| 1. |
- Aktas, A, et al.
(författare)
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Evidence for a narrow anti-charmed baryon state
- 2004
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 588:1-2, s. 17-28
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Tidskriftsartikel (refereegranskat)abstract
- A narrow resonance in D*(-)p and D*(+)(p) over bar invariant mass combinations is observed in inelastic electron-proton collisions at centre-of-mass energies of 300 GeV and 320 GeV at HERA. The resonance has a mass of 3099 +/- 3(stat.) +/- 5(syst.) MeV and a measured Gaussian width of 12 +/- 3(stat.) MeV, compatible with the experimental resolution. The resonance is interpreted as an anti-charmed baryon with a minimal constituent quark composition of uudd (c) over bar, together with the charge conjugate. (C) 2004 Elsevier B.V. All rights reserved.
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| 2. |
- Armesto, Nestor, et al.
(författare)
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Coherence effects and broadening in medium-induced QCD radiation off a massive q(q)over-bar antenna
- 2012
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; :1
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Tidskriftsartikel (refereegranskat)abstract
- Studies of medium-induced QCD radiation usually rely on the calculation of single-gluon radiation spectrum off an energetic part on traversing an extended colored medium. Recently, the importance of interference effects between emitters in the medium has been explored. In this work we extend previous studies by calculating the single-gluon coherent spectrum off an antenna consisting of a massive quark-antiquark pair. Interferences dominate the spectrum of soft gluons, which are mainly emitted outside of the cone made by the antenna opening angle, while the antenna results in a superposition of independent emitters above a critical gluon energy scale. We study the interplay between the dead-cone effect and medium-induced jet broadening in both cases of soft and hard gluons and present results on energy loss distributions.
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| 3. |
- Armesto, Nestor, et al.
(författare)
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Mass effect and coherence in medium-induced QCD radiation off a q(q)over-bar antenna
- 2011
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Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 38:12
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Tidskriftsartikel (refereegranskat)abstract
- The medium-induced one-gluon radiation spectrum off a massive quark-antiquark (q (q) over bar) antenna traversing a colored QCD medium is calculated in this contribution. The gluon spectrum off the antenna computed at first order in the opacity expansion is collinear finite but infrared divergent, which is different from the result obtained from an independent emitter which is both infrared and collinear finite. The interference between emitters dominates the soft gluon radiation when the antenna opening angle is small and the emitted gluon is soft, whereas the antenna behaves like a superposition of independent emitters when the opening angle is large and the radiated gluon is hard. As a phenomenological consequence, we investigate the energy lost by the projectiles due to the radiation. In general, the size of the mass effects is similar in both cases.
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| 4. |
- Casalderrey-Solana, Jorge, et al.
(författare)
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New picture of jet quenching dictated by color coherence
- 2013
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 725:4-5, s. 357-360
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Tidskriftsartikel (refereegranskat)abstract
- We propose a new description of the jet quenching phenomenon observed in nuclear collisions at high energies in which coherent parton branching plays a central role. This picture is based on the appearance of a dynamically generated scale, the jet resolution scale, which controls the transverse resolution power of the medium to simultaneously propagating color probes. Since from the point of view of the medium all partonic jet fragments within this transverse distance act coherently as a single emitter, this scale allows us to rearrange the jet shower into effective emitters. We observe that in the kinematic regime of the LHC, the corresponding characteristic angle is comparable to the typical opening angle of high-energy jets such that most of the jet energy is contained within a non-resolvable color coherent inner core. Thus, a sizable fraction of the jets is unresolved, losing energy as a single patron without modifications of their intra-jet structure. (C) 2013 Elsevier B.V. All rights reserved.
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| 5. |
- Mehtar-Tani, Yacine, et al.
(författare)
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Jets in QCD media: From color coherence to decoherence
- 2012
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 707:1, s. 156-159
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Tidskriftsartikel (refereegranskat)abstract
- We investigate soft gluon radiation off a quark-antiquark antenna in both color singlet and octet configurations traversing a dense medium. We demonstrate that, in both cases, multiple scatterings lead to a gradual decoherence of the antenna radiation as a function of the medium density. In particular, in the limit of a completely opaque medium, total decoherence is obtained, i.e., the quark and the antiquark radiate as independent emitters in vacuum, thus losing memory of their origin. (C) 2011 Elsevier B.V. All rights reserved.
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| 6. |
- Mehtar-Tani, Y., et al.
(författare)
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Onset of color decoherence for soft gluon radiation in a medium
- 2011
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Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 38:12
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Tidskriftsartikel (refereegranskat)abstract
- We report on recent studies of the phenomenon of color decoherence in jets in QCD media. The effect is most clearly observed in the radiation pattern of a quark-antiquark antenna, created in the same quantum state, traversing a dense color deconfined plasma. Multiple scattering with the medium color charges gradually destroys the coherence of the antenna. In the limit of opaque media, this ultimately leads to independent radiation off the antenna constituents. Accordingly, radiation off the total charge vanishes implying a memory loss effect induced by the medium.
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| 7. |
- Mehtar-Tani, Yacine, et al.
(författare)
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The radiation pattern of a QCD antenna in a dense medium
- 2012
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; :10
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Tidskriftsartikel (refereegranskat)abstract
- We calculate the radiation spectrum off a q (q) over bar pair of a fixed opening angle theta(q (q) over bar) traversing a medium of length L. Multiple interactions with the medium are handled in the harmonic oscillator approximation, valid for soft gluon emissions. We discuss the time-scales relevant to the decoherence of correlated partons traversing the medium and demonstrate how this relates to the hard scale that govern medium-induced radiation. For large angle radiation, the hard scale is given by Q(hard) = max(r(perpendicular to)(-1), Q(s)), where r(perpendicular to) = theta L-qq is the probed transverse size and Q(s) is the maximal transverse momentum accumulated by the emitted gluon in the medium. These situations define in turn two distinct regimes, which we call "dipole" and "decoherence" regimes, respectively, which are discussed in detail. A feature common to both cases is that coherence of the radiation is restored at large transverse momenta, k(perpendicular to) > Q(hard).
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| 8. |
- Mehtar-Tani, Yacine, et al.
(författare)
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The radiation pattern of a QCD antenna in a dilute medium
- 2012
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; :4
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Tidskriftsartikel (refereegranskat)abstract
- Radiative interferences in the multi-parton shower is the building block of QCD jet physics in vacuum. The presence of a hot medium made of quarks and gluons is expected to alter this interference pattern. To study these effects, we derive the gluon emission spectrum off a color-correlated quark-antiquark pair (antenna) traversing a colored medium to first order in the medium density. The resulting induced gluon distribution is found to be governed by the hardest scale of the problem. In our setup, this can either be the inverse antenna transverse size, r(perpendicular to)(-1), or the scale related to the transverse color correlation length in the medium, which is given by the Debye mass m(D). This emerging scale opens the angular phase space of emissions off the antenna compared to the vacuum case and gives rise to a typical transverse momentum of the medium-induced emitted gluons, < k(perpendicular to)(2)>(med) similar to max(r(perpendicular to)(-1)m(D)). Above the hard scale interference effects suppress the spectrum resulting in the restoration of vacuum coherence.
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