119118563
Transverse momentum broadening in semi-inclusive deep inelastic scattering at next-to-leading order
Within the framework of higher-twist collinear factorization, transverse momentum broadening for the final hadrons in semi-inclusive deeply inelastic $e+A$ collisions is studied at the next-to-leading order (NLO) in perturbative QCD. Through explicit calculations of real and virtual corrections at twist-4, the transverse momentum weighted differential cross section due to double scattering is shown to factorize at NLO and can be expressed as a convolution of twist-4 nuclear parton correlation functions, the usual twist-2 fragmentation functions and hard parts which are finite and free of any divergences. A QCD evolution equation is also derived for the renormalized twist-4 quark-gluon correlation function which can be applied to future phenomenological studies of transverse momentum broadening and jet quenching at NLO.
33523602
Role of multiple minijets in high-energy hadronic reactions.
The multiplicity distributions of charged particles in high-energy hadron collisions including the production of multiple minijets are considered in the framework of the eikonal formalism. Large-multiplicity events at high energies are found to be dominated by the production of many jets with 2{le}{ital P}{sub {ital T}}{le}4 GeV. The contributions from larger-{ital P}{sub {ital T}} minijets become prevailing for high-multiplicity fluctuations in narrow rapidity intervals.
42468399
Berry curvature and four-dimensional monopoles in the relativistic chiral kinetic equation.
We derive a relativistic chiral kinetic equation with manifest Lorentz covariance from Wigner functions of spin-1/2 massless fermions in a constant background electromagnetic field. It contains vorticity terms and a four-dimensional Euclidean Berry monopole which gives an axial anomaly. By integrating out the zeroth component of the 4-momentum p, we reproduce the previous three-dimensional results derived from the Hamiltonian approach, together with the newly derived vorticity terms. The phase space continuity equation has an anomalous source term proportional to the product of electric and magnetic fields (FσρF[over ˜]σρ∼EσBσ). This provides a unified interpretation of the chiral magnetic and vortical effects, chiral anomaly, Berry curvature, and the Berry monopole in the framework of Wigner functions.
126140598
Report of the RHIC Workshop p + A subgroup
119298211
Relics of Minijets amid Anisotropic Flows in High-energy Heavy-ion Collisions
Two dimensional low-$p_T$ dihadron correlations in azimuthal angle $\phi$ and pseudo-rapidity $\eta$ in high-energy heavy-ion collisions are investigated within both the HIJING Monte Carlo model and an event-by-event (3+1)D ideal hydrodynamic model. Without final-state interaction and collective expansion, dihadron correlations from HIJING simulations have a typical structure from minijets that contains a near-side two-dimensional peak and an away-side ridge along the $\eta$-direction. In contrast, event-by-event (3+1)D ideal hydrodynamic simulations with fluctuating initial conditions from the HIJING+AMPT model produce a strong dihadron correlation that has an away-side as well as a near-side ridge. Relics of intrinsic dihadron correlation from minijets in the initial conditions still remain as superimposed on the two ridges. By varying initial conditions from HIJING+AMPT, we study effects of minijets, non-vanishing initial flow and longitudinal fluctuation on the final state dihadron correlations. With a large rapidity gap, one can exclude near-side correlations from minijet relics and dihadron correlations can be described by the superposition of harmonic flows up to the 6th order. When long-range correlations with a large rapidity gap are subtracted from short-range correlations with a small rapidity gap, the remaining near-side dihadron correlations result solely from relics of minijets. Low transverse momentum hadron yields per trigger ($p_T^{\rm trig} <4$ GeV/$c$, $p_T^{\rm asso}<2$ GeV/$c$) in central heavy-ion collisions are significantly enhanced over that in p+p collisions while widths in azimuthal angle remain the same, in qualitative agreement with experimental data.
17734649
Probe initial parton density and formation time via jet quenching
Medium modification of jet fragmentation function due to multiple scattering and induced gluon radiation leads directly to jet quenching or suppression of leading particle distribution from jet fragmentation. One can extract an effective total parton energy loss which can be related to the total transverse momentum broadening. For an expanding medium, both are shown to be sensitive to the initial parton density and formation time. Therefore, one can extract the initial parton density and formation time from simultaneous measurements of parton energy loss and transverse momentum broadening. Implication of the recent experimental data on effects of detailed balance in parton energy loss is also discussed.
198138925
Oscillations of moments in high-energy nucleus-nucleus collisions
The definitions of density function and moment of multiplicity distribution are introduced, and the method of moment analysis in e+e- and proton-proton (pp) interactions is extended into nucleus-nucleus (AA) interactions. We analyze the data for relativistic nucleus-nucleus collisions and calculate the values of Hq for charged particle multiplicity distributions, by which we study systematically the dependences of Hqon incident energy, mass of colliding system, pseudorapidity interval, centrality and truncation of multiplicity. We compare the oscillation structures induced by e+ e-, pp and AA interactions, and the comparison and analysis are carried out between experimental data and QCD prediction. The latest results are given in this paper.
59430123
Drive Laser and Optical Transport Line for Photoinjector
A Photo-Cathode RF Gun is under development at NSRL. In this paper, the drive laser system is introduced and performance parameters are presented. We adopt a BNL type gun with laser illuminating the cathode at oblique incidence. To correct “time slew” and “elliptical spot” problems arisen on the cathode, an adjustable optical transport line is designed. INTRODUCTION Drive laser system is the key component of photocathode high-brightness injector. To ensure the high quality of electron beams offered for FEL, the injector request a reliable laser with prominent performance parameters, such as: pulse duration, beam profile, energy stability, pulse to pulse stability, pointing stability and phase jitter. We adopted a BNL type gun with p-polarized laser at oblique incidence, as to acquire high quantum efficiency and low thermal emittance [1]. But, the problems of “time slew” and “elliptical spot” will arise on the cathode. To correct them, an adjustable optical transport line was designed. DRIVE LASER SYSTEM We employed a drive laser system developed by High Q Laser Production GmbH [2]. It consisted of three main parts: oscillator with a timing stabilizer, a regenerative amplifier, and the frequency conversion part. Fig.1 is the layout of the drive laser system. Figure 1: Layout of the drive laser system Oscillator The seeding laser is a passive mode-locked laser with a semiconductor absorber mirror (SESAM). Its repetition rate is 102MHz, equal to 1/28 of 2856MHz S-band radio frequency, which is used for RF-gun. The timing stabilizer measure the phase offset between laser pulses and reference RF signal,then adjust the cavity length by putting one laser resonator mirror on a voltage controlled piezo to synchronize the two signals. Regenerative Amplifier The Pockels Cell captures pulses from the continuous seeding laser and determines the pass times of pulse in the regenerative amplifier cavity. The repetition rate of amplified pulses is optional from 10 to 100Hz. Frequency Conversion Part The SHG convert the IR light (1047nm) to green light (523nm), then the FHG convert the green light to UV light (262nm). The conversion efficiency is about 20% from the fundamental to the 4-th harmonics. LASER PERFORMANCE Pulse Duration The autocorrelation measurement result of IR pulse width was 8.3ps FWHW (deconvolved value taken from the Fig.2). The UV pulse width could be close to this value. Figure 2: Pulse width @ 1047 nm measured after Regenerative Amplifier @ 10Hz Beam Profile and Diameter The beam profile and diameter of UV laser pulse was measured by a CCD camera. Beam profile was shown as Fig.3. The beam diameter in X and Y direction were 2.051mm and 1.927mm respectively, which were statistical results of 300 shots. ___________________________________________ *Work supported by the second phase of “985” project hezhg@mail.ustc.edu.cn Proceedings of IPAC’10, Kyoto, Japan TUPEA035 07 Accelerator Technology T24 Lasers 1405 Pulse to Pulse Stability The UV pulse to pulse stability was measured by a photodiode connected with an oscilloscope. The area integration was measured. The fluctuation was calculated as: σ/μ∗100%. The result was about 0.8% over two hours, as shown in Fig.4. Figure 3: Beam profile of UV laser Figure 4: Pulse stability of UV over 2h: measured with 50 Ohm feed-through-terminated input; 500 MHz Bandwidth Tektronix TDS 3052, DC-coupled) Figure 5: Pointing stability measurement Figure 6:Long term energy stability measurement results Pointing Stability Beam pointing stability was measured with a lens of 600mm focal length. The CCD camera was placed at a distance of 700mm from the lens. Pointing stability of the beam centroid were 6.13μrad rms in X direction and 19.31μrad rms in Y direction. Fig.5 showed us the measured pointing stability of centroid point and also peak point. Energy Stability The long term (over 17 hours) energy fluctuation of UV measured by an energy meter was about 0.6% rms, as shown in Fig.6. The measurement precision is dependent on resolution of energy sensor. We think the actual value is higher than the measured one. Phase Jitter The phase jitter between oscillator and reference signal (signal generator: E8257D) was measured. The output signal was presented in Fig.7. Jitter calculation as: 6 0 1 1 14.2 360 102 10 360 rms rms OSC Jitter U mV f Hz = = × ∗ × o 387 rms Jitter fs = Scaling: 1000 1 mV = o To gain a low jitter, a signal generator with low phase noise is required. Signal generators E8257D and E8663B from Agilent are suitable. All of the laser performance parameters were listed on Table 1. OPTICAL TRANSPORT LINE Because of oblique incidence design of BNL type gun, two problems of “time slew” and “elliptical spot” will arise on photo-cathode. To correct them, two prisms were used to add appropriate negative time slew and TUPEA035 Proceedings of IPAC’10, Kyoto, Japan 1406 07 Accelerator Technology T24 Lasers ellipticity on laser pulse wave front. The added time slew is: τ=f(r,α), α is the angle of prism, r is the laser diameter on the prism. A variable beam expander was used to adjust the r . Therefore, the added time slew can be adjustable. The beam diameter on cathode can be controlled by a movable lens at the end of optical line. The Y direction beam diameter was also fore-adjusted by prisms. The sketch of optical transport line was shown as Fig.8. The beam profile after the two prisms was measured by a CCD camera, which was showed in Fig.9. The X direction diameter was compressed to 1.0mm, The Y direction diameter was still about 1.9mm. To compress the Y direction diameter, one just needs to rotate the prisms. The transmission efficiency of the two prisms is about 92%. Figure 7: SYNC-phase output signal, RMS=14.2mV Figure 8: Sketch of optical transport line Figure 9: Beam profile after two prisms Table 1: The performance of drive laser system 1 Wave length/nm 262 2 Pulse duration (FWHM) /ps 8.3 3 Oscillator frequency/MHz 102 4 UV repeat rate/Hz 10-100 5 UV energy/mJ 0-0.65 6 Energy fluctuation/rms 0.6% 7 Pulse to pulse stability/rms 0.8% 8 X direction Point stability/μrad 6.13 9 Y direction Point stability/μrad 19.31 10 Phase jitter/fs 387 11 X direction beam diameter/(1/emm) 2.051 12 Y direction beam diameter/(1/emm) 1.927 SUMMARY We described the drive laser system and presented the measured laser performance parameters. We also reported a preparatory design of optical transport line used to correct “time slew” and “elliptical spot” problems. We are going to reshape the laser pulse. In the aspect of spatial shaping, a commercial production from pi-shaper [3] and GBS-UVH [4] may be considered. Both of them showed favourable shaping effects [5] [6]. In the aspect of temporal shaping, we are going to try the pulse stacking method [6] [7]. REFERENCES [1] Xiang D et al. Nuclear Instruments and Methods in Physics Research A, 2006, (562): 48-52. [2] http://www.highqlaser.at/ [3] http://www.pishaper.com/ [4] http://search.newport.com/?sku=GBS-UV-H [5] D.H. Dowell et al., Proceedings of PAC07, Albuquerque, New Mexico, USA TUPMS058. [6] A.K. Sharma, T, Tsang, and T. Rao, PHYSICAL REVIEW SPECIAL TOPICS ACCELERATORS AND BEAMS 12, 033501 (2009). [7] H. Tomizawa et al., Proceedings of FEL 2007, Novosibirsk, Russia WEBAU01. Proceedings of IPAC’10, Kyoto, Japan TUPEA035 07 Accelerator Technology T24 Lasers 1407
118833690
Experimental spectra analysis in THM with the help of simulation based on the Geant4 framework
The Coulomb barrier and electron screening cause difficulties in directly measuring nuclear reaction cross sections of charged particles at astrophysical energies. The Trojan-horse method (THM) has been introduced to solve the difficulties as a powerful indirect tool. In order to understand experimental spectra better, Geant4 is employed to simulate the method. Validity and reliability of simulation data are examined by comparing the experimental data with simulated results. The Geant4 simulation of THM improves data analysis and is beneficial to the design for future related experiments.
15351369
Charm production in deep inelastic scattering from threshold to high Q2
Charm final states in deep inelastic scattering constitute ~ 25% of the inclusive cross-section at small x as measured at HERA. These data can reveal important information on the charm and gluon structure of the nucleon if they are interpreted in a consistent perturbative QCD framework which is valid over the entire energy range from threshold to the high energy limit. We describe in detail how this can be carried out order-by-order in PQCD in the generalized MSbar formalism of Collins (generally known as the ACOT approach), and demonstrate the inherent smooth transition from the 3-flavor to the 4-flavor scheme in a complete order αs calculation, using a Monte Carlo implementation of this formalism. This calculation is accurate to the same order as the conventional NLO F2 calculation in the limit Q/mc >> 1. It includes the resummed large logarithm contributions of the 3-flavor scheme (generally known in this context as the fixed-flavor-number or FFN scheme) to all orders of αsln (mc2/Q2). For the inclusive structure function, comparison with recent HERA data and the existing FFN calculation reveals that the relatively simple order-αs (NLO) 4-flavor (mc≠0) calculation can, in practice, be extended to rather low energy scales, yielding good agreement with data over the full measured Q2 range. The Monte Carlo implementation also allows the calculation of differential distributions with relevant kinematic cuts. Comparisons with available HERA data show qualitative agreement; however, they also indicate the need to extend the calculation to the next order to obtain better description of the differential distributions.
54894329
The ESS Cryogenic System
The European Spallation Source (ESS) is a neutron science facility funded by a collaboration of 17 European countries currently under design and construction in Lund, Sweden. Cryogenic cooling is vital for large sections at ESS. Mainly there is a 2.0 GeV proton linac using superconducting RF cavities operating at 2 K. In addition to cooling the SRF cavities, cryogenics is also used for the cold hydrogen moderator surrounding the target. ESS furthermore uses both liquid helium and liquid nitrogen in a number of the neutron instruments. There is also a cryogenic installation associated with the site acceptance testing of the ESS cryomodules [1]. This paper describes the conceptual design of the ESS cryogenic system including the expected heat loads and cryoplant features. Challenges associated with the required high reliability and turn-down capability will also be discussed.