Problem with JPA [closed]

Classes and persistence.xml below. The problem is: entityManager is coming NULL.

 @ManagedBean(name="pessoaController")
    @SessionScoped
    public class PessoaController{
    private List<Pessoa> pessoas = new ArrayList<Pessoa>();

    public PessoaController() {
        new PessoaHome().findById(1);
    }

    public List<Pessoa> getPessoas(){
        return pessoas;
    }
    public void setPessoas(List<Pessoa> pessoas){
        this.pessoas = pessoas;
    }

}    


@Stateless
public class PessoaHome {

private static final Log log = LogFactory.getLog(PessoaHome.class);

@PersistenceContext
private EntityManager entityManager;

public void persist(Pessoa transientInstance) {
    log.debug("persisting Pessoa instance");
    try {
        entityManager.persist(transientInstance);
        log.debug("persist successful");
    } catch (RuntimeException re) {
        log.error("persist failed", re);
        throw re;
    }
}

public void remove(Pessoa persistentInstance) {
    log.debug("removing Pessoa instance");
    try {
        entityManager.remove(persistentInstance);
        log.debug("remove successful");
    } catch (RuntimeException re) {
        log.error("remove failed", re);
        throw re;
    }
}

public Pessoa merge(Pessoa detachedInstance) {
    log.debug("merging Pessoa instance");
    try {
        Pessoa result = entityManager.merge(detachedInstance);
        log.debug("merge successful");
        return result;
    } catch (RuntimeException re) {
        log.error("merge failed", re);
        throw re;
    }
}

public Pessoa findById(int id) {
    log.debug("getting Pessoa instance with id: " + id);
    try {
        Pessoa instance = entityManager.find(Pessoa.class, id);
        log.debug("get successful");
        return instance;
    } catch (RuntimeException re) {
        log.error("get failed", re);
        throw re;
    }
}



<persistence-unit name="postgresDS" transaction-type="JTA">
    <jta-data-source>java:/postgresDS</jta-data-source>     

    <properties>
        <property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQLDialect"/>      
        <property name="hibernate.transaction.manager_lookup_class" value="org.hibernate.transaction.JBossTransactionManagerLookup"/>

        <property name="hibernate.show_sql" value="false"/>
        <property name="hibernate.format_sql" value="false"/>

        <property name="hibernate.hbm2ddl.auto" value="none" />
    </properties> 

</persistence-unit>