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Recent background observation in operation by ALICE A. Alici

Recent background observation in operation by ALICE A. Alici. Reminder: ALICE trigger detectors in the central barrel. V0A. BEAM1. ITS. V0C. SPD. V0C r in =8 cm r out = 76 cm. V0A r in =8 cm r out =100 cm. 340 cm. 90 cm.

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Recent background observation in operation by ALICE A. Alici

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  1. Recent background observation in operation by ALICE A. Alici A. Alici – LBS #24, 16/05/2011

  2. Reminder: ALICE trigger detectors in the central barrel V0A BEAM1 ITS V0C SPD V0C rin=8 cm rout= 76 cm V0A rin=8 cm rout=100 cm 340 cm 90 cm SPD: silicon pixel detector, 2 innermost layers of Inner Tracking System V0: small angle detector consisting of two arrays of scintillator counters (V0A and V0C). Time spectra allow beam-gas events rejection A. Alici – LBS #24, 16/05/2011

  3. Reminder: MB trigger classes CINT1B  (SPD FO || V0A || V0C) && beam1 && beam2  collisions + beam background + noise CINT1A  (SPD FO || V0A || V0C) && beam1 && (!beam2)  beam background + noise CINT1C (SPD FO || V0A || V0C) && (!beam1) && beam2  beam background + noise CINT1E (SPD FO || V0A || V0C) for fixed “empty” BXs noise Beam-Background (BG) = CINT1A + CINT1C – 2 CINT1E * * assuming the same bunch intensities for colliding/non-colliding beam1/beam2 A. Alici – LBS #24, 16/05/2011

  4. Beam BG simulation • Machine Induced Background sources: • Proton – gas elastic and inelastic (dominant) interactions occurring in the last long straight section (LSS) before ALICE. The source is calculated by distributuing proton-H2 interactions along the LSS according to a pressure profile obtained from simulation of the vacuum conditions. The p-H2 interactions and computed with DPMJETIII, while the cascades are calculated using FLUKA. • Betatron halo: beam losses simulated with Sixtrack, followed by the calculation of the hadronic and electromagnetic (EM) showers initiated by the lost protons using FLUKA. • Collision cross-talk at IRs (negligible) • Machine Induced Background simulation: simulated beam1 + beam-halo on a scoring plane 20m away from the IP, then particles transport, full detector simulation and trigger emulation (with Geant). A. Alici – LBS #24, 16/05/2011

  5. Comparison between data and simulation: SPD clusters SPD cluster distribution @ 7 TeV: the distributions are normalized to the same number of events A. Alici – LBS #24, 16/05/2011

  6. Comparison between data and simulation: SPD clusters Real data Simulation Non – interacting beams collisions Correlation between tracklets and clusters in the SPD: you need more cluster to make a tracklet if the event is not produced in the interaction region. Tracklet: track segment made out of 2 points in the 2 SPD layers A. Alici – LBS #24, 16/05/2011

  7. Comparison between data and simulation: V0 multiplicity Charged-particle multiplicity distribution in V0’s arrays @ 7 TeV A. Alici – LBS #24, 16/05/2011

  8. V0 Beam-Gas rejection V0A V0C IP V0OR beam1 beam2 340cm ~11.3ns 90cm ~3ns V0A+V0C ≈ 14.3ns V0A-V0C ≈ 8.3ns IP beam1 beam2 ~-11.3ns ~3ns V0OR V0A+V0C ≈ -8.3ns V0A-V0C ≈ -14.3ns IP beam1 beam2 ~11.3ns ~-3ns V0A+V0C ≈ 8.3ns V0A-V0C ≈ 14.3ns A. Alici – LBS #24, 16/05/2011

  9. Background Measurements in ALICE Pile-up factor μ=500[Hz]/11.2[kHz] 150ns bunch trains LHC11 data 50ns_336bunches 50ns_228bunches A. Alici – LBS #24, 16/05/2011

  10. Background Measurements in ALICE Selected runs where VGPB.120.4L2.X.PR < 5*10-9 mbar 50ns filling scheme A. Alici – LBS #24, 16/05/2011

  11. Background in ALICE – 50ns filling scheme Beam2 BG Beam1 BG collisions satellites Beam1 BG collisions satellites Beam2 BG A. Alici – LBS #24, 16/05/2011

  12. Background in ALICE – 50ns filling scheme A. Alici – LBS #24, 16/05/2011

  13. Scrubbing runs Beam intensities VGPB Vacuum gauges Scrubbing very effective (ratio between beam intensities and vacuum pressure has clearly increased)! A. Alici – LBS #24, 16/05/2011

  14. backup A. Alici – LBS #24, 16/05/2011

  15. Scrubbing runs Fill 1645– before scrubbing Intensity ~1.9E13 charges (200 bunches) BLM ~ 0.7 Gy/s Fill 1704 – after scrubbing Intensity ~2.5E13 charges (288 bunches) BLM ~ 0.45 Gy/s Background reduced by a factor 2 with scrubbing A. Alici – LBS #24, 16/05/2011

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