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1. chinaXiv:201609.01073 [pdf]

Design and analysis of 5045 S-band klystron DC electron gun

Abdul Rehman; Munawar Iqbal; Z. Zhou
Subjects: Physics >> Nuclear Physics

The design and performance analysis of DC electron gun for 5045 S-band klystron has been worked out using SLAC beam trajectory program (EGUN) and Computer Simulation Technology Particle Studio (CST-PS), Codes. Specifications of electron gun were focused on beam; current, perveance, size and emittance. Optimized beam; current, perveance, diameter and emittance were 414.00A, 2.00uP, 26.82 mm and 103.10 pi mm mrad, respectively. Furthermore, the optimized characteristic parameters of the gun were also calculated and compared with the simulated and experimental values which were in agreement. Accuracy of simulation was verified by comparison of emitted beam current which has error of zero percent.

submitted time 2016-09-22 Hits1798Downloads721 Comment 0

2. chinaXiv:201609.01072 [pdf]

A Promising Interpretation of Diphoton Resonance at 750 GeV

Xiao-Jun Bi; Ran Ding; ,Yizhou Fan; Li Huang; Chuang Li; Tianjun Li; Shabbar Raza; Xiao-Chuan Wang; Bin Zhu
Subjects: Physics >> Nuclear Physics

Recently, an excess of events in diphoton channel with invariant mass of about 750 GeV has been reported by the ATLAS and CMS Collaborations. Considering it as a tantalizing hint for new physics beyond the Standard Model (SM), we propose a simple extension of the SM with an additional doublet Higgs?H′?and a singlet?s. We consider the neutral component?H′0?of?H′?as the 750 GeV resonance, and assume that?s?is lighter than 2.6 GeV. In particular,?H′0?can be produced at tree level via?qq??production, and decay into a pair of?s?at tree level. And then?s?can decay into a pair of collimated photons, which cannot be distinguished at the LHC. We show that the diphoton production cross section can be from 3 to 13?fb, the decay width of?H′0?can be from 30 to 60 GeV, and all the current experimental constraints including dijet constraint can be satisfied.

submitted time 2016-09-22 Hits2459Downloads1027 Comment 0

3. chinaXiv:201609.01070 [pdf]

The Second Law of Thermodynamics and Entropy-Decreasing Processes With Helium-4 Superflows

Yongle Yu
Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties

We review on a recently proposed quantum exception to the second law of thermodynamics. We emphase that helium-4 superflows, like any other forms of flows, shall carry entropy or heat in a thermal environment. Following that, one can use a heterogeneous helium-4 superflow loop to realize entropy-decreasing processes. We also mention that the heat content of a superflow has an unusual dependence on flow velocity, which is an important factor contributing to the entropy-decreasing processes.

submitted time 2016-09-21 Hits2354Downloads1109 Comment 0

4. chinaXiv:201609.01068 [pdf]

Limits on Excited Quarks from the ATLAS Multi-jet Search

Ning Zhou; Kechen Wang; Kuhan Wang
Subjects: Physics >> Nuclear Physics

We interpret the recent ATLAS multi-jet search results using 20.3 fb-1 data at sqrt(s)=8 TeV in the context of searching for excited quarks. Within the effective field theory framework, using the null results of that search, our analysis shows that the excited quark mass below 5 TeV can be excluded at the 95% confidence level. Our analysis also indicates that when the validation of effective field theory is considered, the limit can be largely compromised.

submitted time 2016-09-20 Hits2100Downloads816 Comment 0

5. chinaXiv:201609.01067 [pdf]

Electroweak Vacuum Stability and Diphoton Excess at 750 GeV

Jue Zhang; Shun Zhou
Subjects: Physics >> Nuclear Physics

Recently, both ATLAS and CMS collaborations at the CERN Large Hadron Collider (LHC) have announced their observations of an excess of diphoton events around the invariant mass of?750?GeV?with a local significance of?3.6σ?and?2.6σ, respectively. In this paper, we interpret the diphoton excess as the on-shell production of a real singlet scalar in the?pp→S→γγ?channel. To accommodate the observed production rate, we further introduce a vector-like fermion?F, which is carrying both color and electric charges. The viable regions of model parameters are explored for this simple extension of the Standard Model (SM). Moreover, we revisit the problem of electroweak vacuum stability in the same scenario, and find that the requirement for the electroweak vacuum stability up to high energy scales imposes serious constraints on the Yukawa coupling of the vector-like fermion and the quartic couplings of the SM Higgs boson and the new singlet scalar. Consequently, a successful explanation for the diphoton excess and the absolute stability of electroweak vacuum cannot be achieved simultaneously in this economical setup.

submitted time 2016-09-20 Hits2679Downloads1242 Comment 0

6. chinaXiv:201609.01065 [pdf]

Cosmic Reionization Study : Principle Component Analysis After Planck

Yang Liu; Hong Li; Si-Yu Li; Yong-Ping Li; Xinmin Zhang
Subjects: Physics >> Nuclear Physics

The study of reionization history plays an important role in understanding the evolution of our universe. It is commonly believed that the intergalactic medium (IGM) in our universe are fully ionized today, however the reionizing process remains to be mysterious. A simple instantaneous reionization process is usually adopted in modern cosmology without direct observational evidence. However, the history of ionization fraction,?xe(z)?will influence cosmic microwave background (CMB) observables and constraints on optical depth?τ. With the mocked future data sets based on featured reionization model, we find the bias on?τ?introduced by instantaneous model can not be neglected. In this paper, we study the cosmic reionization history in a model independent way, the so called principle component analysis (PCA) method, and reconstruct?xe(z)?at different redshift?z?with the data sets of Planck, WMAP 9 years temperature and polarization power spectra, combining with the baryon acoustic oscillation (BAO) from galaxy survey and type Ia supernovae (SN) Union 2.1 sample respectively. The results show that reconstructed?xe(z)?is consistent with instantaneous behavior, however, there exists slight deviation from this behavior at some epoch. With PCA method, after abandoning the noisy modes, we get stronger constraints, and the hints for featured?xe(z)?evolution could become a little more obvious.

submitted time 2016-09-19 Hits3089Downloads1365 Comment 0

7. chinaXiv:201609.01064 [pdf]

Precisely determined the spent nuclear fuel antineutrino flux and spectrum for Daya Bay antineutrino experiment

X.B.Ma; Y.F.Zhao; Y.X.Chen; W.L.Zhong; F.P.An?
Subjects: Physics >> Nuclear Physics

Spent nuclear fuel (SNF) antineutrino flux is an important source of uncertainties for a reactor neutrino flux prediction. However, if one want to determine the contribution of spent fuel, many data are needed, such as the amount of spent fuel in the pool, the time after discharged from the reactor core, the burnup of each assembly, and the antineutrino spectrum of the isotopes in the spend fuel. A method to calculate the contribution of SNF is proposed in this study. In this method, reactor simulation code verified by experiment have been used to simulate the fuel depletion by taking into account more than 2000 isotopes and fission products, the quantity of SNF in each six spend fuel pool, and the antineutrino spectrum of SNF varying with time after SNF discharged from core. Results show that the contribution of SNF to the total antineutrino flux is about 0.26%~0.34%, and the shutdown impact is about 20%. The SNF spectrum would distort the softer part of antineutrino spectra, and the maximum contribution from SNF is about 3.0%, but there is 18\% difference between line evaluate method and under evaluate method. In addition, non-equilibrium effects are also discussed, and the results are compatible with theirs considering the uncertainties.

submitted time 2016-09-19 Hits1828Downloads630 Comment 0

8. chinaXiv:201609.01063 [pdf]

Beyond Higgs Couplings: Probing the Higgs with Angular Observables at Future e$^+$ e$^?$ Colliders

Nathaniel Craig; Jiayin Gu; Zhen Liu; Kechen Wang
Subjects: Physics >> Nuclear Physics

We study angular observables in the?e+e?→ZH→?+??bb??channel at future circular?e+e??colliders such as CEPC and FCC-ee. Taking into account the impact of realistic cut acceptance and detector effects, we forecast the precision of six angular asymmetries at CEPC (FCC-ee) with center-of-mass energy?s√=?240 GeV and 5 (30)?ab?1?integrated luminosity. We then determine the projected sensitivity to a range of operators relevant for the Higgs-strahlung process in the dimension-6 Higgs EFT. Our results show that angular observables provide complementary sensitivity to rate measurements when constraining various tensor structures arising from new physics. We further find that angular asymmetries provide a novel means of both probing BSM corrections to the?HZγ?coupling and constraining the "blind spot" in indirect limits on supersymmetric scalar top partners.

submitted time 2016-09-19 Hits2510Downloads1039 Comment 0

9. chinaXiv:201609.01062 [pdf]

The 750 GeV diphoton excess at the LHC and dark matter constraints

Xiao-Jun Bi; Qian-Fei Xiang; Peng-Fei Yin; Zhao-Huan Yu
Subjects: Physics >> Nuclear Physics

The recent reported 750 GeV diphoton excess at the 13 TeV LHC is explained in the framework of effective field theory assuming the diphoton resonance is a scalar (pseudoscalar) particle. It is found that the large production rate and the broad width of this resonance are hard to simultaneously explain if only visible final states are considered. Therefore an invisible decay channel to dark matter (DM) is strongly favored by the diphoton excess with a broad width, given a large coupling of the new scalar to DM. We set constraints on the parameter space in this scenario using the results from LHC Run 1, DM relic density, and DM direct and indirect detection experiments. We find that the DM searches can exclude a large portion of the parameter regions accounting for the diphoton excess with a broad width.

submitted time 2016-09-19 Hits2752Downloads1206 Comment 0

10. chinaXiv:201609.01061 [pdf]

750 GeV Diphoton Excess from Cascade Decay

Fa Peng Huang; Chong Sheng Li; Ze Long Liu; Yan Wang
Subjects: Physics >> Nuclear Physics

Motivated by the recent 750 GeV diphoton excess observed by the ATLAS and CMS collaborations, we propose a simplified model to explain this excess. Model-independent constraints and predictions on the allowed couplings for generating the observed diphoton excess are studied in detail, and the compatibility between Run 1 and Run 2 data is considered simultaneously. We demonstrate that the possible four photon signal can be used to test this scenario, and also explain the interesting deviation for a diphoton mass of about 1.6 TeV by ATLAS, where the local significance is 2.8?σ. Meanwhile, this scenario also provides us with the dark matter candidates.

submitted time 2016-09-19 Hits2223Downloads1112 Comment 0

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