Instrumentation of the very forward region of the TESLA detector – summary of the Workshop on Forward Calorimetry and Luminosity Measurement, Zeuthen, November 2002 L.Suszycki †‡ Faculty of Physics and Nuclear Techniques, University of Mining and Metallurgy,Cracow, Poland ECFA DESY Linear Collider Workshop Prague, 15th-18th November 2002 †For the LCAL group: K. Afanaciev, V. Drugakov, G. Klämke, E. Kousnetzova, W. Lohmann, A. Stahl, M. Ternick ‡For the LAT group: H. Abramowicz, A. Eskreys, S. Kananov, D. Kisielewska, A. Kowal, A. Levy, L. Suszycki, W. Wierba

November 17, 2002L.Suszycki: Instrumentation...2 Very forward region of TESLA Two calorimeters: LCAL – Luminosity CALorimeter covering angles 5 – 27.5 mrad, actually it is “Beam Calorimeter” LAT – Low Angle Tagger covering angles 27.5 – 83.1 mrad, actually it is “Luminosity Calorimeter”

November 17, 2002L.Suszycki: Instrumentation...3 Tasks for the very forward region detectors Precision luminosity measurement Beam diagnostics Detection and measurement of electrons and photons at small angles Extension of the energy flow measurement down to small angles Shielding of the tracking detectors against backscattered beamstrahlung

November 17, 2002L.Suszycki: Instrumentation...4 Beamstrahlung Energy deposition via e+e- pairs ~20 TeV/bunch cr. One year of runs makes a dose ~10 Mgy/year in LCAL  a need of radiation hard sensors Radial distribution up to ~4 - 5cm  LAT should be save Azimuthal anizotropy caused by magnetic field

November 17, 2002L.Suszycki: Instrumentation...5 LCAL design Shape Two technology options:  crystal PbWO 4 – Moliere radius ~2 cm LSO crystals considered  diamond-tungsten sandwich - Moliere radius ~1 cm Segment size ~half of R M Readout via optical fibres

November 17, 2002L.Suszycki: Instrumentation...6 LCAL segmentation R-z projection x-y projection 30 layers = 30 radiation lengths 12 rings

November 17, 2002L.Suszycki: Instrumentation...7 LCAL calorimeter Half barrel of the diamond- tungsten sandwich calorimeter

November 17, 2002L.Suszycki: Instrumentation...8

November 17, 2002L.Suszycki: Instrumentation...9 Background in LCAL Example of a 250 GeV electron event 1. Generated 2. Background added 3. Reconstructed

November 17, 2002L.Suszycki: Instrumentation...10 Detection of particles in LCAL  Simple algorithm to find electron or gamma: search for cells with signal > 3 sigma of background require longitudinal chain of such cells  Efficiency and energy resolution depend on number of ADC bits  10 bits sufficient

November 17, 2002L.Suszycki: Instrumentation...11 Energy measurement in LCAL Energy resolution as functions of : R Energy

November 17, 2002L.Suszycki: Instrumentation...12 Angular resolution of LCAL Energy dependence R dependence

November 17, 2002L.Suszycki: Instrumentation...13 Fake events in LCAL High energetic particles in background Beamstrahlung fluctuations Electron energy spectrum generated (tail >20 GeV only is shown)...and reconstructed

November 17, 2002L.Suszycki: Instrumentation...14 Beam diagnostics in LCAL Measurement of  x and  z Exercise Input:  x = 600 nm,  z = 250  m Result:  x = 597 nm,  z = 241  m More about: see A.Stahl talk at this workshop

November 17, 2002L.Suszycki: Instrumentation...15 LAT geometry 14 `cylinders` in R 24 `sectors` in  40 `rings` in z  cells assumed for MC studies Conical setup R: 4 to 12 cm z: 140 to 200 cm Silicon-tungsten sandwich 40 X 0 deep

November 17, 2002L.Suszycki: Instrumentation...16 Bhabha scattering Elastic e + e -  e + e - radiative e + e -  e + e -  Example of elastic Bhabha event  (scale ratio 8:1!) Born approximation d  /d  ~  -3  tot (27.5, 83.1mrad)  5nb

November 17, 2002L.Suszycki: Instrumentation...17 Luminosity measurement R = L ·  obs, where  obs =  theor  acceptance For L = 3.4 · cm -2 s -1 rate R  170 Hz  `one minute` luminosity possible on-line Systematic errors: 1. from detector acceptance Since  tot (  min,  max ) ~  min -2 -  max -2   min -2 then  L/L = 2  min /  min = 2  r min / r min With r min  5 cm,  L/L = needs  r min = 2.5  m Challenging for mechanics and thermal stability! Use of interferometry to monitor position and shape? 2. from theory At LEP energy theor. error achieved At TESLA may be harder

November 17, 2002L.Suszycki: Instrumentation...18

November 17, 2002L.Suszycki: Instrumentation...19 Luminosity measurement (cont`d) Luminosity spectrum due to ISR Beamstrahlung Beam energy spread can be measured through acolinearity of Bhabha events - - resolution better than 0.1 mrad necessary Background and corrections Beamstrahlung Synchrotron radiation Beam-gas bremsstrahlung Thermal photons from the rest gas Beam size effect So far no estimations done...

November 17, 2002L.Suszycki: Instrumentation...20 LAT shower example Only photons (blue) and electrons (red) over 5 MeV are displayed

November 17, 2002L.Suszycki: Instrumentation...21 LAT calorimetry Showers well contained within ~ 30 radiation lengths:

November 17, 2002L.Suszycki: Instrumentation...22 LAT – showers... Two examples of hits generated by 250 GeV electrons: Upper plots show all hits, lower plots show the shower cores Strong scattering may affect energy measurement

November 17, 2002L.Suszycki: Instrumentation...23 LAT energy response and resolution

November 17, 2002L.Suszycki: Instrumentation...24 LAT angular uniformity Energy response Energy resolution Much poorer performance in the first bin (first cylinder)  the effect increasing with energy

November 17, 2002L.Suszycki: Instrumentation...25 LAT angular resolution  rec calculated using a simple energy weighting Accuracy not satisfactory Background not incorporated More sophisticated algorithm must be used for Bhabha measurement

November 17, 2002L.Suszycki: Instrumentation...26 LAT fiducial volume Remark: LAT size is 27.5 to 83.1 mrad

November 17, 2002L.Suszycki: Instrumentation...27 LAT fiducial volume (cont`d). Energy deposit as a function of polar angle All events cut E dep > 2.5 GeV

November 17, 2002L.Suszycki: Instrumentation...28 LAT performance improved Energy cut E dep > 2.5GeV applied Energy response and resolution Angular resolution

November 17, 2002L.Suszycki: Instrumentation...29 Summary and outlookLCAL Advanced studies of the several technologies Detection of hard electrons and gammas with high efficiency feasible Fake events due to beamstrahlung fluctuations may be a problem Beam diagnostics looks promising R&D started LAT First MC studies done Problems with energy resolution and angular resolution Shape and segmentation is still an open question  flat LAT “ l=5m” option is very recommended: 1. Makes mechanical design more realistic 2. Improves resolution Single module for tests will be prepared soon The LCAL+LAT proposal will be recommended by the PRC, so let`s look forward in this adventure!