Heavy Flavor Puzzle at LHC: A Serendipitous Interplay of Jet Suppression and Fragmentation

Abstract

Both charged hadrons and D mesons are considered to be excellent probes of QCD matter created in ultra relativistic heavy ion collisions. Surprisingly, recent experimental observations at LHC show the same jet suppression for these two probes, which -contrary to pQCD expectations -may suggest similar energy losses for light quarks and gluons in QCD medium. We here use our recently developed energy loss formalism in a finite size dynamical QCD medium to analyze this phenomenon that we denote as the "heavy flavor puzzle at LHC". We show that this puzzle is a consequence of an unusual combination of the suppression and fragmentation patterns, and in fact does not require invoking the same energy loss for light partons. Furthermore, we show that this combination leads to a simple relationship between the suppressions of light hadrons and D mesons and the corresponding bare quark suppressions. Consequently, a coincidental matching of jet suppression and fragmentation allows considerably simplifying the interpretation of the corresponding experimental data.

Suppression and energy loss in Quark-Gluon Plasma

“…Even more surprisingly, as shown in Fig. 2 (see also [6]), we see that our theoretical predictions, which are based on pQCD, are actually in excellent agreement with the data. We therefore ask why both the experimental data and the theoretical predictions are not in agreement with the qualitative expectations that we summarized in the previous slide.…”

“…Moreover, the gluons have significant (even dominant in the lower momentum region) contribution to charged hadron production [6]. Also, from the left panel in Fig.…”

“…There is also good agreement for non-prompt J/ψ, except for the last data point, which comes with large error bars. Now, if we look at the D mesons and charged hadrons, we can see that they reveal a puzzle, which we call the heavy flavor puzzle at LHC, and which we will briefly overview below (for more details, please refer to [6]). …”

“…With regard to the D mesons, it is well known that fragmentation does not modify bare charm quark suppression (see e.g. [6]). Consequently, the D meson suppression is indeed a genuine probe of the charm quark suppression in QCD medium.…”

“…Due to this, we will mainly concentrate on theoretical energy loss and suppression predictions, and how well these predictions can explain the experimental data. Note that in these proceedings only the main results will be reviewed; for the full account, the reader should refer to [4][5][6][7][8]. Figure 1 shows a scheme, which represents the main steps in the suppression calculations.…”