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)

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

Forward Wall control plots (2) Small cell 26 Middle cell 204 Large cell 258 Time distributions (calibrated) ADC distributions Time vs. ADC distributions

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.

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.

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

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/be1122901465*_dst_aug11*.root

(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

(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

(Au@1.25AGeV)+Au HADES 2011 test beam FW azimuthal anisotropy (day 229 be1122901465*) 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

(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

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 (Au@1.25AGeV)+Au: FW at 8m behind the target, no trigger simulation

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

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

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