August 25 2005 Hernan Wahlberg, HADRON05 1/26 Open and Hidden Beauty in 920 Open and Hidden Beauty in 920 GeV Proton-Nucleus Collisions GeV Proton-Nucleus Collisions Hernan Wahlberg Hernan Wahlberg Utrecht University/NIKHEF Utrecht University/NIKHEF For the HERA-B Collaboration For the HERA-B Collaboration
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August 25 2005Hernan Wahlberg, HADRON051/26 Open and Hidden Beauty in 920 GeV Proton-Nucleus Collisions Hernan Wahlberg Utrecht University/NIKHEF For the.
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August 25 2005 Hernan Wahlberg, HADRON05 1/26
Open and Hidden Beauty in 920 Open and Hidden Beauty in 920 GeV Proton-Nucleus CollisionsGeV Proton-Nucleus Collisions
For the HERA-B CollaborationFor the HERA-B Collaboration
August 25 2005 Hernan Wahlberg, HADRON05 2/26
OutlineOutline
• HERA-B detector• Reference prompt J/ sample
for beauty analysis• Open cross section ( ) production cross
section• Summary
bbbb
August 25 2005 Hernan Wahlberg, HADRON05 3/26
HERA-B Detector (I)HERA-B Detector (I)
August 25 2005 Hernan Wahlberg, HADRON05 4/26
HERA-B Detector (II)HERA-B Detector (II)
Fixed target detector at p ring HERA, DESYProton beam at 920 GeV/c (√s = 41.6 GeV)Interaction rate ~ 5 MHzWire targets (different materials: C,W,Ti) in proton haloMultiple trigger level (Hardware + Software) for lepton pairsHigh resolution vertexing (~ 500 m-longitudinal)Very good particle ID for e, , , K and p
August 25 2005 Hernan Wahlberg, HADRON05 5/26
Data SampleData Sample
HERA-B has finished data taking (March 2003)
Dilepton triggerPretriggers: high ET ECAL clusters, MUON hitsFLT (hardware trigger): track finding behind magnetSLT (software trigger): track finding behind magnet
and in silicon detector + vertex reconstruction
165 M dilepton triggered events ≈ 300.000 J/Ψ (>1000 per hour to tape)
3 target wires of different materials Carbon (A=12, ≈ 64% of total statistics) Titanium (A=48, ≈ 9%) Tungsten (A=184, ≈ 27%)
B Selection: (~ 40% Efficiency)Lepton impact to the wire Distance J/ to wire
pA bb + Xb(b) B J/ + X
J/ ; e+e-
August 25 2005 Hernan Wahlberg, HADRON05 10/26
B: Principle of MeasurementB: Principle of Measurement
)/(
1
)/(
)(
/ XJbbBrn
n
J
bbR
zBRJ
B
ss
s
B Meson has a long life time ( ~ 9 mm at HERA-B kinematics) ~ 0.5 mm dilepton vertex resolution J/ from a B decay will be detached from primary interaction Only needed to count detached J/
Measurement relative to direct J/ production to minimize trigger/reconstruction uncertainties R= relative efficiency1
B selection efficiency from MC
August 25 2005 Hernan Wahlberg, HADRON05 11/26
B: Data and MC SamplesB: Data and MC Samples
Good agreement between data and MC simulationGood separation between direct and detached J/
August 25 2005 Hernan Wahlberg, HADRON05 12/26
B: Detached J/B: Detached J/ (muons) (muons)
Detachment cuts (on significance) optimized blindly and simultaneously:
Δz > 9 σ Iwl > 2.6 σIwJ/Ψ < 9σ
Upstream Downstream
46.2+8.6-7.9-0.1±1.4
Upstream from target: unphysical region Downstream from target:
Lifetime of candidates in agreement with expectationsCompatibility between different channelsThe complete HERA-B sample (~90 events) is significantly larger than previous fixed target experiments Based on σJ/Ψ = (352 ± 2 ± 26) nb/n (average E789-E771)
Ongoing fit of existing experimental results on σ(J/) with COM parametrisation to provide absolute bb cross section
Large acceptance: 15-220 mrad in x (bending plane),15-160 mrad in y (vertical plane)
Target – up to 8 wires inserted into the halo of 920 GeV proton beam (C, Ti, W)
VDS – Vertex Detector System. Dilepton vertex resolutions: sz 600 m, sx,y 70 m
Dipole Magnet- field integral 2.13 Tm OTR – Outer Tracker. Honeycomb drift cells; wire pitch 5/10
mm; spatial hit resolution 350 m; Backward hemisphere in CM (negative xF)World largerst honeycomb tracker: 1000 modules, 115000 channels
ITR – Inner Tracker: MicroStrip Gas Chambers, pitch 100 m, resolution 100 m; Forward hemisphere in CM (positive xF)Not used in this analysis (stability issues)
August 25 2005 Hernan Wahlberg, HADRON05 31/26
Detector characteristics (II)Detector characteristics (II)
RICH – Ring Imaging Cherenkov Detector C4F10 radiator gas, 2 planes of PMT
4s separation: e/ p [3.4, 15] GeV/c, /K p [12,54] GeV/c ECAL – Electromagnetic CALorimeter – Sandwich sampling
calorimeter (“Shashlik”); Pb and W as converter; 3 regions MUON detector – 4 tracking stations; Gas pixel chambers,
Proportional tube chambers, some with segmented cathodes DAQ system – High bandwidth, high trigger and logging
rates TRIGGER.
- Pretriggers on ECAL & MUON seeds- FLT hardware based on ITR/OTR- SLT software trigger; Tracking+Vertexing; linux farm with 240
nodes
Event reconstruction; on-line, linux farm with 200 nodes
August 25 2005 Hernan Wahlberg, HADRON05 32/26
MUON AND ELECTRON CHANNEL: MUON AND ELECTRON CHANNEL: RELATIVE X-SECTION RESULTSRELATIVE X-SECTION RESULTS