  According to string theory, string ball is a highly excited long string which
decays to standard model particles at the Hagedorn temperature with thermal
spectrum. If there are extra dimensions, the string scale can be $\sim$ TeV,
and we should produce string balls at CERN LHC. In this paper we study top
quark production from string balls at LHC and compare with the parton fusion
results at NNLO using pQCD. We find significant top quark production from
string balls at LHC which is comparable to standard model pQCD results. We also
find that $\frac{d\sigma}{dp_T}$ of top quarks from string balls does not
decrease significantly with increase in $p_T$, whereas it deceases sharply in
case of standard model pQCD scenario. Hence, in the absence of black hole
production at LHC, an enhancement in top quark cross section and its abnormal
$p_T$ distribution can be a signature of TeV scale string physics at LHC.
String theory is also studied at LHC via string Regge excitations in the weak
coupling limit in model independent framework. Since massive quark production
amplitude is not available in string Regge excitations scenario, we compute
massless quark production in string Regge excitations scenario and make a clear
comparison with that produced from string balls at LHC for a given luminosity.
