HADES XXIII collaboration meeting Reaction plane reconstruction with FW in Au+Au beam test run Alexander Sadovsky sadovsky@inr.ru Institute for Nuclear Research RAS, Moscow Introduction Guideline from simulation What do we learn from test beam data Backup slides HADES XXIII collaboration meeting October 14 - 18, 2011 GSI, Darmstadt

Flow analysis and azimuthal angular distributions K+ in (Au@1AGeV)+Au by (KaoS) Azimuthal angular distribution of K+ for peripheral, semi-central and central events in collisions of (Au@1AGeV)+Au by KaoS collaboration. PRL.81(1998)1576-1579 In the frames of Fourier decomposition of obtained azimuthal distributions: which allows determination of directed (a1) and elliptic (a2) flows one may draw conclusions about the in-plane and out-of plane emission of K+, in medium potential... peripheral semi-central central 𝑑𝑁 𝑑φ =𝐶 1+2 𝑎 1 cos φ +2 𝑎 2 cos 2φ 1+2 𝑎 1 cos φ +2 𝑎 2 cos 2φ φ= φ 𝑖 − ψ 𝑅 2

Reconstruction of reaction plane (transverse momentum method) 𝑄 = 𝑖=1 𝑁𝑠𝑝 𝑤 𝑖 𝑝 𝑖 𝑡 Transverse momentum space Pti where: Q – reaction plane vector; Nsp – number of spectators detected; wi – weight factor: wi>0 flying forward, wi<0 flying backward; pit – transverse momentum vector. See e.g. [PL.157B,146,1985]. Projectile spectators Secondaries reaction plane Target spectators 3

Reconstruction of reaction plane (modified transverse momentum method) Hits in cells 𝑄 = 𝑖=1 𝑁𝑠𝑝 𝑤 𝑖 𝑟 𝑖 ∣ 𝑟 𝑖 ∣ Forward Wall (or HCAL) where: Q – reaction plane vector estimate; Nsp – number of fragments; wi – weight factor: wi>0 if flying forward, wi<0 if flying backward, absolute value is set to mass (m) or charge (Z) of the spectator; ri – position vector of cell with a hit-i. Transverse momentum space Pti (projectile spectators) Projectile spectators Secondaries reaction plane Target spectators 4

HADES Forward Wall, installed: March 2007 Fully operational: summer 2010, 2011 Distance to target 8 m 140 small 4x4cm 64 middle 8x8cm 84 large 16x16cm cells 5

Simulation (Au@1.25AGeV)+Au SHIELD + hGeant FW is 8m from target, spectators selected by time-of-flight. Higher values of |Q| lead to better reaction plane determination: 0<|Q|<4 : poor RP angle resolution 4<|Q|<14 : higher resolution By selecting |Q|>4 we also suppress peripheral events drp=(ϕrec-ϕgen) Q Impact parameter b [fm] 6

Method to determine resolution of reaction plane angle (RPA) suitable for real data QRPA QARPA QBRPA Hits in each event are randomly divided into two equal subgroups: A and B and RPA determination is done separately for cells A and B. Difference between the reaction plane reconstruction in two subgroups determines the reaction plane resolution of the whole event. 7

Method to determine resolution of reaction plane angle (RPA) suitable for real data But first we apply it for simulation 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. dN/dΦRPA for whole event (group A + B) dN/dΦRPA: group A dN/dΦRPA: group B 8

Simulation (Au@1.25AGeV)+Au SHIELD + hGeant Simulation w/o trigger conditions: 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) Gaussian fit sigma=37o {5<b<10 & Q>6} / K.Lapidus HADES coll.meeting. 2010 / NB: the estimate is done comparing with reaction plane from SHIELD. Estimate of reaction plane resolution based on 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. NB: this estimate is also applicable to exp. data. * Known only in simulation drp=ϕrec- ϕgen 9

(Au@1.24AGeV)+Au HADES 2011 test beam (spectators selection by FW information) Time-of-flight needed by spectators to travel from target to FW cell is selected Time [ns] FW cell # All charges accepted, but pedestals are taken away dE/dx [arb.u] FW cell # 10

(Au@1.24AGeV)+Au HADES 2011 test beam (events selection: target) Data selection: several files from day 227, 229, 230 Target selection: {(x2+y2)½<3.33mm} && z-unrestricted 3<vertex.Chi2<60 vertexClus.getSumOfWeights>6 Target Y [mm] Target X [mm] be1122718423* be1122901465* be11230233* Target Z [mm] Target Z [mm] Target Z [mm] 11

(Au@1.25AGeV)+Au HADES 2011 test beam FW azimuthal anisotropy (day 229 be1122901465*) 𝑄 = 𝑖=1 𝑁𝑠𝑝 𝑟 𝑖 ∣ 𝑟 𝑖 ∣ All sp. charges are treated as Z=1 (wi=1) (H-L)/(H+L) = 20% = (2500-1650)/(2500+1650) y [mm] x [mm] Reconstructed phiRP [o] Adjusting for beam shift x = x - (0mm) y = y - (0mm); Rmin = 220mm (to gain isotropy) (H-L)/(H+L) = 13% = (2250-1750)/(2250+1750) y [mm] x [mm] Reconstructed phiRP [o] 12

(Au@1.25AGeV)+Au HADES 2011 test beam RPA distribution (Rmin=220mm) Experiment: RMS(A^B)=74o RMS(RPA)~52o 4<|Q|<9 Simulation: RMS(A^B)=83o RMS(RPA)=59o (63o)* Preferable directions (systematics) Data files: be1122901465* Moderate 4<|Q|<9 values closest to flat RPA distribution 12-20% diff Experiment: RMS(A^B)=69o RMS(RPA)~49o 4<|Q|<14 Simulation: RMS(A^B)=80o RMS(RPA)~57o (61o)* Range of |Q|-values suggested by the simulation 4<|Q|<14 still too anisotropic w.r. RPA reconstructed 16-22% diff No selection on |Q|-values NB: partially explained by the azimuthal anisotropy in phiRP of 13% obvious correlation to +/- 120o |Q|>14 ( excluded ) 13

FW ϕ(cell) distributions for different Rmin cut (beginning of beam time, day 227: be1122718423*) Rmin>40mm Rmin>120mm Rmin>220mm ϕcell [o] ϕcell [o] ϕcell [o] 14

RPA, ϕ(A^B) distributions for different Rmin cut (beginning of beam time, day 227: be1122718423*) Rmin>40mm Rmin>120mm Rmin>220mm Moderate transverse momentum transfer selected 4<|Q|<14 exp: RMS(ϕ(A^B)) = 68o sim: RMS(ϕ(A^B)) = 81o sim/exp=1.19 exp: RMS(ϕ(A^B)) = 68o sim: RMS(ϕ(A^B)) = 81o sim/exp=1.19 exp: RMS(ϕ(A^B)) = 67o sim: RMS(ϕ(A^B)) = 80o sim/exp=1.19 15

(one of “non-isotropic” days 229: be1122901465*) Some guilty cells?? (one of “non-isotropic” days 229: be1122901465*) Selecting events with Rmin=0 Dis: dN/d{#cell} for |Q|<7 – very isotropic part from of RPAs Dun: dN/d{#cell} for |Q|>17 – most non-isotropic part of RPAs Make normalized difference: Dun*(Int{Dis}/Int{Dun}) - Dis Dis cell# Dun cell# cell# 16

Conclusions and possible improvements * Given anisotropy leads to systematic error in RPA determination * Source of anisotropy shall be studied: 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 (~time of flight dectease) 3. Try to weight cell response to force isotropy

Summary First test beam Aug'11 data of (Au@1.25AGeV)+Au reaction were analyzed aiming determination of the reaction plane angle from FW. Some non-trivial azimuthal anisotropy of beam profile on FW is seen. This leads to non-flat distribution of reconstructed reaction plane angle. A suppression of this anisotropy can be done to some extend by shifting the center of gravity of the beam spot on FW and by geometrical cutoff of the FW acceptance. An estimate of reconstruction accuracy of RPA is by ~25% “better” in real data compared to the simulation, while remaining RPA anisotropy is seen on the level of ~15%. More investigations needed. Suggestion: move FW closer to target Forward wall team: INR Moscow: O.Busygina, M.Golubeva, F.Guber, A.Ivashkin, A.Reshetin, A.Sadovsky, E.Usenko NPI Řež: A.Kugler, Yu.Sobolev, O.Svoboda, P.Tlusty, V.Wagner.

Backup slides

(Au@1.25AGeV)+Au HADES 2011 test beam FW azimuthal anisotropy (day 227 be1122718423*) R R R 220mm 20

(Au@1.25AGeV)+Au HADES 2011 test beam FW azimuthal anisotropy (day 229 be1122901465*) R R R 220mm 21

(Au@1.25AGeV)+Au HADES 2011 test beam FW azimuthal anisotropy (day 230 be11230233*) R R R 220mm 22

FW cell response after new time calibration with walk correction dN/dt[ns] 23

(Au@1.24AGeV)+Au HADES 2011 test beam FW azimuthal anisotropy (day 229) no targ.cut y [mm] y [mm] TOF multiplicity>20 (no improvement) x [mm] 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] x [mm] Reconstructed phiRP [o] 24

Simulation: FW fired cells distribution Au+Au@1.25AGeV (selection of spectators in FW) Selecting spectators by peak at time-of-flight distrib. in FW cells (left ): inside 2sigma (right): outside2sigma Spectators Secondaries y y 100% hits x [cm] x [cm] 16% dN/dx dN/dx Time [ns] Mean =18.1 Sigma=0.87 74% x [cm] Time [ns] x [cm]

Reaction plane reconstr.: Au+Au@1.25GeV/u no selection 0 < b < 5 no weight Z weight 5 < b < 10 10 < b < 15 43° ⇉ K.Lapidus (HADES coll.meet 2010, GSI)

Reaction plane recons. : Au+Au@1.25GeV/u Cut on Q value helps in suppression of tails and improves the resolution 5 < b < 10 Q > 6 Q > 3 No cut 37o Simulations with FW located at 5-7m from target ⇉ K.Lapidus (HADES coll.meet. 2010, GSI)