My thoughts about necessary calibration accuracy for a successful W program at STAR

Endcap

Calibration accuracy

1. towers : 5% absolute accuracy of reco electron energy of ET=40 GeV to see Jacobian peak for W+, see Fig 1.
2. Pres1,pres2, post shower:
   • 10% absolute calibration for energy deposit of few MIPs, energy deposit of few MeV , see Fig 2, 3.
   • 100 MeV of energy deposit should be in the dynamic range of electronics.
3. SMD 10% absolute calibration for electron energy of   ET=40 GeV, to allow  e/h discrimination, see Fig 4.

Suggestions/concerns:

1. maintain 99%+ of live channels from all layers by annual fix of dead channels (Will, Jim great job over all those years!!!)
2. commission (existing) high power laser light injection system allowing study of linearity up to 60 GeV ET, known problems:
   • no interface to STAR trigger
   • possible damaged high power optical cable
   • slow control for remote operation of attenuator(s)
3. develop new absolute calibration methods, may need dedicated trigger:
4. electrons ET 3-4 GeV, eta [1-1.4] using TPC de/dx, 
   • rho+ decay to pi+ & pi0, use TPC for pi+ tracking 
   • J/Psi, upsilon reco at larger ET
   • bumps in the di-jet cross section invariant mass at W & Z mass, @ pp 500 GeV
5. process fine granularity timing scan of ETOW data from pp 2008 run to asses tower to tower gain sensitivity to crate timing 
6. abandon pi0 calib as primary method, too many year passed, use it for crosscheck

 Barrel

Calibration accuracy:

• follow Endcap requirements

Suggestions/concerns:

1. list of not functioning channels from all layers as of June 2008, list reasons if possible
2. set HV for BTOW so all towers have hardware gains within +/-10% of ideal gains, max ADC @ ET=60 GeV
3. verify BPRS mapping for all tiles, demonstrate MIP peak in every tail
4. discuss optimal BSMD HV setting satisfying low energy probes (J/Ps, upsilon) and high energy e from W.
5. develop offline QA for BSMD, BPRS peds and status tables.

Trigger in 2009

Use L2 HT.TP algo run over eta [-1.,+1.5] to tag events with 2x2 EMC ET>15 GeV and store those events in the separate daq stream "st_highEnergy" , for both 200 GeV & 500 GeV pp running. To be used for :

• calibration of B+E EMC with high energy electrons
• develop e/h discrimination algo based on private production of those events

Both tasks will be accomplished ~6 months faster if we keep those events separately. 

2009 W-boson measurement at mid rapidity 

Preparation for run , February 2009. Few months of work to prepare Barrel detector.

1. BSMD
   • verify data-based calibration 
   • lower HV , to reduce gain by a factor of 3 and achieve saturation at 30 GeV EM
2. BPRS
   • aim to see MIP peak at ADC=ped+20
   • determine mapping
   • determine gains using MIPs, TPC tracks
3. BTOW
   • set HV to achieve max ADC @ 60 GeV over all eta 
   • eliminate:
     • to low HV on the East barrel
     • to high HV at  eta=+1, -1
   • method: electrons, use BSMD, drop M-C dependence

Fig 1. Expected lepton yield from W +/- decay

Fig 2. Presh2 response to 30 GeV ET electron and pi+, X axis in GeV

Fig 3. Postshower response to 30 GeV ET electron and pi+, X axis in GeV

Fig 4. SMD energy sum for high pT electrons and QCD background jets

Fig 5. Dead material in front of trackers. Current SSD mass 14.95 kg with aluminum support structure (case 1), lighter SSD 11.35 kg with carbon based support structure (case 2)