1. FW calibration and analysis status Test beam 2011: (Au@1.25AGeV)+Au
Calibration status:
Gen0 Aug2011 DSTs were used to produce FW plots
(day 230, ~1M events)

2. Forward Wall control plots (1)
4 “dead” cells

3. Forward Wall control plots (2)
Small cell Middle cell Large cell 258
Time distributions
(calibrated)
ADC distributions
Time vs. ADC
distributions

4. Forward Wall performance in test beam 2011
4 dead cells (3%)
47 modules (16%)
can separate Z={1,2}
116 modules (40%)
can separate Z={1,2,3}
125 modules (43%)
can separate Z={1,2,3,...}
See report by Yu. Sobolev
The main source is add-on plates on front-end electronics.
Another source is due to noise in PMTs because of overstate HV.

5. Forward Wall time calibration
Distance to each cell is known,
so time can calibrated.
Small cells
ADC, Chan.
Time, nsec
Middle cells
Time calibration:
Z=1 selected
on-average for
small/middle/large
cells: 3 common cuts.
NB: selection is
not individually adjusted in each cell
Cell #
ADC, Chan.
“pedestal”
see ADC spectra
Large cells
Time, nsec
ADC, Chan.

6. Necessary improvements in calibration procedure
Cell 21
Adc, Chan.
Time-Adc correction (“walk” correction)
Individual windows for all FW cells to select peaks corresponding to different Z
- as a result – better time resolution

7. Reaction plane angle resolution Test beam 2011: (Au@1.25AGeV)+Au
Using the achieved calibration we looked forward to estimate the reaction plane angle (RPA) resolution.
Exp. data files used in analysis:
/lustre/hades/dst/aug11gen0/229/root/be *_dst_aug11*.root

8. (Au@1.25AGeV)+Au HADES 2011 test beam
(spectators selection by FW information)
Time-of-flight for spectators needed travel from target to FW cell is selected
Time [ns]
FW cell #
All charges accepted,
pedestals are taken away
dE/dx [arb.u]
FW cell # 8

9. (Au@1.25AGeV)+Au HADES 2011 test beam
(events selection)
Target Y [mm]
Target X [mm]
Target Z [mm]
Data selection:
day 229 several files after 01:46
Rough target selection:
{x*x+y*y<10}mm && {-40<z<-23}mm
Spectator selection by time-of-flight
Spectator charge identification is ignored so far
in RPA determination. 9

10. (Au@1.25AGeV)+Au HADES 2011 test beam
FW azimuthal anisotropy (day 229 be *)
𝑄 = 𝑖=1 𝑁𝑠𝑝 𝑤 𝑖 𝑟 𝑖 ∣ 𝑟 𝑖 ∣
y [mm]
y [mm]
TOF multiplicity>20
(no improvement)
x [mm]
Reconstructed phiRP [o]
Adjusting for beam shift x=x-(-7.2mm) y=y-(-1mm); and Rmin = 138mm (to gain isotropy)
TOF multiplicity>20
(no improvement)
y [mm]
y [mm]
x [mm]
Reconstructed phiRP [o] 10

11. (Au@1.25AGeV)+Au HADES 2011 test beam RPA distribution
RMS(A^B)=77o
RMS(RPA)~55o
NB:
Simulation 4<|Q|<9
RMS(A^B)=85o
RMS(RPA)=63o
No selection on
|Q|-values
Moderate
4<|Q|<9 values
closest to flat RPA
distribution
RMS(A^B)=72o
RMS(RPA)~51o
NB:
Simulation 4<|Q|<14
RMS(A^B)=81o
RMS(RPA)=60o
Preferable directions
(systematics)
Range of |Q|-values
suggested by the simulation 4<|Q|<14
still too anisotropic w.r. RPA reconstructed
Reasonable agreement
with simulation
for the given
azimuthal anisotropy
|Q|>14
Obvious correlation
to +/- 90o 11

12. Conclusions and possible improvements
* Given anisotropy leads to systematic error in RPA determination
* Source of anisotropy shall be studied:
1. E.g. by studying of possible influence from trigger by looking into TOF/RPC
azimuthal distribution (proposed by Pavel T. and Andrej K.)
2. In simulation: shift of mean X, mean Y does not reproduce neither
half-moon shape, no the RPA phi-distribution.
* Depending on the source of the anisotropy one may try:
1. Increase minimal radius cut-off in analysis (~loosing resolution)
2. Move FW closer to target
3. Try to weight cell response to force isotropy
Hints from simulation, are given in backup slides
FW at 8m behind the target, no trigger simulation

13. Simulation (Au@1.25AGeV)+Au
SHIELD + hGeant
Spectators selected by time-of-fl.
Higher values of |Q| lead to better
reaction plane determination
Poor RP resolution for 0<|Q|<4
Higher resolution for 4<|Q|<14
By selecting |Q|>4 we also suppress peripheral events
drp=(RPrec-RPgen) Q
Impact parameter b [fm] 13

14. Simulation (Au@1.25AGeV)+Au
SHIELD + hGeant
Standard procedure to estimate the resolution of the reaction plane determination in real data
is following:
hits of an event are randomly divided into two equal groups:
A and B determining the reaction plane in each group separately.
Reaction plane angle determination based
on whole hits in FW of the event and in two subgroups A and B show flat distribution.
Difference between the reaction plane reconstruction in two subgroups determines the
reaction plane resolution of the whole event. 14

15. Simulation (Au@1.25AGeV)+Au
SHIELD + hGeant
Simulation:
Event selection: for 4<|Q|<14
reaction plane angle resolution for all hits in FW from each event:
RMS=60o
Gaussian fit sigma=48o (in central part)
NB: the estimate is done comparing
with reaction plane from SHIELD.
Estimate of reaction plane resolution
from two subgroups (A and B) of
hits in each event:
RMS=81.34o /√2 = 58o
i.e. in a good agreement with the one
obtained with knowledge of reaction plane angle from simulation. 15