Consequences of laser transverse imperfections on laser wakefield acceleration at the Apollon facility

With the currently available laser powers, it is possible to reach the blowout regime in the Laser WakeField Acceleration (LWFA) where the electrons are completely expelled off-axis behind the laser pulse. This regime is particularly interesting thanks to its linear focusing forces and to its accelerating forces that are independent of the transverse coordinates. In fact, these features ensure a quite stable propagation of electron bunches with low phase-space volume. In this context, the Apollon laser is designed to reach an exceptional multi-petawatt laser peak power, thus aiming at achieving unprecedented accelerating gradients and bringing a scientific breakthrough in the field of LWFA. Since the quality of the self-injected electron bunches is very sensitive to the condition of the laser, it is very important to take into account realistic laser features when performing LWFA simulations. In this paper, we aim at understanding the implications of laser imperfections on the electrons produced with the self-injection scheme in the bubble regime. For this purpose, we carry on a numerical study of LWFA where we include experimentally measured laser profiles from the Apollon facility in full three dimensional Particle-In-Cell simulations

Forward pi^0 Production and Associated Transverse Energy Flow in Deep-Inelastic Scattering at HERA

Deep-inelastic positron-proton interactions at low values of Bjorken-x down to x \approx 4.10^-5 which give rise to high transverse momentum pi^0 mesons are studied with the H1 experiment at HERA. The inclusive cross section for pi^0 mesons produced at small angles with respect to the proton remnant (the forward region) is presented as a function of the transverse momentum and energy of the pi^0 and of the four-momentum transfer Q^2 and Bjorken-x. Measurements are also presented of the transverse energy flow in events containing a forward pi^0 meson. Hadronic final state calculations based on QCD models implementing different parton evolution schemes are confronted with the data.Comment: 27 pages, 8 figures and 3 table

Multi-Jet Event Rates in Deep Inelastic Scattering and Determination of the Strong Coupling Constant

Jet event rates in deep inelastic ep scattering at HERA are investigated applying the modified JADE jet algorithm. The analysis uses data taken with the H1 detector in 1994 and 1995. The data are corrected for detector and hadronization effects and then compared with perturbative QCD predictions using next-to-leading order calculations. The strong coupling constant alpha_S(M_Z^2) is determined evaluating the jet event rates. Values of alpha_S(Q^2) are extracted in four different bins of the negative squared momentum transfer~\qq in the range from 40 GeV2 to 4000 GeV2. A combined fit of the renormalization group equation to these several alpha_S(Q^2) values results in alpha_S(M_Z^2) = 0.117+-0.003(stat)+0.009-0.013(syst)+0.006(jet algorithm).Comment: 17 pages, 4 figures, 3 tables, this version to appear in Eur. Phys. J.; it replaces first posted hep-ex/9807019 which had incorrect figure 4

Measurement of Leading Proton and Neutron Production in Deep Inelastic Scattering at HERA

Deep--inelastic scattering events with a leading baryon have been detected by the H1 experiment at HERA using a forward proton spectrometer and a forward neutron calorimeter. Semi--inclusive cross sections have been measured in the kinematic region 2 <= Q^2 <= 50 GeV^2, 6.10^-5 <= x <= 6.10^-3 and baryon p_T <= MeV, for events with a final state proton with energy 580 <= E' <= 740 GeV, or a neutron with energy E' >= 160 GeV. The measurements are used to test production models and factorization hypotheses. A Regge model of leading baryon production which consists of pion, pomeron and secondary reggeon exchanges gives an acceptable description of both semi-inclusive cross sections in the region 0.7 <= E'/E_p <= 0.9, where E_p is the proton beam energy. The leading neutron data are used to estimate for the first time the structure function of the pion at small Bjorken--x.Comment: 30 pages, 9 figures, 2 tables, submitted to Eur. Phys.

Measurement of inclusive jet cross-sections at low Q 2 at HERA ∗

The single-inclusive cross-section for jet production in deep inelastic e-p scattering (DIS) at HERA is measured for photon virtualities Q 2 between 5 and 100 GeV 2, differentially in Q 2, in transverse jet energy ET, in E 2 T/Q 2 and in pseudorapidity ηLAB. In most of the phase space these data are well described by QCD calculations in next-to-leading order (NLO) using a renormalization scale µR = ET. Significant discrepancies are observed only for jets in the proton beam direction with ET below 20 GeV and Q 2 below 20 GeV 2. Jet production in DIS is an ideal testing ground for perturbative QCD (pQCD). Experimental results on (multi) jet production at HERA and elsewhere cover a wide range of Q 2 and have been found to be well described by pQCD in next-to-leading order in the strong coupling constant αS. The study of inclusive jet production, in particular, gives access to a bigger phase space, and avoids phase space regions where pQCD calculations are infrared sensitive. The data presented here close the gap of inclusive jet production at Q 2 below 100 GeV 2. For details on the experimental measurement and on the theory predictions see [1] and references therein. Event Selection and Measured Observables The present analysis is based on a total integrated luminosity of 21.1 pb −1 of e +-p collision data collected with the H1 detector [2] in 96 and 97. DIS events are selected by requiring the presence in the electromagnetic calorimeter of an electron with E&gt; 10 GeV and with an angle above 157 o with respect to the proton beam direction. The kinematic range is then defined by requiring a virtuality Q 2 between 5 and 100 GeV 2 and an inelasticity y between 0.2 and 0.6, as determined from the scattered electron

Mesure de la constante de couplage forte as avec les jets hadroniques en diffusion inelastique profonde

PALAISEAU-Polytechnique (914772301) / SudocSudocFranceF

Consequences of laser transverse imperfections on laser wakefield acceleration at the Apollon facility

International audienceWith the currently available laser powers, it is possible to reach the blowout regime in the Laser WakeField Acceleration (LWFA) where the electrons are completely expelled off-axis behind the laser pulse. This regime is particularly interesting thanks to its linear focusing forces and to its accelerating forces that are independent of the transverse coordinates. In fact, these features ensure a quite stable propagation of electron bunches with low phase-space volume. In this context, the Apollon laser is designed to reach an exceptional multi-petawatt laser peak power, thus aiming at achieving unprecedented accelerating gradients and bringing a scientific breakthrough in the field of LWFA. Since the quality of the self-injected electron bunches is very sensitive to the condition of the laser, it is very important to take into account realistic laser features when performing LWFA simulations. In this paper, we aim at understanding the implications of laser imperfections on the electrons produced with the self-injection scheme in the bubble regime. For this purpose, we carry on a numerical study of LWFA where we include experimentally measured laser profiles from the Apollon facility in full three dimensional Particle-In-Cell simulations