# Presentation: 669114

##  Latest results from dE/dx

- Yuri Fisyak

## Outlook

- CDR expectations for TPC dE/dx resolution
- Old /new calibration schemes
- AuAu 2002
- dAu 2003
- Time of flight
- Bichsel’s calculations for P10
- Conclusions

## TPC dE/dx  resolution 

- STAR CDR (p. 4C-33)
- 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

## dAu data

- 9.7 % after gain
- corrections only

**μ**** = -.5692**

- dE/dx Offset
- for MIP: 1.5=> 2.5keV/cm

- Z= ln (dE/dx/BB)

- Track Length in TPC (cm)

**σ**** = 9.73%**

## What does calibration means?

**For good clusters (used in fit, no overlaps) **
**For good global tracks (No. fit points ****≥ 30, Track length in TPC > 40 cm)**
**Most probable value of Z =log[(dE/dx)****measured****/(dE/dx)****predicted for ****π****] should not depend on anything (except ****βγ****) ****i.e.**

** ****fit Z-distribution with Gauss(****μ****,****σ****)**** + pol3 in ****±****3****σ**** range (we have ~80% ****π****).**
**μ**** should not depend on**
**Time, ****Pressure**
**Sector, row**
**Drift distance**

## What does prediction mean ?

**0.45 GeV/c**

-  Predictions:
-  **Girrf (BetheBloch):  GEANT3 was used for very first dE/dx calibration**
**  ****Sirrf : parameterization of Year 1 data, and**
** ****Bichsel calculations for Ar:**
**(dE/dx)****Bichsel ****= f(****βγ****,dX)**

## Old calibration scheme (StdEdxMaker) 

- The old dE/dx calibration scheme
-  was based on dst_point and global track tables (StdEdxMaker has to be before StEventMaker in the chain),
- for all reconstructed tracks (no momentum restriction),
- Sirrf prediction.
- Last calibration in this scheme was done in March, 2002, for AuAu data:
- σ(dE/dx)/(dE/dx) = 8.2% for 76 cm track
- I was not happy that ~1.4% is still missing with respect to CDR

## Red – 40% truncation

**Red**** – 40% truncation**
**Green**** – 30% truncation**
**Black  - fit**

- 8.2% @ 76 cm

## New calibration (StdEdxY2Maker)

- Calibration is based on StEvent (StTpcHit and StTrack, after StEventMaker)
- Calibration is based on tracks within [0.4,  0.5] GeV/c interval (~MIP for pions: βγ= p/m = 4) only.
- As prediction it was used Bichsel’s calculation with dX dependence

## Y2 Calibration

- dE/dx corrections:              table names
- R “ADC” nonlinearity => “TpcAdcCorrection”
- Z Drift distance     	     =>“TpcZCorrection”
- account O2                            =>“TpcDriftDistOxygen
- Pressure:                      => “tpcPressure”
- All time dependence is accounted via above corrections for Pressure and Oxygen contamination
- SecRow                      => “TpcSecRowB”
-    		has to be redone after Fabrice’s pulser corrections
- dX correction              => “TpcdXCorrection”
- TPC track length        => “TpcLengthCorrection”
- 		has to be redone after Fabrice’s pulser corrections

## New calibration for Y2 data

**6.8 % @ 76 cm**

## dAu data with Y2 calibration

**6.6% @ 76 cm**

- Calibration for dAu has not been done yet

## dE/dx for pions selected by ToF

- ~4% offset

- σ = 6%

## Systematic in dE/dx versus βγ

- Thanks ToF group (Lijuan Ruan)

## Resolution depends on βγ

## Bichsel’s Ar/P10 calculations for different dX

- These are preliminary calculations but they have the same trend as we see in ToF analysis

## Conclusions

- New calibration scheme allows to reach resolution 6.8% which has been expected in STAR CDR
- For dAu production has been used AuAu calibration from Y2002.
- Resolution is quite good (6.6%), but
- there is offset in dE/dx ~ 4% which has been accounted on the level of MuDST reproduction (P03ia).
- A new component is data with ToF information. This information provides calibration sample for dE/dx.
- It has been observed ~5% variation versus βγ with respect to H.Bichsel calculations for Ar
- H.Bichsel calculations for P10 shows the same trend
- Next step is to calibrate Bichsel’s model using ToF sample in order to do this we need to have ToF in the standard chain.