Charmonia production and suppression at the SPS results and perspectives

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Charmonia production and suppression at the
SPSresults and perspectives
Christensen et al.,Phys. Rev. D8 (73) 2016

• The J/y suppression saga ? results and puzzles
• Near future perspectives ? with proton and ion
  beams

?
First observationof J/y suppression, in the late
60s, by Lederman
p-U mm at 20-30 GeV
Carlos Lourenço - CERN-EP IWHQ, CERN, Nov. 8-10,
2002
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• 1986 J/y suppression proposed as a signal of
  the QCD phase transition from
  confined hadronic matter to a deconfined partonic
  plasma
• we thus conclude that
• there appears to be no mechanism for J/y
  suppression in a nuclear collision except the
  formation of a deconfining plasma
• and if such a plasma is produced, there seems to
  be no way to avoid J/y suppression
  Matsui Satz

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• 1987/88 NA38, approved in 1985 to search for
  thermal dimuon production, finds that the J/y
  is suppressed w.r.t. the dimuon continuum
• from p-U to O-U and S-U
• in S-U, from peripheral to central collisions

When p-U was the only p-A data, and high mass
Drell-Yan had poor statistics
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1988/89 Could the J/y be suppressed by normal
nuclear matter ? or by hadronic comovers
(produced secondaries pions, rhos, etc) ? or
by both processes ?
NA3 had measured ay 0.95 for 0.0 lt xF lt 0.4
equivalent to sabs 4 mb ? Not enough to
explain the observed suppression Adding
absorption by hadronic comovers could describe
the p-U / O-U / S-U data (but requiring very high
pion densities)
Normal absorption of charmonia production ?
Aa parametrization ? lt r L gt parametrization
? Glauber calculation
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Remark Comparison between three formulations
of charmonia nuclear absorption
Shahoyan
Aa widely used but very rough the lighter is
the first target, the higher is the extracted
a ltrLgt average amount of matter seen by the
meson from its production until exiting the
nucleus Glauber meson is produced in NN
interaction and absorbed in nuclear matter with
cross section sabs
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1990/91 Fermilab E772 experiment ?
measures ay 0.92, or sabs 6-7 mb ? observes
the same nuclear absorption for J/y and y
DY
NA3
E772
a
E772
xF
The lightest target of NA3 was Hydrogen, while
E772 used Deuterium
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1992 Nuclear absorption with sabs 6-7 mb
describes the p-A / O-U / S-U data ?
No room left for suppression by produced hadronic
comovers Gerschel Hufner
Glauber fit ? sabs 6.4 ? 0.8 mb

• However, the p-A data points are rather poor
• no points between pd and p-W
• pp/pd at different energy from p-W/p-U
• poor statistics

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• 1992 Puzzles
• Why is sabs much larger than the J/y
  geometrical cross section ?
• Why is sabs the same for the J/y and for the y
  mesons, in spite of their different sizes ?

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1993/94 heavy quark (short distance) QCD
rediscovered ? s (h-J/y) 0 mb until quite
high hadrons energy ? hadronic matter cannot
dissociate J/y formed states ? suppression of
physical J/y states requires deconfinement ?
something else is being absorbed in the p-A, O-U,
S-U data
caveat short distance QCD only works for heavy
quarks ? is the charm quark heavy enough ? ?
s(N-J/y) must be measured experimentally
the inverse kinematics experiment ! slow
J/y s in the nucleus rest frame can only
be measured if the nucleus is the beam
Kharzeev Satz, 1995
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Also E789 has seen that J/y and y production
require K factors of 7 and 25 relative to the
colour singlet model calculations
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p-A
Kharzeev et al.
S-U
Pb-Pb
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1996 Status of the charmonia suppression saga
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1999 Anomalous suppression pattern evidence
of deconfinement in Pb-Pb collisions
J/y suppression ?
Pb-Pb
centrality
Open questions ? Onset of what exactly ? ? As
a function of which variable ? ? Is there really
a second step ? ? Are peripheral Pb-Pb
collisions normal ?
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1999/2000 E866 and NA50 news (from high
statistics data) ?
stronger nuclear absorption for y than for J/y
(for low xF ) ? lower
values for sabs 4.7 mb instead of 6-7 mb ...
a 0.95
Normal J/y nuclear absorption (NA50) a
0.927 ? 0.012 from Aa fitsabs 4.7 ?
0.8 mb from Glauber fitsabs 4.3 ? 0.7 mb
from ltrLgt fit
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2001/02 Further NA50 news from high statistics
p-A data
a(DY) 0.995 ? 0.016 ? 0.019
Glauber fit sabs (J/y) 4.4 ? 1.0 mb sabs
(y) 6.4 ? 1.5 mb
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Correcting for the feed-down from the y decays
Simultaneous Glauber fitto p-A and S-U J/y
data ? sabs 4.3 ? 0.6 mb
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J/y suppression in peripheral Pb-Pb collisions
agrees with normal absorption curve

• Peripheral collisions collected in 1996 were
  contaminated by Pb-air collisions
• Year 2000 data collected with target in vacuum
• Absorption curve determined from p-A and S-U
  data (not correcting for y feed-down)
• Drell-Yan in the mass range 4.2-7.0 is less
  sensitive to fitting systematics

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• Some open questions
• Is the open charm yield enhanced in
  nucleus-nucleus collisions ? How does it
  compare to the suppression pattern of bound
  charm states ?
• What is the physical origin of charmonia
  suppression ? What is the variable that
  rules the onset of ?, ?c and J/? suppression ?
• Which fraction of J/? comes from ?c decays ?
  Does it change from p-Be to p-Pb ?
• Is there comover absorption in S-U collisions
  ? What is the break-up cross section of
  formed charmonia states in hadronic matter ?

Measuring charmonia suppression in a lighter
collisionsystem will confirm or rule out
specific models
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The detector concept of the NA60 experiment

• Track matching through the muon filter
• Improved mass resolution
• Improved signal / background ratio (rejection
  of p and K decays)
• Muon track offset measurement
• Separate charm from prompt (thermal ?) dimuons

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Improved dimuonmass resolution
Adding pixel detectors
D ct 317 mm D0 ct 124 mm
interaction vertex
D meson tagging using the impact parameter of
the muon tracks
D
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The NA60 silicon pixel telescope

• 16 silicon pixel planes
• 720 000 pixels of 50 ? 425 mm2
• Accurate track and vertex reconstruction in
  a high multiplicity environment

Beamscope
beam
primary vertex
Pixel Telescope
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( Instead of ) Conclusions

• After considerable progress quarkonia
  hadro-production remains full of puzzles even in
  pp and p-nucleus elementary collisions
• Heavy quarkonia production is a rare
  process detailed understanding requires good
  statistics and controlled systematics
• A third generation experiment is now ready for
  precision p-A and A-A studies built on the
  shoulders of a 15-year long learning
  curve future running requires very good and
  competitive physics cases
• The QWG is invited to suggest interesting
  measurements to be made in NA60 in p-A
  collisions at 400 GeV