Fragmentation functions for light charged hadrons with complete quark flavour separation

We define a general scheme for the evolution of fragmentation functions which resums both soft gluon logarithms and mass singularities in a consistent manner and to any order, and requires no additional theoretical assumptions. Using the Double Logarithmic Approximation and the known perturbative results for the splitting functions, we present our scheme with the complete contribution from the double logarithms, being the largest soft gluon logarithms. We show that the resulting approximation is more complete than the Modified Leading Logarithm Approximation even with the fixed order contribution calculated to leading order only, and find, after using it to fit quark and gluon fragmentation functions to experimental data, that this approximation in our scheme gives a good description of the data from the largest xp values to the peak region in ξ = ln(1/xp), in contrast to other approximations. In addition, we develop a treatment of hadron mass effects which gives additional improvements at large ξ.

show abstract

“…[2] by using the method of the last paragraph of Sec. IV, since the current range of 0.1 < x p < 1 is very limited.…”

Section: Discussionmentioning

confidence: 99%

Resummation of soft gluon logarithms in the DGLAP evolution of fragmentation functions

et al. 2006

Self Cite

View full text Add to dashboard Cite

show abstract

“…This is to some degree surprising, as the AKK fragmentation functions [2] (which roughly describe the STAR data on proton production in p-p collisions [3]) indicate that ∼ 80 % of p+p production comes from gluon jets whereas only ∼ 40 % of pion production is gluon-driven. This is not so in the older KKP set of fragmentation functions [4] which consequently underpredict proton production at STAR.…”

mentioning

confidence: 99%

“…the fragmentation function with momentum fraction z at scale µ 2 F [2], and from this we compute the nuclear modification factor R AA as R AA (p T , y) = dN h AA /dp T dy T AA (b)dσ pp /dp T dy .…”

mentioning

confidence: 99%

Proton-antiproton suppression in200AGeV Au-Au collisions

Renk

Eskola

2007

Phys. Rev. C

View full text Add to dashboard Cite

We discuss the measured nuclear suppression of p + p production in 200 AGeV Au-Au collisions at RHIC within radiative energy loss. For the AKK set of fragmentation functions, proton production is dominated by gluons, giving rise to the expectation that the nuclear suppression for p + p should be stronger than for pions due to the stronger coupling of gluons to the quenching medium. Using a hydrodynamical description for the soft matter evolution, we show that this is indeed seen in the calculation. However, the expected suppression factors for pions and protons are sufficiently similar that a discrimination with present data is not possible. In the high pT region above 6 GeV where the contributions of hydrodynamics and recombination to hadron production are negligible, the model calculation is in good agreement with the data on p + p suppression. The STAR collaboration has measured the nuclear suppression ratio R CP (yield for 0 − 12% central collisions divied by yield for 60 − 80% peripheral collisions) for π + + π − and p + p in 200 AGeV Au-Au collisions [1], finding that the suppression pattern of both pions and protons is very similar in the 6+ GeV momentum region. This is to some degree surprising, as the AKK fragmentation functions [2] (which roughly describe the STAR data on proton production in p-p collisions [3]) indicate that ∼ 80 % of p+p production comes from gluon jets whereas only ∼ 40 % of pion production is gluon-driven. This is not so in the older KKP set of fragmentation functions [4] which consequently underpredict proton production at STAR. However, gluons as colour octet states are expected to undergo stronger energy loss in medium than quarks, thus the dominance of gluon jets in hard proton production should map into a stronger suppression of p + p production as compared to π + + π − production. It becomes thus a quantitative question in the energy loss model to check how large this difference in suppression should be and if present data are able to resolve it. A framework to study energy loss within full expansion dynamics of soft matter has been presented in [5] and extended to a 3-d hydrodynamical model [6] in [7]. We utilize this framework to address the above question. We stress that given the scenario describing pionic R AA , the change to study the suppression of protons is only the trivial change of the fragmentation function, no further parameters are adjusted. Furthermore, since the AKK fragmentation function overpredicts p + p production in the high p T region in p-p collisions (and the fragmentation function of q(q) → p(p) is well constrained), thus overemphasizing the role of gluons, we stress that our results are an upper limit for the expected difference between proton and pion suppression. Let us now discuss the treatment of partons propagating * Electronic address: trenk@phys.jyu.fi † Electronic address: kari.eskola@phys.jyu.fi through the medium: our calculation follows the BDMPS formalism for radiative energy loss [8] using quenching weights as introduced by Salgado and W...

show abstract

“…How did these protons acquire their moderately high p T is an unknown. The successful reproduction of STAR proton cross-section at mid-rapidity in p+p collisions [10] with NLO calculations that make use of a newly released set of fragmentation functions dubbed the AKK set [11], has been advanced as an indication of the important contribution of the gluon fragmentation into protons or anti-protons. The same comparison, done with the p +p sum at y=2.95, can be seen in the right-most panel of Fig.…”

Section: Figurementioning

confidence: 99%