The Spaghetti Calorimeter in H1

1
The Spaghetti Calorimeter in H1

• why do we need the SpaCal ?
• SpaCal general features
• Three SpaCal electronics chains (energy, time
  and trigger branch)
• conclusion

2
Physics motivation

• To extend DIS region for low Q2 (1 - 100 GeV2)
• to measure e- and hadronic final state in the
  backward region with high resolution
• to reject photoproduction, beam-gas and beam-wall
  background (to improve E - pz resolution)

3
SpaCal general features
4
The SpaCal electronics chain
5
SpaCal construction 1
Principle - active region consist of the lead
sheets and scintillating fibres - the whole
incident particle energy E is absorbed in lead
making a shower - shower products cause the
fibres to scintillate - the number of shower
particles N is proportional to the particle
energy E - the light from scintillator is
recorded by photomultiplier (PMT) and liberate
the electrons from the cathode by photoelectric
effect (required good cathode efficiency for
given wavelength)
A??
light (N?)
accelerated e-

---------------------
? Q (charge)
?kathode
E(e/?)
shower
----------------------------------

• photomultiplier
• very low noise level MeV - important for
  measurement of MIP
• operates in the high magnetic field

A??
A - A, one layer
6
SpaCal construction 2
7
SpaCal energy branch

• provides
• raw cell energy (raw data)
• calibrated cluster energy (from the SpaCal
  reconstruction, POT, DST)
• Energy resolution for EM and HA
• very good resolution for electromagnetic
  interacting particles (active length L 27
  radiation lengths)
• much more worse resolution for strongly
  interacting particles
• (L one hadronic interaction length )

8
SpaCal trigger branch

• Provides
• veto for the events coming not in the time (not
  from IP) (ToF/AToF Trigger)
• trigger for electron candidates (Inclusive
  Electron Trigger)

1. IET Trigger
IET trigger 4 x 4 EM cells 1 cluster bit
9
2. ToF/AToF Trigger

• particles coming from interaction point are late
  with respect
• to the proton background
• electron background comes in the time

10
The SpaCal TDC system

• timing for all SpaCal channels with a precision
  of ? 1 ns
• monitoring of the trigger electronics by
  histogramming
• visual online information about the cell rates
  (Timon
• monitor in the North hall)

• TDC is able to measure the time within 32 ns
  (1/3 of HERA clock)
• peak at 7ns - proton background
• events between 15 - 27 ns are
• e-p events coming in the time
• ToF Window has width of 12ns
• peak at 17ns comes from high energetic
  particles, called TDC offset

N
later e-p events because of ? the slewing
effect
proton background ?
TDC offset ?
ToF (e-p)
lt--------------gt
TDC ns
11
Time - energy dependence

• clear time-energy dependence up
  to 1GeV, so called slewing effect
• feature (imperfection) of the CFD
• very important effect at low energy (even gt 5
  ns)

Idea correct the time by slewing with one common
5 - order polynomial function and offset (to put
the time to zero)
12
Slewing correction
? for EM SpaCal - time resolution of 0.59 ns and
for HA 0.86 ns !!!
13
Conclusion

• EM SpaCal has very good energy resolution (at
  30 GeV 2 )
• final calibration (KP double angle method)
  provides (in absolute energy scale) precision 1

• SpaCal timing with slewing correction provides
  resolution of 0.59 ns for EM, 0.86 ns for HA
  SpaCal (it was very important tool for looking
  for the source of the synchrotron radiation)
• there are 2 online tdc histograms with slewing
  correction on the L45 (numbers of the histogram
  in zubr 20151, 20152)
• SpaCal trigger provides IET and ToF/AToF trigger