1. Background issues for the Super-B background simulation team
G.Calderini (LPNHE, Paris)
for the
Super-B background simulation team
5th Super B Workshop
Paris, May 9-11, 2007

2. Status of the background simulations
for the CDR
The different background processes
The approximations used
The implementation
Post-CDR effort
Adding what is missing
The tools
For the Beamline
For the Detector
The interaction with the final focusing and
detector design

3. General approach Collection of background generators
primaries
Transport inside a Geant4 beamline description
(magnetic fields and material)
shielding
Propagation in a Geant4 detector description
hit collections
Background impact determination in the subsystems

4. Other sources of background
The machine design presented in the CDR gives reasonable but still important backgrounds
Luminosity sources
- beam-beam
- radiative Bhabha
Linear with currents
lost particles
synchrotron radiation
Other sources of background
Touschek background
Thermal outgassing due to HOM losses; Not an issue with these currents
Injection background

5. Pair production Studied with Guinea Pig and Diag-36 generators
After some debugging, the two results are no more
incompatible
Very high production rate but particles have low energy
and they loop in the solenoid field
30MHz/cm2
Pt accept. @ 1.5 T , 1.2 cm
~Angular acceptance
1.2
1.5
R(cm)

6. Due to this feature, it is a source of background
only relevant for the tracker
Expected average rate O(15MHz/cm2) at R=1.2cm,
decreasing to 5MHz at R=1.5cm (Guinea Pig)
Not fully simulated with Geant for the CDR.
Background analysis in the tracker is based
on kinematical distributions
A more detailed simulation will be mandatory
as a next step for the post-CDR effort

7. Radiative Bhabhas Bremsstrahlung process in the forward direction in
BhaBha scattering: e+e- -> e+e- g
Simulated with the BBBrem generator and fully propagated
in the Geant-4 description
The outgoing particles are not the direct responsible for
detector backgrounds but they generate very dangerous
showers and backscattered particles in the downstream
beamline elements
Beamline and shielding design is very important

8. Radiative BhaBhas
At small radii, with the present simulation, it is negligible wrt to pairs. Rate O(100KHz) at 1.2cm
Present also at higher radii, (as in BaBar) due to backscattering from downstream machine elements (must be cured with suitable shielding)

9. Radiative Bhabhas
Need serious amount of shielding to prevent the produced shower from reaching the detector.

10. IFR
EMC
Given the importance of this source for most of the
Super-B subdetectors, it will be necessary to integrate
the studies with other generators
BHLUMI/BHWIDE for larger angles
Neutrons ???

11. Touschek
The study prepared for the CDR was based on the Boscolo code (LNF). This contains an approximate description of the ring and transport the off-energy particles due to intra-bunch scattering. The primaries
hitting the beampipe are passed to Geant-4
Expected loss particle rate in a +/- 4m from the
IP = 2.3 MHz/bunch, reduced to 90kHz after collimators
deployment.
Further effort necessary at this point to optimize
mechanical aperture of chambers, position of collimators
and masks

12. Lost particles
Mainly Coulomb/Bremsstrahlung interactions with residual
gas molecules in the beampipe
For the CDR effort, the estimate was based on PEP-II rates and rescaled for beam currents.
Found to be negligible with respect to other sources
(1-2 MHz/cm2 in Layer_0, decreasing with R).
Probably a pessimistic extrapolation, given the absence of
permanent dipoles very close to the IP in SuperB final
focusing.
Further effort necessary for a more quantitative
description
As soon as an updated final focus design will be
available, we should try to implement a Turtle
description or something equivalent

13. Synchrotron radiation
The interaction region has been designed to reduce the
bending of incoming beam trajectories, but some photons
can still hit the beampipe.
With the present final focusing, the expected rate on
the IR mask tip is about 800 g/BX for energies above 20KeV, reducing to a few g/BX on the Be pipe, a rate similar to BaBar.
Preliminary design of adequate mask system already
available.
Update necessary to the next final focus design, and
additional studies for the residual backgrounds in the
detector.

14. Some words on tools In the present version of the work, the C++ code
describing both the beamline (B fields/material) and the detector was written by hand in Geant-4.
This made the iterations rather slow every time there was a change in the accelerator optics or in the detector.
In the future it will be necessary to develop or import tools to help with
this, similarly to what we
did with the PEP-II
beamline in the BaBar
background simulation

15. Interfaces for the beamline optics
Some software, like the BDSIM interface, used for
ILC studies, allows to import MAD configurations into
a Geant-4 description. That could help!
Interfaces for the geometry/detector
As in the case of BaBar (for which we developed an
interface to SolidEdgeTM ) it’s possible to use CAD
oriented extensions to Geant-4: GDML ?
Better organization of the software
Presently the code is under CVS but organized as
a single package. Difficult for different people to
work on different parts at the same time

16. Organization In the CDR phase, the integration between background
simulations and final focusing design was rather limited,
as well as the interaction with some subdetector.
This needs absolutely to be improved in the next phase.
Background studies are not intended to determine simply
if a certain detector is feasible, but should be used to
optimize the machine and the detector design
Hopefully this will be easier after the use of the above
tools which should reduce the response time in the
interaction

17. Manpower and timescale
Many Institutions have already expressed their interest
to participate to Super-B background studies.
Some preliminary (but not necessarily unique) layout was
even already suggested in the context of the Eurocrab
project proposal.
We hope that this Super-B workshop will be a chance to
discuss the involvement of the new people/Institutions
and to define the fields of interest
The timescale is shorter than what it could look like:
after the summer the new final focusing might be ready
and by then all the bells and whistles ideally should be
fixed and tested with the present configuration!

18. Conclusions A change from a individual homemade standard to
A very big effort has been made on background simulations
by a small group of people for the CDR publication.
In my opinion, the work has been much more detailed and
elaborate with respect to what expected for a CDR
standard, but it is definitely small with respect to what
is needed next.
A change from a individual homemade standard to
a mass-production standard is necessary in the
organization of the work.
It is the right time for all the interested people
to come onboard