Papers by Laila Giannetti
Journal of High Energy Physics, 2016
We continue the effort of defining and evaluating the quantum entropy function for supersymmetric... more We continue the effort of defining and evaluating the quantum entropy function for supersymmetric black holes in 4d N = 2 gauged supergravity, initiated in [1]. The emphasis here is on the missing steps in the previous localization analysis, mainly dealing with one-loop determinants for abelian vector multiplets and hypermultiplets on the non-compact space H 2 × Σ g with particular boundary conditions. We use several different techniques to arrive at consistent results, which have a most direct bearing on the logarithmic correction terms to the Bekenstein-Hawking entropy of said black holes.
The European physical journal. C, Particles and fields
A search is performed for heavy long-lived charged particles using 3.0 [Formula: see text] of pro... more A search is performed for heavy long-lived charged particles using 3.0 [Formula: see text] of proton-proton collisions collected at [Formula: see text][Formula: see text] 7 and 8 TeV with the LHCb detector. The search is mainly based on the response of the ring imaging Cherenkov detectors to distinguish the heavy, slow-moving particles from muons. No evidence is found for the production of such long-lived states. The results are expressed as limits on the Drell-Yan production of pairs of long-lived particles, with both particles in the LHCb pseudorapidity acceptance, [Formula: see text]. The mass-dependent cross-section upper limits are in the range 2-4 fb (at 95 % CL) for masses between 14 and 309 [Formula: see text].
Physical Review Letters, 2015
Using a pp collision data sample corresponding to an integrated luminosity of 3.0 fb −1 , collect... more Using a pp collision data sample corresponding to an integrated luminosity of 3.0 fb −1 , collected by the LHCb detector, we present the first search for the strangenesschanging weak decay Ξ − b → Λ 0 b π −. No b hadron decay of this type has been seen before. A signal for this decay, corresponding to a significance of 3.2 standard deviations, is reported. The relative rate is measured to be f Ξ − b f Λ 0 b B(Ξ − b → Λ 0 b π −) = (5.7 ± 1.8 +0.8 −0.9) × 10 −4 , where f Ξ − b and f Λ 0 b are the b → Ξ − b and b → Λ 0 b fragmentation fractions, and B(Ξ − b → Λ 0 b π −) is the branching fraction. Assuming f Ξ − b /f Λ 0 b is bounded between 0.1 and 0.3, the branching fraction B(Ξ − b → Λ 0 b π −) would lie in the range from (0.57 ± 0.21)% to (0.19 ± 0.07)%.
Physical Review D, 2015
The associated production of a W boson with a jet originating from either a light parton or heavy... more The associated production of a W boson with a jet originating from either a light parton or heavy-flavor quark is studied in the forward region using proton-proton collisions. The analysis uses data corresponding to integrated luminosities of 1.0 and 2.0 fb −1 collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, respectively. The W bosons are reconstructed using the W → µν decay and muons with a transverse momentum, p T , larger than 20 GeV in the pseudorapidity range 2.0 < η < 4.5. The partons are reconstructed as jets with p T > 20 GeV and 2.2 < η < 4.2. The sum of the muon and jet momenta must satisfy p T > 20 GeV. The fraction of W +jet events that originate from beauty and charm quarks is measured, along with the charge asymmetries of the W +b and W +c production cross-sections. The ratio of the W +jet to Z+jet production cross-sections is also measured using the Z → µµ decay. All results are in agreement with Standard Model predictions.
Physical Review D, 2015
The resonant substructures of B 0 → D 0 π + π − decays are studied with the Dalitz plot technique... more The resonant substructures of B 0 → D 0 π + π − decays are studied with the Dalitz plot technique. In this study a data sample corresponding to an integrated luminosity of 3.0 fb −1 of pp collisions collected by the LHCb detector is used. The branching fraction of the B 0 → D 0 π + π − decay in the region m(D 0 π ±) > 2.1 GeV/c 2 is measured to be (8.46 ± 0.14 ± 0.29 ± 0.40) × 10 −4 , where the first uncertainty is statistical, the second is systematic and the last arises from the normalisation channel B 0 → D * (2010) − π +. The π + π − S-wave components are modelled with the Isobar and K-matrix formalisms. Results of the Dalitz plot analyses using both models are presented. A resonant structure at m(D 0 π −) ≈ 2.8 GeV/c 2 is confirmed and its spin-parity is determined for the first time as J P = 3 −. The branching fraction, mass and width of this structure are determined together with those of the D * 0 (2400) − and D * 2 (2460) − resonances. The branching fractions of other B 0 → D 0 h 0 decay components with h 0 → π + π − are also reported. Many of these branching fraction measurements are the most precise to date. The first observation of the decays B 0 → D 0 f 0 (500), B 0 → D 0 f 0 (980), B 0 → D 0 ρ(1450), B 0 → D * 3 (2760) − π + and the first evidence of B 0 → D 0 f 0 (2020) are presented.
Journal of High Energy Physics, 2015
The secluded dark matter resides within a hidden sector and self-annihilates into lighter mediato... more The secluded dark matter resides within a hidden sector and self-annihilates into lighter mediators which subsequently decay to the Standard Model (SM) particles. Depending on the coupling strength of the mediator to the SM, the hidden sector can be kinetically decoupled from the SM bath when the temperature drops below the mediator's mass, and the dark matter annihilation cross section at freeze-out is thus possible to be boosted above the conventional value of weak interacting massive particles. We present a comprehensive study on thermodynamic evolution of the hidden sector from the first principle, using the simplest secluded vector dark matter model. Motivated by the observation of Galactic center gamma-ray excess, we take two mass sets ∼ O(80 GeV) for the dark matter and mediator as examples to illustrate the thermodynamics. The coupled Boltzmann moment equations for number densities and temperature evolutions of the hidden sector are numerically solved. The formalism can be easily extended to a general secluded dark matter model. We show that a long-lived mediator can result in a boosted dark matter annihilation cross section to account for the relic abundance. We further show the parameter space which provides a good fit to the Galactic center excess data and is compatible with the current bounds and LUX-ZEPLIN projected sensitivity. We find that the future observations of dwarf spheroidal galaxies offer promising reach to probe the most relic allowed parameter space relevant to the boosted dark matter annihilation cross section.
Journal of High Energy Physics, 2015
Take-down policy If you believe that this document breaches copyright please contact us providing... more Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Journal of High Energy Physics, 2015
Starting with the seminal work of Arkani-Hamed et al. [1], in [2], the "Amplituhedron program" wa... more Starting with the seminal work of Arkani-Hamed et al. [1], in [2], the "Amplituhedron program" was extended to analyzing (planar) amplitudes in massless φ 4 theory. In this paper we show that the program can be further extended to include φ p (p > 4) interactions. We show that tree-level planar amplitudes in these theories can be obtained from geometry of polytopes called accordiohedron which naturally sits inside kinematic space. As in the case of quartic interactions the accordiohedron of a given dimension is not unique, and we show that a weighted sum of residues of the canonical form on these polytopes can be used to compute scattering amplitudes. We finally provide a prescription to compute the weights and demonstrate how it works in various examples.
Physical review letters, Jan 16, 2015
A search is presented for hidden-sector bosons, χ, produced in the decay B^{0}→K^{*}(892)^{0}χ, w... more A search is presented for hidden-sector bosons, χ, produced in the decay B^{0}→K^{*}(892)^{0}χ, with K^{*}(892)^{0}→K^{+}π^{-} and χ→μ^{+}μ^{-}. The search is performed using pp-collision data corresponding to 3.0 fb^{-1} collected with the LHCb detector. No significant signal is observed in the accessible mass range 214≤m(χ)≤4350 MeV, and upper limits are placed on the branching fraction product B(B^{0}→K^{*}(892)^{0}χ)×B(χ→μ^{+}μ^{-}) as a function of the mass and lifetime of the χ boson. These limits are of the order of 10^{-9} for χ lifetimes less than 100 ps over most of the m(χ) range, and place the most stringent constraints to date on many theories that predict the existence of additional low-mass bosons.
Journal of High Energy Physics, 2015
We investigate the relation between 3d N = 2 theories and 2d free field correlators or Dotsenko-F... more We investigate the relation between 3d N = 2 theories and 2d free field correlators or Dotsenko-Fateev (DF) integrals for Liouville CFT. We show that the S 2 × S 1 partition functions of some known 3d Seiberg-like dualities reduce, in a suitable 2d limit, to known basic duality identities for DF correlators. These identities are applied in a variety of contexts in CFT, as for example in the derivation of the DOZZ 3-point function. Reversing the logic, we can try to guess new 3d IR dualities which reduce to more intricate duality relations for the DF correlators. For example, we show that a recently proposed duality relating the U(N) theory with one flavor and one adjoint to a WZ model can be regarded as the 3d ancestor of the evaluation formula for the DF integral representation of the 3-point correlator. We are also able to interpret the analytic continuation in the number of screening charges, which is performed on the CFT side to reconstruct the DOZZ 3-point function, as the geometric transition relating the 3d U(N) theory to the 5d T 2 theory.
Journal of High Energy Physics, 2015
Starting with the seminal work of Arkani-Hamed et al. [1], in [2], the "Amplituhedron program" wa... more Starting with the seminal work of Arkani-Hamed et al. [1], in [2], the "Amplituhedron program" was extended to analyzing (planar) amplitudes in massless φ 4 theory. In this paper we show that the program can be further extended to include φ p (p > 4) interactions. We show that tree-level planar amplitudes in these theories can be obtained from geometry of polytopes called accordiohedron which naturally sits inside kinematic space. As in the case of quartic interactions the accordiohedron of a given dimension is not unique, and we show that a weighted sum of residues of the canonical form on these polytopes can be used to compute scattering amplitudes. We finally provide a prescription to compute the weights and demonstrate how it works in various examples.
Journal of High Energy Physics, 2015
A measurement of the time-integrated CP asymmetry in D 0 → K 0 S K 0 S decays is reported. The da... more A measurement of the time-integrated CP asymmetry in D 0 → K 0 S K 0 S decays is reported. The data correspond to an integrated luminosity of about 2 fb −1 collected in 2015-2016 by the LHCb collaboration in pp collisions at a centre-of-mass energy of 13 TeV. The D 0 candidate is required to originate from a D * + → D 0 π + decay, allowing the determination of the flavour of the D 0 meson using the pion charge. The D 0 → K + K − decay, which has a well measured CP asymmetry, is used as a calibration channel. The CP asymmetry for D 0 → K 0 S K 0 S is measured to be
![Research paper thumbnail of Measurement of the Ratio of Branching Fractions B(B[over ¯]^{0}→D^{*+}τ^{-}ν[over ¯]_{τ})/B(B[over ¯]^{0}→D^{*+}μ^{-}ν[over ¯]_{μ})](https://a.academia-assets.com/images/blank-paper.jpg)
Physical review letters, Jan 11, 2015
The branching fraction ratio R(D^{*})≡B(B[over ¯]^{0}→D^{*+}τ^{-}ν[over ¯]_{τ})/B(B[over ¯]^{0}→D... more The branching fraction ratio R(D^{*})≡B(B[over ¯]^{0}→D^{*+}τ^{-}ν[over ¯]_{τ})/B(B[over ¯]^{0}→D^{*+}μ^{-}ν[over ¯]_{μ}) is measured using a sample of proton-proton collision data corresponding to 3.0 fb^{-1} of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode τ^{-}→μ^{-}ν[over ¯]_{μ}ν_{τ}. The semitauonic decay is sensitive to contributions from non-standard-model particles that preferentially couple to the third generation of fermions, in particular, Higgs-like charged scalars. A multidimensional fit to kinematic distributions of the candidate B[over ¯]^{0} decays gives R(D^{*})=0.336±0.027(stat)±0.030(syst). This result, which is the first measurement of this quantity at a hadron collider, is 2.1 standard deviations larger than the value expected from lepton universality in the standard model.
Journal of High Energy Physics, 2015
An angular analysis of the decay B 0 s → K * 0 K * 0 is performed using pp collisions correspondi... more An angular analysis of the decay B 0 s → K * 0 K * 0 is performed using pp collisions corresponding to an integrated luminosity of 1.0 fb −1 collected by the LHCb experiment at a centre-of-mass energy √ s = 7 TeV. A combined angular and mass analysis separates six helicity amplitudes and allows the measurement of the longitudinal polarisation fraction f L = 0.201 ± 0.057 (stat.) ± 0.040 (syst.) for the B 0 s → K * (892) 0 K * (892) 0 decay. A large scalar contribution from the K * 0 (1430) and K * 0 (800) resonances is found, allowing the determination of additional CP asymmetries. Triple product and direct CP asymmetries are determined to be compatible with the Standard Model expectations. The branching fraction B(B 0 s → K * (892) 0 K * (892) 0) is measured to be (10.8 ± 2.1 (stat.) ± 1.4 (syst.) ± 0.6 (f d /f s)) × 10 −6 .
Journal of High Energy Physics, 2015
A search is performed for the as yet unobserved baryonic Λ 0 b → Λη and Λ 0 b → Λη decays with 3 ... more A search is performed for the as yet unobserved baryonic Λ 0 b → Λη and Λ 0 b → Λη decays with 3 fb −1 of proton-proton collision data recorded by the LHCb experiment. The B 0 → K 0 S η decay is used as a normalisation channel. No significant signal is observed for the Λ 0 b → Λη decay. An upper limit is found on the branching fraction of B(Λ 0 b → Λη) < 3.1 × 10 −6 at 90% confidence level. Evidence is seen for the presence of the Λ 0 b → Λη decay at the level of 3σ significance, with a branching fraction B(Λ 0 b → Λη) = (9.3 +7.3 −5.3) × 10 −6 .
Physical Review Letters, 2015
Top quark production in the forward region in proton-proton collisions is observed for the first ... more Top quark production in the forward region in proton-proton collisions is observed for the first time. The W +b final state with W → µν is reconstructed using muons with a transverse momentum, p T , larger than 25 GeV in the pseudorapidity range 2.0 < η < 4.5. The b jets are required to have 50 < p T < 100 GeV and 2.2 < η < 4.2, while the transverse component of the sum of the muon and b-jet momenta must satisfy p T > 20 GeV. The results are based on data corresponding to integrated luminosities of 1.0 and 2.0 fb −1 collected at center-of-mass energies of 7 and 8 TeV by LHCb. The inclusive top quark production cross-sections in the fiducial region are σ(top)[7 TeV] = 239 ± 53 (stat) ± 38 (syst) fb , σ(top)[8 TeV] = 289 ± 43 (stat) ± 46 (syst) fb. These results, along with the observed differential yields and charge asymmetries, are in agreement with next-to-leading order Standard Model predictions.
Physical review letters, Jan 31, 2015
The first observation of the B 0 s → η η decay is reported. The study is based on a sample of pro... more The first observation of the B 0 s → η η decay is reported. The study is based on a sample of proton-proton collisions corresponding to 3.0 fb −1 of integrated luminosity collected with the LHCb detector. The significance of the signal is 6.4 standard deviations. The branching fraction is measured to be [3.31 ± 0.64 (stat) ± 0.28 (syst) ± 0.12 (norm)] × 10 −5 , where the third uncertainty comes from the B ± → η K ± branching fraction that is used as a normalisation. In addition, the charge asymmetries of B ± → η K ± and B ± → φK ± , which are control channels, are measured to be (−0.2 ± 1.3)% and (+1.7 ± 1.3)%, respectively. All results are consistent with theoretical expectations.
Physical review letters, Jan 14, 2015
Observations of exotic structures in the J/ψp channel, which we refer to as charmonium-pentaquark... more Observations of exotic structures in the J/ψp channel, which we refer to as charmonium-pentaquark states, in Λ_{b}^{0}→J/ψK^{-}p decays are presented. The data sample corresponds to an integrated luminosity of 3 fb^{-1} acquired with the LHCb detector from 7 and 8 TeV pp collisions. An amplitude analysis of the three-body final state reproduces the two-body mass and angular distributions. To obtain a satisfactory fit of the structures seen in the J/ψp mass spectrum, it is necessary to include two Breit-Wigner amplitudes that each describe a resonant state. The significance of each of these resonances is more than 9 standard deviations. One has a mass of 4380±8±29 MeV and a width of 205±18±86 MeV, while the second is narrower, with a mass of 4449.8±1.7±2.5 MeV and a width of 39±5±19 MeV. The preferred J^{P} assignments are of opposite parity, with one state having spin 3/2 and the other 5/2.
Physical Review Letters, 2015
Observations of exotic structures in the J/ψ p channel, that we refer to as pentaquarkcharmonium ... more Observations of exotic structures in the J/ψ p channel, that we refer to as pentaquarkcharmonium states, in Λ 0 b → J/ψ K − p decays are presented. The data sample corresponds to an integrated luminosity of 3 fb −1 acquired with the LHCb detector from 7 and 8 TeV pp collisions. An amplitude analysis is performed on the three-body final-state that reproduces the two-body mass and angular distributions. To obtain a satisfactory fit of the structures seen in the J/ψ p mass spectrum, it is necessary to include two Breit-Wigner amplitudes that each describe a resonant state. The significance of each of these resonances is more than 9 standard deviations. One has a mass of 4380 ± 8 ± 29 MeV and a width of 205 ± 18 ± 86 MeV, while the second is narrower, with a mass of 4449.8 ± 1.7 ± 2.5 MeV and a width of 39 ± 5 ± 19 MeV. The preferred J P assignments are of opposite parity, with one state having spin 3/2 and the other 5/2.
Nature Physics, 2015
In the Standard Model of particle physics, the strength of the coupling of the b quark to the u q... more In the Standard Model of particle physics, the strength of the coupling of the b quark to the u quark, |V ub |, is governed by the coupling of the quarks to the Higgs boson. Using data from the LHCb experiment at the Large Hadron Collider, it is shown that |V ub | = (3.27 ± 0.23) × 10 −3 , from a measurement of Λ 0 b → pµ − ν µ decays. This is consistent with previous determinations of |V ub | using B meson decays to specific final states and confirms the existing incompatibility with those using an inclusive sample of final states. This measurement is the first ever to use a baryonic decay.
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Papers by Laila Giannetti