IHEPProtvino Group:

1
Backgrounds at FP420

• IHEP/Protvino Group
• Igor Azhgirey
• Igor Bayshev
• Igor Kurochkin
• one post-graduate student
• Tools
• STRUCT for particles tracking around LHC ring
• MARS/IHEP for cascades simulations.

2
Backgrounds at FP420

• Distant BG
• - protons only
• - well-collimated with strong gradient on X
• - mostly coincides in time with signal.
• Local BG
• - all particles, mostly products of
  electromagnetic showers
• - wide angular distribution
• - has a low-E fraction that may overlap several
  bunch crossings.
• We do not take into account particles generated
  in the FP420 setup material.

3
Distant Background at 420 m

• PU pile-up minibias protons from IP
• DGas protons from distant beam-gas interactions
• MC tails of momentum cleaning halo
• LPU late pile-up (2nd turn pile-up protons or
  protons from alien IP)

4
Background to forward detectors FP420 Point 1
Horizontal distribution of hits at FP420 for the
different background sources. Here IP1
pile-up, IP5 alien IP, MC momentum
cleaning, BG distant beam-gas.
Beam 1
Beam 2
5
Background to forward detectors FP420 Point 5
Horizontal distribution of hits at FP420 for the
different background sources
Beam 2
Beam 1
6
Distant BG Simulations

• Source DPMJET III
• Nominal LHC conditions, L 1034
• Tracking STRUCT code (I.Bayshev)
• Beam-gas beam lifetime 100 h
• Momentum cleaning beam lifetime 200 h
• MC intensity here was suppressed with factor
  0.033
• (equal to the bunch length / bunch spacing
  ratio, supposing uniform time distribution for MC
  halo)
• Number of hits calculated for detector
  acceptance
• -27 mm lt x lt -dxmin
• -3 mm lt y lt 3 mm

7
Detector positioning

• Distance dx (in mm) from detector edge to the
  beam.
• Normalization
• sinel 84 mb
• 27 inelastic interactions per 1 bunch crossing

8
Distant BG in IP1 detectors

• Number of hits produced by distant background
  protons in FP420 detectors
• per 1 bunch crossing depending on minimal
  distance from the beam

9
Distant BG in IP5 detectors

• Number of hits produced by distant background
  protons in FP420 detectors
• per 1 bunch crossing depending on minimal
  distance from the beam

10
Local Background at 420 m

• Showers from B11B dipole magnet, caused by losses
  of the protons, generated in IP.
• Showers from the local beam-gas interactions.
• Secondary particles from first 2 sources,
  scattered on the machine equipment and tunnel
  walls, including low-E neutrons and photons from
  thermal neutrons capture.

11
B11B Background

• PL/BC average number of protons, lost on B11B,
  per 1 bunch crossing
• BC/PL average number of bunch crossings per 1
  proton lost on the B11B dipole.
• ?
• B11B BG is a rare event, but probably
  catastrophical for associated bunch crossing
  registration (and maybe for several subsequent
  bunch crossings too due to slow low energy tails
  of cascades)

12
Background due to losses upstream FP420
13
B11B Background

• Average multiplicity of background particles
  crossing the acceptance of detector at 420 m (-27
  mm lt x lt -20 sx -3 mm lt y lt 3 mm) per one lost
  proton.
• Most of the lost protons will be absorbed in B11B
  (14 m long) without any leakage therefore
  average multiplicity for irradiating losses
  will be several times higher.

14
B11B Background

• Simple estimation of the average number of B11B
  BG tracks in the 1st plane of the FP420 detector
  per one lost proton.
• Fast charged hadrons (with E gt 5 GeV) and
  electrons (with E gt 10 MeV) were counted with
  100 efficiency, photons (with E gt 1 GeV) were
  taken into account with 0.75 efficiency (equal
  to the probability to generate ee- pair in 1 mm
  of Si for 1 GeV photon).
• Again, average multiplicity of hits for
  irradiating losses will be several times
  higher.

15
Plans

• To continue with B11B BG multiplicity
  distribution (together with Manchester)
• To produce local beam-gas BG distributions
• To prepare model of FP420 region (equipment
  tunnel) and make simulations of the low-E BG and
  irradiation levels for FP420 electronics e.t.c.
• To prepare algorithm of the background sources
  mixing for full simulation package.