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A. Datta

Publications and source records attributed to A. Datta.

157 records · Page 9Linked to original sources
arXiv2003

Spin-based all-optical quantum computation with quantum dots: understanding and suppressing decoherence

We present an all-optical implementation of quantum computation using semiconductor quantum dots. Quantum memory is represented by the spin of an excess electron stored in each dot. Two-qubit gates are realized by switching on trion-trion interactions between different dots. State selectivity is achieved via conditional laser excitation exploiting Pauli exclusion principle. Read-out is performed via a quantum-jump technique. We analyze the effect on our scheme's performance of the main imperfections present in real quantum dots: exciton decay, hole mixing and phonon decoherence. We introduce an adiabatic gate procedure that allows one to circumvent these effects, and evaluate quantitatively its fidelity.

quant-ph↗
arXiv2002

Sfermion Precision Measurements at a Linear Collider

At future e+- e- linear colliders, the event rates and clean signals of scalar fermion production - in particular for the scalar leptons - allow very precise measurements of their masses and couplings and the determination of their quantum numbers. Various methods are proposed for extracting these parameters from the data at the sfermion thresholds and in the continuum. At the same time, NLO radiative corrections and non-zero width effects have been calculated in order to match the experimental accuracy. The substantial mixing expected for the third generation sfermions opens up additional opportunities. Techniques are presented for determining potential CP-violating phases and for extracting tan(beta) from the stau sector, in particular at high values. The consequences of possible large mass differences in the stop and sbottom system are explored in dedicated analyses.

hep-ph↗
arXiv2000

Effects Of Kaluza-Klein Excited W On Single Top Quark Production At Tevatron

In extra dimension theories if the gauge bosons of the standard model propagate in the bulk of the extra dimensions then they will have Kaluza-Klein excitations that can couple to the standard model fermions. In this paper we study the effects of the first excited Kaluza-Klein mode of the W on single top production at the Tevatron. We find that the cross section for the single top production can be significantly reduced if the mass of the first Kaluza-Klein excited $W \sim 1$ TeV. Hence, a measurement of the single top production cross section smaller than the standard model prediction would not necessarily imply $V_{tb} <1$ or evidence of extra generation(s) of fermions mixed with the third generation.

hep-ph↗
arXiv1999

Measuring $β$ in $B \to D^{*+}D^{*-}K_s$ Decays

We consider the possibility of measuring both $\sin (2 β)$ and $\cos (2 β)$ in the KM unitarity triangle using the process $B^0 \to D^{*+}D^{*-}K_s$. This decay mode has a higher branching fraction (O(1%)) than the mode $B^0 \to D^{*+}D^{*-}$. We use the factorization assumption and heavy hadron chiral perturbation theory to estimate the branching fraction and polarization. The time dependent rate for $B^0(t) \to D^{*+} D^{*-} K_s$ can be used to measure $\sin (2 β)$ and $\cos(2 β)$ . Furthermore, examination of the $D^{*+} K_s$ mass spectrum may be the best way to experimentally find the broad $1^+$ p-wave $D_s$ meson.

hep-ph↗
arXiv1998

CP Violation in Quasi-inclusive $B\to K^{(*)} X$ Decays

We consider the possibility of observing CP violation in quasi-inclusive decays of the type $B^-\to K^- X$, $B^-\to K^{*-} X$, $\bar B^0\to K^- X$ and $\bar B^0\to K^{*-} X$, where $X$ does not contain strange quarks. We present estimates of rates and asymmetries for these decays in the Standard Model and comment on the experimental feasibility of observing CP violation in these decays at future $B$ factories. We find the rate asymmetries can be quite sizeable.

hep-ph↗
arXiv1997

R-parity-violating SUSY effects and signals in single top production at the Tevatron

We discuss single top quark production via u^i+\bar d^j \to t+\bar b at the Fermilab Tevatron in the minimal supersymmetric model with R-parity violation. We find that within the allowed range of coupling constants, the lepton-number violating couplings can give rise to observable effects when the slepton mass lies in a specific narrow range. For the baryon-number violating couplings, the contribution to the production rate can be quite large in the presently allowed range of the coupling constants. We show that the measurement of single top production at the upgraded Tevatron can be used to constrain a linear combination of products of the R-parity violating couplings.

hep-ph↗
arXiv1997

b b-bar Production on the Z Resonance and Implications for LEP2

In terms of an effective lagrangian, we examine the effect of new physics associated with third-generation fermions on b b-bar production at the Z resonance and study its implications for LEP2. We obtain the constraints on such operators with derivative couplings at LEP1 and the SLC, and determine the prospects for detecting their presence at LEP2. We find that despite the small observed deviations from the standard model on the Z resonance, much larger deviations from standard model predictions are possible at LEP2, and the corresponding couplings can be determined rather precisely.

hep-ph↗
arXiv1996

Non-Universal Correction to $Z \to b {\overline b}$ and Single Top Quark Production at Tevatron

New physics associated with the heavy top quark can affect top quark production and the partial decay width of $Z \rightarrow b \bar b$. In this paper, we examine the correlated effects of possible new physics on ${R_b}$ measured at LEP I and the single top quark production rate at Tevatron by using an effective lagrangian technique. We point out that certain operators in the effective lagrangian, constrained by the measured value of $R_b$, can lead to significant and potentially observable effects in single top production.

hep-ph↗
arXiv1996

Implications Of A Non-Standard Light Higgs Boson

Analyses of the vacuum stability of the electroweak theory indicate that new physics occur at a scale of order of 1 TeV if a light Higgs is discovered at LEP II. In this paper, we parameterize the effects of new physics in the effective Lagrangian approach and examine its implication on the Higgs boson production at LEP II. We consider the effect of higher dimension operator on the Higgs potential and calculate the lower bound on the Higgs boson mass from the requirement of vacuum stability. We show that if a Higgs boson is seen at LEP II then under favourable conditions the deviation of the production cross section from the standard model value could be significant and therefore the presence of the new physics is detectable at LEP II.

hep-ph↗
arXiv1995

Hunting virtual LSPs at LEP200.

Relatively light sneutrinos, which are experimentally allowed, may significantly affect the currently popular search strategies for supersymmetric particles by decaying dominantly into an invisible channel. In certain cases the second lightest neutralino may also decay invisibly leading to two extra carriers of missing energy -- in addition to the lightest supersymmetric particle (LSP) \zi\ -- the virtual LSPs (VLSPs). It is shown that these VLSPs are allowed in supergravity models with common scalar and gaugino masses at the unification scale for a sizable region of parameter space and are consistent with all constraints derived so far from SUSY searches. The pair production of right handed sleptons, which can very well be the lightest charged SUSY particles in this scenario, at LEP 200 and their decay signatures are discussed. The signal survives kinematical cuts required to remove the standard model background. Charginos are also pair produced copiously if kinematically accessible; they also decay dominantly into hadronically quiet di--lepton + \etmiss\ modes leading to interesting unlike sign dilepton events which are again easily separable from the Standard Model backgrounds at LEP 200 energies.

hep-ph↗
arXiv1994

Signatures of Virtual LSPs at the Tevatron

Relatively light sneutrinos which are experimentally allowed and are not theoretically disfavoured may significantly affect the currently popular search strategies for supersymmetric particles by decaying dominantly into an invisible channel. In certain cases the second lightest neutralino may also decay invisibly leading to two extra carriers of missing energy (in addition to the lightest supersymmetric particle (LSP) ) - the virtual LSPs (VLSPs). The lighter charginos which would be produced in pairs with reasonably large cross-sections at TEVATRON energies, decay dominantly into the hadronically quiet lepton + sneutrino ($\not{E_T}$ ) modes with large branching ratios leading to interesting unlike sign dilepton events which are not swamped by the standard model background. The kinematical cuts required to eliminate the backgrounds from WW, Drell-Yan and $τ$ pair production are discussed in detail. With 100 $pb^{-1}$ luminosity 10 - 35 background free events can be found in a large region of the SUSY parameter space.

hep-ph↗
arXiv1993

Probing Lepton Number Violation via Majorana Neutrinos at Hadron Supercolliders

The possibility of discovering heavy Majorana neutrinos and lepton number violation via the like sign dilepton signal at hadron super- colliders is investigated. The cross-sections for the production of these neutrinos singly as well as in pairs are computed both in three and four generation scenarios within the framework of the gauge group $SU(2)_L \otimes U(1)_Y$ and the dominant processes are identified. The suppression of the Standard model background by suitable kinematical cuts is also discussed.

hep-ph↗