physics performance of lhc-b neville harnew university of oxford beauty-97, los angeles october...
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Physics Performance of LHC-B
Neville Harnew
University of Oxford
Beauty-97, Los Angeles
October 13-17 1997
Outline• Introduction
• The LHC-B Experiment
New Developments :
The Trigger
The RICH
• Physics Performance
• Summary
• LHC will provide an intense source of B-hadrons : bbb
Unprecedented source of bb pairs.
• Probe consistency of the Standard Model :
CKM Physics
CP Violation
Bs-Bs mixing
Rare B decays, FCNC’s
• LHC-B specialised detector :
Measure xs, ’,
in SINGLE EXPERIMENT.
• Precision probe of new physics beyond SM.
MOTIVATION FOR B PHYSICS AT LHC-B
Measure angles Side VV**
tdtd ( ’ )
Unitarity Triangle Unitarity Triangle
V*ubVud+V*
cbVcd+V*tbVtd) = 0 V*
udVtd+V*usVts+V*
ubVtb) =0
(, i)(, i)) (1-, i)
0 Re 1 0 Re 1
’
Im Im
V*ub V*
td
Test of Standard Model
2 unitarity conditions of CKM matrix out of 6which give triangles which do not have a side much shorter than the other two :
112
11
2
11
23
22
32
AiA
A
iA
VVV
VVV
VVV
tbtstd
cbcscd
ubusud
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Production angle b vs b
Advantages
• bb production sharply peaked forward-backward
• Low luminosity is sufficient (1.5x1032 cm-2s-1) Less radiation >80% single interactions
• Threshold for pt trigger can be set low, 1.1-1.25 GeV/c
• Fast B hadrons < pB >Accepted ~ 80 GeV/c Mean flight path of B’s ~ 7 mm • Open geometry allows for easy installation and maintenance
• Vertex detector close to interaction region.
Disadvantages
• Minimum bias also peaks forward• High occupancy, high track density• Needs more sophisticated trigger than high pt
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Advantages of LHC-B
Rhobust and efficient 4 Level Trigger system
Level 0 : Muon pT > 1.25 GeV/c Electron pT > 1.4 GeV/c Dihadron pT > 3 and 2 GeV/c Level 1 : Vertex and track trigger Level 2 and 3 : Software triggers
Very good particle identification :
Muon system Electron (e-separation > 100) p/K// separation with two RICH detectors (3 /K separation between ~2 to 150 GeV/c)
Good decay time resolution
Decay distance resolution ~ 120 m
Decay time resolution ~ 0.04 ps
Bunch crossing rate 40 MHzBunch crossing with single interaction 9 MHzb-hadron production rate 75 kHz
inelastic = 80 mb , bb = 500 b
Nominal luminosity = 1.5 x1032 cm-2s-1
(Max luminosity = 5 x1032 cm-2s-1 )
• Interaction rate (single interaction) = 9 MHz
• Fraction of bunch crossings with no interaction = 0.68
• Fraction of bunch crossing with one interaction = 0.26
Choice of Luminosity
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Number of interactions vs. Luminosity
Probability of B interaction vs. Luminosity
BEvent
• Full GEANT simulation• dN/dAR2 particles/cm2 (<5% occupancy)
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LHC-B TriggerTitle:(frontend1.eps)Creator:Adobe Illustrator(r) 6.0Preview:This EPS picture was not savedwith a preview included in it.Comment:This EPS picture will print to aPostScript printer, but not toother types of printers.
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LHC-B -VertexTitle:(si_detector_elements.eps)Creator:Adobe Illustrator(r) 6.0Preview:This EPS picture was not savedwith a preview included in it.Comment:This EPS picture will print to aPostScript printer, but not toother types of printers.
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Precision vertexing :
zprimarym
tBs mixing
ps
Level 1Trigger Device
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Vertex detector L1 trigger provides ~10 suppression withefficiency 75% for B- and 90% for BsDs -
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• Track-finding with 3 successive planes of r-strip detectors : reconstruct primary vertex by histogramming combinations with opposite ( sectors).• Calculate impact parameters (IP) wrt primary and cut on this quantity• Add -strip information for tracks with large IP• Construct 2-track vertices in space
LHC-B Level 1 Vertex Trigger
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LHC-B RICH /K Separation
3 /K separation between ~2 to 150 GeV/c
LHC-B RICH DETECTOR CHARACTERISTICS
RICH-1 :
• Combined Aerogel and gas (C4 F10)• Approx 125 HPDs, 250000 pads. C4 F10 : n=1.0014 ; <> ~ 55 Thresholds : 2.7 GeV/c, K 9.4 GeV/c Aeogel : n=1.03 ; <> ~ 15 Thresholds : 0.6 GeV/c, K 2.0 GeV/c
RICH-2 :
• Gas (CF4)• Approx 125 HPDs, 250000 pads. CF 4 : n=1.0005 ; <> ~ 30 Thresholds : 4.6 GeV/c, K 16.3 GeV/c
RICH 1,2 Detectors provide/K separation in LHC-B between 1 and 150 GeV/c
LHC-B will develop HPD in collaboration with industry
• 2000 Si pads per HPD, 2x2 mm pads• Amplifier/Shaper/L0-Pipeline inside the gas envelope• Large area coverage (11 cm diameter photocathode)• 80% photocathode active area (HPD)• 90% packing active area
PATTERN RECOGNITION IN RICH-1
• Aerogel: n=1.03, <>=15
• C4F10: n=1. 0014, <>=55
• B event
• Reconstruction efficiency and purity both better than 90% (for and K)
• Random hits - Rayleigh scattered ’s
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Scalein cm
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LHC-B Prototype RICH
• Aerogel and C4F10 Cerenkov rings for 10 GeV/c Pions : 1/4 scale prototype
• Aerogel : approx 1.4 mean no. of photons observed, 2.0 expected (N0 ~ 100 cm-1 prelim.)
• C4F10 : approx 7.9 mean no. of photons observed, 6 expected (N0 ~ 230 cm-1 prelim.)
• First Ring Imaging Counter using hybrid photo diodes
• SEE TALK BY N.BROOK
Scale in mm
PRELIM
LHC-B Event Rates (LoI)
L=1.5x1032, 1 year running (=107s)
Event Sample VisibleB.R.
DecayAccept.
EfficiencyLevel-1 Level-2
Eventson Tape
Measuredquantity
B0 +
2.0 x 10-5 17.8% 20.6% 33.1% 110k B0 J/ Ks
0 () 2.1 x 10-5 14.0% 73.5% 34.5% 340k
B0 J/ Ks0 (ee) 2.1 x 10-5 12.4% 44.6% 34.5% 183k
B0 D0K* (KK) 8.0 x 10-7 12.8% 15.4% 43.3% 3k
Bs0 Ds
K+ 1.1 x 10-5 12.6% 14.6% 47.5% 13k
Bs0 Ds
+K
5.3 x 10-6 12.6% 14.6% 47.5% 6k
Bs0 J/
() 4.2 x 10-5 14.2% 71.8% 42.0% 246k
Bs0 J/ (ee) 4.2 x 10-5 12.5% 44.0% 42.0% 133k
Bs0 Ds
+ 1.4 x 10-4 13.0% 14.7% 46.8% 171k xs
Bs0 Ds
++ 3.5 x 10-4 9.6% 12.0% 50.8% 277k xs
Bs0 + 4.0 x 10-9 19.2% 84.3% 33.5% 30 FCNC
B0 + K* 2.9 x 10-6 14.3% 70.0% 42.2% 17k FCNCB0 J/ K* () 6.3 x 10-5 13.7% 75.3% 42.8% 1270k controlB0 J/ K* (ee) 6.3 x 10-5 12.1% 45.5% 42.8% 679k control
recon 0.3, tag 0.4 not included • These are LoI values, tabulated values are conservative Expect improvement with new L1 trigger scheme
-
LHC-B PHYSICS PERFORMANCE
• xS measurement
• sin2
• sin 2
• Note : All sensitivities quoted are still LoI.New calculations in progress : Improvement expected.
Bs-Bs Oscillations• Look at time evolution of BsDs
No CP violation expected
• Time evolution of Bs (Bs) given by : Rt) exp(-t/s) (cosh(s/2 t) 1-2cos(mst) )
• Fit ms , s , s ; xs= ms /s
• LHC-B in one year: 35k tagged BsDs
events (wrong tag fraction, Title:xs_mix.epsCreator:HIGZ Version 1.21/10Preview:This EPS picture was not savedwith a preview included in it.Comment:This EPS picture will print to aPostScript printer, but not toother types of printers.
LHC-B xs reach
Bs tag
Bs tag
Xs
Proper time distributions for reconstructed Ds- (ie. Bs decay)
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Interference via Bd0 Bd
0 mixing and decay
LHC-B Events on tape J/: 340k J/e+ e : 183k L=1.5x1032, 1 year =107s, BR x (e BR) =2.1x10-5
recon 0.3, tag 0.4
Reconstructed and tagged events=55k/year
Measure decay asymmetry : N(B0 J/s
0 )(t) - N(B0 J/s0 )(t)
N(B0 J/s0 )(t) + N(B0 J/s
0 )(t)
Nb(t) - rNb(t) = a sin(m t)
Nb(t)+ rNb(t) d
a : fitted parameter sin 2 a / (1-r=Bd/Bd tagged ratio (found from control sample)=wrong tag fraction=0.290 (0.00
And sin ) = 0.023 (statistics dominated)
Sin 2from BJ/s0
BJ/s0
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J/
s0
d
e+ e
LHC-B Events on tape : 110k L=1.5x1032, 1 year =107s, BR=2x10-5 NB
recon 0.3, tag 0.4
Reconstructed and tagged events=14k/year
Measure decay asymmetry :
Nb(t) - rNb(t) = a cos(m t) + b sin(m t)
Nb(t)+ rNb(t) d d
a, b fitted parameters (if no penguin, a=0)r=Bd/Bd tagged ratio (found from control sample)
Background : Predominantly BdK BsKBsK
Particle ID with RICH is vitally important
If a=0, then : sin 2 = b/(1-=wrong tag fraction=0.260 (0.00
And sin ) = 0.039 (statistics dominated)
Sin 2from B
4 channels : BsDs-K+ , BsDs
+K-
BsDs+K- , BsDs
-K+
Reconstructed and tagged events=3000/year
Measure decay time evolution for Bs , Bs Ds-K+
Nb,bt) exp(-t/s) (cosh(s/2 t) A sinh(s/2 t) a cos(mst) b sin(mst))
Measure decay time evolution for Bs , Bs Ds+K-
Coefficients a, b a’, b’ a, b, a’, b’ fitted parameters b, b’ give sin
Sin from BDsK
Background
to BsDsK is
BsDs
Mass resolution
m=8.5 MeV
and particle ID
(RICH) vital.
Measure 6 relative branching fractions
BdD K*, D K*, D CP K*
BdD K*, D K*, D CP K*
LHC-B sin 2) = 0.14 - 0.24
(dependent)
Small CP violation in BsJ/s/Bs time-dependent asymmetry. Reconstruct 44k events with a tag.LHC-Bsin 2) = 0.02 (xs=25)
Sin from BsJ/
Sin 2from BdDK*
Error on depends on xs … eg. 10o o, 80o o
LHC-B ) = 6o - 16o
(This measurement is unique to 2nd generation
hadron-machine dedicated CP experiments)
(600, 200, 50 events/year per channel)
LHC-B CP Reach Summary : One year’s running at 1.5 x 1032 cm-2s-1
CPParameter
Decay mode No. ofEvents
Uncertainty inone Year
Importantdetectorproperties
sin 2 Bd J/ Ks 55k (sin2)= 0.023
sin 2 Bd
14k (sin2)= 0.039 Particle ID
Bd D
0.9k () = 7 -12 Particle ID
' Bs Ds
3.3k () = 6 -16 Particle ID (Decay time)
sin Bs J/ 44k ( (Decay time)
xs Bs
Ds 35k < 55
(Decay time)
(sin2) assumes penguin contribution known, and BR(Bd x
• All measurements are statistics, not systematics, limited.• Table is based on LoI (Summer 1995). Expect improvement with new L1 trigger.
• LHC provides an opportunity to study CP (and other physics) in B-decay with very high statistics
• LHC-B: Optimized Forward Detector
- Flexible, efficient, robust triggers
- Particle ID
- Excellent decay-time precision
• CKM-PHYSICS: Angles and sides of Unitarity Triangle overconstrained through measurements of 'xs .
Different decay channels, triggers, tags allow redundancy and control of systematics
• “LOW” Luminosity:
- LHC-B can “choose”: LLHCB = 1.5 x 1032 cm-2 s-1
- No Pile-up
- Exploit initial (& subsequent) LHC running
• End 1995 : LoI approved
Feb 1998 : Technical Proposal submitted
2005 : Beam (Day 1 experiment)
LHC-B can run for MANY YEARS at optimal luminosity to study CP-violation
SUMMARY