G. Eigen, U. Bergen

The Homestead 6/17/00

OUTLINEOUTLINE

Introduction

Issues of individual Subsystems

Trigger

Data Acquisition/Computing

Silicon Vertex Tracker

Drift Chamber

Electromagnetic Calorimeter

Particle Identification

Instrumented Flux Return

Conclusion

INTRODUCTIONINTRODUCTION

Presently we have 3 B-factories operating CESR, KEKB, PEP II

Present luminosities range from L= 0.81033 cm-2 s-1

to L=21033 cm-2 s-1

PEP II expects to reach L= 31033 cm-2 s- 1 by fall 2000

L= 61033 cm-2 s- 1 by 2001

L=101033 cm-2 s- 1 by 2002

L=151033 cm-2 s- 1 by 2003

(similar plans for BELLE, CLEO L= 31033 cm-2 s- 1 )

PEP II will run with L=31034 cm-2 s- 1 by 2005

BABAR &BELLE will have accumulated ~1700 fb-1 of data by end of 2009 ~1.5 109 BB events assuming 90% at Y(4S) [lower if running at Y(5S)] (factor 5 higher than original design ~300 fb-1 )

This is not enough for some rare decays

Starting a new machine in 2008 with L>11035 cm-2 s- 1

yields >7000-8000 fb-1 after 10 years >4.7-5.3109 BB events [for 2/3 at Y(4S)]

INTRODUCTIONINTRODUCTION

To exploit the physics potentials at the Y(4S) one needs general purpose detector like BABAR, BELLE, CLEO

For measurement of CP asymmetries & tagging good vertex measurement

For charged track reconstruction good tracking device in high B field

For B00, B Xse+e-

good electromagnetic calorimeter For K/ separation for tagging, B0+-/ B0+-

good particle identification system For & KL identification instrumented flux return

Design depends symmetric/asymmetric machine

Need to worry about backgrounds, all subdetectors, triggers, data acquisition & computing

THE BABAR DETECTOR

IFR

EMC

DIRC

SVT

DCH

e+

e-

Coil

PRIMARY SOURCES OF BACKGROUNDS

Beam-gas interactions Produce particles with large oscillation amplitudes

that may hit beam-line elements near IR

Bremsstrahlung BG is generated local to IR mainly in horizontal plane Coulomb scattering produces BG from whole ring

Interactions with B1 magnet & Q2 septum produce shower debris detector occupancy radiation damage

BG scales like Ib PV maintain low pressure near IR

Synchrotron radiation

generated in bends and focussing quads near IR strikes vacuum chamber and detectors

BG scales Ib reduce by masking

Two-beam background

enhanced beam-gas due to synchrotron shine into other ring

beam tails due to beam-beam disturbance

QED physics of radiative Bhabha scattering (presently no issue)

BACKGROUND ISSUES

Acceptable levels of backgrounds are determined by

Radiation hardness of subdetectors

Trigger rate

Detector occupancies

Occupancy and trigger rate determine acceptable dynamic running conditions

Total integrated radiation dose determines lifetime of subdetectors

Dose is accumulated under normal running conditions, during injection, machine studies and beam-loss events At PEP II dose accumulated during running dominates

Maximal currents in PEP II

at design luminosity: 0.8 A (HER) 2.0 A (LER) at L=1.51034 cm-2 s-1: 1.3 A (HER) 3.8 A (LER)

BABAR TRIGGER

Hardware Level 1 trigger (rate < 2 kHz)

Decision within 12 s delivered to fast control system (common front end electronics pipeline buffer depth)

Limitation coupled to DAQ readout speed (dead time)

L1 consists of drift chamber trigger (DLT) calorimeter trigger (EMT) IFR trigger (IFT) each trigger generates a primitive sends it to global trigger (GLT) at 8 MHz

Current L1 system logic is based on r-projection sufficient for design L= 31033 cm-2 s-1

Software Level 3 trigger (rate < 100 Hz) L3 operates on 32 online farms with processing speed of ~10 ms/event (close to 2 kHz input) Prescale bhabhas since L1 triggered cross section of ~45 nb yields 135 Hz rate

BABAR TRIGGER

Present L1 trigger rate is ~ 700 Hz at L= 11033 cm-2 s-1 with recent firmware improvements expect ~550 Hz

Incorporate DCZ trigger to reduce beam-wallBG ease demand on dataflow reduce L3 input rate

Level 3 track z0 for L1 passthrough in typical colliding beam run

Colliding beam events

Lost particles interacted

with beampipe flange

L1 TRIGGER RATES

Consider 2 scenarios: linear scaling, quadratic scaling

For high L modifications are needed (DCZ trigger)

For luminosities above L= 31034 cm-2 s-1 need to to reduce BG further, prescale QED events and need a system that accepts increased L1/L3 rates

L3 TRIGGER

At L= 11033 cm-2 s-1 total rate is 60 Hz, of which physics rate: 6 Hz, prescale bhabhas: ~10 Hz, other QED: 4 Hz, evading bhabha veto: 13.5 Hz, BG: 21 Hz , L1 passthrough: 5 Hz

With improved BG (11Hz) and bhabha veto (6Hz) yield total rate of 45 Hz 90 Hz at L= 31033 cm-2 s-1

(Physics:Bhabha:BG + 6:6:11nb)

At L= 1.51034 cm-2 s-1 total rate is ~370Hz (upper limit) physics rate is ~ 90 Hz improvements in DCH tracking needed (>CPU) improve tracking pattern map for pt<250 MeV tracks tracks must have 5 segments in 6 layers exclude tracks exiting below layer 5 employ more sophisticated track segment pattern that is less sensitive to dead cells improve L3 track resolution prescale other QED processes?

Other improvements Reduce beam-wall BG Improve bhabha veto Improve d0 & z0 cuts

At L= 11035 cm-2 s-1 need > accepted L3 trigger rate L3 physics rate alone will be 560 Hz

DATA ACQUISITION SYSTEM

Set of standard Readout Module (ROM) to interface front-end electronics of detector subsystem

Each ROM has two 2 modes of operation untriggered version to collect input from ≤ 3 data streams (EMC) triggered version to collect input of triggered L1 events from ≤ 2 data streams (all other + L1)

Each ROM consists of VME board + 3 custom boards

Collected data segments are read out via VME bus by master ROM in each crate

Data fragments built by master ROM from individual segments are sent via 100 Mbps switched ethernet to nodes of Online Event Processing (OEP) farm

DAQ is designed to have performance that is scaled to bandwidth limits of front-end electronics scaled by addition of more ROM’s and OEP nodes

DATA ACQUISITION SYSTEM

DAQ system is designed to have performance that can be scaled to higher trigger rates and higher occupancies to data bandwidth (BW) limits of front-end electronics

Presently event building rate handles 2.5-2.6kHz L1 trigger rates with low deadtime (`~1%)

Overall performance will be limited by portion of DAQ system serving detector subsystem that first encounters BW restriction due to occupancy or L1 rate

Potential Restrictions on DAQ System

BW on data links from front-end electronics to ROMs increase # links or decrease # data read

ROM performance due to internal BW limitations, processing limitations or both: BW on PCI bus limit data transport rate to memory BW ROM CPU &memory limit feature extraction rate CPU performance can also limit feature extraction rate increase # ROMs, input data links, faster CPUs

Rate of master ROM in each crate to perform its backplane build of data segments from ROMs into data fragments increase # ROM crates

network build of data fragments from master ROMs into events in OEP nodes limited by master ROM output rates or the network (BW of network link on DAQ crate side, network switch itself, BW of network link on DAQ crate side) increase # master ROMs, DAQ crates & network links use higher-capacity backplane of network switch, increase # network links, add OEP nodes

(# DAQ crates is limited to 32 by Fast Control System)

DATA ACQUISITION SYSTEM

For L< 61033 cm-2 s-1 present BABAR DAQ system will provide adequate performance w/o significant upgrade (L1 ~ 2.8 kHz w/o trigger upgrades )

For L= 11034 cm-2 s-1 with L1 trigger upgrade rates will be reduced to levels of L= 61033 cm-2 s-1

For L= 1.51034 cm-2 s-1 beam currents are expected to be similar to those for L= 11034 cm-2 s-1 and L1 trigger rate increases by ~ 400 Hz

For BABAR behavior of DAQ system will be studied Potential bottlenecks will be parameterized as function of L1 trigger rate and occupancy in each detector system Eventual problem areas will be upgraded

For L> 31034 cm-2 s-1 (new machine + detector) DAQ system needs to be designed to have sufficient capacity to handle data flow

COMPUTING

Computing aspects have to consider software, processing, storage & networking

These aspects are present at all levels: data acquisition, pattern recognition, simulation & physics analysis

Scalability was built into BABAR computing system uncertainties in scaling of BG rates & occupancies vs Ib

BABAR considers two scenarios:

low BG scenario: L1 Ib

high BG scenario: L1 Ib2

Normalization: total L1 = 700 Hz at L= 11033 cm-2 s-1 (cosmic 150 Hz, physics collisions 80 Hz, BG 470 Hz) Machine-induced occupancy contributes to event size, assume event size of 35 kB at L= 11033 cm-2 s-1

(half of which stems from occupancy)

Physics Model: do everything or focus on core topics? loose L3 - tight L3 scenarios (“interesting” physics cross section: 2 nb)

COMPUTING

Computing power is assumed to follow Moore’s law

COMPUTING

Computing power is assumed to follow Moore’s law Doubling every 2 years

Constant processing costs per CPU

Disk storage costs evolve with Moore’s law behavior

Primary tertiary storage utilizes STK Eagle technology 1999 40 GB costs ~ $75 with factor of two compression costs per tape decrease 20% a year effective tape capacities 80 GB by summer 2000 & 160 GB by 2002

Cost of network switch remain constant

IMPACT ON SILICON VERTEX DETECTOR

Luminosity increases have impact on Si vertex tracker radiation damage to silicon detectors radiation damage to on detector readout electronics increased occupancy in silicon strips

Presently accumulated dose in BABAR SVT at L= 21033 cm-2 s-1

200KRad/yr

STUDIES OF SILICON VERTEX DETECTOR

SVT irradiation is focussed on horizontal plane of layers 1-3 (layers 4-5 are essentially immune)

SVT is designed to withstand total dose of ~2 MRad without significant performance degradation

Budget 200 kRad/yr, 1999 measurements yield 8 Rad/pb-1 outside horizontal plane 75 Rad/pb-1 in horizontal plane (best: 25 Rad/ pb-1 )

For total 300 fb-1 integrated luminosity horizontal plane receives at best 7.5 MRad (on average 22MRad)

exceed 2 MRad by middle of 2002 (worst case)

(based on 60 Co source and beam dump experiment)

Projected doses in the horizontal plane

Linear scaling

Linear+quadratic

scaling

June 2002 (1034)

RADIATION DAMAGE IN SILICON

P-stop short creation reduction in charge collection efficiency extra current draw (depends on HV supply) use modules w thicker oxide layer

Increase in leakage current Calculation with coefficient 2A/cm2/MRad yields

Even at 20 MRad modules would operate need increased threshold efficiency drop MIP yields 24000 e- at normal incidence dropping to 7000 e- under large angle

Increase in interstrip capacitance after 1 MRad 10-15% increase, non linear effect w dose

Depletion voltage shift high Rad doses can cause change in effective doping C change V of module make material more p-type ok till Rad-induced acceptor doping compensates initial donor doping doping inversion point when junction &ohmic sides switch roles SVT sensors are not designed to work this way life time limit 3-4 MRad

Radiation Damage of On-Detector Electronics

Atom chips have been irradiated up to 2 MRad show 10% increase in noise and 10% decrease in gain

Extrapolation to higher doses is difficult as most damage appears to happen early on

High irradiation can cause failures in chip’s digital circuitry make entire chip unusable

OCCUPANCY & BAND WIDTH LIMITATIONS

Higher BG & larger detector noise from irradiation

yield increase in occupancy

High occupancy has drawbacks

pattern recognition may associate wrong hit deteriorates track quality

in single-hit electronics a BG hit arriving at same time window will shadow a real hit cause inefficiency

pile up may occur if BW is not sufficient to transfer information out of busiest module

Presently in BABAR occupancy in worst regions is 3-4%

Increases in occupancy by > factor 5 would be problematic

Background Effects on Drift Chamber

Drift chamber performance can be compromised by

wire surface contamination due to aging makes parts of chamber inoperable ability of HV power supply to provide current necessary at higher luminosity increased occupancy in chamber could push DAQ rates & limits offline track reconstruction to find tracks buried in BG

Collective experience with DCH in high radiation environments suggest aging effects start to occur when total Q drawn by wire reaches 0.1-1.0 Cb/cm Chemistry of this aging process is not well-understood & depends on gas mix & levels of impurities leaking in formation of hydrocarbon deposits on anode wire yielding regions of reduced gain or discharge points

Precautions: Use radiation hard gases Operating drift chamber at lower HV eg 1900 V plus use of low-noise amplifier IC Adding water (3000-4000 ppm) to stop formation of hydrocarbon deposits

Extra shielding of drift chamber endplates

STUDIES OF DRIFT CHAMBER CURRENTS

At PEP II perform dedicated beam studies to measure dependence of DCH current on LER & HER currents and separate L-dependent term (beam-beam effects)

Dependence is best fit by a quadratic form Use this to extrapolate to higher currents (accuracy ?)

With improved vacuum quadratic component will decrease, but L-dependent term is not yet understood

For comparison also look at a linear fit

STUDIES OF DRIFT CHAMBER CURRENTS

Integrated charge on worst wire vs t for BABAR DCH assuming specific luminosity profile shown

If chamber starts to show aging effects at 0.2 Cb/cm this level is reached in 2008 assuming quadratic fit

Studies of Drift Chamber Performance

Predicted IDCH vs Ib on typical HV supply for 2 fits

Typical chamber has 448-1024 channels per layer determines # channels per HV power supply (50 -100 nA/wire)

Projected occupancy vs beam currents for 2 fits from random beam crossings during single-beam running

Track finding ok to 10%

Occupancy impacts L1 trigger rate & DAQ (ROMs)

[%] [%]

Electromagnetic Calorimeter Issues

Beam related backgrounds have two effects on EMC Radiation damage to CsI(Tl) crystals Increased tower occupancy

Observation that ILER and IHER are largely decoupled in their effect on radiation dose and tower occupancy IHER contributes mainly in forward direction ILER contributes mainly in backward direction central region of calorimeter is only weakly affected

Since ILER = ~3 IHER crystal closest to beam in backward barrel (140.8o) sees highest radiation dose

crystal closest to beam in forward endcap is at 15.8o

EMC TOWER OCCUPANCY

Observe nearly quadratic dependence of tower hits vs HER beam current (E> 5 MeV)

Occupancy increases only by ~hundreds of hits while ~1000 hits/events due to 0.3 MeV incoherent noise in preamplifier/crystal & 1 MeV threshold cut

CRYSTAL RADIATION HARDNESS

BABAR EMC is designed to survive 10 kRad of dose over 10 years with ~20% light loss in each crystal

115 RADFETs measure integrated dose continuously

Doses peak in horizontal plane

Highest doses scale ~ linearly with integrated Ib

Lower-energy Compton & bremsstrahlung ’s dominate

CRYSTAL RADIATION HARDNESS

Integrated doses scale linearly with beam currents as backward barrel: 40 amp hr/Rad from LER barrel/endcap interface: 20 amp hr/Rad from HER endcap (lowest 3 rings): 30 amp hr/Rad from HER

Expected integrated dose vs time

CRYSTAL LIGHT LOSS

From light-yield measurements of worst & average Xtals extrapolate light loss vs time

Fractional light loss vs dose

Expected light loss vs time

MONITORING CRYSTAL LIGHT LOSS

Use 6.1 MeV peak from neutron-activated fluorocarbon to calibrate crystals (stable to 0.5%)

Crystal in endcap have ~1% larger light loss than average behavior is that of typical crystals (need to confirm with higher dose)

If light loss were to degrade faster than expected replace crystals if light loss > 30% (option for EC)

Light loss measured with 6.1 MeV source

EFFECTS ON PHYSICS

Radiation damage alters linearity of crystal response along crystal length

Induced non-linearity will decrease energy resolution

If exact nature of change is understood & predictable some recovery is possible

Perform study of mapping linearity of one “worst” crystal vs dose and input result into MC to look at impact on mass resolution

Study of improving performance in endcap with finer segmentation or timing information

Change in width vs dose

INSTRUMENTED FLUX RETURN

Only issue is high occupancy in outer layer due to beam-related backgrounds

Presently outer RPC layer has random occupancy of several %

At design currents and at higher luminosity this will become an unacceptably high contribution to / misidentification

Solution: build 5 cm thick Fe shield following outer-most chamber

DIRC PARTICLE IDENTIFICATION SYSTEM

Radiation hardness of quartz bars & glue joints is ok Transmission properties of synthetic fused quartz are reasonable up to 100’s of kRad dose

Glue joints show 1% transmission loss for 70 kRad exposure

Photocathode lifetime of 100 Cb at 500kHz is several 1000 years

Light transmission in quartz bars before / after irradiation

DIRC PARTICLE IDENTIFICATION SYSTEM

Main issue is counting rate due to beam-related BG

At L= 11033 cm-2 s-1 physics rate is 1 Hz, while

RBG (kHz) = 0.15 + 3.5 ILER + 14.0 ILER2 (A)+

4.2 IHER+ 20.4 IHER2 + 20

L(1034 )

0.5 MHz per tube at L= 1.51034 cm-2 s-1

PMT base tolerates rate up to > 1MHz

At 500 kHz/tube and 1s readout window for TDC get get ~ 5000 TDC channels/event (50% occupancy) readout by 6 ROM’s running a 15MHz fiber optic link

DIRC inefficiency

vs counting rate

kHz

1

.1

.01

.001

high dead times

DIRC PERFORMANCE W/O UPGRADE

K/ separation vs inefficiency normalization: 3.6 at 3 GeV for 30 pe/track a single photon resolution of 9.6 mr per track resolution varies with Nph of photons added add in quadrature with systematic term 2.3 mr/track

Effect of background is worse than it appears K/ separation is significantly affected by inefficiencies especially at low momenta where 1 relevant hypothesis is in veto mode

DIRC performance for N1 (=1) and N2 in veto mode

MODIFICATION IN THE DIRC SYSTEM

DIRC counting rates are dominated by BG from LER install shielding of stand-off-box

Increase data transfer rate ( ~ factor 4)

Reduce trigger window (~ factor 2)

Further improvements -redesign FE electronics &DAQ Improve timing resolution of photon detectors by 10 Increase pixelization of detector Improve photon resolution by new imaging method Increase geometrical acceptance in forward direction

DIRC readoutprocessing timein ROM vs #TDChits

CONCLUSIONSCONCLUSIONS

Detector operating at luminosities > L=31034 cm-2 s- 1 needs to be well-designed Explicit design depends on machine parameters (beam currents)

Backgrounds need to be cut down as much as possible very low vacuum pressure near IR, excellent masking & shielding

L1 & L3 triggers need to be designed to accept larger rates than BABAR

DAQ needs to be able to handle L3 w/o deadtime plus sufficient margin

Computing power must be able to handle online, offline analysis & MC

SiVD needs radiation hard sensor+electronics, operated with low occupancy (pixel detectors ?)

Drift chamber needs radiation hard gas and reasonable occupancy (problematic > 3 1034 cm-2 s-1)

EM calorimeter should use “radiation hard” crystals operated with reduced occupancy

Particle ID system needs to be radiation hard and operated with reasonable occupancy IFR with appropriate shielding is basically ok