#### 1. Introduction

Hot and dense matter is produced in heavy-ion collisions at relativistic energies. Anisotropic expansion of this matter results in azimuthal asymmetry of particle production relative to the reaction plane, the so-called azimuthal anisotropic flow. Azimuthal anisotropic flow as result of non-central nuclear collisions is a very informative observable closely linked with the properties of the created matter.

To quantify the anisotropic flow a standard Fourier decomposition of the distribution of the azimuthal angle

(1)
where

#### 2. The NA49 experiment

The scientific goal of the NA49 experiment [1], which recorded data in 1994-2002, was to create an extended "quark-gluon-plasma" state of strongly interacting matter and search for indications of a critical point. NA49 was one of the fixed target experiments at the CERN SPS accelerator.

Four large volume time projection chambers (TPC) are the main components of the experimental setup [1]. They were used for measurement and identification of charged particle tracks. The ring calorimeter (RCAL) with pseudorapidity acceptance

#### 3. Elliptic flow measurement

The current analysis used Pb+Pb collision events at 40

#### Event plane corrections

Evaluation of the symmetry plane angle is based on flow vectors [3]:

(2)

(3)
where the weights

Then, the event plane angle

(4)

Next, the recentering procedure [3] was applied for each 5% centrality window in order to correct non-uniform detector acceptance:

(4)

Finally, the flattening procedure was applied to remove higher order fluctuations [3]:

(4)

#### Event plane resolution correction

Two and three subevent methods were used to determine the event plane resolution correction

(4)

(4)

(4)
where subevent A and B are random subevents from the TPCs and C a subevent from RCAL. Results for

#### Results

Elliptic flow coefficients of negatively charged pions measured with the event plane method [3] are shown in Fig . 2 and Fig . 3 for different event classes and detectors. The values of

(4)
where

Measured elliptic flow of negatively charged pions from the NA49 experiment is compared with results from the STAR collaboration in Fig. 4. Results on

#### 4. Summary

Elliptic flow

#### Acknowledgments

We thank P. Seyboth for providing information about the RCAL. Also this work was partially supported by the Ministry of Science and Education of the Russian Federation, grant N 3.3380.2017/4.6, and by the National Research Nuclear University MEPhI in the framework of the Russian Academic Excellence Project (contract No. 02.a03.21.0005, 27.08.2013).