Magnetized hadronic calorimeter and muon veto for the K +   +  experiment L. DiLella, May 25, 2004 Purpose:  Provide pion – muon separation (muon veto)  Bend the beam away from the small angle photon veto located at the end of the hall

Detector elements as in Niels’ geometry file (k12hika.txt):  Blue tube starts at z = m  Kevlar window at z = m (~ 12.2 m upstream of present position)  Double spectrometer with two identical MNP33 dipole magnets 12.6 m apart  p T kick = ± 0.21 GeV/c (in opposite directions )  Six Drift Chambers (assumed to be identical in shape, performance and resolution to the present ones)  Liquid Krypton calorimeter untouched – cryostat ends at z = m  Small angle photon veto near the end of the hall ( z = 257 m) Beam spot after the second dipole magnet  + flux : .  x   per spill detector axis 2 cm diam. beam spot; centre 3.52 cm from detector axis muons from pion decay (few % of  + flux) 7.2 cm

A problem with the photon veto beam LKr cryostat photon shower detected in LKr Liquid Krypton Hadronic calorimeter front face photon shower NOT detected in LKr beam pipe Need additional photon veto behind LKr and increase of beam pipe diameter Additional photon veto

Criteria for the design of the hadronic calorimeter and muon veto  Integration with LKr calorimeter  Distinguish hadronic showers from electromagnetic showers  need longitudinal and lateral segmentation  Sensitivity to minimum ionizing particles (MIP)  Bending power ~ .  T x m  p T kick  .  GeV/c deflects 75 GeV/c beam by 18 mr (18 cm lateral displacement at 10 m) An important background from K +   +   decay: “catastrophic” muon energy losses  muon bremsstrahlung  e + e  pair production  high Q 2  + e  scattering  muon decay in flight  deep inelastic muon – nucleon scattering  + + N   + + hadrons electromagnetic shower In general, the outgoing  +  has enough residual energy to be detected

Acceptance for K +   +  decay “Toy” MonteCarlo includes:  beam momentum spread  (p)  p =  %, no angular spread  gaussian multiple scattering and chamber resolution (tuned on measured K         mass resolution in NA48/2)  K  decay region from blue tube entrance to kevlar window  parametrization of LKr energy resolution (with gaussian shape) Results agree with G. Ruggiero’s calculations using FLYO (see ) Measurement of   momentum: weighted average of the measurements from the two magnets; angle with respect to beam axis given by DCH1+2 Cuts:  p   GeV/c (Missing Mass)   MM  in two separate regions (to exclude K      ):  MM   GeV  (Region I)  MM   GeV  (Region II)

  momentum (GeV/c) MM  (GeV  ) Results from 10 7 simulated      decays Accepted events after   momentum cut: Region I: .  % Region II:  % Region I Region II

x (cm) y (cm) Distribution of accepted   on the front face of LKr  x  cm  area

Proposed magnetized hadronic calorimeter and muon veto  Iron plates  cm thick Rectangular hole  x  cm Weight of each plate  kg  cm gap between plates Total length  m Front face at z =  m (0.6 m behind LKr cryostat) 4 vertical coils instead of 2 horizontal coils for full access to gaps between plates from the two sides (Niels’ suggestion) B = ~  T in beam region ~ 8 m between calorimeter end and beam dump at the end of the hall

Plates are bolted together to top and bottom support plates Proposed longitudinal segmentation: three independent sections of  plates each One section :  x 0, ~  int a reasonable matching to LKr ( ~  x 0, ~  int ) Gaps  through  are not instrumented The last 17 gaps are again instrumented to veto muons surviving catastrophic energy losses

Active detector material : Extruded polystyrene scintillator strips 130 cm long,  cm high, 1 cm thick read out by a single 1.2 mm diameter wave-length shifting fibre (as in the MINOS and OPERA experiments) Scintillator is extruded with TiO  white cladding and groove where fibre is glued The  fibres from strips at the same y coordinate in one section go to a single  cm diam. PMT to form a calorimeter “cell” In total:  strips per instrumented gap  strips per section  cells  PMT’s per section  fully instrumented sections Vertical segmentation only (  cm) Performance of MINOS strip 8 m long, 4 cm high, 1 cm thick Observe two fibre light attenuation lengths: 1  0.7 m, 2  3.9 m For our case expect  photoelectrons per strip from a minimum ionizing particle

Calibration Calibrate LKr + hadronic calorimeter “in situ” by sending low intensity pion beams of variable energy to different points on the front face of LKr (another application of “Italo’s runs”) Expected energy resolution for hadronic shower ( Iron sections only): (as measured by MINOS) Need optimized algorithm to combine hadronic shower information from LKr and Iron calorimeter for optimal energy resolution Event rate in Hadronic Calorimeter Main contribution: K  decays (  x   per spill  ~ 5 MHz) Rate of hit cells  (5 MHz  130) x n   kHz x n n : number of hit cells per K  decay ( n =  –  )

Pion selection and muon veto  Hadronic shower must start before Section 2 (LKr + Section 1   int )  E(shower)  track momentum  1 within calorimeter energy resolution  Reject tracks associated with an electromagnetic shower  Reject tracks associated with a m.i.p. signal in sections 2, 3 or 4 (the end section) Background from K  decays can be measured from the data themselves (events with m.i.p. signal in first 4 int and late showers)

A simple example from the “Toy” MonteCarlo: K  decay followed by  decay in the calorimeters MM  assuming   mass (GeV  )   simulated K      decays  track momentum  GeV/c  events in Region I of the MM  distribution (this number depends critically on momentum and angular resolution) Track momentum (GeV/c) Track momentum distribution for K     signal is ~flat between  and  GeV/c

Muon decay in calorimeters E  p (including muon polarisation effects) Decay in LKr (E in GeV) Decay in Iron calorimeter Assumed resolution: (E in GeV)

Cost estimate OPERA Proposal (CERN/SPSC ):   x  m  scintillator planes (  m  in total)  Each plane:  m long strips read out INDIVIDUALLY from both sides using  -channel multi-anode PMTs  Total number of strips  channel multi anode PMTs  Estimated cost (including fibres and PMTs): kCHF  Proposed magnetized Iron Calorimeter:   x  m  scintillator planes (  m  in total)  Each plane:   m long strips  Total number of strips  read out in groups of  by  cm diam. PMTs  Total number of  cm diam. PMTs =  Estimated cost  0.1 x OPERA + cost of Iron