS.
S. Ricciarini 2010-01-05
EAS: Extensive Air Showers
• Determination of E and M of HECR primary
depends on comparison between Monte Carlo and
experimental description of EAS.
• The dominant contribution to the energy flux is in
the very forward region ( ≈ 0) and mainly
depends on the first hadronic interaction.
• Hadronic Monte Carlo codes need tuning with beam-test data.
• In this forward region the highest energy measurements of π0 production
cross section were obtained by UA7 at SppS: Elab = 1014 eV.
• For LHCf: √s = 14 TeV → Elab = 1017eV
S. Ricciarini 2010-01-05
Cosmic ray spectra at GZK cutoff
GZK cutoff (1020 eV) would
limit energy to 1020 eV for
protons, due to Cosmic
Microwave Background
p γ(2.7K) → Δ → N π
Based on data
presented at the 30th ICRC
Merida (Mexico).
Figure prepared by Y. Tokanatsu
Different results between
different experiments.
Agasa points toward
super-GZK events (and
therefore exotic physics).
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Importance of Monte Carlo tuning
Berezinsky 2007
AGASA energy systematics 18% of which
10% from hadron interaction model
(QGSJET, SYBILL)
Berezinsky 2007
Same data after
arbitrarily
scaling energy:
AGASA
HiRes
Yakutsk
Auger
x 0.9
x 1.2
x 0.75
x 1.2
S. Ricciarini 2010-01-05
HECR composition
The depth of the
shower maximum
Xmax in the
atmosphere
depends on energy
and type of primary
particle.
Unger, ECRS 2008
Different hadronic
interaction models
give different
answers about the
composition of
HECR.
S. Ricciarini 2010-01-05
2.
LHCf experimental setup
LHCf experimental setup
• Two independent electromagnetic calorimeters equipped with different
position sensitive layers, on both sides of IP1.
• Measure energy and impact point of γ from π0 decays and neutrons from pp
interaction with “very-forward” kinematics: pseudorapidity η > 8.4 or,
equivalently, angle from beam axis θ < 450 μrad.
”Arm 1”:
”Arm 2”:
W absorber +
scintillator layers.
W absorber +
scintillator layers.
ATLAS interaction
point (IP1)
Scintillating fibers.
140 m
140 m
8 cm
n
Silicon microstrips.
π0
γ
6 cm
γ
S. Ricciarini 2010-01-05
LHCf experimental setup
• Each “arm” is installed in the “Total
Absorber for Neutral particles” (TAN)
140 m away from IP 1.
• Here the beam pipe splits in 2 separate
tubes.
TAN
Arm 1 (or 2)
Protons - Beam 2
9.6 cm
• No background from charged
particles, swept away by magnets
(dipole D1).
Charged particles
Arm 1 Neutral particles
IP 1
Protons - Beam 1
S. Ricciarini 2010-01-05
“Arm 1” detector
Calorimeter:
17 W layers (7 mm or
14 mm thick);
16 scintillator layers
(3 mm thick).
Total thickness 22 cm:
44 X0
1.7 λI
4 cm
2 towers
stacked
vertically
with 5 mm 2 cm
gap.
beam axis
Tracking: 4 X-Y double layers of scintillating fiber
(SciFi, 1mm cross-section) at 6, 10, 30, 42 X0.
S. Ricciarini 2010-01-05
“Arm 2” detector
2 towers stacked on their edges and offset from one another.
Same structure of calorimetric layers as Arm 1.
3.2 cm
2.5 cm
beam axis
Tracking: 4 X-Y double layers of Si microstrips
(read-out pitch 160 μm) positioned at 6, 12, 30, 42 X0.
S. Ricciarini 2010-01-05
Arm 2 assembly
scintillator
and light guide
front-end hybrid
W layer
Si X
Si Y (on
opposite
side)
Si microstrip
sensor
fiberglass pitch adapter
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Arm 2 assembly
Si microstrip sensor
scintillator layer (2 towers)
S. Ricciarini 2010-01-05
Assembled LHCf
Arm 2
Arm 1
29 cm
9 cm
S. Ricciarini 2010-01-05
3.
LHCf physics performances
Transverse projection in the TAN slot
Arm 1: maximization of the
acceptance for vertical beam
crossing angle (it can be moved
down by 2 cm)
Dimensions in mm
Arm 2: maximization of the
acceptance in R (distance
from beam center)
Both detectors are kept at +12 cm
(“garage”) when beam is not stable, to
minimize radiation damage of scintillators
S. Ricciarini 2010-01-05
Detectable kinematics for γ (Arm 1)
140
0
kinematics depend
on beam vertical
crossing angle at IP1
detectable kinematics
limited by the projection
of dipole D1 vacuum
pipe on the detector
impact plane (first W
layer)
expected background (beam-gas/pipe) < 1%
S. Ricciarini 2010-01-05
Detector acceptance vs. γ impact point
of the incoming γ
Arm 1
Arm 2
0 rad beam crossing angle
Fraction of showers
fully contained in the
fiducial acceptance
volume (2 mm cut on
lateral tower edge) for
0μrad beam vertical
crossing angle.
It does not depend on
energy.
of the γ impact point
Effective geometrical acceptance depends on impact point on detector.
Detectors can be moved up/down by few cm to efficiently cover the
whole kinematic range allowed by D1 projection.
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Position resolution for EM shower
σX = 40 μm
Measured at SPS beam
test by using auxiliary
tracking system
(ADAMO) with few μm
resolution
X position (mm)
number of events
number of events
Position of shower centre on Arm 2 first Si module for 200 GeV electrons
σY = 64 μm
Y position (mm)
Similar results for Arm 1 first module (SciFi): σ ≈ 170 μm
(with a design requirement < 200 μm)
S. Ricciarini 2010-01-05
Position resolution for EM shower
With impact point:
- transverse momentum;
- correction for lateral shower
leakage (ρMol (W) = 9 mm).
NOTE: correction is
independent from energy.
MIP equivalent particles
Arm 2 (Si)
Measured energy before and after
correction (SPS beam test data)
MIP equivalent particles
Measured position resolution
improves with energy
fiducial volume
S. Ricciarini 2010-01-05
Energy resolution for EM shower
Measured at SPS beam test with
electrons.
Energy defined as sum of
signals over all the scintillator
layers, after applying fiducial
volume cut and leakage
correction.
Excellent agreement between
simulation and beam-test data
for two different PMT gain
settings.
Resolution improves with
energy.
Linearity of read-out for all scintillator
layers and different PMT gains was
characterized with laser light up to
2x105 MIP equivalent particles.
S. Ricciarini 2010-01-05
Expected energy resolution for γ
Simulation for Arm 1 inner (smaller) tower.
Simulation validated with beam test as previously shown.
only physics
physics + PMT (L.G.)
physics + PMT (H.G.)
5%
region of interest
By using different PMT gains
(to avoid saturation of readout stages), resolution is
better than 5%
S. Ricciarini 2010-01-05
Model discrimination with γ
particles/bin (arbitrary units)
Expected gamma energy spectrum on Arm 1
inner tower at beam centre
- Simulation of 106 LHC interactions (i.e. 1 minute
exposure at 1029 cm-2s-1 luminosity) with 5% energy
resolution (conservative).
- Discrimination between various models is feasible.
Quantitative
discrimination with the
help of a properly
defined χ2 discriminating
variable based on the
spectrum shape.
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Model discrimination with neutrons
Expected neutron energy spectrum on Arm 1
inner tower at beam center
After introducing energy resolution
particles/bin (arbitrary units)
Original n spectrum
Given the limited depth (1.7 λI) only n interacting in the first
half of the calorimeter can be efficiently characterized
contamination
from K0
S. Ricciarini 2010-01-05
Model discrimination with π0
10mm Lower
Detector segmentation in two towers specifically
designed for π0 → γγ identification.
Detectable kinematics can be improved
by moving down the towers.
Arm 1 in “normal”
position
Arm 1 moved
down by 1 cm
gap between
towers
S. Ricciarini 2010-01-05
Model discrimination with π0
Simulated reconstructed spectrum
after 20 min at 1029 cm-2s-1 is in good
agreement with original spectrum
(using DPMJETIII).
Main systematic error comes
from energy resolution (here
assumed 5% conservatively).
S. Ricciarini 2010-01-05
Reconstructed π0 mass
Powerful tool:
- absolute energy calibration;
- reject background from
randomly correlated γ pairs.
From simulation, expected mass
resolution is better than 4%.
Performance verified at SPS beam
test (350 GeV proton beam on C
target) with worse conditions than
LHC:
- low γ energy (20 to 50 GeV);
- direct protons in the towers;
- multiple hits in the same tower.
≈ 250 π0 events
sigma: 8 MeV
resolution: 6%
Peak:
134 ± 5 MeV
π0 mass [MeV]
S. Ricciarini 2010-01-05
4.
Preliminary results
for 2009 operation
LHCf 2009 operation
• From End of October 2009 LHC restarted operation.
• LHCf collected > 6000 shower events at 450+450 GeV in stable beam
conditions with typically 4x4 or 5x5 bunch configuration.
– effective running time ~ 1 day, peak luminosity at IP1 < 1027 cm-2s-1.
• To minimize radiation damage, LHCf is allowed to move to running position
on beam axis from “garage” (+12 cm) only with stable beam.
• No stable beam at 1.2+1.2 TeV which means no data for LHCf at this energy
for this year.
S. Ricciarini 2010-01-05
Arm 1 γ event in inner tower
longitudinal profile
(inner tower)
(outer tower)
lateral profile
SciFi X
lateral profile
SciFi Y
S. Ricciarini 2010-01-05
Arm 2 γ event in inner tower
longitudinal profile
(inner tower)
lateral profile
Si microstrip X
lateral profile
Si microstrip Y
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Arm 2 neutron event in inner tower
longitudinal profile
(inner tower)
S. Ricciarini 2010-01-05
γ/neutron discrimination
Discrimination achieved
with longitudinal
profile.
Here L(90%) and
L(20%) expressed in X0.
L(90%) < 20 X0
for most γ.
neutrons
photons
Cut with 99%
hadron rejection power
(verified at beam test with protons)
S. Ricciarini 2010-01-05
Dipole D1
shadow
affects
only
particles
coming
from IP1
dN/(dE*BC)
Arm 1 preliminary γ plots
Collision data are identified by coincidence with
signal of “bunch crossing” at IP1.
“Single bunch” data are background from beamgas or beam-pipe interactions.
S. Ricciarini 2010-01-05
dN/(dE*BC)
Arm 2 preliminary γ plots
Different profiles of two data samples point out their different
origin (IP1 collision or beam background).
S. Ricciarini 2010-01-05
5.
Future programme
LHCf future running scenario
• After LHC restarts in February 2010, LHCf will take data for 1.2+1.2 TeV and
3.5+3.5 TeV collisions.
• LHCf will be removed when luminosity becomes too high (>1031 cm-2s-1,
with integrated luminosity 2 pb-1).
• LHCf will be reinstalled when beam energy reaches 5+5 TeV (end 2010).
• A second removal and a subsequent third installation are foreseen for 7+7 TeV
collisions.
• Why remove LHCf? Its scintillator and SciFi layers are designed to run during
beam commissioning (low luminosity).
S. Ricciarini 2010-01-05
Study of scintillator radiation damage
at 1 kGy light output
is reduced by 20%
scintillators and
SciFi used in LHCf
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Luminosity and radiation damage
• Initial LHC schedule implied a fast, low-luminosity energy ramp up to 7+7
TeV, but now long high-luminosity runs at lower energies are scheduled.
• 1 kGy total absorbed dose is reached, with detectors in running position, with
an integrated luminosity of 2 pb-1 for 3.5+3.5 TeV collisions.
• At 1030 cm-2s-1 this means ~ 1 month effective running time (but: with such
luminosity, few hours are already sufficient to collect enough statistics).
• Garage position is used when beam not stable (dose is reduced by 103).
• Light output and transparency is continuously calibrated by sending laser
pulses from ATLAS underground counting room (USA15) to the scintillator
layers.
S. Ricciarini 2010-01-05
Improve LHCf radiation hardness
• A new detector concept is being prepared for the second LHCf installation.
• Plastic scintillator will be replaced by GSO (rad-hard).
• The order and number of silicon X-Y double layers will be changed to
improve the energy measurement with the Si system and use it as cross-check
for scintillator measurement.
• The new detector will be precisely calibrated with a dedicated beam test before
installation.
S. Ricciarini 2010-01-05
γ energy measurement with Si layers
Showers from γ
mostly develop in
the first half of the
detector, where
currently there are 2
Si double layers (at
6 and 12 X0).
(whole calorimeter)
S. Ricciarini 2010-01-05
Conclusions
• LHCf is an interesting link between High Energy Cosmic Rays and accelerator
physics.
• LHCf is working very fine and already got its first data at LHC.
• With more statistics and increase of beam energy, as foreseen for the first
months of 2010, it will be possible to publish the first spectra and begin
discriminating among different Monte Carlo models.
S. Ricciarini 2010-01-05