| 1. |
- Collaboration, The PANDA, et al.
(författare)
-
Feasibility studies of time-like proton electromagnetic form factors at PANDA at FAIR
- 2016
-
Ingår i: European Physical Journal A. - : Springer Publishing Company. - 1434-6001 .- 1434-601X. ; 52:10
-
Tidskriftsartikel (refereegranskat)abstract
- Simulation results for future measurements of electromagnetic proton form factors at P ¯ ANDA (FAIR) within the PandaRoot software framework are reported. The statistical precision with which the proton form factors can be determined is estimated. The signal channel p¯ p→ e+e- is studied on the basis of two different but consistent procedures. The suppression of the main background channel, i.e.p¯ p→ π+π-, is studied. Furthermore, the background versus signal efficiency, statistical and systematical uncertainties on the extracted proton form factors are evaluated using two different procedures. The results are consistent with those of a previous simulation study using an older, simplified framework. However, a slightly better precision is achieved in the PandaRoot study in a large range of momentum transfer, assuming the nominal beam conditions and detector performance.
|
|
| 2. |
- Singh, B., et al.
(författare)
-
Feasibility study for the measurement of pi N transition distribution amplitudes at (P)over-barANDA in (P)over-barp -> J/psi pi(0)
- 2017
-
Ingår i: Physical Review D. - : AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 95:3
-
Tidskriftsartikel (refereegranskat)abstract
- The exclusive charmonium production process in (P) over barp annihilation with an associated pi 0 meson (p) over barp -> J/psi pi(0) is studied in the framework of QCD collinear factorization. The feasibility of measuring this reaction through the J/psi -> e(+) e(-) decay channel with the AntiProton ANnihilation at DArmstadt ((P) over bar ANDA) experiment is investigated. Simulations on signal reconstruction efficiency as well as the background rejection from various sources including the (P) over barp -> pi(+)pi(-)pi(0) and (p) over barp -> J/psi pi(0)pi(0) reactions are performed with PANDAROOT, the simulation and analysis software framework of the (P) over bar ANDA experiment. It is shown that the measurement can be done at (P) over bar ANDA with significant constraining power under the assumption of an integrated luminosity attainable in four to five months of data taking at the maximum design luminosity.
|
|
| 3. |
- Singh, B. P., et al.
(författare)
-
Experimental access to Transition Distribution Amplitudes with the PANDA experiment at FAIR
- 2015
-
Ingår i: European Physical Journal A. Hadrons and Nuclei. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 51:8
-
Tidskriftsartikel (refereegranskat)abstract
- Baryon-to-meson Transition Distribution Amplitudes (TDAs) encoding valuable new information on hadron structure appear as building blocks in the collinear factorized description for several types of hard exclusive reactions. In this paper, we address the possibility of accessing nucleon-to-pion (pi N) TDAs from (p) over barp -> e(+)e(-)pi(0) reaction with the future PANDA detector at the FAIR facility. At high center-of-mass energy and high invariant mass squared of the lepton pair q(2), the amplitude of the signal channel (p) over barp -> e(+)e(-)pi(0) admits a QCD factorized description in terms of pi N TDAs and nucleon Distribution Amplitudes (DAs) in the forward aid backward kinematic regimes. Assuming the validity of this factorized description, we perform feasibility studies for measuring (p) over barp -> e(+)e(-)pi(0) with the PANDA detector. Detailed simulations on signal reconstruction efficiency as well as on rejection of the most severe background channel, i.e. (p) over barp -> pi(+)pi(-)pi(0) were performed for the center-of-mass energy squared s = 5 GeV2 and s = 10 GeV2, in the kinematic regions 3.0 < q(2) < 4.3 GeV2 and 5 < q(2) < 9 GeV2, respectively, with a neutral pion scattered in the forward or backward cone vertical bar cos theta(pi 0)vertical bar > 0.5 in the proton-antiproton center-of-mass frame. Results of the simulation show that the particle identification capabilities of the PANDA detector will allow to achieve a background rejection factor of 5 . 10(7) (1 . 10(7)) at low (high) q(2) for s = 5 GeV2, and of 1 . 10(8) (6 . 10(6)) at low (high) q(2) for s = 10 GeV2, while keeping the signal reconstruction efficiency at around 40%. At both energies, a clean lepton signal can be reconstructed with the expected statistics corresponding to 2 of integrated luminosity. The cross sections obtained from the simulations are used to show that a test of QCD collinear factorization can be done at the lowest order by measuring scaling laws and angular distributions. The future measurement of the signal channel cross section with PANDA will provide a new test of the perturbative QCD description of a novel class of hard exclusive reactions and will open the possibility of experimentally accessing pi N TDAs.
|
|
| 4. |
- Singh, B., et al.
(författare)
-
Study of doubly strange systems using stored antiprotons
- 2016
-
Ingår i: Nuclear Physics A. - : Elsevier. - 0375-9474 .- 1873-1554. ; 954, s. 323-340
-
Tidskriftsartikel (refereegranskat)abstract
- Bound nuclear systems with two units of strangeness are still poorly known despite their importance for many strong interaction phenomena. Stored antiprotons beams in the GeV range represent an unparalleled factory for various hyperon-antihyperon pairs. Their outstanding large production probability in antiproton collisions will open the floodgates for a series of new studies of systems which contain two or even more units of strangeness at the PANDA experiment at FAIR. For the first time, high resolution gamma-spectroscopy of doubly strange Lambda Lambda-hypernuclei will be performed, thus complementing measurements of ground state decays of Lambda Lambda-hypernuclei at J-PARC or possible decays of particle unstable hypernuclei in heavy ion reactions. High resolution spectroscopy of multistrange Xi(-) -atoms will be feasible and even the production of Omega(-) -atoms will be within reach. The latter might open the door to the vertical bar S vertical bar = 3 world in strangeness nuclear physics, by the study of the hadronic Omega(-) -nucleus interaction. For the first time it will be possible to study the behavior of Xi(+) in nuclear systems under well controlled conditions.
|
|
| 5. |
- Adlarson, Patrik, et al.
(författare)
-
Backward single-pion production in the pd -> He-3 pi(0)reaction with WASA-at-COSY
- 2018
-
Ingår i: European Physical Journal A. - : SPRINGER. - 1434-6001 .- 1434-601X. ; 54:9
-
Tidskriftsartikel (refereegranskat)abstract
- New data on the production of single neutral pions in the pd -> He-3 pi(0) reaction are presented. For fifteen proton beam momenta between p(p) = 1.60GeV/c and p(p) = 1.74 GeV/c, differential cross sections are determined over a large fraction of the backward hemisphere. Since the only previous systematic measurements of single-pion production at these energies were made in collinear kinematics, the present work constitutes a significant extension of the current knowledge on this reaction. Even this far above the production threshold, significant changes are found in the behaviour of the angular distributions over small intervals in beam momentum.
|
|
| 6. |
- Adlarson, Patrik, et al.
(författare)
-
Examination of the production of an isotensor dibaryon in the pp -> pp pi(+)pi(-) reaction
- 2019
-
Ingår i: Physical Review C. - : AMER PHYSICAL SOC. - 2469-9985 .- 2469-9993. ; 99:2
-
Tidskriftsartikel (refereegranskat)abstract
- The quasifree pp -> pp pi(+)pi(-) reaction has been measured by means of pd collisions at T-p = 1.2 GeV using the WASA detector setup at COSY enabling exclusive and kinematically complete measurements. Total and differential cross sections have been extracted for the energy region T-p = 1.08-1.36 GeV (root s = 2.35-2.46 GeV) covering thus the regions of N* (1440 ) and Delta(1232)Delta(1232) resonance excitations. Calculations describing these excitations by t-channel meson exchange as well as isospin relations based on the pp -> pp pi(0)pi(0) data underpredict substantially the measured total cross section. The calculations are also at variance with specific experimental differential cross sections. An isotensor Delta N dibaryon resonance with I(J(P)) = 2(1(+) ) produced associatedly with a pion is able to overcome these deficiencies. Such a dibaryon was predicted by Dyson and Xuong [Phys. Rev. Lett. 13, 815 (1964)] and more recently calculated by A. Gal and H. Garcilazo [Nucl. Phys. A 928, 73 (2014)].
|
|
| 7. |
- Adlarson, Patrik, et al.
(författare)
-
Importance of d-wave contributions in the charge symmetry breaking reaction dd -> He-4 pi(0)
- 2018
-
Ingår i: Physics Letters B. - : ELSEVIER SCIENCE BV. - 0370-2693 .- 1873-2445. ; 781, s. 645-650
-
Tidskriftsartikel (refereegranskat)abstract
- This letter reports a first quantitative analysis of the contribution of higher partial waves in the charge symmetry breaking reaction dd -> He-4 pi(0) using the WASA-at-COSY detector setup at an excess energy of Q = 60 MeV. The determined differential cross section can be parametrized as d sigma/d Omega = a + b cos(2) theta*, where theta* is the production angle of the pion in the center-of-mass coordinate system, and the results for the parameters are a = (1.55 +/- 0.46(stat)(-0.8)(+0.32)(syst)) pb/sr and b = (13.1 +/- 2.1(stat)(-2.7)(+1.0)(syst)) pb/sr. The data are compatible with vanishing p-waves and a sizable d-wave contribution. This finding should strongly constrain the contribution of the A isobar to the dd -> He-4 pi(0) reaction and is, therefore, crucial for a quantitative understanding of quark mass effects in nuclear production reactions.
|
|
| 8. |
- Adlarson, Patrik, et al.
(författare)
-
Isoscalar single-pion production in the region of Roper and d*(2380) resonances
- 2017
-
Ingår i: Physics Letters B. - : ELSEVIER SCIENCE BV. - 0370-2693 .- 1873-2445. ; 774, s. 599-607
-
Tidskriftsartikel (refereegranskat)abstract
- Exclusive measurements of the quasi-free pn -> pp pi(-) and pp -> pp pi(0) reactions have been performed by means of pd collisions at T-p= 1.2 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region T-p= 0.95-1.3 GeV (root s = 2.3-2.46 GeV), which includes the regions of triangle(1232), N*(1440) and d*(2380) resonance excitations. From these measurements the isoscalar single-pion production has been extracted, for which data existed so far only below T-p = 1 GeV. We observe a substantial increase of this cross section around 1 GeV, which can be related to the Roper resonance N*(1440), the strength of which shows up isolated from the triangle resonance in the isoscalar (N pi)(I=0) invariant-mass spectrum. No evidence for a decay of the dibaryon resonance d*(2380) into the isoscalar (NN pi)(I=0) channel is found. An upper limit of 180 mu b (90% CL.) corresponding to a branching ratio of 9% has been deduced.
|
|
| 9. |
- Adlarson, Patrik, et al.
(författare)
-
Isotensor Dibaryon in the pp -> pp pi(+)pi(-) Reaction?
- 2018
-
Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 121:5
-
Tidskriftsartikel (refereegranskat)abstract
- Exclusive measurements of the quasifree pp -> pp pi(+)pi(-) reaction have been carried out at WASA@ COSY by means of pd collisions at T-p = 1.2 GeV. Total and differential cross sections have been extracted covering the energy region T-p = 1.08-1.36 GeV, which is the region of N* (1440) and Delta(123)Delta(1232) resonance excitations. Calculations describing these excitations by t-channel meson exchange are at variance with the measured differential cross sections and underpredict substantially the experimental total cross section. An isotensor Delta N dibaryon resonance with I(J(P)) = 2(1(+)) produced associatedly with a pion is able to overcome these deficiencies.
|
|
| 10. |
- Adlarson, Patrik, et al.
(författare)
-
Search for C violation in the decay eta -> pi(0)e(+)e(-) with WASA-at-COSY
- 2018
-
Ingår i: Physics Letters B. - : ELSEVIER SCIENCE BV. - 0370-2693 .- 1873-2445. ; 784, s. 378-384
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the search for the rare decay eta -> pi(0)e(+)e(-) which is of interest to study C violation in the electromagnetic interaction which would indicate contributions from physics beyond the Standard Model, since the allowed decay via a two-photon intermediate state is strongly suppressed. The experiment has been performed using the WASA-at-COSY installation, located at the COSY accelerator of the Forschungszentrum Julich, Germany. In total 3 x 10(7) events of the reaction pd -> He-3 eta have been recorded at an excess energy of Q = 59.8MeV. Based on this data set the C parity violating decay eta -> pi(0)gamma* -> pi(0)e(+)e(-) via a single-photon intermediate state has been searched for, resulting in new upper limits of Gamma(eta -> pi(0)e(+) e(-))/Gamma(eta -> pi(+) pi(-) pi(0)) < 3.28 x 10(-5) and Gamma(eta -> pi(0)e(+) e(-))/Gamma(eta -> all)< 7.5 x 10(-6) (CL=90%), respectively.
|
|
| 11. |
- Adlarson, Patrik, et al.
(författare)
-
Spin Dependence of eta Meson Production in Proton-Proton Collisions Close to Threshold
- 2018
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 120:2
-
Tidskriftsartikel (refereegranskat)abstract
- Taking advantage of the high acceptance and axial symmetry of the WASA-at-COSY detector, and the high polarization degree of the proton beam of COSY, the reaction →pp→ppη has been measured close to threshold to explore the analyzing power Ay. The angular distribution of Ay is determined with the precision improved by more than 1 order of magnitude with respect to previous results, allowing a first accurate comparison with theoretical predictions. The determined analyzing power is consistent with zero for an excess energy of Q=15 MeV, signaling s-wave production with no evidence for higher partial waves. At Q=72 MeV the data reveal strong interference of Ps and Pp partial waves and cancellation of (Pp)2 and Ss∗Sd contributions. These results rule out the presently available theoretical predictions for the production mechanism of the η meson.
|
|
| 12. |
- Adlarson, Patrik, et al.
(författare)
-
Total and differential cross sections of η-production in proton–deuteron fusion for excess energies between Qη = 13 MeV and Qη = 81 MeV
- 2018
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 782, s. 297-304
-
Tidskriftsartikel (refereegranskat)abstract
- New data on both total and differential cross sections of the production of eta mesons in proton-deuteron fusion to He-3 eta in the excess energy region 13.6 MeV <= Q(eta) <= 80.9 MeV are presented. These data have been obtained with the WASA-at-COSY detector setup located at the Forschungszentrum Julich, using a proton beam at 15 different beam momenta between p(p) = 1.60 GeV/c and p(p) = 1.74 GeV/c. While significant structure of the total cross section is observed in the energy region 20 MeV less than or similar to Q(eta) less than or similar to 60 MeV, a previously reported sharp variation around Q(eta) approximate to 50 MeV cannot be confirmed. Angular distributions show the typical forward- peaking that was noted earlier. For the first time, it is possible to study the development of these angular distributions with rising excess energy over a wide interval.
|
|
| 13. |
- Adlarson, Patrik, et al.
(författare)
-
ABC effect and resonance structure in the double-pionic fusion to He-3
- 2015
-
Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 91:1, s. 015201-
-
Tidskriftsartikel (refereegranskat)abstract
- Exclusive and kinematically complete measurements of the double pionic fusion to He-3 have been performed in the energy region of the so-called ABC effect, which denotes a pronounced low-mass enhancement in the pi pi-invariant mass spectrum. The experiments were carried out with the WASA detector setup at COSY (the cooler synchrotron at Forschungszentrum Julich). Similar to the observations in the basic pn -> d pi(0)pi(0) reaction and in the dd -> He-4 pi(0)pi(0) reaction, the data reveal a correlation between the ABC effect and a resonance-like energy dependence in the total cross section. Differential cross sections are well described by the hypothesis of d* resonance formation during the reaction process in addition to the conventional t-channel Delta Delta mechanism. The deduced d* resonance width can be understood from collision broadening due to Fermi motion of the nucleons in initial and final nuclei.
|
|
| 14. |
- Adlarson, Patrik, et al.
(författare)
-
Measurement of the (n)over-right-arrowp -> d pi(0) pi(0) reaction with polarized beam in the region of the d(*)(2380) resonance
- 2016
-
Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 52:5, s. 1-7
-
Tidskriftsartikel (refereegranskat)abstract
- We report on a high-statistics measurement of the most basic double-pionic fusion reaction over the energy region of the d (*)(2380) resonance by use of a polarized deuteron beam and observing the double fusion reaction in the quasifree scattering mode. The measurements were performed with the WASA detector setup at COSY. The data reveal substantial analyzing powers and confirm conclusions about the d(*) resonance obtained from unpolarized measurements. We also confirm the previous unpolarized data obtained under complementary kinematic conditions.
|
|
| 15. |
- Adlarson, Patrik, et al.
(författare)
-
Measurement of the ω → π+π−π0 Dalitz plot distribution : The WASA-at-COSY Collaboration
- 2017
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 770, s. 418-425
-
Tidskriftsartikel (refereegranskat)abstract
- Using the production reactions pd -> He-3 omega and pp -> pp omega, the Dalitz plot distribution for the omega -> pi(+)pi(-)pi(0)decay is studied with the WASA detector at COSY, based on a combined data sample of (4.408 +/- 0.042) x 10(4) events. The Dalitz plot density is parametrised by a product of the P-wave phase space and a polynomial expansion in the normalised polar Dalitz plot variables Z and phi. For the first time, a deviation from pure P-wave phase space is observed with a significance of 4.1 sigma. The deviation is parametrised by a linear term 1+2 alpha Z, with alpha determined to be +0.147 +/- 0.036, consistent with the expectations of rho-meson-type final-state interactions of the P-wave pion pairs. (C) 2017 The Author. Published by Elsevier B.V.
|
|
| 16. |
- Adlarson, Patrik, et al.
(författare)
-
Measurements of branching ratios for eta decays into charged particles
- 2016
-
Ingår i: PHYSICAL REVIEW C. - 2469-9985. ; 94:6
-
Tidskriftsartikel (refereegranskat)abstract
- The WASA-at-COSY experiment has collected 3 x 10(7) events with eta mesons produced via the reaction pd -> He-3 eta at T = 1.0 GeV. Using this data set, we evaluate the branching ratios of the decays eta -> pi(+)pi(-)gamma, eta -> e(+)e(-)gamma, eta -> pi(+)pi(-)e(+)e(-), and eta -> e(+)e(-)e(+)e(-). The branching ratios are normalized to the eta -> pi(+)pi(-) pi(0) decay. In addition an upper limit on a CP-violating asymmetry in eta -> pi(+)pi(-)e(+)e(-) is extracted.
|
|
| 17. |
- Adlarson, Patrik, et al.
(författare)
-
Search for an isospin I=3 dibaryon
- 2016
-
Ingår i: Physics Letters B. - : ELSEVIER SCIENCE BV. - 0370-2693 .- 1873-2445. ; 762, s. 455-461
-
Tidskriftsartikel (refereegranskat)abstract
- Various theoretical calculations based on QCD or hadronic interactions predict that in addition to the recently observed dibaryon resonance d*(2380) with I(J(P)) = 3(0(+)) there should also exist a dibaryon resonance with mirrored quantum numbers I(J(P)) = 3(0(+)). We report here on a search for such a NN-decoupled state in data on the pp -> pp pi(+) pi(+) pi(-) pi(-) reaction. Since no clear-cut evidence has been found, we give upper limits for the production cross section of such a resonance in the mass range 2280-2500 MeV.
|
|
| 18. |
- Adlarson, Patrik, et al.
(författare)
-
Search for eta-mesic He-4 in the dd -> (3)Hen pi(0) and dd -> (3)Hep pi(-) reactions with the WASA-at-COSY facility
- 2017
-
Ingår i: Nuclear Physics A. - : ELSEVIER SCIENCE BV. - 0375-9474 .- 1873-1554. ; 959, s. 102-115
-
Tidskriftsartikel (refereegranskat)abstract
- The search for He-4-eta bound states was performed with the WASA-at-COSY facility via the measurement of the excitation function for the dd -> (3)Hen pi(0) and dd -> (3)Hep pi(-) processes. The deuteron beam momentum was varied continuously between 2.127 GeV/c and 2.422 GeV/c, corresponding to the excess energy for the dd -> He-4 eta reaction ranging from Q = 70 MeV to Q = 30 MeV. The luminosity was determined based on the dd -> (3)Hen reaction and the quasi-free proton proton scattering via dd -> ppn(spectator)n(spectator) reactions. The excitation functions, determined independently for the measured reactions, do not reveal a structure which could be interpreted as a narrow mesic nucleus. Therefore, the upper limits of the total cross sections for the bound state production and decay in dd -> (4He-eta)(bound) -> (3)Hen pi(0) and dd -> (He-4-eta)(bound) -> (3)Hep pi(-) processes were determined taking into account the isospin relation between the both of the considered channels. The results of the analysis depend on the assumptions of the N* (1535) momentum distribution in the anticipated mesic-He-4. Assuming, as in the previous works, that this is identical with the distribution of nucleons bound with 20 MeV in He-4, we determined that (for the mesic bound state width in the range from 5 MeV to 50 MeV) the upper limits at 90% confidence level are about 3 nb and about 6 nb for n pi(0) and p pi(-) channels, respectively. However, based on the recent theoretical findings of the N*(1535) momentum distribution in the N*-He-3 nucleus bound by 3.6 MeV, we find that the WASA-at-COSY detector acceptance decreases and hence the corresponding upper limits are 5 nb and 10 nb for n pi(0) and p pi(-) channels respectively. (C) 2017 Elsevier B.V. All rights reserved.
|
|
| 19. |
- Adlarsona, Patrik, et al.
(författare)
-
Measurement of the np -> np pi(0)pi(0) reaction in search for the recently observed d* (2380) resonance
- 2015
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 743, s. 325-332
-
Tidskriftsartikel (refereegranskat)abstract
- Exclusive measurements of the quasi-free np --> np pi(0)pi(0) reaction have been performed by means of dp collisions at T-d = 2.27 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region root s = (2.35-2.46) GeV, which includes the region of the ABC effect and its associated d* (2380) resonance. Adding the d* resonance amplitude to that for the conventional processes leads to a reasonable description of the data. The observed resonance effect in the total cross section is in agreement with the predictions of Faldt and Wilkin as well with those of Albadajedo and Oset. The ABC effect, i.e. the low-mass enhancement in the pi(0)pi(0)-invariant mass spectrum, is found to be very modest - if present at all, which might pose a problem to some of its interpretations.
|
|
| 20. |
- Anastasi, A., et al.
(författare)
-
Combination of KLOE sigma (e(+) e(-) -> pi(+)pi(-) gamma(gamma)) measurements and determination of a(mu)(pi+pi-) in the energy range 0.10 < s < 0.95 GeV2
- 2018
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; :3
-
Tidskriftsartikel (refereegranskat)abstract
- The three precision measurements of the cross section sigma (e(+)e(-) -> pi(+)pi(-)gamma(gamma)) using initial state radiation by the KLOE collaboration provide an important input for the prediction of the hadronic contribution to the anomalous magnetic moment of the muon. These measurements are correlated for both statistical and systematic uncertainties and, therefore, the simultaneous use of these measurements requires covariance matrices that fully describe the correlations. We present the construction of these covariance matrices and use them to determine a combined KLOE measurement for sigma (e(+)e(-) -> pi(+)pi(-)gamma(gamma)). We find, from this combination, a two-pion contribution to the muon magnetic anomaly in the energy range 0.10 < s < 0.95 GeV2 of a(mu)(pi+pi-) (489.8 +/- 1.7(stat) +/- 4.8(sys)) x 10(-10).
|
|
| 21. |
- Anastasi, A., et al.
(författare)
-
Combined limit on the production of a light gauge boson decaying into mu(+) mu(-) and pi(+) pi(-)
- 2018
-
Ingår i: Physics Letters B. - : ELSEVIER SCIENCE BV. - 0370-2693 .- 1873-2445. ; 784, s. 336-341
-
Tidskriftsartikel (refereegranskat)abstract
- We searched for the mu(+) mu(-) decay of a light vector gauge boson, also known as dark photon, in the e(+) e(-) -> mu(+) mu(-) gamma(ISR) process by means of the Initial State Radiation (ISR) method. We used 1.93fb(-1) of data collected by the KLOE experiment at the DA Phi NE phi-factory. No structures have been observed over the irreducible mu(+) mu(-) background. A 90% CL limit on the ratio epsilon(2)= alpha'/alpha between the dark coupling constant and the fine structure constant of 3 x 10(-6)-2 x 10(-7) has been set in the dark photon mass region between 519 MeV and 973 MeV. This new limit has been combined with the published result obtained investigating the hypothesis of the dark photon decaying into hadrons in e(+) e(-) -> pi(+) pi(-) gamma(ISR) events. The combined 90% CL limit increases the sensitivity especially in the rho-omega interference region and excludes epsilon(2) greater than (13 - 2) x 10(-7). For dark photon masses greater than 600 MeV the combined limit is lower than 8 x 10(-7) resulting more stringent than present constraints from other experiments.
|
|
| 22. |
- Anastasi, A., et al.
(författare)
-
Limit on the production of a low-mass vector boson in e(+)e(-) -> U gamma, U -> e(+)e(-) with the KLOE experiment
- 2015
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 750, s. 633-637
-
Tidskriftsartikel (refereegranskat)abstract
- The existence of a new force beyond the Standard Model is compelling because it could explain several striking astrophysical observations which fail standard interpretations. We searched for the light vector mediator of this dark force, the U boson, with the KLOE detector at the DA Phi NE e(+)e(-) collider. Using an integrated luminosity of 1.54 fb(-1), we studied the process e(+)e(-) -> U gamma, with U -> e(+)e(-), using radiative return to search for a resonant peak in the dielectron invariant-mass distribution. We did not find evidence for a signal, and set a 90% CL upper limit on the mixing strength between the Standard Model photon and the dark photon, epsilon(2), at 10(-6)-10(-4) in the 5-520 MeV/c(2) mass range.
|
|
| 23. |
- Anastasi, A., et al.
(författare)
-
Limit on the production of a new vector boson in e+e− → Uγ, U → π+π− with the KLOE experiment
- 2016
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 757, s. 356-361
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract The recent interest in a light gauge boson in the framework of an extra U(1) symmetry motivates searches in the mass range below 1 GeV. We present a search for such a particle, the dark photon, in e + e − → U γ , U → π + π − based on 28 million e + e − → π + π − γ events collected at DAΦNE by the KLOE experiment. The π + π − production by initial-state radiation compensates for a loss of sensitivity of previous KLOE U → e + e − , μ + μ − searches due to the small branching ratios in the ρ – ω resonance region. We found no evidence for a signal and set a limit at 90% CL on the mixing strength between the photon and the dark photon, ε 2 , in the U mass range between 527 and 987 MeV . Above 700 MeV this new limit is more stringent than previous ones.
|
|
| 24. |
- Anastasi, A., et al.
(författare)
-
Measurement of the charge asymmetry for the K-S -> pi e nu decay and test of CPT symmetry with the KLOE detector
- 2018
-
Ingår i: Journal of High Energy Physics (JHEP). - : SPRINGER. - 1126-6708 .- 1029-8479. ; :9
-
Tidskriftsartikel (refereegranskat)abstract
- Using 1.63 fb(-1) of integrated luminosity collected by the KLOE experiment about 7 x 10(4) K-S -> pi(+/-)e(-/+)nu decays have been reconstructed. The measured value of the charge asymmetry for this decay is A(S) = (-4.9 +/- 5.7(stat) +/- 2.6(syst)) x 10(-3) which is almost twice more precise than the previous KLOE result. The combination of these two measurements gives A(S) = (3.8 +/- 5.0(stat) +/- 2.6(syst)) x 10(-3) and, together with the asymmetry of the K-L semileptonic decay, provides significant tests of the CPT symmetry. The obtained results are in agreement with CPT invariance.
|
|
| 25. |
- Anastasi, A., et al.
(författare)
-
Measurement of the running of the fine structure constant below 1 GeV with the KLOE detector
- 2017
-
Ingår i: Physics Letters B. - : ELSEVIER SCIENCE BV. - 0370-2693 .- 1873-2445. ; 767, s. 485-492
-
Tidskriftsartikel (refereegranskat)abstract
- We have measured the running of the effective QED coupling constant alpha(s) in the time-like region 0.6 < root s < 0.975 GeV with the KLOE detector at DA Phi NE using the Initial-State Radiation process e(+) e(-) -> mu(+) mu(-)gamma. It represents the first measurement of the running of alpha(s) in this energy region. Our results show a more than 5 sigma significance of the hadronic contribution to the running of alpha(s), which is the strongest direct evidence both in time- and space-like regions achieved in a single measurement. By using the e(+) e(-) -> pi(+) pi(-) cross section measured by KLOE, the real and imaginary parts of the shift Delta alpha(s) have been extracted. From a fit of the real part of Delta alpha(s) and assuming the lepton universality the branching ratio BR(omega -> mu(+) mu(-)) = (6.6 +/- 1.4(stat) +/- 1.7(syst)) (.) 10 (5)has been determined.
|
|
| 26. |
- Anastasi, A., et al.
(författare)
-
Precision measurement of the η → π + π − π 0 Dalitz plot distribution with the KLOE detector
- 2016
-
Ingår i: Journal of High Energy Physics (JHEP). - 1126-6708 .- 1029-8479. ; :5
-
Tidskriftsartikel (refereegranskat)abstract
- Using 1.6 fb−1 of e + e − → ϕ → ηγ data collected with the KLOE detector at DAΦNE, the Dalitz plot distribution for the η → π + π − π 0 decay is studied with the world’s largest sample of ∼ 4.7 · 106 events. The Dalitz plot density is parametrized as a polynomial expansion up to cubic terms in the normalized dimensionless variables X and Y . The experiment is sensitive to all charge conjugation conserving terms of the expansion, including a gX 2 Y term. The statistical uncertainty of all parameters is improved by a factor two with respect to earlier measurements.
|
|
| 27. |
- Anastasi, A., et al.
(författare)
-
Search for dark Higgsstrahlung in e(+0)e(-) -> mu(+)mu(-) and missing energy events with the KLOE experiment
- 2015
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 747, s. 365-372
-
Tidskriftsartikel (refereegranskat)abstract
- We searched for evidence of a Higgsstrahlung process in a secluded sector, leading to a final state with a dark photon U and a dark Higgs boson h', with the KLOE detector at DA Phi NE. We investigated the case of h' lighter than U, with U decaying into a muon pair and h' producing a missing energy signature. We found no evidence of the process and set upper limits to its parameters in the range 2m(mu) < m(U) < 1000 MeV, m(h') < m(U). (C) 2015 The Authors. Published by Elsevier B.V.
|
|
| 28. |
- Babusci, D., et al.
(författare)
-
Study of the Dalitz decay phi -> eta e(+)e(-) with the KLOE detector
- 2015
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 742, s. 1-6
-
Tidskriftsartikel (refereegranskat)abstract
- We have studied the vector to pseudoscalar conversion decay phi -> eta e(+)e(-), with.. eta -> pi(0)pi(0)pi(0), with the KLOE detector at DA phi NE. The data set of 1.7 fb(-1) of e(+)e(-) collisions at root s similar to M-phi contains a clear conversion decay signal of similar to 31,000 events from which we measured a value of BR(phi -> eta e(+)e-) = (1.075 +/- 0.007 +/- 0.038) x 10(-4). The same sample is used to determine the transition form factor by a fit to the e(+)e(-) invariant mass spectrum, obtaining b(phi eta)=( 1.28 +/- 0.10(-0.08)(+0.09)) GeV-2, that improves by a factor of five the precision of the previous measurement and is in good agreement with VMD expectations.
|
|
| 29. |
|
|
