Current Background Situation in BaBar

1
Current Background Situation in BaBar

• Always a concern, often an issue but never a
  showstopper
• The background sources
• (Synchrotron Radiation), Beam-Gas, Radiative
  Bhabbas , Beam-Beam effects, Radiation bursts,
  Injection, (Touscheck)
• The background effects
• integrated dose, instantaneous damage,
  operational issues, data quality
• The background remediation strategy
• Babar protection system, budget policy, forward
  looking to bottlenecks
• using projection and simulations
• Todays questions
• Trickle injection
• Injection quality
• Preparation for tomorrow
• Conclusion

2
The background sources

• Synchrotron radiation very well masked, has
  never been a problem for BABAR
• Beam-Gas BABAR sees debris from electromagnetic
  showers of scattered electrons and photons.
• Two subcomponents Brems and Compton scattering
• Well described by simulation
• Efficient collimator scheme

3
The background sources (2)

• Radiative Bhabbas
• Showers debris from off-energy electrons or
  positrons after Bhabbas scattering swept away by
  magnetic elements in interaction regions
• Beam-beam effects
•  Trapped/Dust events  (HER specific)
• Touschek effects not observed yet

4
Predictability score

• Predictables sources
• Synchrotron
• Beam gas
• Bremstralhung
• Compton
• Touschek
• In principle predictable source
• Radiatvie Bhabbas
• Unreliably predictable sources
• Beam-beam
• Electron cloud effects
• Injection doses
• Unpredictable sources
• Radiation bursts, dust events

5
Agressive PEP-II plans
Can BABAR keep up? Present headroom
limited! Historically, the same challenge has
always been met!
6
Background parametrization based on February 2002
data
The observed background is roughly twice larger
than the sum of the single beam contributions
7
DCH background history
M. Kelsey
8
Serious problem in DCH readout if nothing is done
9
Remediation and Forward looking of bottlenecks

• Example of DIRC TDC
• In 1999, we predicted that the single rate PMT
  in the DIRC would in 2002-2003 exceed the 200 kHz
  limit
• A lot of effort to improve the shiedling
• Launch design of a new TDC, implemented in summer
  2002 with a 2 MHz capability.
• The 200 kHz limit was indeed reached in fall 2002
• Next on line DCH read out!

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DIRC main source of background Radiative Bhabhas
striking Q4 magnet inboard flange

• Source discovered empirically with a Geiger
  counter.
• Shielding erected step-by-step slowly building
  empirically a proof that things are improving.
• A final shield erected in 2001, and the whole job
  completed in 2002.
• Carsten proved later, with a Turtle program, that
  a major source of DIRC background is the
  radiative Bhabhas striking Q4 inboard flange,
  which is too small.

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IFR issues

• IFR is the only BABAR subdetector where the
  existing hardware capabilities are presently
  significantly degraded because of background
• Layers 13, 15,16 turned off in the forward endcap
  (loss of factor 2 in the mu/pi rejection in that
  region)
• IFR background comes losses near collimator
  BSC3042 which is very sensitive to beam-beam
  effects and thus very useful to the rest of
  BABAR
• Must provide a shielding wall (summer 2004)

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IFR issues
13
IFR and beam loss monitor
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SVT Background from HER
HER sensitive SVT module (Does not have threshold
shift problem)
(BWMID)
Background almost doubled after move to
half-integer Again it has come down a bit
during run-4 Note peak occupancy is 150 higher
than average occupancy!
Moves toward half-integer
For occupancies in all SVT modules, see
http//www.slac.stanford.edu/babarsvt/SectionOcc
upancies.ps
15
SVT rates in 2003 compared to 2002 extrapolation
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Single beam and lumi sensitivity
HER HER2 LER LER2 Lumi
SVT(mid) X Y 0
DCH 110 30 25 7 52
DRC 13 0 18 0 10
EMC 2.2 0 2.2 0 1.4
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MID Plane Doses
Stable beam contribution of FWMID and BWMID is
overestimated
Damage in SVT modules starts
Run 34 dose is 40-60 of Run12 Luminosity is
55 of Run12
18
TOP Doses
Dominated by injection dose (up to 90)
Getting HER to trickle quality would provide
large gains
19
Summary of Detector sensivities and main issues

• SVT Integrated Dose, Occupancy, single beam and
  beam-beam, FE electronics strange effects
• DCH Readout capabilities, radiative Bhabbas
• DIRC No problem for now, radaitive Bhabbas
• EMC Integrated dose in Endcap for the long term,
  leakage current in Diodes (neutrons?), occupancy,
  
• IFR Single rate for external layers, beam-beam
  effects
• SVTRAD integrated dose, will need to be
  replaced soon
• Integrated dose SVT 2Mrad in the most exposed
  regions, EMC 1 krad in the most exposed regions
• Rather similar to what BELLE received ?

20
MID Dose Rates until 2009
Use Seeman model for beam currents to predict
dose rates
Dose rates do not looking forbiddingly high Rates
peak at roughly the current soft abort limits -
DQ should still be reasonable
21
Midplane Doses until 2009

• Module exchange in 2005 looks well timed with 4
  Mrad budget
• One rotation in 2007 should be able to keep MID
  modules installed in 2005 below 5 Mrad

A rotation will move the high dose in FEMID to
other module
22
BABAR scorecard July 2004
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BABAR scorecard July 2006
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Dose in calorimeter
25
BABAR scorecard 2009
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Data quality issues in SVT
27
Resolution degration with occupancy
28
Example in
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HER Injection Problems
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Characterization of injection aborts/inhibits
BP / LP ODF
31
A variety of fast radiation spikes (stored beams)
B. Petersen G. Wormser
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A variety of fast radiation spikes (stored beams)
B. Petersen G. Wormser
33
Run 4 Trip Summary
Average of 4 trips/day Run 3 average was 3
trips/day
A couple of aborts are due to broken thermistor
Only one other abort looked suspicious
Last two weeks average is down to almost 1
trip/day
34
Some exemple of  Dust events 
35
Trickle solved top of fill beam_beam effects
36
Revided simulation efforts

• Locations of the sources of Lumi terms and
  possible shielding
• Improvment of collimators locations
• Validation of new IR design

37
Evidence for neutron radiation?

• Diode leakage current in EMC read-out
• IFR background ?
• J. Vavra developped a neutron detector very
  insensitive to photons that will be placed
  shortly along the beam pipe

38
Conclusions for short term issues

• We have to look far ahead Minimum 3 years
• Look for worst case scenarios!
• Look for end-product effects!
• BABAR issues
• Immediate concerns SVT ATOM chip, IFRForward
  endcap
• Next on-line DCH DAQ
• Longer term issues SVT and EMC in 2008
• Changes in background issues
• Beam-beam tails
• injections
• trapped events

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Background issues for a Super B factory

• Detector has to stay always on!
• Detector Protection system can we get rid of
  it? If not, it has to stand 100 MRad
• Avoid all detector susceptible to instantaneous
  damage
• Once proper rad hard technology has been chosen,
  occupancy will become the next major issue
  ultra fast and hyper-segmented

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BABAR scorecard today
x(trickle)
X visible effect with non-zero impact -
visible effect with no impact ? yet unknown
fixed det
upgrade to fix a significant issue