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Status of the dE/dx calibration in Run VII

Status of the dE/dx calibration in Run VII. Yuri Fisyak. Outlook. History of dE/dx calibration Where we are with the dE/dx calibration? Undershoot Conclusions. History of dE/dx calibration. Expected dE/dx resolution (STAR CDR): σ (dE/dx)/(dE/dx) = 0.47 N -0.46 (Ph) -0.32 , P = 1atm

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Status of the dE/dx calibration in Run VII

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  1. Status of the dE/dx calibrationin Run VII Yuri Fisyak STAR Analysis meeting

  2. Outlook • History of dE/dx calibration • Where we are with the dE/dx calibration? • Undershoot • Conclusions STAR Analysis meeting

  3. History of dE/dx calibration • Expected dE/dx resolution (STAR CDR): • σ(dE/dx)/(dE/dx) = 0.47 N-0.46(Ph)-0.32, P = 1atm • σInner = 14.3%, h = 1.15 cm, N = 12; • σOuter = 7.7%, h = 1.95 cm, N = 32; • σ = 6.8% for 76 cm track in TPC (90 track) • H.Bichsel simulation: • σ = 7.0 % for 13 * 1.2 cm + 32 * 2.0 cm • σ = 7.2 - 7.5 % has been set as an achievable goal for dE/dx calibrations • The last revision of dE/dx calibration procedure was done in 2003 and used for calibration starting from Run IV: • Usage of Bichsel’s model for dE/dx (= f(dx)) • Correction for ADC non linearity (rounding and saturation) STAR Analysis meeting

  4. The point of today discussion is Run VII resolution: σ~8% which is ~0.5-1% worse than resolutions achieved so far. • This degradation has been attributed to increased cluster occupancy in TPC due to higher luminosity and multiplicity of AuAu collisions (a factor of ~2.5 with respect to Run V CuCu). • Even in CuCu we see track multiplicity dependence of dE/dx. • Probably this is due cluster overlaps and undershoot which is created by non perfect TPC shaper tail cancellation. STAR Analysis meeting

  5. Undershoot These are plots of pulser signal obtained without zero suppression. We see clear undershoot on the level ~2% with time decay constant ~1.2 µsec for Inner and ~1.6 µsec Otter pad rows. Pad row 1 Pad row 44 STAR Analysis meeting Time bucket

  6. Undershoot (cont.) • There is clear dependence of dE/dx π peak position on estimated undershoot charge (Q) using parameterization from pulser. • But the first attempt to account this undershoot was non successful. We need more understanding of : • electronics (nobody knows the parameters which were used to adjust TPC shaper except that it has  = 55 nsec) • cluster finder and • in order to get this understanding we need TPC simulation which will account for these effects Outer Inner STAR Analysis meeting

  7. Conclusions • We have observed degradation of dE/dx resolution with increasing TPC occupancy • With increasing luminosity the situation will become worse • The only hope is new electronics which will handle increasing occupancy • For understanding both old and new electronics we need new, more precise TPC simulation STAR Analysis meeting

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