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S. Ahmed

Publications and source records attributed to S. Ahmed.

At least 271 records · Page 15Linked to original sources
arXiv2017

Cross section measurements of $e^{+}e^{-}\rightarrow p \bar{p} π^{0}$ at center-of-mass energies between 4.008 and 4.600 GeV

Based on $e^+e^-$ annihilation data samples collected with the BESIII detector at the BEPCII collider at 13 center of mass energies from 4.008 to 4.600 GeV, measurements of the Born cross section of $e^{+}e^{-}\rightarrow p \bar{p} π^{0}$ are performed. No significant resonant structure is observed in the measured energy-dependent cross section. The upper limit on the Born cross section of $e^{+}e^{-}\rightarrow Y(4260) \rightarrow p \bar{p} π^{0}$ at the 90\% C.L. is determined to be 0.01 pb.

hep-ex↗
arXiv2016

Measurements of the branching fractions for $D^+\to K^0_SK^0_SK^+$, $K^0_SK^0_Sπ^+$ and $D^0\to K^0_SK^0_S$, $K^0_SK^0_SK^0_S$

By analyzing $2.93\ \rm fb^{-1}$ of data taken at the $ψ(3770)$ resonance peak with the BESIII detector, we measure the branching fractions for the hadronic decays $D^+\to K^0_SK^0_S K^+$, $D^+\to K^0_SK^0_S π^+$, $D^0\to K^0_S K^0_S$ and $D^0\to K^0_SK^0_SK^0_S$. They are determined to be ${\mathcal B}(D^+\to K^0_SK^0_SK^+)=(2.54 \pm 0.05_{\rm stat.} \pm 0.12_{\rm sys.})\times 10^{-3}$, ${\mathcal B}(D^+\to K^0_SK^0_Sπ^+)=(2.70 \pm 0.05_{\rm stat.} \pm 0.12_{\rm sys.})\times 10^{-3}$, ${\mathcal B}(D^0\to K^0_SK^0_S)=(1.67 \pm 0.11_{\rm stat.} \pm 0.11_{\rm sys.})\times 10^{-4}$ and ${\mathcal B}(D^0\to K^0_SK^0_SK^0_S)=(7.21 \pm 0.33_{\rm stat.} \pm 0.44_{\rm sys.})\times 10^{-4}$, where the second one is measured for the first time and the others are measured with significantly improved precision over the previous measurements.

hep-ex↗
arXiv2016

Measurement of the Absolute Branching Fraction for $Λ_c^+\rightarrow Λμ^+ν_μ$

We report the first measurement of the absolute branching fraction for $Λ^+_{c}\rightarrow Λμ^+ν_μ$. This measurement is based on a sample of $e^+e^-$ annihilation data at a center-of-mass energy of $\sqrt{s}=4.6$ GeV collected with the BESIII detector at the BEPCII storage rings. The sample corresponds to an integrated luminosity of 567 pb$^{-1}$. The branching fraction is determined to be $\mathcal B({Λ^+_c\rightarrow Λμ^+ν_μ})=(3.49\pm0.46({\rm stat})\pm0.27({\rm syst}))\%$. In addition, we calculate the ratio $\mathcal{B}(Λ^+_c\rightarrow Λμ^+ν_μ)/\mathcal{B}(Λ^+_c\rightarrow Λe^+ν_{e})$ to be $0.96\pm0.16({\rm stat})\pm0.04({\rm syst})$.

hep-ex↗
arXiv2016

Observation of $e^{+}e^{-} \to η^{\prime} J/ψ$ at center-of-mass energies between 4.189 and 4.600 GeV

The process $e^{+}e^{-}\to η^{\prime} J/ψ$ is observed for the first time with a statistical significance of $8.6σ$ at center-of-mass energy $\sqrt{s} = 4.226$ GeV and $7.3σ$ at $\sqrt{s} = 4.258$ GeV using data samples collected with the BESIII detector. The Born cross sections are measured to be $(3.7 \pm 0.7 \pm 0.3)$ and $(3.9 \pm 0.8 \pm 0.3)$ pb at $\sqrt{s} = 4.226$ and $4.258$ GeV, respectively, where the first errors are statistical and the second systematic. Upper limits at the 90% confidence level of the Born cross sections are also reported at other 12 energy points.

hep-ex↗
arXiv2016

Observation of an anomalous line shape of the $η^{\prime}π^{+}π^{-}$ mass spectrum near the $p\bar{p}$ mass threshold in $J/ψ\rightarrowγη^{\prime}π^{+}π^{-}$

Using $1.09\times10^{9}$ $J/ψ$ events collected by the BESIII experiment in 2012, we study the $J/ψ\rightarrowγη^{\prime}π^{+}π^{-}$ process and observe a significant abrupt change in the slope of the $η^{\prime}π^{+}π^{-}$ invariant mass distribution at the proton-antiproton ($p\bar{p}$) mass threshold. We use two models to characterize the $η^{\prime}π^{+}π^{-}$ line shape around $1.85~\text{GeV}/c^{2}$: one which explicitly incorporates the opening of a decay threshold in the mass spectrum (Flatté formula), and another which is the coherent sum of two resonant amplitudes. Both fits show almost equally good agreement with data, and suggest the existence of either a broad state around $1.85~\text{GeV}/c^{2}$ with strong couplings to $p\bar{p}$ final states or a narrow state just below the $p\bar{p}$ mass threshold. Although we cannot distinguish between the fits, either one supports the existence of a $p\bar{p}$ molecule-like state or bound state with greater than $7σ$ significance.

hep-ex↗
arXiv2015

Ab initio study of structural, electronic, and thermal properties of Ir$_{1-x}$Rh$_{x}$ alloys

The structural, electronic, mechanical and thermal properties of Ir$_{1-x}$Rh$_{x}$ alloys were studied systematically using ab initio density functional theory at different concentrations (x = 0.00, 0.25, 0.50, 0.75, 1.00). A Special Quasirandom Structure method was used to make alloys having FCC structure with four atoms per unit cell. The ground state properties such as lattice constant and bulk modulus were calculated to find the equilibrium atomic position for stable alloys. The calculated ground state properties are in good agreement with the experimental and previously presented other theoretical data. The electronic band structure and density of states were calculated to study the electronic properties for these alloys at different concentrations. The electronic properties substantiate the metallic behavior of alloys. The first principle density functional perturbation theory as implemented in quasiharmonic approximation was used for the calculation of thermal properties. We have calculated the thermal properties such as Debye temperatures, vibration energy, entropy, constant-volume specific heat and internal energy. The ab initio linear-response method was used to calculate phonon densities of states.

cond-mat.mtrl-sci↗
arXiv2013

iMOD LEACH: improved MODified LEACH Protocol for Wireless Sensor Networks

Increased use of Wireless sensor Networks (WSNs) in variety of applications has enabled the designers to create autonomous sensors, which can be deployed randomly, without human supervision, for the purpose of sensing and communicating valuable data. Many energy-efficient routing protocols are designed for WSNs based on clustering structure. In this paper, we have proposed iMODLEACH protocol which is an extension to the MODLEACH protocol. Simulation results indicate that iMODLEACH outperforms MODLEACH in terms of network life-time and packets transferred to base station. The mathematical analysis helps to select such values of these parameters which can suit a particular wireless sensor network application.

cs.NI↗
arXiv2013

AID: An Energy Efficient Decoding Scheme for LDPC Codes in Wireless Body Area Sensor Networks

One of the major challenges in Wireless Body Area Networks (WBANs) is to prolong the lifetime of network. Traditional research work focuses on minimizing transmit power, however, in the case of short range communication the consumption power in decoding is significantly larger than transmit power. This paper investigates the minimization of total power consumption by reducing the decoding power consumption. For achieving a desired Bit Error Rate (BER), we introduce some fundamental results on the basis of iterative message-passing algorithms for Low Density Parity Check Code (LDPC). To reduce energy dissipation in decoder, LDPC based coded communications between sensors are considered. Moreover, we evaluate the performance of LDPC at different code rates and introduce Adaptive Iterative Decoding (AID) by exploiting threshold on the number of iterations for a certain BER. In iterative LDPC decoding, the total energy consumption of network is reduced by 20 to 25 percent.

cs.NI↗
arXiv2013

AMCTD: Adaptive Mobility of Courier nodes in Threshold-optimized DBR Protocol for Underwater Wireless Sensor Networks

In dense underwater sensor networks (UWSN), the major confronts are high error probability, incessant variation in topology of sensor nodes, and much energy consumption for data transmission. However, there are some remarkable applications of UWSN such as management of seabed and oil reservoirs, exploration of deep sea situation and prevention of aqueous disasters. In order to accomplish these applications, ignorance of the limitations of acoustic communications such as high delay and low bandwidth is not feasible. In this paper, we propose Adaptive mobility of Courier nodes in Threshold-optimized Depth-based routing (AMCTD), exploring the proficient amendments in depth threshold and implementing the optimal weight function to achieve longer network lifetime. We segregate our scheme in 3 major phases of weight updating, depth threshold variation and adaptive mobility of courier nodes. During data forwarding, we provide the framework for alterations in threshold to cope with the sparse condition of network. We ultimately perform detailed simulations to scrutinize the performance of our proposed scheme and its comparison with other two notable routing protocols in term of network lifetime and other essential parameters. The simulations results verify that our scheme performs better than the other techniques and near to optimal in the field of UWSN.

cs.NI↗
arXiv2013

Comparative Analysis of Routing Protocols for Under Water Wireless Sensor Networks

Underwater Wireless Sensor Networks are significantly different from terrestrial sensor networks due to peculiar characteristics of low bandwidth, high latency, limited energy, node float mobility and high error probability. These features bring many challenges to the network protocol design of UWSNs. Several routing protocols have been developed in recent years for these networks. One of the major difficulties in comparison and validation of the performance of these proposals is the lack of a common standard to model the acoustic propagation in the harsh underwater environment. In this paper we analyze the evolution of certain underwater routing protocols like VBF, DBR, H2-DAB, QELAR etc. in terms of their localization techniques, energy minimization characteristics and holding time calculations. The design of each protocol follows certain goals i.e. reduction of energy consumption, improvement of communication latency, achievement of robustness and scalability etc. This paper examines the main approaches and challenges in the design and implementation of underwater sensor networks. The detailed descriptions of the selected protocols contribute in understanding the direction of the current research on routing layer in UWSN.

cs.NI↗
arXiv2013

Quantum Cryptography Using Various Reversible Quantum Logic Gates in WSNs

As sensor nodes are deployed anywhere in a wireless sensor network, hence their communication can be easily monitored. In these networks, message protection and node identification are very issues. Hence, security of large scale such networks requires efficient key distribution and management mechanisms. Quantum cryptography and particularly quantum key distribution is such a technique that allocates secure keys only for short distances. While not completely secure, it offers huge advantages over traditional methods by the use of entanglement swapping and quantum teleportation. Reversible logic gates like CNOT, Toffoli, Fredkin etc. are of basic importance in Quantum Computing. In our research, we adopted a EPR-pair allocation scheme in terms of these quantum gates to overcome the susceptibility caused by malicious nodes. As the qubits stored in a sensor node can be used only once and cannot be duplicated, hence risk of information leakage reduced even if the node are compromised.

cs.CR↗
arXiv2012

Simulation Analysis of IEEE 802.15.4 Non-beacon Mode at Varying Data Rates

IEEE 802.15.4 standard is designed for low power and low data rate applications with high reliability. It operates in beacon enable and non-beacon enable modes. In this work, we analyze delay, throughput, load, and end-to-end delay of nonbeacon enable mode. Analysis of these parameters are performed at varying data rates. Evaluation of non beacon enabled mode is done in a 10 node network. We limit our analysis to non beacon or unslotted version because, it performs better than other. Protocol performance is examined by changing different Medium Access Control (MAC) parameters. We consider a full size MAC packet with payload size of 114 bytes. In this paper we show that maximum throughput and lowest delay is achieved at highest data rate.

cs.NI↗
arXiv2012

Analyzing Energy-efficiency and Route-selection of Multi-level Hierarchal Routing Protocols in WSNs

The advent and development in the field of Wireless Sensor Networks (WSNs) in recent years has seen the growth of extremely small and low-cost sensors that possess sensing, signal processing and wireless communication capabilities. These sensors can be expended at a much lower cost and are capable of detecting conditions such as temperature, sound, security or any other system. A good protocol design should be able to scale well both in energy heterogeneous and homogeneous environment, meet the demands of different application scenarios and guarantee reliability. On this basis, we have compared six different protocols of different scenarios which are presenting their own schemes of energy minimizing, clustering and route selection in order to have more effective communication. This research is motivated to have an insight that which of the under consideration protocols suit well in which application and can be a guide-line for the design of a more robust and efficient protocol. MATLAB simulations are performed to analyze and compare the performance of LEACH, multi-level hierarchal LEACH and multihop LEACH.

cs.NI↗
arXiv2012

Monitoring and Controlling Power using Zigbee Communications

Smart grid is a modified form of electrical grid where generation, transmission, distribution and customers are not only connected electrically but also through strong communication network with each other as well as with market, operation and service provider. For achieving good communication link among them, it is very necessary to find suitable protocol. In this paper, we discuss different hardware techniques for power monitoring, power management and remote power controlling at home and transmission side and also discuss the suitability of Zigbee for required communication link. Zigbee has major role in monitoring and direct load controlling for efficient power utilization. It covers enough area needed for communication and it works on low data rate of 20Kbps to 250Kbps with minimum power consumption. This paper describes the user friendly control home appliances, power on/off through the internet, PDA using Graphical User Interface (GUI) and through GSM cellular mobile phone.

cs.NI↗
arXiv2011

Gluons and the quark sea at high energies: distributions, polarization, tomography

This report is based on a ten-week program on "Gluons and the quark sea at high-energies", which took place at the Institute for Nuclear Theory in Seattle in Fall 2010. The principal aim of the program was to develop and sharpen the science case for an Electron-Ion Collider (EIC), a facility that will be able to collide electrons and positrons with polarized protons and with light to heavy nuclei at high energies, offering unprecedented possibilities for in-depth studies of quantum chromodynamics. This report is organized around four major themes: i) the spin and flavor structure of the proton, ii) three-dimensional structure of nucleons and nuclei in momentum and configuration space, iii) QCD matter in nuclei, and iv) Electroweak physics and the search for physics beyond the Standard Model. Beginning with an executive summary, the report contains tables of key measurements, chapter overviews for each of the major scientific themes, and detailed individual contributions on various aspects of the scientific opportunities presented by an EIC.

nucl-th↗
arXiv2007

Single Pion production from Nuclei

We have studied charged current one pion production induced by $ν_μ(\barν_μ)$ from some nuclei. The calculations have been done for the incoherent pion production processes from these nuclear targets in the $Δ$ dominance model and take into account the effect of Pauli blocking, Fermi motion and renormalization of $Δ$ properties in the nuclear medium. The effect of final state interactions of pions has also been taken into account. The numerical results have been compared with the recent results from the MiniBooNE experiment for the charged current 1$π$ production, and also with some of the older experiments in Freon and Freon-Propane from CERN.

nucl-th↗
arXiv2002

Measurement of B(B- to D0 pi-) and B(barB0 to D+ pi-) and Isospin Analysis of B to D pi Decays

We present new measurements of branching fractions for the color-favored decays B^- --> D^0 pi^- and Bbar^0 --> D^+ pi^-. Using 9.67 x 10^6 BBbar pairs collected with the CLEO detector, we obtain the branching fractions BR(B^- --> D^0 pi^- =3D (49.7 +/- 1.2 +/- 2.9 +/- 2.2) x 10^{-4} and BR(Bbar^0 --> D^+ pi^- =3D (26.8 +/- 1.2 +/- 2.4 +/- 1.2) x 10^{-4}. The first error is statistical, the second is systematic, and the third is due to the experimental uncertainty on the production ratio of charged and neutral B mesons in Upsilon(4S) decays. These results, together with the current world average for the color-suppressed branching fraction BR(Bbar^0 --> D^0 pi^0), are used to determine the cosine of the strong phase difference delta_I between the I=1/2 and I=3/2 isospin amplitudes. We find cos(delta_I) = 0.863 (+0.024 -0.023) (+0.036 -0.035) (+0.038 -0.030), and obtain a 90% confidence interval of 16.5 degrees < delta_I < 38.1 degrees. This non-zero value of δ_I strongly suggests the presence of final state interactions in the Dpi system.

hep-ex↗