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Open and Hidden Beauty in 920 GeV Proton-Nucleus Collisions. Hernan Wahlberg Utrecht University/NIKHEF For HERA-B Collaboration. Outline. HERA-B detector Reference prompt J/ y sample for beauty analysis ( ) production cross section Open cross section Summary. Hera-B Detector. - PowerPoint PPT Presentation
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July 3 2004 Hernan Wahlberg, BEACH04 1
Open and Hidden Beauty in 920 GeV Proton-Nucleus
Collisions
Hernan WahlbergUtrecht University/NIKHEFFor HERA-B Collaboration
July 3 2004 Hernan Wahlberg, BEACH04 2
Outline
• HERA-B detector
• Reference prompt J/ sample for beauty analysis
( ) production cross section
• Open cross section• Summary
bb
bb
July 3 2004 Hernan Wahlberg, BEACH04 3
Hera-B Detector
July 3 2004 Hernan Wahlberg, BEACH04 4
Reference Prompt J/ SampleDi-Muon total sample:
Approx. 177,000 J/ eventsWidth: 44 MeV/c2
(2S)
J/ ()
Di-Electron total sample: Approx. 108,000 J/eventsWidth: 64 MeV/c2
(2S)
J/ (ee)
•Long Tracks (Vertex Detector + Tracking System)•PID: likelihood , E/p•Dilepton Vertex Probability > 1%•J/ acceptance: -0.35 < xF < 0.15
July 3 2004 Hernan Wahlberg, BEACH04 5
: Motivation
• Theoretical prediction– Hadronization: Possible
nuclear suppression ?HERA-Bs = 41.6 GeV
• Several measurements available but unclear situation at √s ~ 40GeV
• HERA-B has good coverage in the central region of collisions ( xF ~ [-0.35,0.15])
E772 (A=2)
E605 (A=64)
July 3 2004 Hernan Wahlberg, BEACH04 6
: Method
• Measurement relative to prompt J/ – Less sensitive to systematic effects
• Prompt J/cross section from E771 and E789
pA + X - ; e+e-
July 3 2004 Hernan Wahlberg, BEACH04 7
: Signal• 25% W + 75 % C (targets)• Mass resolution between
140 and 160 MeV/c2
• Background:– Random combinatorial:
estimated by like sign pairs of real data
– Drell-Yan: shape estimated from MC
• (1S) / (2S) / (3S) relative production fixed to E605 results
July 3 2004 Hernan Wahlberg, BEACH04 8
: Preliminary Results
• Both channels are compatible• Extrapolation to √S = 38.8 GeV yields:
Br• d/dyy=0 = 2.4 ± 0.9 pb/n– compatible with E605– (more than 1 ) below E772 and E771
Events Br• d/dyy=0
+- 33 ± 7 3.9 ± 1.1 pb/n
e+e- 31 ± 10 2.9 ± 1.2 pb/n
both 3.4 ± 0.8 pb/n
July 3 2004 Hernan Wahlberg, BEACH04 9
: Global Situation
• Modified Craigie parameterization to include nuclear suppression (parameter
• Data compatible with no nuclear suppression:
= 0.99 0.05
Not usedin fit
As
ms
dy
dBr o
o
y
exp)(0
s (GeV)
July 3 2004 Hernan Wahlberg, BEACH04 10
B: Motivation• Theoretical uncertainties:
– b quark mass 4.5 - 5 GeV– At NLO, scale () dependence
• Previous measurements do not agree
Experiment E p (GeV) (nb/ nucleon) N Events
E789 800 5 ± 1.5 ± 3 ~ 20
E771 800 43 ± 22 ± 7 ~ 6
HERA-B(2000) 920 32 ± 13 ± 6.5 ~ 10
Theory Order
N.Kidonakis et al. NLO + NNLL 30 ± 18
R.Bonciani et al. NLO + NLL 25 ± 17
July 3 2004 Hernan Wahlberg, BEACH04 11
pA bb + Xb(b) B J/ + Y
J/ ; e+e-
B: Principle of the Measurement
)/(
1
//
XJbbBrn
nzBRJ
BJbb
July 3 2004 Hernan Wahlberg, BEACH04 12
B: Principle of the Measurement
• 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: count detached J/• Measurement relative to prompt J/• Prompt J/cross section from E771 and E789
)/(
1
//
XJbbBrn
nzBRJ
BJbb
July 3 2004 Hernan Wahlberg, BEACH04 13
B: Detached Scheme
P P
•B Selection: (30-45% Efficiency)•Lepton impact to the wire •Lepton closest distance of approach to primary •Distance J/ to wire
July 3 2004 Hernan Wahlberg, BEACH04 14
B: Real Data vs. MC
•Vertex z resolution ~ 500 m •Good agreement between real data and MC simulation
July 3 2004 Hernan Wahlberg, BEACH04 15
B: Signal
• Carbon + Tungsten targets
• 35% of total sample• Cuts optimized
simultaneously• Background:
– bb and cc simultaneous semileptonic decays
– Combinatorial– Prompt J/
• Unbinned likelihood fit
July 3 2004 Hernan Wahlberg, BEACH04 16
B: Sample Cross Check
July 3 2004 Hernan Wahlberg, BEACH04 17
•Only statistical errors•Good compatibility of two channels•1.3 lower than HERA–B (2000)
B: Preliminary Result
N/nb12.7 4.23.6bb
n/nb 12.7 : Muons 4.23.6bb
n/nb12.3 3.53.2bb
n/nb 11.5 :Electrons 5.34.5bb
July 3 2004 Hernan Wahlberg, BEACH04 18
B: Ongoing studies
– Simultaneous semileptonic decays– Search of exclusive decays– Lifetime measurement
July 3 2004 Hernan Wahlberg, BEACH04 19
Conclusions
• Events observed in hidden and open beauty in the 2002-2003 data sample
• Preliminary cross section measurement: 3.4 ± 0.8 pb/n– in agreement with E605
• Global fit to data consistent with no nuclear suppression
• Preliminary bb cross section measurement (35% of the total statistics)
– The complete HERA-B sample will be significantly larger than previous fixed target experiments
n/nb12.3 3.53.2bb
July 3 2004 Hernan Wahlberg, BEACH04 20
Back-up slides
July 3 2004 Hernan Wahlberg, BEACH04 21
Essential bibliographyP.NASON, QCD at High Energy, Proc. Of the XX Int. Symp. on Lepton and Photon Interactions at High Energies, hep-ph/0111024P.NASON et al., Adv. Ser. Direct. High Energy Phys. 15(1998), 609H1 Coll. T.Sloan et al., Proc. QCD 2001 Conf., Moriond, March 2001.ZEUS Coll. J.Breitweg et al., Eur.Phys.J.C18(2001)
L3 Coll. M.Acciarri et al., Phys.Lett.B503(2001) 10
OPAL Coll. OPAL Phys.Note PN455, August 29,2001
N. Kidonakis et al., Phys.Rev. D64 (2001) 114001-1
D.M.Jansen et al., Phys.Rev.Lett.74 (1995)3118
T.Alexopoulos et al., Phys.Rev.Lett.82 (1999) 41
R. Bonciani et al., Nucl.Phys.B529 (1998) 424
July 3 2004 Hernan Wahlberg, BEACH04 22
Detector characteristics (I) 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) VDS – Vertex Detector System.
Dilepton vertex resolutions: z 600 m, x,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 hemisfere 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 hemisfere in CM (positive xF)World largerst (gas) micro pattern tracker
July 3 2004 Hernan Wahlberg, BEACH04 23
Detector characteristics (II) RICH – Ring Imaging Cherenkov Hodoscope
C4F10 radiator gas, 2 planes of PMT
4 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
July 3 2004 Hernan Wahlberg, BEACH04 24
b production model systematics
• Changing PDFs from MRST to CTEQ• b quark mass from 4.5 to 5.0 GeV/c2
• QCD renormalization scale from 0.5 o to 2 o
• Fragmentation functions– Peterson form with from 0.002 to 0.008– Kartvelishvili form with from 12.4 to 15.0
• <kT2> from 0.125 to 2.0 GeV2
• Fraction of b-baryons produced in the b-hadronization process from 0 to 12%
±1.5% ±1% ±2% ±3%
±1% ±2%
Default model: MRST PDF, Peterson FF =0.006 22222 GeV/c 0.5kpmGeV/c 4.75m TTbb 0
Total: ±5%
Studied variations: Sys cont. to (bb )
July 3 2004 Hernan Wahlberg, BEACH04 25
J/ from b decays kinematics
92% of J/ are produced in our xF range