YERMIA Frederic Vietri sul mare –Alessandria - Italy, Dipartimento di Scienze e Tecnologie Avanzate dell’Università del Piemonte Orientale P. Cortese and G. Dellacasa –Clermont-Fd - France, LPC, IN2P3/CNRS and Univerité Blaise Pascal A. Baldit, V. Barret, N. Bastid, G. Blanchard, P. Crochet, F. Daudon, A. Devaux, P. Dupieux, P. Force, B. Forestier, S. Grigoryan, F. Guerin, R. Guernane, C. Insa, F. Jouve, F. Manso, P. Rosnet, L. Royer and P. Saturnini –Torino - Italy, INFN and Dipartimento di Fisica Sperimentale dell’Università di Torino R. Arnaldi, E. Chiavassa, A. Colla, N. De Marco, A. Ferretti, M. Gagliardi, M. Gallio, R.Gemme, P. Mereu, A. Musso, C. Oppedisano, A. Piccotti, F. Poggio, E. Scomparin, G. Travaglia, E. Vercellin and F. Yermia members of the ALICE collaboration Machine Induced Background in the ALICE Muon Trigger System in pp Data taking Yermia Frédéric INFN Torino Secondo Convegno Nazionale sulla Fisica di ALICE 30 Maggio - 1 Giugno 2006 – Vietri sul Mare (SA) -

YERMIA Frederic Vietri sul mare 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 ALICE experiment Central detectors (identification of hadrons, electrons and photons) Forward muon spectrometer identification of muons for heavy 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 m 2 ) ● electronics channels

YERMIA Frederic Vietri sul mare Introduction  beam protons may undergo elastic and inelastic scattering with the residual gas nuclei (mainly O & C) in the LHC long straight sections (20 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 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 )

YERMIA Frederic Vietri sul mare 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: 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 Previous pressure calculations (LHC Project Note 273) Previous MIB studies ( ALICE-INT ) New pressure calculations (LHC Project Report 674) A factor 5 in less in mean. Details of the simulation of the p-A collisions Update and study of the beam-gas background environment Arbitrary units

YERMIA Frederic Vietri sul mare ALICE Simulation Framework AliRoot HEAD February 2006 with ROOT v 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 Muon Spectrometer geometry 19 Z (m) Y Trigger stations (16 & 17 m) Muon filter ( m) beamshield Plug (18-18 m & R=1.1 m) X 22

YERMIA Frederic Vietri sul mare Scoring Plane ParticlesMuonsHadronsTotalProtonsNeutrons Pions // Kaons Mean number by second 4.9 e e e e e e+05 // 2.8 e+04 Mean number by bunch (40 MHz) A factor 20 more for hadron contributions w.r.t. muons

YERMIA Frederic Vietri sul mare pA collision Origins in the SS2 All particles on the scoring plane MuonsHadrons Similar structures of the vaccum quality Muons are produced further than hadrons

YERMIA Frederic Vietri sul mare 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 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

YERMIA Frederic Vietri sul mare Flux on scoring plane weighted by E X-Y coordinates (Hz.GeV/cm²)  h+h- Hot Spot

YERMIA Frederic Vietri sul mare Fluxes on MT11 & MT22 X-Y coordinates (Hz./cm²) Hot spot max.  40 Hz/cm² Hot spot max.  80 Hz/cm²

YERMIA Frederic Vietri sul mare Fluxes on MT22 Ring 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 Fluxes on MT22 X-Y coordinates (Hz./cm²) MUONSHADRONSELECTRONS Hot spot max.  60 Hz/cm²Hot spot max.  20 Hz/cm²Hot spot max.  1 Hz/cm²

YERMIA Frederic Vietri sul mare 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

YERMIA Frederic Vietri sul mare Scoring plane: hits from hot spot MT22 High energetic hadron particles

YERMIA Frederic Vietri sul mare 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)

YERMIA Frederic Vietri sul mare 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 m Dipole 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

YERMIA Frederic Vietri sul mare Summary & conclusion Mean rate on trigger stations: 1-10 Hz/cm² Hot spot: 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

YERMIA Frederic Vietri sul mare BACKUP SLIDES

YERMIA Frederic Vietri sul mare Resistive Plate Chambers (RPCs) Small (  150 m 2 ) and accessible system, based on single-gap RPCs with x-y readout. -Low resistivity bakelite (   10 9 .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 ➢ Two bakelite planes of 2 mm (   10 9 .cm) ➢ High voltage of about 8 kV ➢ Gas gap of 2 mm (51% Ar + 7% iC 4 H % C 2 H 2 F 4 + 1% SF 6 ➢ 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 collisions strips + strips - high voltage spacer bakelite gas graphite plastic insulation Alternative working mode for pp data taking: Maxi avalanche mixture: 10% iC 4 H % C 2 H 2 F % SF 6 HV: 10 kV avalanche-like mode with our FEE developed for streamer mode i.e. without an amplification stage. Trigger detector

YERMIA Frederic Vietri sul mare Scoring Plane MUON OriginsHadron Origins Weighted by energy

YERMIA Frederic Vietri sul mare Hot spot MT11 from R1: Interaction Vertex from R1 Particles interact in the front absorber and the iron wall

YERMIA Frederic Vietri sul mare Hit densities & background composition Particles e-/e+pi+/pi - K+/K-proto n muon 78 %2.8 %0.01 % 16.4 % 2.8 % ChambersMT11MT12MT21MT22 Hits/second (x ) Without trigger time cut Hits/second (x ) Wit trigger time cut Max hit density: hits/cm2 w.r.t hits/cm2 in Pb-Pb

YERMIA Frederic Vietri sul mare 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 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 IP Proton beam + Positive particles D2 D1 Secondary particles Proton beam Negative particles