| 1. |
- Abelev, Betty, et al.
(författare)
-
Long-range angular correlations on the near and away side in p-Pb collisions at root S-NN=5.02 TeV
- 2013
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 719:1-3, s. 29-41
-
Tidskriftsartikel (refereegranskat)abstract
- Angular correlations between charged trigger and associated particles are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV for transverse momentum ranges within 0.5 < P-T,P-assoc < P-T,P-trig < 4 GeV/c. The correlations are measured over two units of pseudorapidity and full azimuthal angle in different intervals of event multiplicity, and expressed as associated yield per trigger particle. Two long-range ridge-like structures, one on the near side and one on the away side, are observed when the per-trigger yield obtained in low-multiplicity events is subtracted from the one in high-multiplicity events. The excess on the near-side is qualitatively similar to that recently reported by the CMS Collaboration, while the excess on the away-side is reported for the first time. The two-ridge structure projected onto azimuthal angle is quantified with the second and third Fourier coefficients as well as by near-side and away-side yields and widths. The yields on the near side and on the away side are equal within the uncertainties for all studied event multiplicity and p(T) bins, and the widths show no significant evolution with event multiplicity or p(T). These findings suggest that the near-side ridge is accompanied by an essentially identical away-side ridge. (c) 2013 CERN. Published by Elsevier B.V. All rights reserved.
|
|
| 2. |
- Abelev, Betty, et al.
(författare)
-
Measurement of prompt J/psi and beauty hadron production cross sections at mid-rapidity in pp collisions at root s=7 TeV
- 2012
-
Ingår i: Journal of High Energy Physics. - 1029-8479. ; :11
-
Tidskriftsartikel (refereegranskat)abstract
- The ALICE experiment at the LHC has studied J/psi production at mid-rapidity in pp collisions at root s = 7 TeV through its electron pair decay on a data sample corresponding to an integrated luminosity L-int = 5.6 nb(-1). The fraction of J/psi from the decay of long-lived beauty hadrons was determined for J/psi candidates with transverse momentum p(t) > 1,3 GeV/c and rapidity vertical bar y vertical bar < 0.9. The cross section for prompt J/psi mesons, i.e. directly produced J/psi and prompt decays of heavier charmonium states such as the psi(2S) and chi(c) resonances, is sigma(prompt J/psi) (p(t) > 1.3 GeV/c, vertical bar y vertical bar < 0.9) = 8.3 +/- 0.8(stat.) +/- 1.1 (syst.)(-1.4)(+1.5) (syst. pol.) mu b. The cross section for the production of b-hadrons decaying to J/psi with p(t) > 1.3 GeV/c and vertical bar y vertical bar < 0.9 is a sigma(J/psi <- hB) (p(t) > 1.3 GeV/c, vertical bar y vertical bar < 0.9) = 1.46 +/- 0.38 (stat.)(-0.32)(+0.26) (syst.) mu b. The results are compared to QCD model predictions. The shape of the p(t) and y distributions of b-quarks predicted by perturbative QCD model calculations are used to extrapolate the measured cross section to derive the b (b) over bar pair total cross section and d sigma/dy at mid-rapidity.
|
|
| 3. |
- Hanstorp, Dag, 1960, et al.
(författare)
-
A versatile system for optical manipulation experiments
- 2017
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. SPIE Nanoscience + Engineering, 2017, San Diego, California, United States. - : SPIE. - 0277-786X .- 1996-756X. - 9781510611528
-
Konferensbidrag (refereegranskat)abstract
- Downloading of the abstract is permitted for personal use only. In this paper a versatile experimental system for optical levitation is presented. Microscopic liquid droplets are produced on demand from piezo-electrically driven dispensers. The charge of the droplets is controlled by applying an electric field on the piezo-dispenser head. The dispenser releases droplets into a vertically focused laser beam. The size and position in 3 dimensions of trapped droplets are measured using two orthogonally placed high speed cameras. Alternatively, the vertical position is determined by imaging scattered light onto a position sensitive detector. The charge of a trapped droplets is determined by recording its motion when an electric field is applied, and the charge can be altered by exposing the droplet to a radioactive source or UV light. Further, spectroscopic information of the trapped droplet is obtained by imaging the droplet on the entrance slit of a spectrometer. Finally, the trapping cell can be evacuated, allowing investigations of droplet dynamics in vacuum. The system is utilized to study a variety of physical phenomena, and three pilot experiments are given in this paper. First, a system used to control and measure the charge of the droplet is presented. Second, it is demonstrated how particles can be made to rotate and spin by trapping them using optical vortices. Finally, the Raman spectra of trapped glycerol droplets are obtained and analyzed. The long term goal of this work is to create a system where interactions of droplets with the surrounding medium or with other droplets can be studied with full control of all physical variables.
|
|
| 4. |
- Ivanov, Maksym, et al.
(författare)
-
Intensity modulated terahertz vortex wave generation in air plasma by two-color femtosecond laser pulses
- 2019
-
Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 44:15, s. 3889-3892
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the generation of broadband terahertz (THz) pulses with phase singularity from air plasmas created by fundamental and second harmonic laser pulses. We show that when the second harmonic beam carries a vortex charge, the THz beam acquires a vortex structure as well. A generic feature of this THz vortex is that the intensity is modulated along the azimuthal angle, which can be attributed to the spatially varying relative phase difference between the two pump harmonics. Fully space- and time-resolved numerical simulations reveal that transverse instabilities of the pump further affect the emitted THz field along nonlinear propagation, which may produce additional singularities resulting in a rich vortex structure. The predicted intensity modulation is experimentally demonstrated with a thermal camera, in excellent agreement with simulation results. The presence of phase singularities in the experiment is revealed by astigmatic transformation of the beam using a cylindrical mirror. (c) 2019 Optical Society of America
|
|
| 5. |
- Ivanov, Maksym, et al.
(författare)
-
Optical manipulation for studies of collisional dynamics of micron-sized droplets under gravity
- 2017
-
Ingår i: Optics Express. - 1094-4087. ; 25:2, s. 1391-1404
-
Tidskriftsartikel (refereegranskat)abstract
- © 2017 Optical Society of America.A new experimental technique for creating and imaging collisions of micron-sized droplets settling under gravity is presented. A pair of glycerol droplets is suspended in air by means of two optical traps. The droplet relative velocities are determined by the droplet sizes. The impact parameter is precisely controlled by positioning the droplets using the two optical traps. The droplets are released by turning off the trapping light using electro-optical modulators. The motion of the sedimenting droplets is then captured by two synchronized high-speed cameras, at a frame rate of up to 63 kHz. The method allows the direct imaging of the collision of droplets without the influence of the optical confinement imposed by the trapping force. The method will facilitate efficient studies of the microphysics of neutral, as well as charged, liquid droplets and their interactions with light, electric field and thermodynamic environment, such as temperature or vapor concentration.
|
|
| 6. |
- Ivanov, Maksym, 1990, et al.
(författare)
-
Terahertz wave generation in air by femtosecond optical vortex pulses
- 2019
-
Ingår i: 2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019. - 9781557528209
-
Konferensbidrag (refereegranskat)abstract
- Terahertz (THz) radiation is of great current interest due to many applications such as nonlinear THz spectroscopy and imaging. One of the compact and effective methods to obtain very high THz field strengths and extremely broadband spectral widths is THz wave generation from plasma filaments formed in air by focused bichromatic femtosecond laser pulses consisting of the first and the second harmonics (FH, SH). Here we investigate the effect of an azimuthal phase modulation of the SH carrying an optical vortex charge on the intensity and phase distribution of the THz pulse emitted from the laser induced plasma filament in air. We present both experimental and theoretical results. © 2019 IEEE.
|
|
| 7. |
|
|
| 8. |
- Vaičaitis, Virgilijus, et al.
(författare)
-
Generation of broadband THz beams with azimuthally modulated phase and intensity by femtosecond laser pulses in air plasma
- 2019
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - 0277-786X .- 1996-756X. ; 11370, s. 443-444
-
Konferensbidrag (refereegranskat)abstract
- We report efficient generation of the broadband terahertz (THz) radiation by bichromatic femtosecond laser pulses with flat phase fronts or with a phase singularity focused in air. As a pump source, the fundamental and second harmonic radiations of a femtosecond Ti:sapphire laser were used. While the fundamental laser beam had Gaussian intensity distribution and a flat phase front, the second harmonic beam had either flat or helical phase front forming an optical vortex. In both cases the angular spectra of THz radiation and azimuthal phase distributions of THz beams were investigated. It was found that when both the fundamental and second harmonic laser pulses had Gaussian profiles, the resulting THz radiation was generated as an axially symmetric cone with a flat phase front. However, when the Gaussian second harmonic beam was replaced by the one with optical singularity, the intensity and the phase of generated THz cone became modulated along the azimuthal angle. The spectrum of generated THz pulses spanned up to 50 THz in both cases. Our theoretical analysis based on the photocurrent model was in good agreement with the experimental data.
|
|
