Bottom Quark and Jy Production at CDF

1
Bottom Quark and J/yProduction at CDF

• Thomas J. LeCompte
• High Energy Physics DivisionArgonne National
  Laboratory
• For the CDF Collaboration

2
Outline

• Experimental Outline
• Theoretical Ramblings
• A Digression
• The Data
• More theoretical ramblings
• A Second Digression
• More Data
• Going too fast through the last 10 or 15 slides

• Theoretical Outline
• Theoretical motivation early ideas on
  quarkonium production
• Description of the Experiment
• Measuring Inclusive J/y production
• Theoretical motivation for measuring the b
  cross-section
• Measurements at lower energy
• Measuring J/ys from b quark decays
• Theoretical Post-dictions
• New Charmonium Results on the X(3872)
• Summary

3
An Introduction To Charmonium
Charmonium is a bound stateof a charmed quark
andantiquark. It is almost nonrelativistic b
0.4 Hence the hydrogen atom-likespectrum
threshold
3.8 GeV
y(2S) or y
3S1
3P2
c2
c1
3P1
Only the most important(experimentally)
statesare shown. Many morewith different
quantum numbers exist.
Mass
3P0
c0
J/y
States can make radiative (E1) transitions to
the other column.
3S1
3 GeV
4
Review Quantum Numbers
Spin Angular Momentum
Means Quark Spin1 (3 2 x 1 1) Quark
Orbital Ang. Mom. 0 Total J/y Spin 1
Orbital Angular Momentum
Means Total J/y Spin 1 Parity is Odd
Charge Conjugation is Odd
Total Angular Momentum
5
Early Thinking on J/ys

• The direct production rate should be tiny
• If J/y ? gg is forbidden, so is gg ? J/y
• Hadroproduction through cs (followed by c ? J/y
  g) would be allowed
• This is the dominant source of J/ys.
• The y(2S) rate should be really, really tiny
• it cant come from c decay
• All y(2S) must be from the decay b ? y(2S) X

• The J/y is extremely narrow about 87 keV Why?
• Consider the possible strong decays
• Open charm? Nope kinematically blocked
• Light quarks? Not directly the J/y doesnt
  contain any
• Two gluons? No
• Reason 1 Quantum Mechanics (Yang-Landau Theorem)
  a spin-odd particle cannot decay to two
  identical massless spin-1 particles
• Reason 2 Violates charge conjugation symmetry
• Three gluons? Allowed, but suppressed
• In fact, electromagnetic decays compete with the
  strong decays!
• About 30 of the decays are electromagnetic/radiat
  ive

Color Singlet Model
OZI Rule
6
Why this is utter nonsense

• Theoretically
• The same Yang-Landau Theorem prevents c1
  production via gg interactions but that didnt
  seem to bother anybody

• Experimentally
• At fixed target energies, there is roughly the
  same ratio N(y(2S))/N(J/y) as at colliders
• This is true even at fixed target energies below
  b threshold!
• At all energies, roughly 40 (not 100) of J/ys
  come from c decays

We should have known better. This model should
have beendead on arrival it was only the
absence of alternatives that keptit going as
long as it did.
The field was in denial.
7
How Bad Was This Model?
CDF Data (20 pb-1) publishedin PRL79, 572 (1997)

• J/y is a factor 10 higher than predictions
• Thats less bad by comparison
• y(2S) is a factor 100 higher than predictions

Even astronomers wouldcall this disagreement!
8
The Color Octet Model

• Its fairly clear that the CSM is missing some
  source of J/ys
• By the rate, it appears to be the dominant source
• Consider the addition of two SU(3) (color) octets
• 88 1 8 8 10 10bar 27
• This allows 88 8 i.e. two gluons can be in a
  color octet state
• This is analogous to the three-gluon vertex
• Think of this as a two-step process
• 1. The charm-anticharm pair is produced in a
  color octet state
• 2. The octet state radiates a gluon, and becomes
  colorless

This gets us our third gluon painlessly.Instead
of ggg ? J/y, we have gg ? J/y g
This is analogous to c production instead of a
singlet c radiating a photonthere is an octet
c radiating a gluon.
The J/y
Other octet states also contribute
9
No Free Lunch

• The Color Octet Model gives us a third gluon for
  free
• Because its soft, there is little penalty for an
  extra power of as
• For exactly the same reason, the matrix element
  for the coupling between the octet c-cbar and the
  J/y gluon is non-perturbative
• It must be fit from experiment
• All is not lost
• There are only a small number of non-perturbative
  parameters
• While they have to be fit from experiment, they
  have to be consistent across different
  measurements
• There is at least one other prediction J/ys
  show a large spin-alignment at large pT

Strictly speaking, the COM accommodates a
largecross section it doesnt predict it.
10
Fitting COM Parameters
A consistent set of COM parameters can predict
reproduceboth the measured J/y and y(2S)
cross-sectionsA major success of the model!
11
Theoretical Summary Experimental Strategy

• Color singlet prediction of 3S1 charmonium
  production is low by orders of magnitude
• Other models can explain this, but not really
  predict it
• Collider measurements see only the top 6 or so
  (in pT) of the cross-section
• NLO production of bottom quarks is also low by a
  factor of 2 or 3
• More details on this later in the talk
• A substantial (10-20) source of J/ys is from b
  decay
• Collider measurements see only the top 10 or so
  (in pT) of the cross-section
• Experimental plan measure both cross-sections at
  ALL pTs using the decay J/y ? mm
• This will settle the issue of the b
  cross-sections
• Experiment will be ahead of theory for the J/y
  and y(2S).

12
The CDF Detector All you need to know
Central Muon (CMU) detectors2304 wire chambers
Central Calorimeter For this analysis, its
used as passive steel, lead and plastic absorbers
(4.7l)
Open cell tracker wire Chamber in 1.5T
magneticfield (COT)
Silicon vertex detector (SVX) five layers
for Precision track measurement
Beams-eye view of CDF
13
The CDF DetectorMore Than You Need To Know
Silicon Vertex Detector being installed
CDF rolling into the collision hall
(uphill both ways)
14
Triggering in Words

• Triggering is the key to hadron collider physics
• You cant analyze an event you didnt trigger on
  (and thus record)
• Collision rate (when this data was taken) is 106
  Hz
• Event recording rate is 100 Hz
• Need to reject 99.99 of events
• CDF Uses a 3 Level Trigger
• Level 1
• Identify muon stubs (short tracks in the muon
  chambers)
• Identify tracks in the transverse plane in the
  COT tracker with the XFT
• XFT eXtremely Fast Tracker
• Level 2
• At the time this data was taken, Level 2 was in
  auto-accept mode for muons
• Level 3
• A fast version of offline reconstruction is done
• Tracks are required to have a good r-f match to
  the stubs
• Tracks are required to have a coarse r-z match to
  the stubs
• We dont match east-going muons with west-going
  tracks
• Certain kinematic cuts are made

15
Triggering In Pictures
Two stubs in the muon chambers
Two tracks in the XFTpT 1.5 GeV
Level 1
A good match between them (nominally 5 degrees)
Mass between 2.6-4.0 GeVOpposite chargeGood
match in r-f planeFair match in r-z plane
Level 3
(This event cant really be a J/y its shown
for illustrative purposes only)
16
Measuring the Cross-Section

• Ingredients
• Number of J/ys
• Integrated Luminosity
• Detector Acceptance
• Detector Trigger Efficiency
• Product of several sub-efficiencies Level-1
  trigger, Level-3 trigger, tracking and muon
  reconstruction

I will attack the denominator first
17
Luminosity

• We used 39.7 2.7 pb-1 of data in this
  measurement
• At the time we started, this was the largest
  single contiguous chunk of data with common
  trigger conditions (February-October 2002)
• Even this is broken into two pieces
• 24 pb-1 taken with Df(mm) trigger
• Kills low pT J/ys (oops!)
• 15 pb-1 taken with this cut removed
• Uncertainty is due to uncertainties at every step
  of the chain
• Connecting our luminosity counter response to the
  total inelastic cross-section
• Connecting the total inelastic cross-section to
  the total elastic cross-section (strictly
  speaking, the imaginary part of the forward
  scattering amplitude)
• Connecting the total elastic cross-section to the
  QED Coloumb part of the elastic cross-section,
  which is calculable
• Theoretical extrapolation between 1800 GeV (where
  many of the measurements have been taken) and
  1960 GeV (the Run II energy)
• After all this, 5.9 is what we end up with

18
Level 1 Trigger Efficiency

• We also have a one-muon trigger with somewhat
  different requirements than the dimuon trigger
• J/y events that pass this trigger have an
  unbiased second leg
• We see how often this second leg does pass the
  trigger vs. pT
• Note that this efficiency is for events that pass
  all subsequent analysis cuts

19
Other Efficiencies

• The Level 3 and online muon reconstruction code
  is identical so the efficiencies are 100
  correlated
• Inefficiencies vary with pT and average 1.4
  1.0
• Inefficiencies are due to events failing the
  tight (3s) track-stub matching
• Failing muons either
• have an early wide-angle scatter as the enter the
  absorber
• scatter more often than typical muons
• Efficiency is determined by relaxing this
  requirement and counting the J/ys that have one
  leg fail
• Offline Tracking Efficiency
• Measured by embedding Monte Carlo tracks in data
  events and extracting them again
• Efficiency is 99.6 (0.4, -0.9)
• Results are consistent with W ? en events that
  come in on a trackless trigger
• The Level 3 Tracking efficiency is measured like
  the L1 efficiency
• One unbiased leg
• Efficiency is 99.7 0.1 0.2

20
Acceptance Calculation

• Use a Monte Carlo with just the J/y tracks
• Any confusion with the rest of the event has been
  taken out already in the tracking efficiency
• Apply the same geometric requirements to the MC
  as in the data
• Dead region near z0 in the central tracker
  excluded
• Inefficient muon wedge (HV problems with field
  shaping) excluded
• Minor trigger error with one trigger card modeled
  and included

21
Is that bump at low pT real?
high pT
zero pT
The threshold for a muon to penetrate the
steel is 1.44 GeV, and the threshold to pass the
triggeris 1.5 GeV both close to ½ the J/y
mass.
At rest, both muons are above threshold. At high
pT, both muons are above threshold. With just a
little boost, though, one muon is usually below
threshold and ranges out.
low pT
22
Acceptance vs. rapidity

• Our acceptance in rapidity is driven by the
  length of the muon chambers ( 0.6 units)
• There is almost no correlation between acceptance
  in pT and in y.
• We calculate the acceptance in 2-D bins of pT and
  y anyway.

23
Acceptance vs. J/y polarization

• J/ys are always produced unpolarized ( 0)
• They can, however, have alignment or tensor
  polarization
• i.e. the density matrix is not equally populated
• ( 0)
• Gives a 1a cos2(q) distribution
• Symmetry of the J/y decay is a function of q, so
  alignment affects the acceptance
• Affects when the softer muon ranges out
• We use a 0.15 0.3
• Mix of prompt and bottom J/ys
• This corresponds to a 5-10 effect on the
  acceptance

Run I Data
24
J/y Signal
We have hundreds of thousands of events we will
not be statisticslimited except at the very
highestpT bins.
Raw pT spectrum
25
J/y yield in selected pT bins
12 pT 5.0 Yield is fit in each bin, corrected for
acceptance and efficiency,and the cross-section
bin-by-bin is calculated.There is very little
feeddown from bin to bin (because the resolution
is good and our bins are narrow) but we do
correct for it.
26
Systematic Uncertainties
The pT dependentterms tend to belargest at very
smalltransverse momenta The first few bins.
pT dependent
pT independent
Combined about 7 systematic uncertainty
27
The J/y Cross-Section
(for y 28
The J/y cross-sectionin terms of pT2
Results are in excellent agreement with Run I,
where there is overlap (pT 4 GeV) (both in
normalization and shape)
29
Turning to b production
But First, A Little History
Sherman, set the Wayback Machine for 1989.
30
Ancient History The Stone Age (1989)

• P. Nason, S. Dawson and R.K. Ellis calculated the
  heavy flavor cross-section and found it to be in
  agreement with UA1 measurements at 630 GeV.
• See Nucl. Phys. B327, 49

31
Understanding the x-axispT(min)

• Ideally, one would like to measure the
  differential cross-section ds/dpT.
• Allows comparison with theory in magnitude and
  shape of the cross-section.
• If this is difficult, one could quote just the
  total cross-section.
• Many experiments are insensitive to the
  cross-section below a pT threshold.
• It makes no sense to quote the total
  cross-section if you have no acceptance to
  anything below (e.g.) 10 GeV, where the bulk of
  the cross-section is.
• To deal with this, experiments quote the
  cross-section at a certain pT(min) the point
  where 90 of the bs lie above.
• This 90 is pure convention we could have
  picked some other number
• We had to pick something, so we follow the UA1
  convention

32
Ancient HistoryThe Bronze Age (1992)

• At DPF92, CDF reported bottom quark
  cross-sections a factor of at least two greater
  than theory.
• This was at a center of mass energy of 1800 GeV.

33
A Jump Ahead to 1997

• More recent CDF measurements show the same
  difficulty the theory underpredicts the data by
  the same factor
• This problem is not going away
• Note that we measure only the high pT tail of the
  cross-section
• Most bs were invisible to us.

34
Commentary on measuring the top 10 of something
Just how important could the other 90 be anyway?
35
Questions one might ask

• Is the cross-section rising with center-of-mass
  energy faster than we expect?
• If we take the measurements at face value, thats
  what we would conclude
• Not a completely crazy idea
• the NLO contributions are larger at 1800 GeV than
  630 GeV
• The scale dependence of the calculation is worse
  at NLO than LO
• This is due to a numerical accident, but was not
  widely known at this time
• Large NNLO contributions might produce additional
  growth with center-of-mass energy
• Did (at least) one experiment get the measurement
  wrong?
• Is something wrong with our theoretical models?
• Extra b sources? (ANL group)
• Fragmentation? (P. Nason et al.)
• Is there anything we can do to put the
  experimental result on a more solid footing?

36
The Enlightenment (1995-6)

• In the winter of 1995-6, we ran for 9 days at 630
  GeV to address this question.
• We estimated 50 to 100 bs at the lower energy,
  depending on whether this factor of 2 was real or
  not.
• Not many, but enough to measure a factor of 2
• At the same time, we could collect jets and
  photons and do other QCD measurements
• Several Ph.D. theses have resulted from these
  measurements, and they were important in
  untangling the high ET jet excess
• Eleven papers were published by CDF and D0 based
  on this data
• This run was proposed and largely executed by 6
  people

37
The Dark Ages 1995-2000 The Renaissance
2001-2002

• Work beyond the preliminary stages stopped the
  CDF upgrade expanded to consume all available
  time
• 4 Lehman reviews
• 3.6 million dollars
• 15 change requests
• innumerable monthly reports
• Yellowing scintillator
• Not yellow like Coors beer
• Yellow like a lemon
• shady vendors
• squabbling collaborators
• Only when the upgrade was behind us did this
  start moving again see Phys.Rev.D66032002,2002

And this was just the muon upgrade!
38
The Measurement Some Key Ideas

• We measure a ratio of cross-sections because it
  is both theoretically better determined and
  experimentally more certain
• Theory uncertainty is 10-15 rather than a factor
  of 2 or more
• This measurement is statistically limited by the
  number of bottom events collected at 630 GeV
• Complications to improve understanding of other
  aspects like acceptance or efficiency will make a
  minimal impact on the final answer
• We took pains to make the 1800 GeV sample as
  similar to the 630 GeV sample as possible.
• We rejected larger samples with more differences
  for example, we could have used a sample that
  used an earlier version of our silicon detector,
  but we didnt.
• Every event is taken within 3 weeks of the 630
  GeV run
• Much of this sample is taken from the period at
  1800 GeV where we tested the 630 GeV trigger
  table

39
Luminosity and Datasets

• Run I CDF used a three tier trigger. For this
  analysis, we required
• Level 1 a 6 GeV muon stub in the central muon
  chambers, plus at least 2 hits in the
  corresponding outer chamber
• Level 2 that stub matched to a 4.7 GeV r-f track
• Level 3 a 4.5 GeV muon with good matching to
  both the inner and outer muon chambers
• Offline, we required
• A 5 GeV muon with a good match between the track
  and the muon stub
• These are the same requirements for both 630 and
  1800 GeV
• Integrated luminosity
• At 1800 GeV 1932 nb-1
• At 630 GeV 582 nb-1

40
Finding Beautiful Hadrons

• Start with a beautiful muon
• I will spare you the details
• Find all the tracks with pT above 1 GeV and m(mh)
  
• Select the highest pT track
• Find the vertex of that track and the muon
• Perform quality cuts
• Again, Ill spare you the details
• Count the excess of events with the vertex
  forward of the interaction point vs. behind the
  interaction point

hadron
m
muon
The Goldilocks Principle Inclusive semileptonic
decays are too impure. Exclusive decays are too
rare. These are just right.
Lxy
Interaction Point
41
Counting bs at 1800 GeV

• 3083 events ahead of the primary vertex (by at
  least 250 mm)
• 1527 events behind
• Yield is 1556 68 bottom events
• Lifetime (as a check) is 1.4 0.1ps

42
Counting bs at 630 GeV

• 383 events ahead of the primary vertex (by at
  least 250 mm)
• 200 events behind
• Yield is 183 24
• You dont get many bs in a short, low energy run
  
• Lifetime is 1.4 0.3 ps

43
Cross-Section Ratio

• We can put it all together to find the
  cross-section ratio
• Comparison with NDE predictions and MRS-A parton
  densities is good
• Other PDFs (MRSA, CTEQ 6M) give essentially the
  same prediction

44
Comparison with UA1

• We take the CDF measured b cross-section at 1800
  GeV, multiply it by the derived ratio, and place
  the cross-section obtained on the UA1 plot.
• It shows
• We are a factor of 2 higher than NLO QCD
• How could it be otherwise?
• We have smaller error bars than UA1
• This is the best single measurement of the b
  cross section at these energies!

45
Summary of 630 GeV Run

• CDF is marginally consistent with UA1
• Reject UA1 at 90 confidence level
• Fail to reject UA1 at 95 confidence level
• The CDF central value is above theoretical
  predictions by a similar factor at 630 GeV as at
  1800 GeV
• There is no indication as to why this is
• But we can exclude the cross section growing with
  center of mass energy
• Precision measurements are possible in heavy
  flavor production experiments
• Uncertainties of 15, not factors of 2
• Its a heckuva lot of fun to propose and run your
  own small experiment
• And 11 papers out of 9 days of running is not too
  shabby

46
Back to 1960 GeVThe b cross-section using J/ys

• Basic strategy
• We know the J/y cross-section
• We know the branching fraction of bs to J/ys
  (about 1.1)
• If we can measure the fraction of J/ys from bs,
  were one multiplication and one division away
  from the b quark cross-section
• Lifetime is the key
• B hadrons live 1.5 ps
• We can use the SVX (silicon vertex detector) to
  identify J/ys that were not produced at the
  primary vertex these must be from b decay.
• Complications
• The most probable decay time is zero some bs
  are identified as non-bs
• Our measurement is not perfect some non-bs are
  identified as bs.
• Slowly moving b hadrons dont get very far before
  they decay
• Separation power is poor at low pT

47
Two acceptance complications

• For us to separate prompt and non-prompt bs
  accurately, we need to impose tight silicon
  requirements
• No more than one hit missed
• At least three hits
• Avoid bad regions e.g. crossing silicon
  barrels
• Since we have some dead silicon ladders, these
  requirements may sculpt the acceptance (only
  about 1 in 3 J/ys have both muons pass these
  criteria)
• Events where we can measure the b fraction may
  not be representative of unbiased J/ys.
• We checked this, and the acceptance ratio (good
  silicon/total) is flat in pT(J/y)
• The spin alignment parameter a is different for
  bs and inclusive J/ys
• This means the acceptance is different
• We have to (and do) correct for this its a 10
  effect
• For prompt J/ys we use our Run I measurement
• For bs, we take the (better more recent) BaBar
  measurement and boost into our frame
• This is not entirely trivial, since BaBar
  measures this in the U(4S) frame
• a(BaBar) -0.09 0.10

48
Choice of Separation Variable

• Variables of Interest
• Rxy
• The transverse flight distance
• Has the best separation power
• Lxy
• The transverse flight distance dotted into the
  unit y momentum vector
• Differs from Rxy by cos(q)
• A signed quantity
• Pseudo-ct
• Lxy boosted to B rest frame based on average
  boost derived from MC
• Differs from Lxy by a known multiplicative
  constant
• ct
• The true B lifetime
• Differs from Rxy by an unknown multiplicative
  constant

We use Lxy/pT we trade statisticalseparation
power for better control over systematics. The
/pTcorrects for the Lorentz boost
49
A word on b decay kinematics

• Above 2 GeV, is proportional to
• Below 1.5 GeV, is more or less constant
• This is because is driven largely by the
  b decay kinematics, not by the b production
  dynamics
• The distribution looks like this as well
  (it has to)
• The distribution looks qualitatively like
  this
• Once we get to J/ys of pT are probing bs down to pTs of 0.

50
Fitting the B fraction

• Prompt component
• Resolution function is determined from the
  zero-lifetime component
• Double-Gaussian with some small tails at large
  negative lifetime
• B component
• Exponential convolved with the resolution
  function determined from the prompt component
• Sidebands
• We assume the background under the J/y mass peak
  is modeled by the weighted average of the
  sidebands
• Note that there are Bs (double semileptonic
  decays) in the sidebands

51
Fitting bin-by-bin
1.25 5.0 10 14.3 0.5 bs
27.9 1.0 bs
9.7 1.0 bs
52
Table of Systematic Uncertainties
pT dependent
pT independent
Again, the systematics are largest in the low pT
bins
53
The Fraction of J/ys from bs

• The trend is clear
• High transverse momentum means a larger beauty
  component
• Flattening out at low pT is because the J/y pT
  is dominated by B decay kinematics, not pT(B)

54
Why is our lowest bin at 1.25 GeV?

• The fit has problems converging down here
• Its bitten by four factors at once
• The b fraction is small about 9
• The J/y acceptance (and therefore yield) is small
• At 1 GeV, acceptance is 20 of what it is at 2
  GeV
• The variable Lxy (Rxy cos(q) ) loses separation
  power
• Not because the flight distance is small
• Because the J/y flight direction is no longer
  aligned along the b flight direction
• Bs are being miscategorized as prompt
• The sideband subtraction becomes less certain
• We lose the left sideband
• However, we have already reached pT(b) 0 at
  1.25 GeV
• Pushing lower improves the precision of our
  measurement, but
• it does not improve the pT reach!

55
The J/y-from-b Cross-section
We almost get to the turnover at low pT.
This is what we considerthe primary
measurementand should be used tocompare with
theory points are uncorrelated
Approximately 80of the cross-sectionis
measured.
56
Unfolding the Spectrum

• We know the region of J/y pT will be populated by
  a B of a given pT
• From Monte Carlo
• Nothing mysterious this is the measured (CLEO,
  BaBar, Belle) pT distribution plus a Lorentz
  boost
• We can use this to find the parent B-hadron
  spectrum that gives rise to the measured J/y
  spectrum
• We use an iterative method
• Process converges after 2-3 passes. We use 10
  passes.
• The bins in the B-hadron spectrum will be
  correlated.

57
The B-hadron Cross-Section
58
and in terms of pT2
Note that even at pT 0the deconvolution
resultis free of artifacts.
59
Does this Agree with Run I?

• The J/y inclusive cross-section matches to within
  a few percent where we have overlap (pT 5 GeV)
• Run I 17.4 0.1 2.7 nb
• Run II 16.88 0.12 2 nb
• The b fraction is the same to within a few
  percent
• We can put in and take out the appropriate
  branching fractions, and convert this to a B
  cross-section
• Run IA 2.7 0.6 nb
• Run 1B 3.6 0.6 nb

This measurement 2.75 0.20 nb
One would expect from center of mass energy the
cross-section to be 10 higher than Run I. Its
15 lower (but consistent within uncertainties)
60
More on Run I Comparisons
B cross-section
J/y cross-section
One would expect from center of mass energy the
cross-section to be 10 higher than Run I. Its
15 lower (but consistent within uncertainties)
61
The Total Cross-Section

• We can correct this to s(b)
• Remove the 5.88 J/y branching fraction to mu
  pairs
• Remove the 1.16 b-hadron (inclusive) branching
  fraction to J/y X
• Correct to 1.0 units of rapidity vs. 0.6
• Divide by two to get the single flavor b
  cross-section

NLO QCD predicts 20-40 mb
62
What Does this All Mean?

• Experimentally
• The high pT 10 or so of the b cross-section
  agrees with past measurements a factor of 2-3
  above theory
• The total cross-section agrees with theory
• Conclusion the pT spectrum is stiffer (shifted
  to higher transverse momenta) than predicted
• Theoretically
• Theory is a fixed order calculation (NLO)
• At LO, you have only 2 ? 2 processes
• At NLO, you add gluon radiation to those 2 ? 2
  processes
• Simplistic model one b gets its transverse
  momentum increased, the other one gets its
  transverse momentum decreased. Because there is
  a steeply falling spectrum, this produces a net
  stiffening of the spectrum.
• At NLO, you also add new processes gluon
  splitting, flavor excitation
• These processes double the cross-section
• The stiffening effect in the 2 ? 2 processes
  doesnt kick in until NNLO
• It may not be crazy to think that the spectrum
  predicted at NLO will be softer than that
  predicted by NNLO

63
Detailed comparison with theory

• Agreement with modern theory is substantially
  better
• No more factor of 2
• Experimental uncertainties are now 3x smaller
  than theoretical uncertainties

Theory Cacciari, Frixione, Mangano, Nason
Ridolfi hep-ph/0312132
64
Theoretical Developments

• PDFs have changed
• About a 20 effect
• Calculations now available to NLL
• About a 20 effect
• Fragmentation functions have changed
• remember, pQCD predicts quark production, but
  experiments measure hadron production
• Fragmentation cannot change the total cross
  section, but does change the spectrum
• About a 20-50 effect

From M. Mangano
All these pull in the same direction, so the
agreement is now substantially better than in the
past.
65
The Joy of X X(3872)

• At Lepton-Photon 2003, Belle announced a new
  charmonium state seen in B decays
• You dont get a new charmonium state every day
• Much less an unpredicted one!

Blow-up of right-hand peak
66
More Joy of X

• With a speed uncharacteristic of hadron
  colliders, both CDF and D0 confirmed this
  particle
• Also, they identified that it is produced both
  promptly and in B decays

D0
67
What is the cause of all the X-Citement?

• Charmonium?
• It has to have the right quantum numbers to decay
  to Ypp and
• It has to have the wrong quantum numbers to decay
  to a pair of D-mesons
• Some Options are
• hc (1P1) mass too low should be near the
  center of mass of the cs, or 3525 GeV
• First radial excitation hc 1P1(2P) okay, so
  where is the regular hc then?
• Y2 (3D2) potential models predict this around
  3790 MeV
• Why the peak in the wrong spot?
• Should also decay to c1 g not observed
• Prediction exists for the m(pp) spectrum
  agreement not great
• h3c (1F3) potential models predict this around
  4000 MeV
• Again, why is the peak in the wrong spot?
• No quantitative prediction exists for the m(pp)
  spectrum, but since the two pions are in a
  relative l 2 state, the centrifugal barrier
  will favor a large m(pp).

68
Dipion Mass X-perimental Results
Belle
Belle
Belles measurement of m(pp) is peaked at large
mass. CDF confirms this qualitatively.
Belle shows the dipion mass distribution to be
peaked at high m(pp) for the y(2S).This was
explained by Brown and Cahn (1975) as a
consequence of chiral symmetry.I find the
paper somewhat difficult to follow by
theorists, for theorists.
Obscure and under-noticed m(pp) prediction by
Yan.Note the D-wave is not so prominent at high
mass.
69
X-otic possibilities

• No charmonium states seem to match the data
• If its charmonium, theres something we dont
  understand also going on
• This may be related to the states proximity to
  DD threshold
• Could this be a bound state of a D and an
  anti-D?
• Naturally explains the mass just under
  threshold
• We know hadrons bind were made of bound
  hadrons!
• Not only are there nuclei in QCD, there are
  hypernuclei
• The high m(pp) may be from the decay y r
• But watch out the kinematics are such that any
  high mass enhancement looks like a r
• There may be precedent with a kaon anti-kaon
  bound state in the f0(980) and its isotriplet
  partner the a0(980)
• These are 0 states that fit poorly into the
  meson nonet
• The f0 is narrow on the low mass side, where it
  decays to pp, but wide on the high mass side,
  where it decays to KK
• Other, more advanced arguments c.f. Jaffe and
  Weinstein
• Expected quantum numbers 1

A new kind ofstrongly interacting matter?
Hot Off The Presses angular distributions from
CDF the acceptable fits are 1 and 2-
70
Summary

• We have a measurement of the J/y cross-section at
  all pT
• The cross-sections violently contradict the Color
  Singlet Model
• The cross-sections are self-consistent with the
  Color Octet Model
• The spin-alignment data agrees poorly with the
  COM
• This measurement is being repeated with the
  larger Run II dataset
• At DPF92, it was asked why is CDFs b
  cross-section so high?
• Twelve years later we have an answer It isnt
  just the high pT tail is high
• Theory now explains the data quantitatively at
  both 630 and 1800 GeV
• 30 years after its discovery, charmonium still
  has the potential to surprise us what is this
  X?
• D-D molecule seems to fit many of the observed
  properties

71
Backup Slides
72
J/y Spin Alignment, Run I vs. Run II
Agreement between Run I and Run II is poor, and
not well understood. Agreement between flipped
sign Run I and Run II is better, but still not
good.
73
Accelerator Operations at 630 GeV

• The Good News the Tevatron had to operate at 630
  GeV to get to 1800 GeV
• The Bad News Tevatron collisions at 630 GeV had
  not been attempted before.
• Recall the Luminosity Equation

74
Going to 630 GeV

• e e(normalized)/6pg
• The Luminosity drops by a factor 630/1800 0.35
• We have a choice with b
• We can either run the focusing magnets at their
  nominal current
• That keeps b the same.
• That requires more beam tuning, since its a new
  Tevatron lattice
• Or we can keep the accelerator lattice the same
  by running them at 35 of their nominal current
• This lowers b to 0.35 of its nominal
• But it keeps the operating point the same
  machine comes on faster
• We chose this deliberately (however, there is
  some evidence things were better than this)
• The net effect is a factor of 10 loss in
  luminosity

75
Implications

• The luminosity is an order of magnitude lower at
  630 GeV.
• 9 days at 630 GeV 1 day at 1800 GeV
• The cross-section is a factor of 6 lower at 630
  GeV
• So now we have an equivalent of four hours worth
  of 1800 GeV data
• We need to grab every b decay that we can

76
The CDF Detector
This analysis uses only trackingand central muon
detectors
77
Events Behind the Primary Vertex

• When we subtract the events behind the primary,
  we are subtracting mostly background, but
  possibly some signal.
• What happens if a real b hadron gets
  reconstructed behind the primary vertex?
• So long as the fraction of times when this
  happens is the same at both energies, the ratio
  measurement is unaffected
• Several Monte Carlos were run
• All show that this ratio to be small (few )
• There is some variation between MCs on this
  exact number
• All show this effect to be the same at both
  energies
• It turns out that if you dont even try to
  subtract the background, the result changes by
  less than ½ s
• We could have done this analysis from trigger
  rates
• (But we didnt know this until after we did the
  work)
• Because of all of this, we believe this is not a
  problem.

78
Quality Cuts

• Muon
• Detected in inner and outer central muon
  detectors
• Behind 5l and 8l of steel
• Good match between extrapolated track and
  detected muon
• pT 5 GeV
• At least 3 hits (of 4) on the silicon track
• Hadron
• pT 1 GeV
• At least 3 hits on the silicon track

• Combination
• Vertex P(c2) 1
• 1.5
• Consistent with bottom
• Rejects charm
• Lxy 250 mm
• If the highest pT track does not make a
  combination passing these cuts, the event is
  rejected.
• If one tries another track instead, the results
  change only minimally. Most of the added events
  are at short life-time

79
Elements of the Cross-Section Ratio

• Luminosity ratio
• Acceptance ratio
• Yield ratio
• Efficiency ratio (e.g. detector aging) is taken
  to be unity

80
Relative Luminosity Determination

• The total cross-section is different at the two
  energies, and we correct for that
• Some of the 1800 GeV data was taken with the 630
  GeV trigger table (as a test run), and this fools
  our luminosity calculation into thinking it was
  really taken at 630 GeV. We correct for this.
• The 1800 GeV data is dynamically prescaled
• Effective prescale is 3.07 0.07
• Determined by seeing how many 12 GeV muons pass
  the prescaled trigger
• Agrees with prescale bookkeeping within
  uncertainties
• L(630)/L(1800) 0.926 0.058
• This includes only those uncertainties that do
  NOT cancel in the ratio

81
Acceptance Calculation

• Part I Monte Carlo
• Generate 10,000,000 bs with our fast Monte Carlo
• Minimum b pT of 6.75 GeV
• Fragment with Peterson (e 0.006)
• Decay with CLEOs Monte Carlo (QQ Version 9.0)
• No decays are forced to muons
• Allows us to keep muons from charm daughters
  (5-18)
• Simulate with our parametric simulator
• Count bs passing cuts, with negative Lxy
  subtracted off
• Results
• 1800 GeV 4045 67 pass
• 630 GeV 2850 56 pass

82
Acceptance Calculation II

• Part II We want to quote the cross-section above
  pT(min)
• Thats the point which 90 of our bs are above
• It works out to 10.75 GeV
• This adds an additional acceptance correction of
  1.282 0.007
• The uncertainty is from varying the b mass and
  scale
• Part III Beam Profile
• The silicon acceptance is not the same at the two
  energies
• The beam is wider and more off-center at 630 GeV
• These two effects partially cancel
• This imposes an additional 0.817 0.014
  correction
• Calculated by counting high pT muons in and out
  of the SVX
• A(630)/A(1800) 0.738 0.023

83
Do we agree with UA1?

• Under the assumption that we agree
• The probability that we would get a result at
  least as high as we got is 1 in 16
• The probability that we would get a result at
  least as discrepant is 1 in 8
• Both calculations assume that the systematic
  uncertainties are Gaussian (which is almost
  certainly not true)
• Paper statement our measurement is above the
  UA1 value, but not so far above that the
  measurements would be inconsistent at the 95
  confidence level

84
The Trouble With Gluons

• Remember, we know that J/y ? gg is forbidden
• J/y is a 3S1 (1--) state
• Violates charge conjugation parity
• Left side is C odd, right is C even
• If that isnt bad enough, spin-statistics forces
  the amplitude to be zero
• That means gg ? J/y is also forbidden
• ggg ? J/y requires a 3-body collision
• Infinitesimal rate

There seems to be no mechanismthat allows
gluons to fuse intoa 3S1 state like the J/y
85
What about Color Evaporation?
The red-headed stepchild of quarkonium
production theories

• Basic idea
• charm-anticharm pairs are produced in a color
  octet state
• These quarks emit one or more gluons in the
  process of forming a colorless charmonium meson
• No attempt to understand this microscopic
  behavior in detail is made
• Many theorists find this unsatisfying
• Predictions?
• Not many most of the information gets washed
  out during the color evaporation
• Many experimentalists find this unsatisfying
• Relative yields of different charmonium states
  goes as (2J1)
• This actually agrees rather well with the data
• Small or zero spin-alignment parameter a