Reaction plane reconstruction

Reaction plane peconstruction 1

Reaction plane reconstruction

M.Kapishin, L.Lytkin, D.Nikitin

• Motivation

• Methods, generators

• Analysis results

• Summary and proposal

• Detector layout


Motivation:


Directed flow v1 & elliptic flow v2

x

zNon-central Au+Au collisions:

Interactions between constituents leads to a pressure gradients => spartial asymmetry is converted in asymmetry in momentum space

=> collective flows

- directed flow

- elliptic flow

V2>0 indicates in-plane emission of particles

V2<0 corresponds to out-of-plane emission (squeeze-out

perpendicular to the reaction plane)

V.Toneev et al.

Motivation:


Generators, Conditions, Tasks

• Two independent generators UrQMD and QGSM to estimate model uncertainty

→ predict different distributions of nucleus fragments

• Min Bias events, Au-Au collisions, √s = 3.8, 5, 9 GeV

→ generated events available in nc2.jinr.ru

• Analysis based on ensemble of generated stable particles;

• No momentum smearing, particle identification efficiency, azimuthal rotation of charged particles in magnetic field implemented yet

• Tasks → optimize method, kinematical range, type of particles, weight to increase sensitivity, estimate achievable RP resolution, formulate requirements to detectors, propose additional detectors if needed


Pseudo-rapidity η / Rapidity y

UrQMD

QGSMUrQMD

QGSM


Directed flow of pions and protons Au + Au collisions at √sNN = 7 GeV, b = 5 – 9 fm

2y

2x

x1

pp

pv

Results of NICA Physics Group UrQMD


Directed Flow v1 vs Rapidity y

UrQMD QGSM

nucleons π-mesons


G.Musulmanbekov et al.NICA Physics Group

→ approximate agreement in shape of directed flow v1 between NA49 experiment and UrQMD predictions


Methods of reaction plane reconstruction

ixi

iyinuclR pw

pw

,

,, arctan

Method 1:

it

iyi

ii

iinuclR p

p

w

w

,

,, sin;cos

sinarctan

Method 2:

• Using 1-st Fourier harmonics → directed flow in a collision in Lab frame:

22

22

)(1)(1

)()()(

RnuclR

RRnuclR

nuclR

R

→ combine measurements for η<0 and η>0 to improve precision, study as a function of impact parameter b

→ Optimize weight wi to increase sensitivity to RP

b

φR


Relation between b and centrality

Impact parameter b: 0 - 3 fm 3 – 6 fm 6 – 9 fm 9 – 12 fm

Fraction of σincltot : 0 - 5% 5 – 15% 15 – 30% 30 – 60%

→ assume that b is measured using independent method (ZDC calorimeter, TPC multiplicity, ZD Neutron calorimeter)


px/pt distribution vs b

b = 0 - 3 fm b = 3 - 6 fm

b = 6 - 9 fm b = 9 -12 fm

Nucleons, UrQMD

• px is defined in reaction plane

• <px/pt> is positive for nucleons (η>0)

• Precision of RP reconstruction ~ (px/pt) / δ(px/pt) → φR

• To increase sensitivity to RP take particles with weight 1 / δφR

• py is ┴ to reaction plane

• <py/pt>~0 for nucleons and π-mesons → no sensitivity to RP


px/pt distribution vs b

b = 0 - 3 fm b = 3 - 6 fm

b = 6 - 9 fm b = 9 -12 fm

π-mesons, UrQMD

• <px/pt> negative for π-mesons (η>0)

→ π-mesons can improve resolution of RP reconstruction

→ but reduce sensitivity to RP if π-mesons are combine with nucleons without identification

• weight 1 / δφR(η,b) is calculated as a function of η and impact parameter b separately for nucleons and π-mesons

→ next slide


Weight 1/δφR as a function of η and b

nucleons π-mesons

• Maximum shifts to larger |η| in collisions with larger impact parameter b


Reaction plane resolution vs b

Nucleons + π-mesons, UrQMD

• best RP resolution ~15-18○ for b=3-9 fm• RP resolution deteriorates to ~45○ for central collision and to ~25○ in peripheral collisions

b = 9 -12 fm

b = 3 - 6 fmb = 0 - 3 fm

b = 6 - 9 fm

Next slide: → plot r.m.s. values as a function of b


Resolution φR○ for nucleons and π-mesons

UrQMD QGSM

nucleons + π-mesons nucleus fragments + π-mesons

• Best resolution is for nucleons (nucleus fragments), adding π-mesons improve resolution a little


Reaction plane resolution vs b

b = 0 - 3 fm b = 3 - 6 fm

b = 6 - 9 fm b = 9 -12 fm

UrQMD

• if nucleons and π-mesons are combined without identification


Resolution φR○ for methods 1 and 2

UrQMD QGSM


→ Precise measurement of particle φ is more crucial than pt


Resolution φR○ vs CME √s = 3.8, 5, 9 GeV

UrQMD QGSM


→ No big change in topology of A-A collisions for NICA energy range


Analysis summary

• directed flow of nucleons (nucleus fragments) provides best sensitivity for RP measurement in pseudo-rapidity range 1 < |η| < 5

• best RP azimuthal resolution of ~15○ can be achieved for impact parameter of nucleus-nucleus collision b = 3 - 9 fm (centrality 5 - 30%), worst resolution - for central collisions

• impact parameter of nucleus-nucleus collision should be measured by independent methods (ZDC, ZDN, TPC detectors)

• identification of π-mesons and nucleons is important in η range where flux of π-mesons is comparable with that of nucleons (0.5 < |η| < 3)

• measurement neutrons is important to improve resolution of RP reconstruction

• two methods give comparable results → precise measurement of particle azimuthal angle φ is more crucial than pt


Detector proposal

• TPC, straw ECT, end-cap IT and ToF detectors provide measurement of momentum and identification of charged particles for |η| < 3

• implementation of Pre-shower detector in front of ZDC calorimeter should improve RP resolution in pseudo-rapidity range 2 < |η| < 5

• coordinate resolution of Pre-shower detector and sensitivity to neutrons is crucial for RP measurement, but energy resolution could be moderate

• simulation of Pre-shower detector response is needed to estimate RP resolution based hadron clusters and optimize detector layout

• Pre-shower detector in combination with ZDC calorimeter will also provide energy flow measurement in nucleus fragmentation region


Position of Pre-shower detector

Outer Pre-shower

Inner Pre-shower

Pre-shower can be installed into available space in front of ZDC (≤ 2 λ)


Layout of Pre-shower detector

• Pb / Scintillator “sandwich” calorimeter: layers of 16:4mm, hexahedrons with rin = 27.5mm

• Inner Pre-shower (IPD) in front of ZDC: RIPD< 330mm, dIPD≤ 400mm (~1.8λ)

• Outer Pre-shower (OPD) outside ZDC: 330 <ROPD< 715mm, dOPD= (2-3) dIPD

• WLS fibers embedded into grooves in Scint tiles, WLS fibers spliced to clear light-guide fibers readout by MAPD (or PMT)


Layout of Pre-shower detector

• 3 successive Scint layers form triplet, hexahedrons in triplet are shifted to form triangle area in coincidence, hexahedron layers with same shift are combined into one longitudinal stack readout by one MAPD (or PMT)

• 458 hexahedrons (90 in IPD + 368 in OPD), 1374 readout channels (270 in IPD + 1104 in OPD) → one side detector ( x2 to cover η>0 and η<0)

To improve coordinate resolution:

Reaction plane reconstruction

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