Fig. 6.2 has been inserted incorrectly. Correct Fig. 6.2:

Fig. 6.2
figure a

The smoothed mass spectrum of hadronic states as a function of mass. Experimental data: long-dashed green line with the 1,411 states known in 1967; short-dashed red line with the 4,627 states of mid 1990s. The solid blue line represents the exponential fit yielding T H = 158 MeV. Depending on the preexponential factor, a range T H = 150 ± 15 MeV is possible. Picture: CERN Courier September 2003 p. 30