High Center Of Mass Energy Research Articles

Collision of particles and energy extraction in hyperscaling violation background

In this paper, we investigate particle collision near the charged black hole with hyperscaling violating factor under different conditions on mass, charge and θ parameters. In that case, we calculate the center of mass (CM) energy of two colliding particles on the black hole horizon. We find that unlike the other stationary black holes that have been studied so far, the center of mass energy on the horizon can be infinite in certain conditions. By computing the effective potential, we found that particles can collide with very high CM energy on the horizon at two states. The first is an uncharged black hole with small mass and small θ. The second is a massive black hole with the small value of charge and θ. In addition, we investigate the geodesic motion of particles and plot some possible orbits around this black hole. Then, we obtain the ergosphere extent of the hyperscaling violation charged black hole and found that increasing value of θ, the ergoregion limit reduces and we can not extract energy with large value of θ. We also found that energy extraction from the black hole only depends on the absorbed charge by the black hole.

Exploring black holes as particle accelerators: hoop-radius, target particles and escaping conditions

The possibility that rotating black holes could be natural particle accelerators has been subject of intense debate. While it appears that for extremal Kerr black holes arbitrarily high center of mass energies could be achieved, several works pointed out that both theoretical as well as astrophysical arguments would severely dampen the attainable energies. In this work we study particle collisions near Kerr black holes, by reviewing and extending the so far proposed scenarios. Most noticeably, we shall focus on the recently advanced target particle scenarios which were claimed to reach arbitrarily high energies even for Schwarzschild black holes. By implementing the hoop conjecture we show that these scenarios involving near-horizon target particles are in principle able to attain, sub-Planckian, but still ultra-high center of mass energies of the order of 1023–1025 eV even for non-extremal Kerr black holes. Furthermore, analysing the properties of particles produced in such collisions, we find that photons can escape to infinity. However, their energy is only of the order of the energy of the colliding particles and hence relatively low, which is the same conclusion previously reached in the literature about the original Bañados-Silk-West process. This finding points towards a general limitation of collisional Penrose processes, at least for what concerns their primary products.

Heavy Higgs bosons in 2HDM at a muon collider

We study the discovery potential of the non-Standard Model (SM) heavy Higgs bosons in the Two-Higgs-Doublet Models (2HDMs) at a multi-TeV muon collider and explore the discrimination power among different types of 2HDMs. We find that the pair production of the non-SM Higgs bosons via the universal gauge interactions is the dominant mechanism once above the kinematic threshold. Single Higgs boson production associated with a pair of heavy fermions could be important in the parameter region with enhanced Yukawa couplings. For both signal final states, ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ annihilation channels dominate over the vector boson fusion (VBF) processes, except at high center of mass energies where the VBF processes receive large logarithmic enhancement with the increase of energies. Single Higgs boson $s$-channel production in ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$-annihilation via the radiative return can also be important for the Type-L 2HDM in the very large $\mathrm{tan}\ensuremath{\beta}$ region, extending the kinematic reach of the heavy Higgs boson mass to the collider energy. Considering both the production and decay of non-SM Higgs bosons, signals can be identified over the Standard Model backgrounds. With the pair production channels via annihilation, 95% C.L. exclusion reaches in the Higgs mass up to the production mass threshold of $\sqrt{s}/2$ are possible when channels with different final states are combined. Including single production modes can extended the reach further. Different types of 2HDMs can be distinguishable for moderate and large values of $\mathrm{tan}\ensuremath{\beta}$.

Validity check of the KATIE parton level event generator in the kt -factorization and collinear frameworks

In the present paper, we check and study the validity of the \textsc{KaTie} parton level event generator, by calculating the inclusive electron-proton (ep) dijet and the Proton-proton (p-p) Drell-Yan electron-pair productions differential cross sections in the $k_t$- and collinear factorization frameworks. The Martin-Ryskin-Watt (MRW) unintegrated parton distribution functions (UPDFs) are used as the input UPDFs. The results are compared with those of ZEUS ep inclusive dijet and ATLAS p-p Drell-Yan electron-pair productions, experimental data. The \textsc{KaTie} parton level event generator can directly calculate the cross sections in the $k_t$-factorization framework. It is noticed that the lab to the Breit transformation in this generator is not correctly implemented by its author, so the produced output does not cover the ep ZEUS experimental data in which the mentioned transformation is applied. By fixing the above transformation in the \textsc{KaTie} generator code, we could appropriately produce the ep inclusive dijet differential cross section, in comparison with those of ZEUS data. It is also shown that the MRW at the NLO level, with the angular ordering constraint can successfully predict the ATLAS p-p Drell-Yan data. Finally, as it is expected, we conclude that the $k_t$-factorization is an appropriate tool for the small longitudinal parton momenta and high center of mass energies, with respect to the collinear one.

Charged particle motion around a magnetized Reissner-Nordström black hole

We investigate the dynamics of neutral and charged test particles around axially symmetric magnetized black hole spacetime. We consider its electromagnetic field in the black hole vicinity and study its impact on the dynamics of test particles. We determine the radius of the innermost stable circular orbit (ISCO) for neutral and charged test particles and show that the combined effect of black hole electric charge and magnetic field strongly affects the ISCO radius, thus shrinking its values. We also show that the ISCO radius of positively (negatively) charged particle initially gets increased (decreased) and then gets radically altered with an increase in the value of both black hole electric charge and test particle charge. It turns out that the repulsive (attractive) Coulomb force dominates over the Lorentz force arising from the black hole magnetic field. Typically, black hole rotation causes axially symmetric spacetime case. Similarly, it turns out that a magnetized black hole solution also causes axially symmetric spacetime as a consequence of the presence of magnetic field. We study a degeneracy for the value of the ISCO between the Kerr and the magnetized Reissner-Nordstr\"om black hole geometries and show that the combined effects of black hole charge and magnetic field can be mimicked by Kerr spacetime with the spin parameter up to $a/M\ensuremath{\approx}0.8$. Finally, we consider the center of mass energy of colliding particles and show that an increase in the values of black hole magnetic field and electric charge leads to high center of mass energy extracted by collision of two particles.

On the energy of the protons producing the very high-energy astrophysical neutrinos

We study the distribution of the energy of the protons that can produce an astrophysical neutrino with a given observed energy, in the TeV–PeV range, both through pp or pγ interactions. Due to the increasing multiplicity of the pion production at high center of mass energies, the resulting average proton energies can be much larger than the often used approximate value Ep ≃ 20Eν . Also the threshold of the pγ process can lead to a pronounced increase in the values of 〈Ep 〉/Eν for decreasing neutrino energies. The results depend sensitively on the assumed proton spectrum, since steeper spectra give less weight to the lower energy neutrino tail resulting from the decays of the abundant low-energy pions. In the pγ scenarios they also depend sensitively on the spectrum of the target photons. The results are in particular relevant to relate possible characteristics of the neutrino spectrum to those of the corresponding cosmic rays that generated them. We also discuss the associated production of gamma rays at the sources.

Collision of particles near a three-dimensional rotating Ho\u0159ava AdS black hole

We consider a three-dimensional rotating AdS black hole, which is a solution of Hořava gravity in the low-energy limit that corresponds to a Lorentz-violating version of the BTZ black hole, and we analyze the effect of the breaking of Lorentz invariance on the possibility that the black hole can act as a particle accelerator by analyzing the energy in the center-of-mass (CM) frame of two colliding particles in the vicinity of its horizons. We find that the critical angular momentum of particles increases when the Hořava parameter xi increases and when the aether parameter b increases. Also, the particles can collide on the inner horizon with arbitrarily high CM energy if one of the particles has a critical angular momentum, possible for the BSW process. Here it is essential that, while for the extremal BTZ black hole the particles with critical angular momentum only can exist on the degenerate horizon, for the Lorentz-violating version of the BTZ black hole the particle with critical angular momentum can exist in a region away from the degenerate horizon. It is worth mentioning that the results exposed in this manuscript can be applied for the covariant version of Hořava gravity, where the covariant definition of the center-of-mass energy is well defined.

Gluon polarization measurements from longitudinally polarized proton-proton collisions at STAR

The gluon polarization contribution to the proton spin is an integral part to solve the longstanding proton spin puzzle. At the Relativistic Heavy Ion Collider (RHIC), the STAR experiment has measured jets produced in mid-pseudo-rapidity, |η| < 1.0, and full azimuth, ϕ, from longitudinally polarized pp collisions to study the gluon polarization in the proton. At center of mass energies = 200 and 510 GeV, jet production is dominated by hard QCD scattering processes such as gluon-gluon (gg) and quark-gluon (qg), thus making the longitudinal double-spin asymmetry (ALL ) sensitive to the gluon polarization. Early STAR inclusive jet ALL results at = 200 GeV provided the first evidence of the non-zero gluon polarization at momentum fraction x > 0.05. The higher center of mass energy = 510 GeV allows to explore the gluon polarization as low as x ∼ 0.015. In this talk we will present the recent STAR inclusive jet and dijet ALL results at = 510 GeV, and discuss the relevant new analysis techniques for the estimation of trigger bias and reconstruction uncertainty, the underlying event correction on the jet energy and its effect on jet ALL . Dijet results are shown for different topologies in regions of pseudo-rapidity, effectively scanning the x-dependence of the gluon polarization.

Stop search in SUSY SO(10) GUTs with nonuniversal Gaugino masses

We explore the stop mass and its possible probe through a set of three different signal processes within a class of SUSY GUTs with non-universal gaugino masses. The stop mass can be realized in a wide range (0.4–8 TeV) consistent with the current experimental constraints. We consider the decay processes; tilde{t}_{1}rightarrow ttilde{chi }_{1}^{0}, tilde{t}_{1}rightarrow b W^{pm }tilde{chi }_{1}^{0} and tilde{t}_{1}rightarrow b q{bar{q}}^{prime }tilde{chi }_{1}^{0} to be possible signals, and explore the impact of the current experimental results as well as the possible mass scales of stop, which can be probed in the future collider experiments. We find that the first and third signal processes can be tested in the current experiments, and significantly probed in future, while the second signal process is not available for the current experiments in this class of SUSY GUTs. We also comment that the second signal process can be available to be tested when the collider experiments are conducted at high center of mass energies and luminosity.

Charged particle motion and electromagnetic field in γ spacetime

We consider the electromagnetic field occurring in the background of a static, axially symmetric vacuum solution of Einstein's field equations immersed in an external magnetic field. The solution, known as the $\gamma$ metric (or Zipoy-Voorhees), is related to the Schwarzschild spacetime through a real positive parameter $\gamma$ that describes its departure from spherical symmetry. We study the motion of charged and uncharged particles in this spacetime and particle collision in the vicinity of the singular surface and compare with the corresponding result for Schwarzschild. We show that there is a sharp contrast with the black hole case; in particular, in the prolate case ($\gamma<1$) particle collision can occur with an arbitrarily high center of mass energy. This mechanism could in principle allow one to distinguish such a source from a black hole.

Effect of the self-gravity of shells on a high energy collision in a rotating Bañados-Teitelboim-Zanelli spacetime

We consider a collision of two dust thin shells with a high center-of-mass (CM) energy including their self-gravity in a Ba\~{n}ados-Teitelboim-Zanelli (BTZ) spacetime. The shells divide the BTZ spacetime into three domains and the domains are matched by the Darmois-Israel junction conditions. We treat only the collision of two shells which corotate with a background BTZ spacetime because of the junction conditions. The counterpart of the corotating shell collision is a collision of two particles with vanishing angular momenta. We compare the dust thin shell collision and the particle collision in order to investigate the effects of the self-gravity of colliding objects on the high CM energy collision. We show that the self-gravity of the shells affects the position of an event horizon and it covers the high-energy collisional event. Therefore, we conclude that the self-gravity of colliding objects suppresses its CM energy and that any observer who stands outside of the event horizon cannot observe the collision with an arbitrary high CM energy.

The effect of hadronic rindler horizon on hadronization process

In this study by extending the recent suggested mechanisms to hadronization processes, the information loss for QCD matter in hadronic Rindler horizon is found. We notice that for all finite values of quark and gluon energies, all information from all hadronization processes experiences some degree of loss. Then the effect of hedonic Rindler horizon on three jet cross section is explored. It is found that the three jet cross section is rising at ycut = 0.0002 exhibits a turn-over at moderate value of ycut = 0.01 and then rapidly decreases as ycut increases. This model is consistent with OPAL data. Finally, different channels for producing Higgs boson near hadronic Rindler horizon are studied. It is shown that the cross section of Higgs boson produced via gluon fusion and quark interaction near a single Hadronic Rindler Horizon is much larger for higher center of mass energies. This is because an increase in the energy of hadronic Rindler horizon raises the temperature, thus intensifying the thermal radiation of QCD matter.

Particle collisions near a three-dimensional warped AdS black hole

In this paper we consider the warped hbox {AdS}_{3} black hole solution of topologically massive gravity with a negative cosmological constant, and we study the possibility that it acts as a particle accelerator by analyzing the energy in the center of mass (CM) frame of two colliding particles in the vicinity of its horizon, which is known as the Bañnados, Silk and West (BSW) process. Mainly, we show that the critical angular momentum (L_c) of the particle decreases when the warping parameter(nu ) increases. Also, we show that despite the particle with L_c being able to exist for certain values of the conserved energy outside the horizon, it will never reach the event horizon; therefore, the black hole cannot act as a particle accelerator with arbitrarily high CM energy on the event horizon. However, such a particle could also exist inside the outer horizon, with the BSW process being possible on the inner horizon. On the other hand, for the extremal warped hbox {AdS}_{3} black hole, the particle with L_c and energy E could exist outside the event horizon and, the CM energy blows up on the event horizon if its conserved energy fulfills the condition E^{2}>frac{(nu ^{2}+3)l^{2}}{3(nu ^{2}-1)}, with the BSW process being possible.

Motion and collision of particles in a rotating linear dilaton black hole

We study the motion of particles in the background of a four-dimensional linear dilaton black hole. We solve analytically the equations of motion of the test particles and we describe their motion. We show that the dilaton black hole acts as a particle accelerator by analyzing the energy in the center of mass (CM) frame of two colliding particles in the vicinity of its horizon. In particular we find that there is a critical value of the angular momentum, which depends on the string coupling, and a particle with this critical angular momentum can reach the inner horizon with an arbitrarily high CM energy. This is known as the Ba\~nados, Silk and West (BSW) process. We also show that the motion and collisions of particles have a similar behavior to the three-dimensional BTZ black hole. In fact, the photons can plunge into the horizon or escape to infinity, and they can not be deflected, while for massive particles there are no confined orbits of first kind, like planetary or circular orbits.

Measurements of B→J/ψ at forward rapidity in p+p collisions at s=510 GeV

We report the first measurement of the fraction of $J/\psi$ mesons coming from $B$-meson decay ($F_{B{\rightarrow}J/\psi}$) in $p$+$p$ collisions at $\sqrt{s}=$ 510 GeV. The measurement is performed using the forward silicon vertex detector and central vertex detector at PHENIX, which provide precise tracking and distance-of-closest-approach determinations, enabling the statistical separation of $J/\psi$ due to $B$-meson decays from prompt $J/\psi$. The measured value of $F_{B{\rightarrow}J/\psi}$ is 8.1\%$\pm$2.3\% (stat)$\pm$1.9\% (syst) for $J/\psi$ with transverse momenta $0<p_T<5$ GeV/$c$ and rapidity $1.2<|y|<2.2$. The measured fraction $F_{B{\rightarrow}J/\psi}$ at PHENIX is compared to values measured by other experiments at higher center of mass energies and to fixed-order-next-to-leading-logarithm and color-evaporation-model predictions. The $b\bar{b}$ cross section per unit rapidity ($d\sigma/dy(pp{\rightarrow}b\bar{b})$) extracted from the obtained $F_{B{\rightarrow}J/\psi}$ and the PHENIX inclusive $J/\psi$ cross section measured at 200 GeV scaled with color-evaporation-model calculations, at the mean $B$ hadron rapidity $y={\pm}1.7$ in 510 GeV $p$$+$$p$ collisions, is $3.63^{+1.92}_{-1.70}\mu$b, and it is consistent with the fixed-order-next-to-leading-logarithm calculations.

Time-dependent mean-field determination of the excitation energy in transfer reactions: Application to the reaction U238 on C12 at 6.14 MeV/nucleon

The internal excitation of nuclei after multi-nucleon transfer is estimated by using the time-dependent mean-field theory. Transfer probabilities for each channel as well as the energy loss after re-separation are calculated. By combining these two informations, we show that the excitation energy distribution of the transfer fragments can be obtained separately for the different transfer channels. The method is applied to the reaction involving a $^{238}$U beam on a $^{12}$C target, which has recently been measured at GANIL. It is shown that the excitation energy calculated with the microscopic theory compares well with the experimental observation, provided that the competition with fusion is properly taken into account. The reliability of the excitation energy is further confirmed by the comparison with the phenomenological HIPSE model at higher center of mass energies.

The ATLAS FTK system: how to improve the physics potential with a tracking trigger

After a very successful data taking run, the ATLAS experiment is being upgraded to cope with the higher luminosity and higher center of mass energy that the Large Hadron Collider (LHC) will provide in the next years. The Fast Tracker (FTK) trigger system, part of the ATLAS trigger upgrade program, is a highly parallel hardware device processor based on a mixture of advanced technologies. FTK provides global track reconstruction in the full inner silicon detector, with resolution comparable to the offline algorithms, in approximately 100 microseconds, allowing a fast and precise detection of the primary and secondary vertex information. The track and vertex information is then used by the high-level trigger algorithms, allowing highly improved trigger performance for the most difficult signatures, such as b-jets. The expected physics performance of FTK in the harsh environment at high pile-up and high luminosities at LHC Run2 are presented.

The LUCID detector ATLAS luminosity monitor and its electronic system

In 2015 LHC is starting a new run, at higher center of mass energy (13TeV) and with 25ns bunch-spacing. The ATLAS luminosity monitor LUCID has been completely rebuilt, both the detector and the electronics, in order to cope with the new running conditions. The new detector electronics features a new read-out board (LUCROD) for signal acquisition and digitization, PMT-charge integration and single-side luminosity measurements, and a revisited LUMAT board for combination of signals from the two detectors. This note describes the new board design, the firmware and software developments, the implementation of luminosity algorithms, the optical communication between boards and the integration into the ATLAS TDAQ system.

NLO QCD corrections to the resonant vector diquark production at the LHC

With the upcoming run of the Large Hadron Collider (LHC) at much higher center of mass energies, the search for Beyond Standard Model (BSM) physics will again take center stage. New colored particles predicted in many BSM scenarios are expected to be produced with large cross sections thus making them interesting prospects as a doorway to hints of new physics. We consider the resonant production of such a colored particle, the diquark, a particle having the quantum number of two quarks. The diquark can be either a scalar or vector. We focus on the vector diquark which has much larger production cross section compared to the scalar ones. In this work we calculate the next-to-leading order (NLO) QCD corrections to the on-shell vector diquark production at the LHC produced through the fusion of two quarks as well as the NLO corrections to its decay width. We present full analytic results for the one-loop NLO calculation and do a numerical study to show that the NLO corrections can reduce the scale uncertainties in the cross sections which can be appreciable and therefore modify the expected search limits for such particles. We also use the dijet result from LHC to obtain current limits on the mass and coupling strengths of the vector diquarks.

Probing shadowed nuclear sea with massive gauge bosons in the future heavy-ion collisions

The production of the massive bosons $Z^0$ and $W^{\pm}$ could provide an excellent tool to study cold nuclear matter effects and the modifications of nuclear parton distribution functions (nPDFs) relative to parton distribution functions (PDFs) of a free proton in high energy nuclear reactions at the LHC as well as in heavy-ion collisions (HIC) with much higher center-of mass energies available in the future colliders. In this paper we calculate the rapidity and transverse momentum distributions of the vector boson and their nuclear modification factors in p+Pb collisions at $\sqrt{s_{NN}}=63$TeV and in Pb+Pb collisions at $\sqrt{s_{NN}}=39$TeV in the framework of perturbative QCD by utilizing three parametrization sets of nPDFs: EPS09, DSSZ and nCTEQ. It is found that in heavy-ion collisions at such high colliding energies, both the rapidity distribution and the transverse momentum spectrum of vector bosons are considerably suppressed in wide kinematic regions with respect to p+p reactions due to large nuclear shadowing effect. We demonstrate that in the massive vector boson productions processes with sea quarks in the initial-state may give more contributions than those with valence quarks in the initial-state, therefore in future heavy-ion collisions the isospin effect is less pronounced and the charge asymmetry of W boson will be reduced significantly as compared to that at the LHC. Large difference between results with nCTEQ and results with EPS09 and DSSZ is observed in nuclear modifications of both rapidity and $p_T$ distributions of $Z^0$ and $W$ in the future HIC.