Machine Induced Background in the ALICE Muon Trigger System in pp Data taking

1. Machine Induced Background in the ALICE Muon Trigger System in pp Data taking Secondo Convegno Nazionale sulla Fisica di ALICE 30 Maggio - 1 Giugno 2006 – Vietri sul Mare (SA) - • 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 Yermia Frédéric INFN Torino 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 Vietri sul mare 2006

3. 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 ALICE experiment Central detectors (identification of hadrons, electrons and photons) Forward muon spectrometer identification of muons for heavy flavour study 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 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) 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: • 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) SCORING PLANE (input of transport simulations) Vietri sul mare 2006

7. Details of the simulation of the p-A collisions Update and study of the beam-gas background environment Arbitrary units Previous pressure calculations (LHC Project Note 273) Previous MIB studies (ALICE-INT-2003-041) Arbitrary units New pressure calculations (LHC Project Report 674) A factor 5 in less in mean. 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) Vietri sul mare 2006

9. Muon Spectrometer geometry Trigger stations (16 & 17 m) Y Muon filter (14.7-15.9 m) X Z (m) 22 19 18 16 Plug (18-18 m & R=1.1 m) beamshield Vietri sul mare 2006

10. Scoring Plane A factor 20 more for hadron contributions w.r.t. muons Vietri sul mare 2006

11. pA collision Origins in the SS2 All particles on the scoring plane Muons Hadrons Similar structures of the vaccum quality Muons are produced further than hadrons Vietri sul mare 2006

12. Scoring Plane: Muons kinematics • Uniformity • Some high energetic muons • Peaked at small emission angle X (m) E (TeV) R (m) E (TeV) Theta (deg) Vietri sul mare 2006

13. Hadronic background • Uniformity • Quasi beam • Machine effect (material) • Energetic hadrons at R= 0.5 m • Small emission angle X (m) E (TeV) Theta (deg) E (TeV) Vietri sul mare 2006

14. Flux on scoring plane weighted by E X-Y coordinates (Hz.GeV/cm²) m+ m- h+ h- Hot Spot Vietri sul mare 2006

15. Fluxes on MT11 & MT22 X-Y coordinates (Hz./cm²) Hot spot max. 40 Hz/cm² Hot spot max. 80 Hz/cm² Vietri sul mare 2006

16. 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 Vietri sul mare 2006

17. Fluxes on MT22 X-Y coordinates (Hz./cm²) MUONS HADRONS ELECTRONS Hot spot max.  1 Hz/cm² Hot spot max.  20 Hz/cm² Hot spot max.  60 Hz/cm² Vietri sul mare 2006

18. 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 Vietri sul mare 2006

19. Scoring plane: hits from hot spot MT22 High energetic hadron particles Vietri sul mare 2006

20. Hit creation vertex from MT22 XY projection of the hit creation vertex at z= - 18 m (Hz./cm²) X (m) Tunnel entrance Scoring plane plug Hot spot in the plug due to hadronic particles Y (m) Hadronic particles interact in the plug Vietri sul mare 2006

21. Hot spot MT22 from R2: p-A collisions Vertex Hadronic particles are created in the lhc tunnel at 120< z < 130 m Vietri sul mare 2006

22. LHC Tunnel (IR8) Dipole D2 IP 120 m The Dipole D2 makes positive particles converge towards IP and makes negative particles diverge Negative particle hot spot on scoring plane Vietri sul mare 2006

23. 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 Vietri sul mare 2006

24. BACKUP SLIDES Vietri sul mare 2006

25. Y Z X Trigger detector II • Resistive Plate Chambers (RPCs) • Small (150 m2) and accessible system, based on single-gap RPCs with x-y readout. • Low resistivity bakelite (r 109.cm) • (Frati laminati) • Two linseed oil layers to smooth the bakelite surface • Copper strips (1 cm, 2 cm or 4 cm width) (General Tecnica production) 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. • 2 trigger stations: • 2 detection planes per station • 18 RPCs per plane Vietri sul mare 2006

26. strips + high voltage bakelite spacer plastic insulation strips - graphite gas Trigger detector RPC working in streamer mode for heavy ions collisions • Two bakelite planes of 2 mm (r 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 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. Vietri sul mare 2006

27. Scoring Plane MUON Origins Hadron Origins Weighted by energy Weighted by energy Vietri sul mare 2006

28. Hot spot MT11 from R1: Interaction Vertex from R1 Particles interact in the front absorber and the iron wall Vietri sul mare 2006

29. Hit densities & background composition • Max hit density: 0.3 10-5 hits/cm2 • w.r.t. 2 10-3 hits/cm2 in Pb-Pb Vietri sul mare 2006

30. Scoring plane: hits from hot spot MT22 Condition: hits inside hot spot Confirmation of the hot spot positionon scoring plane Vietri sul mare 2006

31. Hit creation vertex from MT22 R vs z of the hit creation vertex (Hz./cm²) Trigger stations cavern Iron wall Scoring plane plug beamshield Hit particles are created in the whole trigger region Vietri sul mare 2006

32. Negative particles D2 D1 Proton beam IP Secondary particles Proton beam + Positive particles Vietri sul mare 2006