Search for direct stau production in events with two hadronic tau-leptons in root s=13 TeV pp collisions with the ATLAS detector

A search for the direct production of the supersymmetric partners ofτ-leptons (staus) in final stateswith two hadronically decayingτ-leptons is presented. The analysis uses a dataset of pp collisions corresponding to an integrated luminosity of139fb−1, recorded with the ATLAS detector at the LargeHadron Collider at a center-of-mass energy of 13 TeV. No significant deviation from the expected StandardModel background is observed. Limits are derived in scenarios of direct production of stau pairs with eachstau decaying into the stable lightest neutralino and oneτ-lepton in simplified models where the two staumass eigenstates are degenerate. Stau masses from 120 GeV to 390 GeV are excluded at 95% confidencelevel for a massless lightest neutralino

Suppression of charged particle production at large transverse momentum in central Pb-Pb collisions at sNN=2.76\sqrt{s_{\rm NN}} = 2.76 TeV

Inclusive transverse momentum spectra of primary charged particles in Pb-Pb collisions at $\sqrt{s_{_{\rm NN}}}$ = 2.76 TeV have been measured by the ALICE Collaboration at the LHC. The data are presented for central and peripheral collisions, corresponding to 0-5% and 70-80% of the hadronic Pb-Pb cross section. The measured charged particle spectra in $|\eta|<0.8$ and $0.3 < p_T < 20$ GeV/$c$ are compared to the expectation in pp collisions at the same $\sqrt{s_{\rm NN}}$, scaled by the number of underlying nucleon-nucleon collisions. The comparison is expressed in terms of the nuclear modification factor $R_{\rm AA}$. The result indicates only weak medium effects ($R_{\rm AA} \approx$ 0.7) in peripheral collisions. In central collisions, $R_{\rm AA}$ reaches a minimum of about 0.14 at $p_{\rm T}=6$-7GeV/$c$ and increases significantly at larger $p_{\rm T}$. The measured suppression of high-$p_{\rm T}$ particles is stronger than that observed at lower collision energies, indicating that a very dense medium is formed in central Pb-Pb collisions at the LHC.Comment: 15 pages, 5 captioned figures, 3 tables, authors from page 10, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/98

Two-pion Bose-Einstein correlations in central Pb-Pb collisions at sNN\sqrt{s_{\rm NN}} = 2.76 TeV

The first measurement of two-pion Bose-Einstein correlations in central Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV at the Large Hadron Collider is presented. We observe a growing trend with energy now not only for the longitudinal and the outward but also for the sideward pion source radius. The pion homogeneity volume and the decoupling time are significantly larger than those measured at RHIC.Comment: 17 pages, 5 captioned figures, 1 table, authors from page 12, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/388

Production of pions, kaons and protons in pp collisions at s=900\sqrt{s}=900 GeV with ALICE at the LHC

The production of $\pi^+$, $\pi^-$, $K^+$, $K^-$, p, and pbar at mid-rapidity has been measured in proton-proton collisions at $\sqrt{s} = 900$ GeV with the ALICE detector. Particle identification is performed using the specific energy loss in the inner tracking silicon detector and the time projection chamber. In addition, time-of-flight information is used to identify hadrons at higher momenta. Finally, the distinctive kink topology of the weak decay of charged kaons is used for an alternative measurement of the kaon transverse momentum ($p_{\rm T}$) spectra. Since these various particle identification tools give the best separation capabilities over different momentum ranges, the results are combined to extract spectra from $p_{\rm T}$ = 100 MeV/$c$ to 2.5 GeV/$c$. The measured spectra are further compared with QCD-inspired models which yield a poor description. The total yields and the mean $p_{\rm T}$ are compared with previous measurements, and the trends as a function of collision energy are discussed.Comment: 24 pages, 18 captioned figures, 5 tables, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/388

A Study of 4-Fermion Processes at Lep

Contains fulltext : 26857___.PDF (publisher's version ) (Open Access

Determination of the number of wounded nucleons in Pb+Pb collisions at 158 A GeV/c

The charged particle multiplicity distributions measured by two experiments, WA97 and NA57, in Pb+Pb collisions at 158 A GeV/c have been analyzed in the framework of the Wounded Nucleon Model (WNM). We obtain a good description of the data within the centrality range of our samples. This allows us to make use of the measured multiplicities to estimate the number of wounded nucleons of the collision

Spin Filtering Studies at COSY

none114Understanding the interplay of the nuclear interaction with polarized protons and the electromagnetic interaction with polarized electrons in polarized atoms is crucial to progress towards the PAX goal to eventually produce stored polarized antiproton beams at FAIR. Presently, there exist two competing theoretical scenarios: one with substantial filtering of (anti)protons by atomic electrons, while the second one suggests a self-cancellation of the electron contribution to filtering. The issue can be clarified by studying the energy dependence of the polarization buildup in a proton beam at COSY at energies in the range from 20 to about 800 MeV. This Letter-of-Intent summarizes the physics case and possible experimental approaches to these studies at COSY.noneC. Barschel; U. Bechstedt; J. Dietrich; N. Dolfus; R. Engels; R. Gebel; H. Hadamek; J. Haidenbauer; C. Hanhart; A. Kacharava; G. Krol; M. K¨uven; G. Langenberg; A. Lehrach; B. Lorentz; R. Maier; S. Martin; U.-G. Meißner; M. Nekipelov; N.N. Nikolaev; D. Oellers; G. d’Orsaneo; D. Prasuhn; F. Rathmann; M. Retzlaff; J. Sarkadi; R. Schleichert; H. Seyfarth; A. Sibirtsev; D. Sp¨olgen; H.J. Stein; H. Stockhorst; H. Str¨oher; Chr. Weidemann; D. Welsch; and P. Wieder; L. Barion; S. Bertelli; V. Carassiti; G. Ciullo; M. Contalbrigo; A. Cotta–Ramusino; P.F. Dalpiaz; A. Drago; G. Guidoboni; P. Lenisa; L. Pappalardo; G. Stancari; M. Stancari; M. Statera; T. Azarian; A. Kulikov; V. Kurbatov; G. Macharashvili; S. Merzliakov; I.N. Meshkov; A. Smirnov; D. Tsirkov; u. Uzikov; F.M. Esser; R. Greven; G. Hansen; H. Jadgfeld; J. Kieven; F. Klehr; A. Schwaab; H. Soltner; H. Straatmann; S. Barsov; S. Belostotski; K. Grigoryev; P. Kravtsov; M. Mikirtychiants; S. Mikirtychiants; A. Vasilyev; D. Chiladze; A. Garishvili; N. Lomidze; D. Mchedlishvili; M. Nioradze; M. Tabidze; N. Akopov; A. Avetisyan; G. Elbakyan; H. Marukyan; and S. Taroian; P. Benati; W. Erven; F.–J. Kayser; H. Kleines; and P. W¨ustner; D. Bruncko; J. Ferencei; J. Muˇsinsk´y; and J. Urb´an; W. Augustyniak; B. Marianski; A. Trzcinski; P. Zupranski; S. Dymov; A. Nass; and E. Steffens; K. Rathsman; P.–E. Tegn´er; and P. Th¨orngren Engblom; A.I. Milstein; Y. Shatunov; and V.M. Strakhovenko; R. De Leo; and G. Tagliente; B. K¨ampfer; and S. Trusov; N. Buttimore; H.O. MeyerC., Barschel; U., Bechstedt; J., Dietrich; N., Dolfus; R., Engels; R., Gebel; H., Hadamek; J., Haidenbauer; C., Hanhart; A., Kacharava; G., Krol; M., K¨uven; G., Langenberg; A., Lehrach; B., Lorentz; R., Maier; S., Martin; U. G., Meißner; M., Nekipelov; N. N., Nikolaev; D., Oellers; G., D’Orsaneo; D., Prasuhn; F., Rathmann; M., Retzlaff; J., Sarkadi; R., Schleichert; H., Seyfarth; A., Sibirtsev; D., Sp¨olgen; H. J., Stein; H., Stockhorst; H., Str¨oher; Weidemann, C. h. r.; D., Welsch; P., Wieder; Barion, Luca; Bertelli, Susanna; Carassiti, Vittore; Ciullo, Giuseppe; Contalbrigo, Marco; COTTA RAMUSINO, Angelo; Ferretti, Paola; Drago, Alessandro; Guidoboni, Greta; Lenisa, Paolo; Pappalardo, Luciano Libero; Stancari, Giulio; Stancari, Michelle Dawn; Statera, Marco; T., Azarian; A., Kulikov; V., Kurbatov; G., Macharashvili; S., Merzliakov; I. N., Meshkov; A., Smirnov; D., Tsirkov; U., Uzikov; F. M., Esser; R., Greven; G., Hansen; H., Jadgfeld; J., Kieven; F., Klehr; A., Schwaab; H., Soltner; H., Straatmann; S., Barsov; S., Belostotski; K., Grigoryev; P., Kravtsov; M., Mikirtychiants; S., Mikirtychiants; A., Vasilyev; D., Chiladze; A., Garishvili; N., Lomidze; D., Mchedlishvili; M., Nioradze; M., Tabidze; N., Akopov; A., Avetisyan; G., Elbakyan; H., Marukyan; S., Taroian; P., Benati; W., Erven; Kayser, F. –. J.; H., Kleines; P., W¨ustner; D., Bruncko; J., Ferencei; J., Muˇsinsk´y; J., Urb´an; W., Augustyniak; B., Marianski; A., Trzcinski; P., Zupranski; S., Dymov; A., Nass; E., Steffens; K., Rathsman; Tegn´er, P. –. E.; P., Th¨orngren Engblom; A. I., Milstein; Y., Shatunov; V. M., Strakhovenko; R., De Leo; G., Tagliente; B., K¨ampfer; S., Trusov; N., Buttimore; H. O., Meye

Beam Request Spin-Filtering Studies at COSY

Summary of experiment: We report on the progress of the PAX experimental program since the last PAC meeting. During two blocks of each three weeks beam development intercepted by two weeks of maintenance, systematic machine studies have been carried out. An effective procedure for setting up the machine with the low-β section and a target cell at the new PAX-IP in order to achieve high beam lifetimes has been developed. The effect of flow-limiters and one NEG-pump on the beam lifetime has been studied, as well as the effect of different beam emittances and beam intensities on the beam lifetime. Even though by increasing the beam emittance a reproducible maximum for the beam lifetime was achievable, no effect of the beam intensity was seen and therefore no clear observation of the so-called Touschek-effect was possible. Nevertheless, we learned how to gain a sufficient beam lifetime for spin-filtering studies at COSY and apply for 3 weeks of beam development followed by 4 weeks of beam time

Status Report and Beam-Time Request for COSY experiment #199 Spin–Filtering Studies at COSY

We report on the progress of the PAX experimental programme since the last PAC meeting. During summer shutdown 2009 four new quadrupole magnets and a modified vacuum system have been installed into the COSY ring to form a section with low β functions. With the successful commissioning of this low-β insertion in January 2010 it has also been discovered that intra-beam scattering effects are likely limiting the beam lifetime. In order to get these effects under control and to improve the lifetime, to commission a new detection system, and to finally perform a first series of spin–filtering measurements with transverse polarisation, we request ten weeks of beam time. Content

UvA-DARE (Digital Academic Repository) A test of QCD based on 3-jet events from Z ° decays L3 Collaboration

A test of QCD based on three jet events from Z0 decays Adeva, B.; Adriani, O.; Aguilar-Benitez, M.; Ahlen, S.P.; Akbari, H.; Alcaraz, J.; Aloisio, A.; Alverson, G.; Linde, F.L. General rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulations If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. We present a study of 43 000 3-jet events from Z ° boson decays. Both the measured jet energy distributions and the event orientation are reproduced by second order QCD. An alternative model with scalar gluons fails to describe the data