FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London1 B-Physics at the LHC P J Dornan...
-
Upload
shannon-goodman -
Category
Documents
-
view
213 -
download
0
Transcript of FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London1 B-Physics at the LHC P J Dornan...
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
1
B-Physics at the LHCB-Physics at the LHC
P J DornanP J Dornan
Imperial College, LondonImperial College, London
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
2
Why b-physics at the Why b-physics at the LHCLHC
Millions of b’sMillions of b’sWith full luminosity, 1034, gives 5.1013 bb pairs per year- But events much too difficult to analyse, ~25 interactions
per crossing- So - need to run at lower luminosities for most b-physics
- In the early period max luminosity expected ~ 1033 - ATLAS/CMS
- but will eventually be able to exploit full luminosity for certain rare decays
- LHCb currently plan to run at 2.1032 by detuning the beam
Signal/Background improves with increasing Signal/Background improves with increasing energyenergy
inel = 80 mb, bb = 500 b
All b-species produced, BAll b-species produced, B++, B, B00, B, Bss, B, Bcc, b-baryons, b-baryonsAt these energies b’s are getting ‘light’ At these energies b’s are getting ‘light’
Thus bb pairs produced dominantly forward - backward
-
-
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
3
General PurposeGeneral PurposeATLAS, CMS – 4 ‘standard’ colliding beam detectors
Main aim to search for new states - Higgs and those from BSM so will always aim to run at maximum luminosity, 1033 -> 1034
SpecialisedSpecialisedLHCb – forward spectrometer (10 – 300 mrads), designed specifically for b-physics. Will always run at low luminosity, nominally 2.1032
General Purpose and LHCb operate in complementary kinematic regions
The ExperimentsThe Experiments
b b
b
No
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
4
Experimental Experimental RequirementsRequirements
An excellent vertex detectorAn excellent vertex detectorB-states identified by displaced secondary vertices
Good K-Good K- separation separationDifficult for general purpose detector - a weakness of ATLAS/CMSAn essential feature of LHCb
A good trigger for A good trigger for interestinginteresting b-physics b-physicsFar too many b’s produced to trigger on all of them. Therefore trigger
must reject many b-states and concentrate on those from which CP/CKM physics will result
This is probably the greatest challenge for a hadronic b-This is probably the greatest challenge for a hadronic b-experimentexperiment
-- and has caused failures in the past-- and has caused failures in the past
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
5
ATLASATLAS
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
6
ATLAS TrackerATLAS Tracker
Tracker
Pixel Detector
Pixel Detector designed for b-physics
Radius of inner layer = 5 cm.
3 layers, but middle will not be available at start-up
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
7
ATLAS Pit TodayATLAS Pit Today
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
8
CMSCMS
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
9
CMS TrackerCMS Tracker
CMS Silicon Tracker
Pixel DetectorAll Silicon2 Pixel Layers Radii 4 and 7 cm Low luminosityRadii 7 and 11 cm high luminosity
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
10
CMS TodayCMS Today
Tracker being assembled
In the pit
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
11
LHCbLHCb
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
12
LHCB – VELOLHCB – VELO
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
13
LHCb - VELOLHCb - VELO
Proper time resolution ~ 40 fs
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
14
LHCb - RICH1LHCb - RICH1
RICH1 detector
Vertex locator
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
15
LHCb – RICH1&2LHCb – RICH1&2
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
16
LHCb RICH performanceLHCb RICH performance
MomentumMomentum
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
17
TriggersTriggers
LHCb much better for hadronic B-decays
All comparable for B -> J/decays
ATLAS/CMS better for Rare Decays ->(X)
Vital - Still Evolving - Algorithms depend upon important Vital - Still Evolving - Algorithms depend upon important physics channelsphysics channels
Basic philosophyBasic philosophy
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
18
What physics channels?What physics channels?
Must be interesting and extractable at the trigger levelMust be interesting and extractable at the trigger level
* * * 0ud ub cd cb td tbV V V V V V * * * 0td ud ts us tb ubV V V V V V
Unitarity Triangles
Bd0
Bd0
BS0 DS
Bd0 J/ KS
0
Bd0 DK*0
BS0 DSK
Bd0 BS
0 K+K-
Bd0 D*
BS0 J/
Rare DecaysBs(d) X, b s
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
19
Flavour TaggingFlavour Tagging
In many cases need to In many cases need to know the flavour of know the flavour of the B when producedthe B when produced
Use Decays of the other B state - Opposite Side tagLepton b -> e,
Kaon b -> c -> s
Or from the accompanying /K with the signal B – Same Side tag
Or use vertex charge
l
B0
B0
D
K-
b
b
d
u
d
u
B0
+Prelim. LHCb with Opposite side only
Obtain eD2 = 6.4%
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
20
BBss Oscillation - Oscillation - mmss
With With mmdd yields V yields Vtdtd
Oscillation is fast (>14.4 psOscillation is fast (>14.4 ps-1-1))Need excellent momentum and position resolution, i.e. a fully resconstructable final state and excellent vertex resolution
Use BUse Bss-> D-> Dss(LHCb) Obtain ~80,000 fully reconstructed/year, S/B ~3. Proper time resolution ~40fs
Expected unmixed Bs Ds sample
in one year of data taking (fast MC)
Expect to make a 5 measurement in 1 year to 68 ps-1
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
21
sin2sin2 - B - B00 -> J/ -> J/ K Kss
Classic channel for CP violation studyClassic channel for CP violation studyStill important for LHC experiments to measure with the best possible precision.
Measure time dependent asymmetryMeasure time dependent asymmetry
AAmixmix yields yields sin2sin2AAdirdir direct CP violation - BSM direct CP violation - BSM
Assuming AAssuming Adirdir = 0 = 0
ATLAS quote ATLAS quote (sin2(sin2) = 0.013 after 3 years at 10) = 0.013 after 3 years at 103333
LHCb quote LHCb quote (sin2(sin2) = 0.022 after 1 year at 2.10) = 0.022 after 1 year at 2.103232
( ) cos( ) sin( )dir mixCP CP CP dA t A m t A m t
LHCb
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
22
Sin2Sin2 - B - B00 -> -> ++==
Actually measure Actually measure ----
a very good channel for a very good channel for LHCbLHCb
High pT hadron to give trigger
RICH is essential
ButBut Penguins complicate Penguins complicate the analysisthe analysis
Can reach 5° < () < 10° in one year if P/T known to 10%
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
23
Sin2Sin2 - B - B00 -> ->
Three final statesThree final states
Requires time dependent Dalitz plot analysis
But needs detailed understanding of the acceptance
An analysis is being developedAn analysis is being developed-- looks promising
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
24
LHCbLHCb
Will be a major result for LHCb - relies on the hadronic triggerWill be a major result for LHCb - relies on the hadronic trigger
Many waysMany waysBut none are simple - involve measuring low decay rates, time dependent analyses in the Bs system, theoretical uncertainties
Many approaches necessary to check consistency
4 time dep rates yields
Relate with U-spin yields
4 time dep rates yields 2
6 decay rates yields 0*0
10
0*000*00
*0
00
,,.4
.3
,.2
,.1
KDB
KDBKDB
DB
KKBB
KDBKDB
CP
s
ssss
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
25
Features of LHCb for Features of LHCb for DeterminationDetermination
Vertex Resolution - Time Vertex Resolution - Time Dependent BDependent Bs s AsymmetriesAsymmetries
Separation BSeparation Bss-> D-> Dss/B/Bss --> D> DssK - RICH particle ID and K - RICH particle ID and mass cutsmass cuts
BsDsKBsDs
BsDsK
BsDs
( )~ 12
( )s s
s s
Br B D
Br B D K
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
26
Bd D0 K*0 signal RICH minimises background
Bs KKSeparationWith RICH
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
27
LHCb Expected performance LHCb Expected performance for for
2400 events per year3° < ) < 16°
5000 events per channel per year3° < ) < 16°
~500,000 events per year. ) ~ 10
Some BR’s very small, 10-7 -> 10-8
) ~ 10 ° per year0*01
0
0*000*00
*0
00
,,.4
.3
,.2
,.1
KDB
KDBKDB
DB
KKBB
KDBKDB
CP
s
ssss
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
28
BBss Mixing phase Mixing phase ss= -2= -2
Use BUse Bs s -> J/-> J/
BBss analogue of golden analogue of golden channel, Bchannel, B00 -> J/ -> J/KKss
Asymmetry very small in SM, s ~ -0.04so very sensitive to new physics
But two vectors in final state But two vectors in final state therefore need a time therefore need a time
dependent angular analysisdependent angular analysisSensitivity depends on ms
For ms = 20, Expect ) ~ 2° per year
Analysis also yields s
and s
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
29
BBs,ds,d -> -> XX
Atlas/CMS can here use the high luminosity, so can Atlas/CMS can here use the high luminosity, so can do better than LHCbdo better than LHCb
Full TrackerFull Tracker
= 46 = 46 MeVMeV
CMS – Mass resolutionNeed 30 fb-1 for a 5 observation
BBss -> -> BBss -> -> XX
14041110-6Bd0
29019951.5x10-6Bd0K*
95022210-7Bd0
BGsignalBRchannel
ATLAS statistics with 30 fb-1
F-B Asymmetry sensitive to some SUSY scenarios
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
30
BBcc
Production less peaked forwardProduction less peaked forwardBetter for ATLAS/CMS
For Bc -> J/
p (GeV)
ATLAS, (M(Bc) = 74 MeV Expect between 5 – 10K Bc -> J/ for each of ATLAS, CMS & LHCb per year
Also BAlso Bcc -> J/ -> J/ gives V gives Vbcbc
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
31
An Event in LHCbAn Event in LHCb
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
32
The major problem - The major problem - TriggeringTriggering
B-rates at the LHC are very highB-rates at the LHC are very highThe final states of interest are a very small proportion
For highest efficiency, the High Level Triggers (HLT)) must For highest efficiency, the High Level Triggers (HLT)) must focus very directly on the focus very directly on the predictedpredicted properties of the properties of the final states of interest and aim to distinguish them from final states of interest and aim to distinguish them from the the predictedpredicted backgrounds using the backgrounds using the predictedpredicted properties of the detectorproperties of the detector
Predictions in the forward area depend upon knowledge of the pdf’s at very low x where they are least reliable
The simulation will not be perfect!
The performance of the trigger is key to the The performance of the trigger is key to the success of the experimentsuccess of the experiment
Planned on the simulationToo loose -> low efficiencyToo tight -> potential bias
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
33
Triggering LHCbTriggering LHCb
Dimuon TriggersDimuon TriggersMuch physics, J/ X decays, rare decaysStrong signature, low rates
Safe for LHCb and ATLAS & CMS, Safe for LHCb and ATLAS & CMS,
Triggers for hadronic final statesTriggers for hadronic final statesMuch of the physics is here - quite probably any new
physics will at the few % level - probing this is the justification for LHCb
But rates are low - or very low
NeedNeedStatistical precision -> highly efficient triggerSystematic precision -> minimal biases and these must be
accurately quantified
Highly demanding for the triggerHighly demanding for the trigger
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
34
The ProblemThe Problem
Crossing rate at LHC = 40 MHz
Running at 2.1032 and a 25 nsec bunch spacing expect crossings with interactions at 10 MHz
- of which 200kHz will have bb pairs!
But those useful for CP/CKM physics and having all decay products in the detector is very much less
e.g. For B0 J/()Ks(-) it is 0.02 Hz – or 1 per minute.
For Bs0 it is ~1 per week
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
35
Current LHCb PlanCurrent LHCb Plan
3 Level Trigger3 Level Trigger
Level 0 - reduce rate from 10 Level 0 - reduce rate from 10 Mhz to 1 MhzMhz to 1 Mhz
Pile-up veto, a high pt hadron, electron, muon, photonIncreases b purity from 1% to 3%
Level 1 – reduce rate from 1 Level 1 – reduce rate from 1 Mhz to 40 kHzMhz to 40 kHz
Demand tracks with finite impact parameter and high pt
Divide bandwidth between generic and specific, cuts for special channels, electron, photon, dimuonb-purity now at 9%
High Level trigger – reduce rate High Level trigger – reduce rate from 40 kHz to 200 Hz to tapefrom 40 kHz to 200 Hz to tape
Fast reconstruction, using all detectors except RICH – so far
Bandwidth Division at Level1
To maintain efficiency at this rate, HLT must use tight ‘offline’ type cuts.Efficiency for channels not used to define HLT can be low
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
36
Possible ImprovementPossible Improvement
Keep present philosophy but add a new inclusive stream Keep present philosophy but add a new inclusive stream with simple cuts and a high output ratewith simple cuts and a high output rate
To be based on detection of just a single muon with minimal pt and impact parameter cuts - small modification of level 1 bandwidth
This would beThis would beInclusive - trigger on the ‘other’ bYields tagged eventsRobustUse to reduce/estimate systematic uncertaintiesAccess to states not chosen for HLT optimisation Ks ….Output rate- whatever can be handled - would be 2 – 5 kHz with ~50% events with bb
Under active investigationUnder active investigation - Current 200 Hz stream would - Current 200 Hz stream would be preserved - now Hot Streambe preserved - now Hot StreamInclusive stream to be reconstructed at many sitesInclusive stream to be reconstructed at many sites
Possible futureLevel 1 bandwidth
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
37
The LHCThe LHC
StatusStatusDelays due to problems with the cryolines
Poor quality control by the company charged with installation of work by its sub-contractorsFirst collisions are still scheduled for ‘summer’ 2007Great pressure to maintain this date
ComponentsComponentsAlmost all ontimeCryodipoles, which were a problem now stacking up on the surface waiting for the repair of the cryolines
FPCP04, Daegu, 9 Oct 2004
P J Dornan - Imperial College London
38
SummarySummary
The LHC has great potential to make major advances The LHC has great potential to make major advances in precision CPV b-physicsin precision CPV b-physics
All species of b-hadron state are producedAll species of b-hadron state are producedThousands of events for many important channels Thousands of events for many important channels
with small branching ratios make measurements with small branching ratios make measurements at the few % level possible. at the few % level possible.
ButButThe hadronic environment will be difficultThe hadronic environment will be difficult
still a lot of background - mostly from still a lot of background - mostly from uninteresting b-statesuninteresting b-states
Efficient, well understood triggering will be all Efficient, well understood triggering will be all importantimportant