KLOE-2 is the main experiment of the INFN Frascati National Laboratories and represents the continuation of KLOE. The previous apparatus, consisting in a huge Drift Chamber and an Electromagnetic Calorimeter, both immersed in a 0.5 T magnetic ﬁeld, has been upgraded with new detectors to perform high-precision CPT symmetry and quantum coherence tests using neutral kaons, γγ-physics studies and searches of particles of hidden dark matter sectors. KLOE-2 started its data taking in November 2014 and is presently collecting data, achieving record performance in terms of peak luminosity and maximum daily integrated luminosity, which will allow to integrate more than 5fb−1 of data in the next 2 years

Di Cicco, A.

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DOI 10.1393/ncc/i2017-17036-3Colloquia: IFAE 2016IL NUOVO CIMENTO 40 C (2017) 36The KLOE-2 experiment at DAΦNEA. Di Cicco(∗) on behalf of the KLOE-2 CollaborationDipartimento di Matematica e Fisica, Università “Roma Tre” - Roma, Italyreceived 17 October 2016Summary. — KLOE-2 is the main experiment of the INFN Frascati NationalLaboratories and represents the continuation of KLOE. The previous apparatus,consisting in a huge Drift Chamber and an Electromagnetic Calorimeter, both im-mersed in a 0.5 T magnetic field, has been upgraded with new detectors to performhigh-precision CPT symmetry and quantum coherence tests using neutral kaons,γγ-physics studies and searches of particles of hidden dark matter sectors. KLOE-2started its data taking in November 2014 and is presently collecting data, achiev-ing record performance in terms of peak luminosity and maximum daily integratedluminosity, which will allow to integrate more than 5 fb−1 of data in the next 2 years.1. – IntroductionKLOE-2 is the main experiment of the INFN Frascati National Laboratories(LNF) and represents the continuation of the KLOE experiment [1], upgraded withstate-of-the-art detectors to improve its discovery potential.KLOE-2 started its first data taking campaign at the DAΦNE e+e− collider inNovember 2014 and is presently taking data with the aim of collecting more than5 fb−1 in the next 2 years. Record performance in terms of peak luminosity (Lpeak =2×1032 cm−2s−1) and maximum daily integrated luminosity (Lmax = 13pb−1/day) wereachieved with the innovative crab-waist beam collision scheme, which will be employedin the upgrade of the B-factory currently under construction at the KEK Laboratory inJapan and is considered a valid option in several future projects.KLOE-2 will perform CPT symmetry and quantum coherence tests using neutralkaons with an unprecedented accuracy, high-precision studies of γγ-physics processes,such as e+e− → e+e−γ∗γ∗ → e+e−π0, and searches of hidden-sector dark matterparticles [2].2. – The KLOE-2 detectorAlong with the pre-existing KLOE detector, new detectors have been installedinside the interaction region and along the beam lattice in order to enhance track and(∗) E-mail: alessandro.dicicco@roma3.infn.itCreative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0) 12 A. DI CICCO on behalf of the KLOE-2 COLLABORATIONvertex reconstruction, photon and electron/positron detection to accomplish the KLOE-2physics program: a novel cylindrical GEM Inner Tracker (IT), four tagging stations(LETs and HETs) for γγ-physics studies and new calorimeters (QCALTs and CCLATs)to enlarge the angular acceptance of the apparatus.2.1. Drift Chamber and Electromagnetic Calorimeter . – The KLOE detector consistsin a huge Drift Chamber (DC) and an Electromagnetic Calorimeter (EMC), both im-mersed in a 0.5 T axial magnetic field. Track reconstruction with high momentum resolu-tion (σp/p = 0.4%) is accomplished by the Drift Chamber [3], while cluster reconstructionis performed by the Pb-scintillating fibers Electromagnetic Calorimeter [4] with excellenttime (σt = 54ps/√E (GeV) ⊕ 140 ps) and good energy (σE/E = 5.7%/√E (GeV)) res-olutions. With its stereo-geometry, the DC provides  150μm spatial resolution in thebending plane,  2mm along the beam line,  3mm on decay vertices inside the DCfiducial volume and  6mm on decay vertices close to the interaction point (IP). TheEMC has barrel and end-cap modules specially shaped to ensure a 98% of a solid anglecoverage. A superconductive coil provides a 0.5 T axial magnetic field.DC and EMC performance turn out to be very stable in time, despite the very differentoperational conditions of the present KLOE-2 data taking, with about a factor of fivemore background than the past KLOE run.2.2. The taggers. – Low Energy Taggers (LETs) and High Energy Taggers (HETs)have been installed with the aim of detecting electrons and positrons scattered in e+e− →e+e−γ∗γ∗ → e+e−π0 reactions, which deviate from the equilibrium orbit during thepropagation along the accelerator lattice with energy below 510 MeV.Two identical LET stations [5] have been placed symmetrically at 1 m at both sidesof the IP, in order to tag electrons and positrons with energy 160 < E < 400MeV. EachLET station consists in an array of 5 × 4 LYSO crystals, each read out by a Siliconphotomultiplier (SiPM), with 1.5 × 1.5 cm2 section and 12 cm length, pointing to theaverage direction of the arriving particles (∼ 11◦ with respect to the beam line). Thetwo stations are rotated by an angle of 17◦ with respect to the horizontal plane in orderto maximize the number of collected positrons and electrons. The energy resolution ofthe LET calorimeters, less than 10% in the energy range 150 < E < 400MeV, has beenmeasured with electrons of energy between 50 and 500 MeV at the Frascati Beam TestFacility and it well matches the requirements. Equalization of the LET crystals responseand time calibration have been performed by selecting minimum ionizing particles (MIPs)as high-momentum tracks from cosmic-ray muons collected without circulating beamsin DAΦNE. The absolute energy scale calibration is performed with radiative Bhabhascattering events (e+e− → e+e−γ), with the photon and one lepton reconstructed in theKLOE main detector and the other one detected in the LET.The HET stations [5] are position detectors for measuring the deviation of e± fromthe main beam orbit. Together with time information, this measurement allows to tagscattered the electron and positron with energy grater than 420 MeV in γγ processes. Thetwo HET detectors are placed at 11 m away from the IP, in symmetrical positions. Thesensitive area of each HET station is a set of twenty-eight 3×5×6mm3 plastic scintillatorswith an additional larger one used for coincidence purposes – which are placed at differentdistances from the beam-line, in such a way that the distance between the impingingparticle and the beam can be measured knowing which scintillator has been fired.The KLOE-2 apparatus is synchronized with the DAΦNE bunch crossing, whichoccurs every Tbc = 2.7 ns. Since HET stations are far from the main detector installation,THE KLOE-2 EXPERIMENT AT DAΦNE 3their time synchronization with KLOE-2 detectors is obtained using dedicated runs ofradiative Bhabha scattering events. After calibrations, the HET taggers are able tonicely reproduce the DAΦNE bunch time structure. The time resolution of the HETdetectors is less than Tbc as needed to disentangle leptons coming from two consecutivebunch crossings.A measurement of the counting rate on both HET stations has been also performed.The counting rate timeline on HET stations is expected to be affected by an intra-bunch scattering contribution, which depends on the second power of the beam current.This dependence has been observed in dedicated runs without circulating beams and theintra-bunch contribution has been measured to be < 30% for electrons and < 6% forpositrons.A preliminary study of the reaction e+e− → e+e−γ∗γ∗ → e+e−π0 has been performedusing a sample of 52 pb−1, exploiting both HET stations for tagging scattered e± withtheir time compatible with 2 clusters measured by the EMC. About 100 events in the π0mass range have been observed with simple selection criteria, proving the capability ofthese detectors to serve as γγ-physics taggers.2.3. The tile and crystal calorimeters. – Two new Quadrupole CALorimeters withTiles, QCALTs [6], have been installed around the DAΦNE low-β quadrupoles, at bothsides of the IP, with the goal of improving the acceptance for rejecting KL → 3π0 back-ground events in CP -violating KL → 2π0 decays. Each calorimeter, 1 m long, consistsin a dodecagonal structure, arranged as a sampling of 5 layers of 5 mm thick scintillatorplates, alternated with 3.5 mm thick tungsten plates, for a total ∼ 5X0 thickness. Theactive part of each plane is divided into 20 tiles of 5 × 5 cm2 area with 1 mm diameterwavelength shifter fibers embedded in circular grooves. Each fiber is then optically con-nected to a SiPM, for a total of 2400 channels. QCALT calorimeters have a ∼ 2mmresolution along the beam axis and a time resolution of ∼ 1 ns. Time calibration andchannel-by-channel equalization is performed using cosmic-ray muon runs acquired withand without magnetic field.In order to enlarge the angular acceptance for particles coming from the IP from20◦ to 10◦, with the aim of improving multi-photon detection in rare decays such asKS → γγ, η → π0γγ and KS → 3π0, two identical Crystal CALorimeters with Timing(CCALTs) [6] have been mounted very close to the IP, near the first focusing quadrupolesof DAΦNE. Each CCALT module is made of 4 aluminum shells, with projective geome-try, containing 4 LYSO crystals readout by SiPM. Tests performed at the Frascati BeamTest Facility allowed to measure an energy resolution better than 5% and a time res-olution of about 49 ns (120 ps) at 100 MeV (500 MeV) energy. Similar performance aremeasured with cosmic-ray muons, used also for calibration and equalization of CCALTchannels.2.4. The Inner Tracker . – To improve the resolution on decay vertices close to the IP,reconstructed from low-momentum charged secondaries, the Inner Tracker (IT) has beeninserted in the free space between the beam pipe and the DC inner wall, at 25 cm fromIP. This novel ultra-light detector, with its total material budget below 2% of a radiationlength X0, allows to minimize dead spaces, the multiple scattering of low-momentumtracks and the probability of photon conversions. The resolution on vertices close to theIP is expected to improve of about a factor 3 [7].The IT is composed by four concentric Cylindrical GEM (CGEM) [8] detectors, withradii from 13 cm, to preserve the KSKL quantum interference, up to 20.5 cm, due to4 A. DI CICCO on behalf of the KLOE-2 COLLABORATIONthe constraint from DC inner wall. Each layer, with a total active length of 70 cm, is atriple-GEM detector with 5 concentric cylindrical electrodes: a cathode, to set the driftfield, 3 GEM foils acting as multiplication stages, and an anode/readout plane. Theanode plane is a multi-layer circuit: longitudinal X strips, with a 650μm pitch, and Vpads are patterned at the same level on the same substrate; V pads are then connectedthrough internal vias to form V strips, with a pitch of about 650μm, which angle withrespect to X strips is in the range 25◦–27◦. The total amount of front-end channels is∼30000. Strip signals are read out by front-end 64-channel GASTONE ASIC chips, withdigital output, specifically developed for KLOE-2 [9] and then collected by FPGA-basedboards and then acquired [10].The IT is filled with a Ar:iC4H10 90:10 gas mixture to maximize the effective gain butlimiting the discharge probability measured with α-particles. The measured efficiency [11]with cosmic-ray muon tracks reconstructed by DC is 98% for the single-view and 95%for the two-views.Efficiency measurements allowed to optimize the IT operational parameters withcolliding beams starting from late 2014, during the first KLOE-2 data taking campaign,as a function of the beam currents and background conditions, which are carefully keptunder control thanks to three indicators of the machine background level sent onlineto DAΦNE operators: the current measured on the IT inner layer, the total currentmeasured in the DC and the background level measured on both EMC end-caps.In order to measure efficiency and resolutions, dedicated procedures were developedto exploit cosmic-ray muon data and Bhabha scattering events, profiting of the excellentDC track reconstruction performance. DC track reconstruction is also exploited for ITalignment and calibration.To achieve the best IT reconstruction performance, two effects must be taken intoaccount: a non-radial track effect and the presence of the KLOE-2 magnetic field. Thefirst, due to a non-zero angle between the impinging track and the radial direction ofionization electrons motion, induces a shift and a spread of the reconstructed hit positionon the readout plane. The second, is due to the Lorentz force acting on the signalelectron cloud which is further shifted and spread. The combination of these two effectsresults in a focusing or a defocusing of the electron cloud, depending on the impactparameter of the track on the cylindrical detectors. These effects must be studied andmeasured independently: cosmic-ray muon runs acquired without magnetic field havebeen used to evaluate the non-radial correction, while the magnetic field influence hasbeen investigated using cosmic-ray muon data and Bhabha scattering events. A firstset of alignment and calibration parameters has been obtained: preliminary results ofabout 400 μm are within expectations for the Inner Tracker resolutions. This validatesthe method and also suggests how to improve the alignment and calibration procedurein order to get the best detector performance.Online monitoring of IT temperature is available and used to keep IT operation safe,as well as offline software tools for checking IT occupancy, clustering performance andchannel status (noisy/dead strips) in time [11].3. – ConclusionsKLOE-2 is successfully taking data on the DAΦNE electron-positron collider. Onlineand offline monitors of the detector, together with a feedback for DAΦNE, allow tokeep beam-induced backgrounds and sub-detectors behaviour under control, for achievingTHE KLOE-2 EXPERIMENT AT DAΦNE 5optimal data taking conditions with the aim of collecting more than 5 fb−1 in the nexttwo years.Sub-detectors operation has been optimized and their performance are withinexpectations, as measured by acquiring cosmic-ray muon runs, Bhbaha scattering eventsand collision data for future physics analysis.REFERENCES[1] Bossi F., De Lucia E., Franzini J. L., Miscetti S., Palutan M. andKLOE Collaboration, Nuovo Cimento, 30 (2008) 10.[2] Amelino-Camelia G. et al., Eur. Phys. J. C, 68 (2010) 619.[3] Adinolfi M. et al., Nucl. Instrum. Methods A, 488 (2002) 51.[4] Adinolfi M. et al., Nucl. Instrum. Methods A, 482 (2002) 364.[5] Babusci D. et al., Acta Phys. Pol. B, 46 (2015) 81.[6] Babusci D. et al., Acta Phys. Pol. B, 46 (2015) 87.[7] Archilli F. et al., arXiv:1002.2572v1 and LNF-10/3(P), INFN-LNF, Frascati, 2010.[8] Bencivenni G. and Domenici D., Nucl. Instrum. Methods A, 581 (2007) 581.[9] Balla A. et al., Nucl. Instrum. Methods A, 721 (2013) 523.[10] Branchini P. et al., JINST, 8 (2013) T04004.[11] Di Cicco A. and Morello G., Acta Phys. Pol. B, 46 (2015) 73.

The KLOE-2 experiment at DAΦNE

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The KLOE-2 experiment at DAΦNE

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