Challenges and Opportunities of High Luminosity Tracking Charles Hyde Université Blaise Pascal, and Old Dominion University « Structure of the Nucleon » GDR Instrumentation Workshop 8-9 April 2008, CEA-Saclay

Deeply Virtual Exclusive Reactions Small cross sections at high Q 2. –High luminosity Competition between exclusive and inclusive channels –Tracking and/or particle ID Complicated spin structure –Target and/or recoil spin observables Plus charge- exchange reations

Luminosity Limits Beam Current –All JLab Deeply Virtual experiments operate below available beam limits. –Single exception is Hall C H(e,e’  + )n « Pion Form Factor » Polarized Targets Detector / Tracking – Occupancy, – Ageing. DAQ

Polarized Targets Hall A, 3 He, –neutron luminosity = –Proton + window Luminosity ≈ (2+6)10 36 –Secondary Luminosity ≈ –Recent discussion to boost luminosity by 10x to 100x –Free rotation of long. and transverse polarization Hall B, NH 3, ND 3 Longitudinally polarized –Dilution factor ≈ 0.05 –CLAS Luminosity –CLAS12 Luminosity = –Hall C target operated at 100nA with transverse pol. HD Targets –Low Holding Field: Preferred for Transverse Pol. –Maximum Luminosity  Acceptance TBD.

Detector Limits CLAS DC –2% maximum “safe” occupancy level for high efficiency track reconstruction Probably a good general limit. Drift Chamber rate limits: –HV trips, Ageing, Recovery time after each event –GEM / MicroMegas: extend operating limits by orders of magnitude Does not resolve occupancy problem unless granularity is increased Si tracking: –High Granularity Hall A PbF 2 blocks expected to diminish light output by 20% after 7 days at /cm 2 /s –Cure with blue light ≈ 1 day / week.

DAQ Limits Open Trigger in open geometry –scattered electron; or –Electron + 1 charged particle –High raw data rates from DIS and photo-production limit rate for rare processes CLAS12 DAQ tuned to with open (Q 2 >1 GeV 2 ?) trigger. Hall A DVCS: –DIS electrons (kHz) –>1GeV photon Coincidence rate 100 Hz at

Specialized Triggers for Deeply Virtual Processes The deeply virtual ep  ep  and ep  ep    reactions have a special signature  ≥90% of beam energy is visible in two EM showers  For    one shower is really 2 closely spaced showers.  Each of the two showers has ≥ 30% of beam energy.  Possibility of operating at higher luminosity  Tracking detectors must still operate at high efficiency  A pre-scaled Open Trigger can still provide access to other channels at close to normal count rates.

Photon Background in e+H 2 Two dominant process (X/X 0 <1%) Quasi-real bremsstrahlung followed by  e Compton Scattering Møller (e,e’) scattering followed by internal bremsstrahlung (e,  ) cross sections O (  r e 2 ) Compton/Møller edge at E  =m e /(1-cos  ) Pavel Degtiarenko: DINREG

Bremsstrahlung Compton Model Excellent agreement for naïve estimate

Energy Integrated; Angle Averaged Bremsstrahlung endpoint is too hard

Can Drift Chambers be Shielded against random X-ray and  -ray hits? e+H photon background spectra are ≈ 1/ E  for 0.1 MeV< E  <m/(1-cos  ) –P. Degtiarenko, DINRAD MC –Everything above 13 eV is “high energy” from H Photo-absorption E  >>1 MeV is universal  Z(Z+1)/A and dominated by e + e  creation Photo-absorption at E  ≈1MeV is universal  Z/A and dominated by Compton Scattering on atomic electrons Photo-absorption << 1 MeV is atom specific

Photo-Conversion in Drift Chamber gas If photon spectrum is ≈1/E , then equal numbers of photons per decade –(10-100KeV, 100KeV-1MeV, 1MeV-10MeV, etc). But, low energy  -rays are preferentially converted in chamber gas 5 KeV photon: 1000x greater conversion probability than 10MeV photon ≈MIP signal

Photon Attenuation Thin multi-Z sandwich –Preferentially absorb low energy  -rays –Multi-layer, multi-Z to absorb secondary K-shell X-rays etc. physics.nist.gov/PhysRefData/Xcom/Text/XCOM.html

Gamma-Shield Concept Thin multi-Z sandwich can preferentially absorb low energy  -rays with only 1% radiation length (1mr multiple scattering at 1.5 GeV/c) target DC

Photon Conversion in Unshielded Chamber Background  -flux is ≈1/E  –Arbitrary units Photon conversion probability in 1cm Chamber gas Relative hit rate is semi-dominated by low-energy  -rays

Absorption in 1% multi-Z sandwich Background  -flux is ≈1/E  –Arbitrary units Attenuation coef (cm 2 /g) in 1% radiation length multi-Z absorber Transmission coef. of absorber Transmitted  -ray flux. – Photons below 50KeV strongly absorbed

Random hits in DC after 1% radiator multi-Z sandwich  -flux with and without multi-Z absorber –Left hand axis  conversion rate with and without absorber –Right hand axis  -ray background spectrum is strongly cut-off at high energy –E  <m/(1-cos  ) –20deg  E  <8 MeV

Recoil Tracking for DVCS H(e,e’  p) –Over-complete exclusivity A(e,e’  A) –Nuclear recoil detection required for exclusivity –D(e,e’  D) CLAS (M. Amarian et al, deferred) – 4 He(e,e’  ) CLAS+BONUS H(e,e’  p) Recoil Polarization –Alternative to target polarization.

Acceptance vs. Luminosity CLAS12: (e,e’  )Acceptance  Luminosity ( L ) ≈ 0.5  –Large t-range –All [Q 2,x B ] bins; unequal statistics –Physics luminosity ≈10x lower for polarized targets For an equivalent single [Q 2,x B ] bin –Hall A azimuthal acceptance  V HRS /sin(  ) ≈ (120mr)/sin(20  ) ≈ 0.6rad –(e,e’  )Acc.  L ≈ (0.6/2  ) (0.6/2  ) ≈ Hz/cm 2  t/Q2<<1 Each [Q 2,x B ] requires separate beam time  balance statistics –Is it possible to build a large acceptance recoil tracker for ≥ luminosity in Hall A?

Recoil Tracking at L ≥ ? Separate GPDs via recoil polarization –FOM (500MeV/c < p < 700MeV/c) ≥0.5% –Hall A: L  Acc.  FOM ≥ Hz/cm 2 –CLAS12 polarized target: p L FOM= Dilution  P 2 ≈ 5% L  Acc.  dilution  P 2 ≈ (0.5) (0.05) ≈ Hz/cm 2 Nuclear DVCS –D(e,e’  D) –Recoil deuterons are >5x minimum ionizing Raise detection threshold to suppress single  hits Granularity can be increased to keep random  hit rate below 2%. –Si strips of 250  m  5cm at 20 cm from target.

Recoil Polarimeter Concept

LANL LDRD R&D proposal for high luminosity tracking Four layer Si Tracker –5cm  225mm strips –2000 total channels –LHCb “Beetle” readout chip Measure D(e,e  d) coherent cross section at t min at [Q 2,x B ]=[1.9GeV 2,0.36] during E (2010). –Test occupancy, tracking efficiency. A. Klein, G. Kunde, A. Dangoulian

Conclusions DVCS offers compelling physics for tracking beyond current luminosity limits –[BABAR≈10 34, CLAS12 proposed ] Low level triggers on total EM energy can keep DAQ rate within limits. In situ tests of prototype trackers needed to determine actual limits.

LANL LDRD Proposal R&D for high luminosity tracking Si  -Strips 2.54 cm C (analyzer) HRSe’ 