Download
1 / 14
140 likes | 152 Views
Understand machine-induced backgrounds in BaBar detectors through beam-current dependence characterization. Focus on luminosity, beam-gas interactions, and beam-beam performance. Detailed operational procedures and goals outlined for comprehensive analysis.
E N D
Background characterization: MD plan W. Kozanecki • MD goals • Background sources • Operational procedures • Open questions
MD goals • Main goal: characterize beam-current dependence of • machine-induced backgrounds • all BaBar ‘detectors’: SVT, DCH, EMC, DIRC, IFR + TRG, ODF • dedicated background monitors (pins, CsI counters, collim. BLMs) • beam-beam performance • specific luminosity • vertical & horizontal spot sizes in LER & HER • loss rates @ collimators in PR12 (HER), PR04 + PR02 (LER) • Parasitically: measure thermally-induced motion of IR components • using a ‘witness’ bunch in HER (1mA, feedbacks off) when varying LER current, & vv • take advantage of slow ‘current staircase’ to measure thermal time constants • note this only measures the effect on the OTHER beam (e.g. LER HER)
Background sources • Luminosity (radiative-Bhabha debris) – major concern (DCH future) • BP ~ dP * L (strictly linear with L) • Beam-beam tails • from LER tails: BL, bb ~ bL,bb*IL + fL(xL,H+/-) • from HER tails: BH, bb ~ bH,bb*IH + fH(xL,H+/-) • Beam-gas (bremsstrahlung + Coulomb) • HEB only: BHbg ~ aH*IH + bH*IH2 (aH , bH > 0) • LEB only: BLbg ~ aL*IL + bL*IL2 (aL , bL > 0) • beam-gas cross term: BLHbg ~ cLH * IL * IH (LEB+HEB, out of collision) • BI: LER injection (trickle) background • BLT (exp. signature somewhat similar to bremsstrahlung)
Proposed operational procedure: colliding beam measurements (1) • 2000 & 2002 procedure:
Proposed operational procedure: general guidelines • BaBar taking data! • Perturb as adiabatically as possible • start with stable machine in delivery mode • avoid acrobatics (collisions pedestals single-beam non-colliding pedestals) • LER Touscheck background a separate, dedicated MD • At each current setting • optimize tunes • on luminosity (in collision, coasting so lifetime reasonable) • on lifetime (single beam, for beam-gas measurement) • reset vertical IP angles in both rings • check SLM & interferometer settings • start a new run (also at trickle-coasting transition) • Pedestal runs • 1.5 mA in each ring, non-collidng • Reproducibilty: if beam(s) lost, redo last setting
Proposed operational procedure: colliding beam measurements (2) • Setup: save configs & orbits; check fbcks; change BBR L1 config. • Keep IL ~ constant, vary IH (> 0.30 A, 0.20 A steps) • 2 regimes (to help separate Lumi & beam-beam contributions) • IL ~ 1.20 A (2/3 of peak LER current, moderate beam-beam) • no trickle (LER coasting only) • ~ 7’ steps • IL ~ 1.85 A (or max. sustainable LER current) • to measure trickle contribution differentially, for each HER current setting • trickle LER (~ 5’) • coast LER (~ 5’) (peak L& H currents: 5’ additional for IFR high-stat data) • Keep IH ~ constant, vary IL (> 0.30 A, 0.25 A steps) • 2 regimes (to help separate Lumi & beam-beam contributions) • IH ~ 0.85 A (2/3 of peak HER current, moderate beam-beam) • IH ~ 1.35 A (or max. sustainable HER current, assuming 8 stations) • no trickle, ~ 7’ /setting • Pedestal run • 1.5 mA in LER bucket 0, 1.5 mA in HER bucket 3400
Proposed operational procedure: “single-beam” measurements • Vary IH : 0.30-1.35 A, 0.20 A steps, “no” LEB • no HER bunches in buckets 0-100 (LFB permitting), 1.5 mA in LER bunch 0 • 7’ per setting + 5’ at the highest current (IFR) • Vary IL : 0.3-2 A, 0.25 A steps, “no” HEB • no LER bunches in buckets 0-100 (LFB permitting), 1.5 mA in HER bunch 0 • at topmost (or 2 topmost) LER current(s), trickle then coast • 7’ per setting + 5’ at the highest current (IFR) • Reproducibility check on single beam scans (esp. pins) • repeat middle & top points of previous two scans (HER, then LER) • Non-colliding scan (sparse) • Keep IH ~ constant (1.30 A), vary IL (> 0.30 A, 0.5 A steps) • Keep IL ~ constant (1.85 A), vary IH (> 0.30 A, 0.4 A steps) • Operational aspects • Separate beams vertically by 2 * 400 microns (feasibility ?) • Patterns: 100 bucket truncation at opposite ends of the two trains (YP!) • 7’ per setting • Pedestal run
Total time estimates (ONLY data taking + BBR on-off): 620’ • Setup 10’ • Collision scan @ fixed LER current 170’ • IL = 1200 mA, vary IH 7 x 10’ • IL = 1850 mA , vary IL 7 x 13’ + 5’ • Collision scan @ fixed HER current 140’ • IH = 850 mA , vary IL 7 x 10’ • IH = 1350 mA , vary IL 7 x 10’ • Pedestals 5’ • HER single-beam scan 7 x 10’ + 5’ 80’ • LER single-beam scan 7 x 10’ + 2 x 5’ + 5’ 90’ • Repeat middle & top points of single-beam scans (H, L) 40’ • Non-colliding scans 80’ • IH = 1350 mA , vary IL 4 x 10’ • IL = 1850 mA , vary IH 4 x 10’ • Pedestals 5’
To be clarified • Likely prerequisites • ‘routine’ 8-station running in HER • decent stored-beam & trickle backgrounds during preceding owl shift • Actual trigger rmix to enhance background fraction & minimize duration: tbd by BaBAr trig expert • Run duration/# evts per beam setting: 7’ (coast only) or 7’+5’ (trickle/coast), dominated by pin diode stability • Trickle coast switch • Need volunteer(s) to analyze CsI & BLM data!
Proposed baseline parametrization B = BP + Bbb + BHbg + BLbg + BLHbg + BLT + BI = a0 (from no-beam data ?) + dP * L (from colliding-beam data) + Bbb (IbL, IbH) (from colliding-beam data) + aH*IH + bH*IH2 (from single-beam HER data) + aL*IL + bL*IL2 (from single-beam LER data) + cLH * IL * IH (from 2-beam, non-colliding ?) + BLT (LER only, vary VRF?) + BI (differential, trickle – coasting ?)
