Medium-induced flavor conversion and kaon spectra in electron-ion collisions

Multiple scattering and induced parton splitting lead to a medium modification of the QCD evolution for jet fragmentation functions and final hadron spectra. Medium-induced parton splittings not only lead to energy loss of leading partons and suppression of leading hadron spectra, but also modify the flavor composition of a jet due to induced flavor conversion via gluon emission and quark pair production and annihilation. Through a numerical study of the medium-modified QCD evolution, leading $K^{-}$ strange meson spectra are found to be particularly sensitive to the medium-induced flavor conversion in semi-inclusive deeply inelastic scatterings (SIDIS) off a large nucleus. The induced flavor conversion can lead to an increased number of gluons and sea quarks in a jet shower and, as a consequence, enhance the leading $K^{-}$ spectrum to counter the effect of parton energy loss in SIDIS with large momentum fractions $x_B$, where the struck quarks are mostly valence quarks of the nucleus.

Figure 1

Parton fragmentation functions for $K^{-}$ in vacuum at $Q^2\approx 10{\mathrm{GeV}}^2$ from (a) the HKN parametrization [29] and (b) DSS07 parametrization [30].

Figure 2

Ratios of mFFs to the vacuum ones for $K^{-}$ from different partons with initial energy $\nu =10$ GeV and $Q^2=10{\mathrm{GeV}}^2$ in SIDIS off a Pb target. (a) HKN and (b) DSS07 parametrizations of vacuum FFs are used in these calculations.

Figure 3

The nuclear modification factor for (a) $K^{+}$ and (b) $K^{-}$ for different initial quark energy $\nu$ in SIDIS off a Pb target at $x_B=0.1$ with HKN parametrization of vacuum FFs. Errors are from the HKN parametrization of vacuum FFs with 68% CL propagated through the mDGLAP evolution equations.

Figure 4

The nuclear modification factor for (a) $K^{+}$ and (b) $K^{-}$ for different initial quark energy $\nu$ in SIDIS off a Pb target at $x_B=0.1$ with DSS07 parametrization of vacuum FF's. Errors are from the DSS07 parametrization of vacuum FFs with 90% CL propagated through the mDGLAP evolution equations.

Figure 5

The same as Fig. 3 except for $x_B=0.5$.

Figure 6

The same as Fig. 4 except for $x_B=0.5$.

Figure 7

The nuclear modification factor for $K^{-}$ for an initial quark energy $\nu =10$ GeV in SIDIS off a Pb target at (a) $x_B=0.5$ and (b) $x_B=0.1$ with HKN parametrization of vacuum FFs and nucleon PDFs (solid), EPS09 (dashed) [34] and DSSZ (dotted) [35] parametrization of nPDFs.

Figure 8

The same as Fig. 7 except with DSS07 parametrization of vacuum FFs.