physics of hadron colliders: lecture 4 – heavy flavors
DESCRIPTION
Physics of Hadron Colliders: Lecture 4 – Heavy Flavors. Joseph Kroll University of Pennsylvania 21 June 2004. Tevatron Makes Progress Every Week. Another Record Store: CDF: 9.0 £ 10 31 cm -2 s -1 D Ø: 7.5 £ 10 31 cm -2 s -1. The Competition for B Physics. KEK. Context. - PowerPoint PPT PresentationTRANSCRIPT
Physics of Hadron Colliders:Lecture 4 – Heavy Flavors
Joseph Kroll
University of Pennsylvania
21 June 2004
21 June 2004 Joseph Kroll University of Pennsylvania 2
Tevatron Makes Progress Every Week
Another Record Store:CDF: 9.0 £ 1031 cm-2s-1
DØ: 7.5 £ 1031 cm-2s-1
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The Competition for B Physics
KEK
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Context
You have all heard this before: “The SM is very successful, but…”
Lecture 3 addressed issues related to EW symmetry breaking
Three of the outstanding issues are1. Electroweak symmetry breaking (why MW,MZ ≠ 0)
- does the Higgs exist?- is there supersymmetry?- if neither, what is the mechanism?
2. The flavor problem- are there 3 & only 3 families?- why masses of fundamental fermions so different?- what set values & hierarchy of flavor parameters (quarks & leptons very different)
3. Violation of CP Symmetry- why does matter dominate antimatter in Universe?- is mechanism in SM correct, is it enough?
Today we will talk about addressing the flavor problem and CP violation
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The Flavor Parameters (CKM Matrix)
mass eigenstates ≠ weak eigen.
weak mass
related by Cabibbo-Kobayashi-Maskawa Matrix
V is unitary: VyV = 1 Measurements + Unitarity assuming 3 generations
PDG: K. Hagiwara et al., Phys. Rev. D66 010001 (2002) Ranges are 90% CL
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Different Parameterizations of CKM Matrix
L. L. Chau, W. Y. Keung Phys. Rev. Lett. 53, p. 1802 (1984) - used by PDG
3 £ 3 complex unitary matrix: 3 real & 1 imag. parameters ≡ 3 angles, 1 phase
notation: cij´ cosij & sij´ sinij, i, j = 1st, 2nd, 3rd generation
Advantages of this parameterization:1. Satisfies unitarity exactly2. If ij= 0, generations i & j decouple3. If 13= 23= 0, 3rd generation decouples, 12 is Cabibbo angle4. Same formulation used for lepton mixing matrix U with (£ diag[ei1/2,ei2/2, 1])
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Wolfenstein Parametrization Illustrates Hierarchy
Original reference: L. Wolfenstein, PRL, 51, p. 1945 (1983)Reference for this slide: A. Höcker et al., Eur. Phys. J. C21, p. 225 (2001); ibid, hep-ph/0406184
valid to O(6) ¼ 0.01%, = Vus = sinCabibbo» 0.2
Define:
from hep-ph/0406184
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New Measurement of Vus from KTeV
1st row of CKM matrix provides the most stringent test of unitarity:
The KTeV Collaboration, T. Alexopoulos et al., hep-ex/0406001 (sub. to PRL) – and references there in
PDG 2002
New results from KTeV These results from measuredKL semileptonic decays:f+(0) is the l form factor at q2=0
Vus = 0.2252 § 0.0008KTeV § 0.0021external
Unitarity now satisfied: 0.0018 § 0.0019
}
}Moral: well measured parameters can change
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The Unitarity Triangles
V is unitarity
geometric representation: triangle in complex plane
Im
ReVi1V*
k1
Vi2V*k2Vi3V*
k3
There are 6 triangles
Kaon UT
Beauty UT
flat
n.b. these triangles arerescaled by one of the sides
i = 1 is previous page
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The Beauty Unitary Triangle
of Chau & Keungparametrization is
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How Do Measurements Constrain Triangle?Figure courtesy of CKM Fitter group: ckmfitter.in2p3.fr – as were all of the formulas on previous slides
B0 flavor oscillations (md)constrains one side
How do B0s oscillations (ms)
fit in this picture?
Why is ms consideredone of the most important Run II measurements?
Aside: a key issue is to pickexperimental quantities thatcan be related to CKM para.without large theory errors
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Neutral Meson Flavor Oscillations
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Neutral B Meson Flavor Oscillations
Flavor oscillations occur through2nd order weak interactions
e.g.
Same diagrams and formula for ms for Bs except replace “d” with “s”
All factors known well except “bag factor” £ “decay constant”
md = 0.489 § 0.008 ps-1 (2%) (PDG 2002) from Lattice QCD calculations – see hep-ph/0406184
From measurement of md derive |V*tbVtd|2
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B Meson Flavor Oscillations (cont)
If we measure ms then we would know the ratio ms/md
Many theoretical quantities cancel in this ratio, we are left with
from Lattice QCD calculations – see hep-ph/0406184
Since Vts ¼ Vcb this gives us our side Rt
This is why ms ishigh priority in Run II
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Current Status of ms
Results from LEP, SLD, CDF I ms > 14.5 ps-1 95% CL
see http://www.slac.stanford.edu/xorg/hfag/osc/winter_2004/index.html
Amplitude method:H-G. Moser, A. Roussarie,NIM A384 p. 491 (1997)
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CP Violation Through Mixing in B Decays
Examples
yields sin2
Weak phase in Vts very small very small SM CP asymmetry
Large asymmetry unambiguousevidence of new physics(B0 ! K0)
must know ms to observe
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B Physics at Hadron Machines
Strong interaction produces bb pairs
Example of lowest order (LO) s2
Example of next leading order (NLO) s3
NLO contribution comparable to LO contributionsee P. Nason, S. Dawson, R. K. EllisNucl. Phys. B273, p. 49 (1988)
called “flavor creation”
“gluon splitting”
“flavor excitation”
b pairs produced close in y
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B Physics at Hadron Machines (cont.)
b quarks then fragment to B hadrons
B factories running on Y(4S) only produce lightest B mesons
Hadron colliders (and e+e- colliders running above Y(4S)) produce other B’s
fragmentation is hard: B hadron gets large fraction of b quark E
Many unique B measurements at hadron colliders
e.g., ms, Bs rare decays, observation Bc, b lifetime
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B Production at Tevatron
The inclusive b cross-section is enormous: on the order of 100b
For L = 1031 cm-2s-1 (1032) £ L = 1kHz (10kHz)
Much of this not useful (trigger, acceptance, analysis selection criteria)The useful cross-section is order 10b
This is still well above production cross-section at B Factories, Z pole
The CDF Collaboration, D. Acosta et al., Phys. Rev. D65, 052005 (2002)
B factory rate: L = 1034 cm-2s-1 £ L = 10 Hz
£ L » 100 Hz
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B Production Tests QCD
Measurement of B production an extremely interesting test of QCDThere is an outstanding disagreement between theory and data
The CDF Collaboration, D. Acosta et al., Phys. Rev. D65, 052005 (2002)
Data factor 2 – 3above theory
Recent theoretical workhas reduced discrepancy:b ! B frag. model
Measurement of production fractions (fd, fu, fs, fbaryon, fB**) interesting tooAlso necessary for absolute branching fractions & other studies
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Characteristics of B Production and Decay
b large, butinelastic » 103 larger
Trigger & analysis strategy:Exploit unique aspectsb production & decay
UA1 showed it was possible:b! X, b! X, b mixing
Then CDF fully reconstructed B
B-! J/ K-, J/!+-
F. Abe et al.,PRL 68, 3403 (1992)
CDF “Run 0”2.6§0.2 pb-1
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Silicon trackingDrift chamber
Lumi monitor
Hadronic Calorimetry
Muon systems
Iron shielding
Solenoid and TOF
ElectromagneticCalorimetry
CDF II
New Front-end elec. & DAQ: 7.6 MHz clock (132 ns)
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Some Key Detector Features for B Physics
• Immersed in 1.4 T axial field; covers R = 0.4 m to 1.4 m; full coverage ||<1• High redundancy drift chamber: 4 axial & 4 stereo (2o) layers – 12 wires each• Particle ID with dE/dx from time over threshold
Central Outer Tracker (COT) Resolution pT/pT = (0.15%) pT (in GeV/c)
Particle separation power from dE/dx
K/ separation > 1.4 for pT>2 GeV e/ separation = 3 for pT=1 GeV
K
e
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Some Key Detector Features for B Physics
Silicon Tracking – 3 separate detectors
1. Layer 00: (single sided) • attached to beampipe • 1.4 to 1.6cm from beam line • axial only2. SVXII: (double sided) • 87 cm length, 12 wedges in azimuth • 5 layer with 3D track reconstruction • axial+small angle stereo or axial+90o • 3 barrels (6 half barrels in trigger) • 2.4 cm inner radius, 10.6 cm outer 3. ISL: (double sided) • 1 layer at 22 cm in ||<1 • 2 layers (20 & 28 cm) 1<||<2 • axial+small angle stereo
Online impact parameter resol.47m best wedges55m average of all wedgesincludes » 30m from beam
SVTonline@ L2
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Time of Flight Detector (TOF)
• 216 Scintillator bars, 2.8 m long, 4 £ 4 cm2
• located @ R=140 cm• read out both ends with fine mesh PMT (operates in 1.4 T B field – gain down ~ 400)• anticipated resolution TOF=100 ps• (limited by photostatistics)
Kaon ID for B physics
Measured quantities:s = distance travelledt = time of flightp = momentum
Derived quantities:v = s/tm = p/v
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CDF II Trigger System
Detector
L1 trigger
L2 trigger
L3 trigger
tape
46 L1buffers
1.7 MHz bunchcrossing rate
30 kHz L1 accept
300 Hz L2 accept
70 Hz L3 accept
Hardware tracking for pT 1.5 GeV
Muon-track matching
Electron-track matching
Missing ET, sum-ET
Silicon tracking for pT>2 GeV
300 CPU’s
Jet finding
Full event reconstruction
Refined electron/muon/photon finding
>100Hz with datacompression
4 L2 buffers
courtesy E. Thomson (OSU/Penn)
(XFT)
(SVT)
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Trigger Strategy for B Physics
Exploit the characteristics of B production and decay
1. B mass relatively large decay products have relatively high pT
require pT > 1.5 – 2.0 GeV/c or larger
2. B decay produces high pT leptons (electron and muon)
B! X, e X & B! J/ X, J/!+-
3. B’s have long decay distance trigger on displaced tracks
B0s
D-s +
-
K-
K+
d0
4. Combine lepton & displaced track
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Example of Specific Trigger for B Physics
Hadronic Path – designed for B0s! D-
s+Level 1 - 2 XFT tracks with pT > 1.5 GeV - opposite charge - < 135o
- |pT1| + |pT2| > 5.5 GeV
Level 2 - confirm L1 requirements - both XFT tracks - SVT 2<15 - 120 m< |d0| <1mm - 2o < < 90o
- Decay length Lxy > 200 m
Level 3 - confirm L2 with COT & SVX “offline” quality track reco.
At Level 3 usingtrigger criteria
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CDF = “Charm Detector @ Fermilab”
Most of that charm is prompt charm, i.e., not from B ! DX
We proved that using the D impact parameter - prompt charm points back to the PV (within resolution) - charm from B do not point to PV
Prompt B ! D
Measure d0 resolution in prompt peakapply to model of B! DX
Prompt fraction: (86.6 § 0.4 (stat.))%Systematic error 3-4%
CDF II, D. Acosta et al., PRL 91, 241804 (2003) & C. Chen (UPenn) Ph. D. Dissertation, fermilab-thesis-2003-14
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CDF II, D. Acosta et al., PRL 91, 241804 (2003) & C. Chen (UPenn) Ph. D. Dissertation, fermilab-thesis-2003-14
Data above theory – much less discrepancy than Run I B cross-section vs. theory
Measurement of Prompt Charm Production
1st PRL fromTevatron in Run II
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CDF II B Cross-section from B! J/ X
Measure (B) down to pT(B) = 0
Use B! J/ X, J/! +-
- Trigger on dimuon - Get clean J/ signal - Use t (Lxy) to separate B from prompt - B fraction varies from 10 – 40%
Agreement with theory has improved - CDF II data consistent with Run I - theory changed - updated parton distribution functions - updated b quark fragmentation
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Experimental Steps for Measuring Bs Mixing
1. Extract B0s signal – decay mode must identify b-flavor at decay (TTT)
Examples:
2. Measure decay time (t) in B rest frame (L = distance travelled) (L00)
3. Determine b-flavor at production “flavor tagging” (TOF)
“unmixed” means production and decay flavor are the same
“mixed” means flavor at production opposite flavor at decay
Flavor tag quantified by dilution D = 1 – 2w, w = mistag probability
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Measuring Bs Mixing (cont.)
4. Measure asymmetry
these formulas assume perfect resolution for t
Asymmetry is conceptual: actually perform likelihood fit to expected“unmixed” and “mixed” distributions
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Comment on : Time Integrated Mixing
is the time integrated mixing probability
In principle, a measurement of determines m - the first Bd mixing measurements were measurements - d = 0.181 § 0.004 (PDG 2002) - this does not work for Bs: s = 0.5 (the limit as x!1)
A measurement of
is very interesting
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Example of Bs Oscillations
Example of Asymmetrywith lots of statisticsms = 20 ps-1
Illustrated are - tagging reduces statistics dilution reduces amplitude - decay length resolution damps amplitude further - momentum uncertainty damps amplitude more as decay time t increases
Large ms: Bs! Ds l no goodneed fully reconstructed decayse.g., Bs! Ds
Figures courtesy M. Jones (Penn/Purdue)
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B+, Bd, Bs Signals I. K. Furic Ph. D. Dissertation MIT (2004)
We see signals with good S/B:rate is about 1/10th expected
Results of this analysis
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Common B Meson Selection Criteria
slide courtesy of I. K. Furic (MIT/EFI Chicago)
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Background Dominated by Heavy Flavor
Peaked structure in B+ background is due to D* polarization
Extensive simulation required to study complex background shape
Very little of the reflections/partially reconstructed decays leak into signal
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What About Measuring B Lifetimes?
Lifetime bias from trigger complicates lifetime measurement in B ! D
Must solve this problem eventually for the Bs mixing analysis – in progress
Have measured lifetimes in B! J/ K (dimuon trigger – no bias)Fit mass and lifetime distribution simultaneously
Example: B+! J/ K+ B+ = 1.662 § 0.033 (stat) § 0.008 (syst) ps
240 pb-1
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Bs! J/ 240 pb-1
Decay interesting for CP Violationand search for new physics
CP analysis requires knowingCP composition (% even)
Preliminary tranversity analysisindicates predominantly CP evenin agreement with Bd! J/ K*
K. Anikeev, MIT, Ph. D. Thesis, in preparation
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B Flavor Tagging
We quantify performance with efficiency and dilution D
= fraction of signal with flavor tag
D = 1-2w, w = probability that tag is incorrect (mistag)
Statistical error A on asymmetry A (N is number of signal)
statistical error scales with D2
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Some More Detail
Aside:Total D2 ¼ 30%at the B factories
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Two Types of Flavor Tags
Opposite side
Same side Based on fragmentation tracks or B**
+ Applicable to both B0 and B0s
− other b not always in the acceptance
− Results for B+ and B0 not applicable to B0s
+ better acceptance for frag. tracks than opp. side b
Reminder: for limit on ms must know D
Produce bb pairs: find 2nd b, determine flavor,infer flavor of 1st b
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Types of Opposite Side Flavor Tags
Lepton tags
Jet charge tag
Kaon tag
mistags from
Run II: for muons: D2 = (0.66 § 0.19)%
jet from b (b) has negative (positive) charge on average
Run II:D2 = (0.419 § 0.024)%
expect comparable for elec.
low high D
high low D
Largest D2 @ B factories Run II: no useful tag yet(have seen D, too low)
TOF
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Performance of OST’s is Poor – Why?
Part of the problem is acceptance of opposite side b
Generator Level study from K. Lannon, Ph. D. Dissertation, Illinois, 2003
Also opposite-sideB hadron can mix:D = 1 – 2 = 0.76
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Same Side Flavor Tags
Based on correlation betweencharge of fragmentation particleand flavor of b in B meson
Decay of P-wave mesonsB** also contributesto B0, B+ (not B0
s)
Expected correlationsdifferent for B+, B0, B0
sTOF
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Results on Same Side Flavor Tag
Select track in R = 0.7 around Bwith minimum pT(rel) wrt B + track
Apply to B0! J/ K*0, D-+
Run II: measure D and md simultaneously
Find = 66.0 § 0.6 D = 12.4 § 3.3 D2 = 1.0 § 0.5 (all in %, stat error only)
md = 0.55 § 0.10
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Run I: Understood SST Well
MC explained D+ vs. D0
Data vs.Tuned MCExcellentAgreement
We have to use MC for D of SSKT for limit
F. Abe et al.,PRD 58, 032001 (1999)
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Summary: Bs Flavor Oscillations
We have a long way to go - rates are far below expectations - tagging is far below expectations - lifetime resolution not as good as expected – not as critical yet
BUT we are making progress and there is plenty of reason to be optimisticThe potential significance of a measurementcan be estimated using the following formula
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Acknowledgements
Thanks to organizer Xin Wu (Geneva) & to co-lecturer Paris Sphicas (Athens)
Special thanks to Marjorie Shapiro (Berkeley) for a copy of her 1999 CERNAcademic Lectures & to Evelyn Thomson (OSU/Penn) for discussions onTevatron top physics
Many of my colleagues in CDF provided information including Konstantin Anikeev (MIT),David Ambrose (Penn), Chunhui Chen (Maryland), Frank Chlebana (FNAL), Nathan Eddy (FNAL), Stefano Giagu (INFN-Roma), Chris Hays (Duke),Beate Heinemann (Liverpool), Matt Herndon (JHU), Joey Huston (MSU),Jaco Konigsberg (Florida), Ashutosh Kotwal (Duke), Stephanie Menzemer (MIT),Rolf Oldeman (INFN-Roma), Manfred Paulini (CMU), Kevin Pitts (Illinois),Sal Rappoccio (Harvard), Marco Rescigno (INFN-Roma), Rob Roser (FNAL),Rick Snider (FNAL), Brian Winer (OSU), Peter Wittich (Penn), Kohei Yorita (Waseda)
also Paul Derwent (FNAL), Jens Erler (UNAM), Paul Keener (Penn), Paul Langacker (Penn), Michelangelo Mangano (CERN), Jackie Mileski (Penn), Ron Moore (FNAL), Mary Scott Thomas (Penn)
Finally, special thanks to my wife Monica Kroll for her support