The California Public Employees’ Retirement System, the biggest U.S. public pension fund, on Monday reported a 2.4 percent net rate of return for the 12 months ended June 30, slightly underperfoming its benchmark index. The results were announced by Calpers Chief Investment Officer Ted Eliopoulos at a meeting of the fund’s board in Walnut Creek, California. The total fund’s 12-month return on assets of 2.4 percent underperformed the benchmark by 9 basis points.