YERMIA Frederic Vietri sul mare 2006 1 –Alessandria - Italy, Dipartimento di Scienze e Tecnologie...
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Transcript of YERMIA Frederic Vietri sul mare 2006 1 –Alessandria - Italy, Dipartimento di Scienze e Tecnologie...
YERMIA Frederic Vietri sul mare 2006 1
Machine Induced Background in the ALICE Muon Trigger System
in pp Data taking
Yermia Frédéric
INFN Torino
Yermia Frédéric
INFN Torino
Secondo Convegno Nazionale sulla Fisica di ALICE30 Maggio - 1 Giugno 2006 –
Vietri sul Mare (SA) -
YERMIA Frederic Vietri sul mare 2006 2
Overview
• Introduction:
Sources of beam-related background
Simulation environment
• Scoring plane (simulation Input)
• Fluxes in trigger chambers
• Strategy and conclusions
YERMIA Frederic Vietri sul mare 2006 3
ALICE experiment
Central detectors(identification of hadrons,electrons and photons)
Forward muon spectrometeridentification of muons forheavy flavour study
Muon trigger system :
● 2 stations (MT1 & MT2) of 2 planes each
● 72 Resistive Plate Chambers (RPC) ~2.7 m 0.7 m ( 144 m2)
● 20992 electronics channels
YERMIA Frederic Vietri sul mare 2006 4
Introduction
beam protons may undergo elastic and inelastic scattering with the residual gas nuclei (mainly O & C) in the LHC long straight
sections (20< |z| <270 m) => induce fluxes of secondary particles in ALICE
Affect the ALICE radiation environment
increase of the detector background
Machine induced background is proportional to the beam current (Intensity) while particles fluxes produced in pp collisions scale with luminosity at IP
MIB be crucial in pp collisions
depends on machine operating conditions
is different for different run scenarios
YERMIA Frederic Vietri sul mare 2006 5
Introduction
Among the ALICE detectors, the muon trigger system is one of the most sensitive to the machine induced background.
•The Resistive Plate Chamber’s (RPC’s) rate capability might be saturated by a too high background level.
• Detector lifetime.
PURPOSE: Evaluate the hit rate on the muon trigger detector due to the beam-gas background in pp mode
(update of early studies performed 2 years ago in ALICE-INT-2003-041)
YERMIA Frederic Vietri sul mare 2006 6
Details of the simulation of the p-A collisions
• Original proton interactions with the nucleus of the residual gas were simulated along the whole length of the LHC Ring sectors.
• Beam–gas interactions in the experimental aera not been into account.
• New gas pressure estimates (LHC Project Report 674) (see next slide)
• High energy hadrons and muons are considered
– main component (critical to the detector performance)
– component (and as well) not studied
– Secondary particles from Ring 1 & 2 beam losses were transported up to 2 planes located at |z|= 22 m from IP2:
e
SCORING PLANE (input of transport simulations)
•Secondary particle cascades can be initiated in the SS2 and transport through the LHC tunnel.
•Interactions in machine elements
•residual gas in the vacuum pipe (H, O and C)
YERMIA Frederic Vietri sul mare 2006 7
Previous pressure calculations (LHC Project Note 273)
Previous MIB studies (ALICE-INT-2003-041)
New pressure calculations (LHC Project Report 674)
A factor 5 in less in mean.
Details of the simulation of the p-A collisionsUpdate and study of the beam-gas background environment
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YERMIA Frederic Vietri sul mare 2006 8
ALICE Simulation Framework
• AliRoot HEAD February 2006 with ROOT v5-09-01
• AliGenHaloProtvino event generator (Interface between the scoring plane and ALICE experimental region)
– input file in ASCII format containing the result of the calculation of the particle beam halo at z=+-22 m (scoring plane)
– particles coming from both sides
• Set-up configuration – L3 magnet
– exp. hall
– central detectors : ITS, TPC
– muon spectrometer (detectors and shieldings)
YERMIA Frederic Vietri sul mare 2006 9
Muon Spectrometer geometry
19
Z (m
)
18
16
YTrigger stations (16 & 17 m)
Muon filter (14.7-15.9 m)
beamshield
Plug (18-18 m & R=1.1 m)
X22
YERMIA Frederic Vietri sul mare 2006 10
Scoring Plane
Particles Muons Hadrons Total Protons NeutronsPions // Kaons
Mean number by second
4.9 e+04 8.4 e+05 8.9 e+05 1.0 e+05 4.0 e+053.1 e+05 //
2.8 e+04
Mean number by bunch (40 MHz)
0.0012 0.0210 0.0223 0.0025 0.0100 0.0085
A factor 20 more for hadron contributions w.r.t. muons
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pA collision Origins in the SS2
All particles on the scoring plane
Muons HadronsSimilar structures of the vaccum quality
Muons are produced further than hadrons
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Scoring Plane: Muons kinematics
X (m) E (TeV)
Theta (deg) E (TeV)
• Uniformity
• Some high energetic muons
• Peaked at small emission angle
R (
m)
YERMIA Frederic Vietri sul mare 2006 13
Hadronic background
X (m) E (TeV)
Theta (deg) E (TeV)
• Uniformity
• Quasi beam
• Machine effect (material)
• Energetic hadrons at R= 0.5 m
• Small emission angle
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Flux on scoring plane weighted by EX-Y coordinates (Hz.GeV/cm²)
h+ h-
Hot Spot
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Fluxes on MT11 & MT22X-Y coordinates (Hz./cm²)
Hot spot max.
40 Hz/cm²
Hot spot max. 80 Hz/cm²
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Fluxes on MT22Ring 1 and 2 contributions
Hot spot max. 4 Hz/cm²
Hot spot max. 80 Hz/cm²
Main contribution from Ring 2
YERMIA Frederic Vietri sul mare 2006 17
Fluxes on MT22 X-Y coordinates (Hz./cm²)
MUONS HADRONS ELECTRONS
Hot spot max. 60 Hz/cm² Hot spot max. 20 Hz/cm² Hot spot max. 1 Hz/cm²
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Scoring plane conditioned by the hits on MT22 (Hz./cm²)
Muons are the main source of hits on the MT22 but distributed uniformly
Hadron hot spot which corresponds to energetic particle hot spot
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Scoring plane: hits from hot spot MT22
High energetic hadron particles
YERMIA Frederic Vietri sul mare 2006 20
Hit creation vertex from MT22
Hadronic particles interact in the plug
XY projection of the hit creation vertex at z= - 18 m (Hz./cm²)
Tunnel entrance
Scoring plane
plug
Hot spot in the plug due to hadronic
particles
X (m)
Y (m)
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Hot spot MT22 from R2:
p-A collisions Vertex
Hadronic particles are created in the lhc tunnel at
120< z < 130 m
YERMIA Frederic Vietri sul mare 2006 22
120 mDipole D2
IP
LHC Tunnel (IR8)
The Dipole D2 makes positive particles converge towards IP and makes negative particles diverge
Negative particle hot spot on scoring plane
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Summary & conclusion
• Mean rate on trigger stations: 1-10 Hz/cm²
• Hot spot: 40-80 Hz/cm² => Concentrated on 1 RPC per plane
• RPC ageing test in maxi avalanche mode: carried out successfully up to 500 Mhits/ cm²
However the results presented here should be quite pessimistic.
Not included in this simulation:
• Compensation magnet, at -20 > z > -21m, 0.2 < R < 0.6m
• LEP shielding in the tunnel
• Further shielding could be foreseen if needed
• Increase the transverse side of the plug (agreed)
• Dedicated (small shielding for hot spot)
• Close contributions not included
Strategy
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• BACKUP SLIDES
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•Resistive Plate Chambers (RPCs)Small (150 m2) and accessible system, based on single-gap RPCs with x-y readout.
-Low resistivity bakelite ( 109 .cm)(Frati laminati)
-Two linseed oil layers to smooth the bakelite surface
-Copper strips (1 cm, 2 cm or 4 cm width)
Trigger detector II
2 trigger stations:2 detection planes per station
18 RPCs per plane
The chambers are read-out on both sides by means of 2 planes of orthogonal strips oriented along the horizontal (X) and vertical (Y) directions (perpendicular to the beam axis) and arranged in projective geometry.
Y
Z
X
(General Tecnica production)
YERMIA Frederic Vietri sul mare 2006 26
➢ Two bakelite planes of 2 mm ( 109 .cm)
➢ High voltage of about 8 kV
➢ Gas gap of 2 mm (51% Ar + 7% iC4H10 + 41% C2H2F4 + 1% SF6
➢ Two perpendicular planes of strips (1 cm, 2 cm or 4 cm width)
➢ Signal picked-up at the extremity of the strips with specific connectors➢ Read-out by a dedicated FEE
RPC working in streamer mode for heavy ions collisionsstrips +
strips -
highvoltage
spacerbakelite
gasgraphite
plasticinsulation
Alternative working mode for pp data taking:Maxi avalanche mixture:
10% iC4H10 + 89.7% C2H2F4 + 0.3% SF6
HV: 10 kV
avalanche-like mode with our FEE developed for streamer mode i.e. without an amplification stage.
Trigger detector
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Scoring Plane
MUON Origins Hadron Origins
Weighted by energy Weighted by energy
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Hot spot MT11 from R1: Interaction Vertex from R1
Particles interact in the front absorber and the iron wall
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Hit densities & background composition
Particles
e-/e+ pi+/pi- K+/K- proton
muon
78 % 2.8 % 0.01 %
16.4 %
2.8 %
Chambers MT11 MT12 MT21 MT22
Hits/second (x 100 000)
Without trigger time cut
0.77 0.84 1.16 1.14
Hits/second
(x 100 000)
Wit trigger time cut
0.10 0.12 0.18 0.18
•Max hit density: 0.3 10-5 hits/cm2
w.r.t. 2 10-3 hits/cm2 in Pb-Pb
YERMIA Frederic Vietri sul mare 2006 30
Scoring plane: hits from hot spot MT22
Condition: hits inside hot spot
Confirmation of the hot spot position on scoring plane
YERMIA Frederic Vietri sul mare 2006 31
Hit creation vertex from MT22
Hit particles are created in the whole trigger region
R vs z of the hit creation vertex (Hz./cm²)
plug
Trigger stations
beamshield
Iron wall
cavern
Scoring plane
YERMIA Frederic Vietri sul mare 2006 32
IP
Proton beam
+ Positive particles
D2
D1
Secondary particles
Proton beam
Negative particles