Guy Wormser, Super B-Factory Workshop, Jan 04 1 Current Background Situation in BaBar “Always a concern, often an issue but never a showstopper” zThe background.

Guy Wormser, Super B-Factory Workshop, Jan 04

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 bottlenecksusing projection and simulations

Today’s 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”


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Agressive PEP-II plans

Can BABAR keep up?

Present headroom limited!

Historically, the same challenge has always been met!


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Background parametrization based on February 2002 data

The observed background is roughly twice larger than the sum of the single beam contributions


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DCH background history M. Kelsey


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Serious problem in DCH readout if nothing is done


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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

(BW:MID)

Moves toward half-integer

HER sensitive SVT module (Does not have threshold shift problem):

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!

For occupancies in all SVT modules, see: http://www.slac.stanford.edu/~babarsvt/SectionOccupancies.ps


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SVT rates in 2003 compared to 2002 extrapolation


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Single beam and lumi sensitivity

HER HER**2

LER LER**2

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 FW:MID and BW:MID is overestimated

Run 3+4 dose is 40-60% of Run1+2Luminosity is 55% of Run1+2

Damage in SVT modules starts


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TOP Doses

Dominated by injection dose(up to 90%)

Getting HER to “trickle quality” would provide large gains


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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 ?


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MID Dose Rates until 2009Use Seeman model for beam currents to predict dose rates:

Dose rates do not looking forbiddingly highRates peak at roughly the current soft abort limits- DQ should still be reasonable


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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 FE:MIDto other module


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BABAR scorecard July 2004

July 2004Radiation damage Operation Data Quality

SVT X? xDCH XDRC fixedEMC - ??IFR x X XTRGDAQSVTRAD x improved


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BABAR scorecard July 2006July 2006Radiation damage Operation Data Quality

SVT fixed xxDCH TO BE FIXEDDRC fixedEMC - ???IFR fixed fixed fixedTRGDAQSVTRAD fixed fixed


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Dose in calorimeter


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BABAR scorecard 20092009

Radiation damage Operation Data QualitySVT X xxxDCH fixedDRC fixedEMC X ????IFR X X XTRG XDAQ XSVTRAD fixed fixed


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Data quality issues in SVT


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Resolution degration with occupancy


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Example in


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HER Injection Problems


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Characterization of injection aborts/inhibits

BP / LP + ODF


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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


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Run 4 Trip SummaryAverage of 4 trips/day – Run 3 average was 3 trips/day

Last two weeks average is down to almost 1 trip/day

Only one other abortlooked suspicious

A couple ofaborts are due to broken thermistor


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Some exemple of « Dust events »


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Trickle solved top of fill beam_beam effects


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Revided simulation efforts

Locations of the sources of Lumi terms and possible shielding

Improvment of collimators locationsValidation of new IR design


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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


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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


39

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

TODAYRadiation damage Operation Data Quality

SVT x xDCHDRC fixedEMC - ?IFR x x xTRGDAQSVTRAD x x

X: visible effect with non-zero impact - : visible effect with no impact

? : yet unknown fixed: det upgrade to fix a significant issue

x(trickle)

Guy Wormser, Super B-Factory Workshop, Jan 04 1 Current Background Situation in BaBar “Always a concern, often an issue but never a showstopper” zThe background.

Documents

guy wormser

super bfactory workshop

observed background

background parametrization

kelsey slide

dirc main source of

dch background history

tomorrow z conclusion