Transcript Diapositiva 1

Hadron Physics
•
•
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QCD: are we satisfied with it?
Antiproton’s potentiality
The PANDA enterprise
Paola Gianotti
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what is matter made of?
Our present knowledge of matter is the result of centuries of studies…
Philosophers of ancient Greece
believed it was made of 4
elements
Mendeleev 1869 introduced the
periodic table of elements
1808 Dalton, following their
weights, make a first list of
elements
1963 Murray, Gell-Mann, and Zweig laid
the foundation of quark model
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Quantum Chromodynamics
The QCD Lagrangian is, in principle, a complete description of the strong
interaction.
There is just one overall coupling constant g , and six quark-mass parameters
mj for the six quark flavors
But,
it leads to equations that are hard to solve
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The Confinement
None of the particles that we've actually seen appear in the
formula and none of the particles that appear in the formula
has ever been observed.
Furthermore, we've never seen particles carrying fractional electric charge,
which we nonetheless ascribe to the quarks.
And certainly we haven't seen anything like gluons--massless particles
mediating long-range strong forces.
So if QCD is to describe the world, it
must explain why quarks and gluons
cannot exist as isolated particles. That
is the so-called confinement problem.
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Hadron masses
The elementary particles of the Standard Model gain their mass through the
Higgs mechanism.
However, only a few percent of the mass of the proton is due to the Higgs
mechanism. The rest is created in an unknown way by the strong interaction.
Glueballs would be massless without the
strong interaction and their predicted
masses arise solely from the strong
interaction.
The possibility to study a whole
spectrum of glueballs might therefore
be the key of understanding the
mechanism of mass creation by the
strong interaction.
C. Morningstar and M. Peardon, Phys. Rev. D 60, 034509 (1999)
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The chiral symmetry
There is another qualitative difference between the observed reality and the
world of quarks and gluons.
The phenomenology indicates that if QCD is to describe the world, then the u
and d quarks must have very small masses.
But if u and d quarks have very small masses, then the equations of QCD
possess some additional symmetry, called chiral symmetry.
There is no such symmetry among the observed strongly interacting particles;
they do not come in opposite-parity pairs. So if QCD is to describe the real
world, the chiral symmetry must be spontaneously broken.
and this mechanism is playing an important role in the process of mass
generation
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Chiral symmetry restoration
The mass of light hadrons (u,d,(s))
is dominated by spontaneous chiral
symmetry breaking.
In the nuclear medium (ρ>0) we can
restore, at least partially this
symmetry.
Hints of this effect have been
already observed. We wants to
extend these studies to Charmed
mesons
Mass modifications of mesons
pionic atoms
π
KAOS/FOPI
K
π25 MeV
π+
K+
100 MeV
HESR
D
vacuum
KD50 MeV
D+
nuclear medium
ρ = ρ0
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How do we solve QCD problems?
The first approach is to try to solve the
equations.
That's not easy.
Fortunately, powerful modern computers
have made it possible to calculate a few
of the key predictions of QCD directly.
The second approach is that of
creating phenomenological models
that are simpler to deal with, but
still bear some significant
resemblance to the real thing.
quark
antiqark
Meson
Hybrid
arXiv:hep-lat/9904012v1
The agreement with the measured
masses is at the 10% level.
Glueball
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Can we be satisfied?
Nowadays, QCD prediction can reach precisions at the GeV around 10 %, and
also the phenomenological models are not doing better!
Can we be satisfied of this accuracy?
Just a note: the Tolemaic system allowed to predict the positions of the planets
with the same level of accuracy…..
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but it was wrong!
Experimental tests are needed…
High statistics and high quality data are necessary to help constraining the
models
e-
g
p
Different experimental techniques can be used to focus on different
aspects:
• The selection of special working conditions or of final states helps
filtering initial/final state quantum numbers;
p
p
• In protons-antiproton annihilations complex objects collide
• The interaction occurs between two beams of (anti)quarks and gluons
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Physics with antiprotons had a great past
High Energy:
pp-Colliders (CERN, Fermilab)
Discovery of Z0, W±
Discovery of t-quark
Medium Energy:
Conventional p-beams (LBL, BNL, CERN, Fermilab, KEK, ...)
p-Storage Rings (LEAR (CERN); Antiproton Accumulator (Fermilab))
Meson Spectroscopy (u, d, s, c)
p-nucleus interaction
Hypernuclei
Antihydrogen first production
CP-violation
Low Energy (Stopped p‘s):
Conventional p-beams
p-Storage Rings (LEAR, AD (CERN))
p-Atoms (pHe)
p/p-mass ratio
Antihydrogen
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Physics with antiprotons have a great future
High Energy:
pp-Collider (Fermilab)
B physics, Top, Electroweak, QCD, Higgs
Medium Energy:
Conventional p-beams (Fermilab, (KEK), ...)
p-Storage Rings (HESR, (Fermilab))
Charmonium spectroscopy
Exotic search
D physics
Baryon spectroscopy
Hypernuclei
CP-violation
Low Energy (Stopped p‘s):
Conventional p-beams
p-Storage Rings (FLAIR, AD (CERN))
p-Atoms
Antihydrogen spectroscopy
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Spectroscopy studies
Two are the mechanisms to access particular final states:
p
Production
p
G
_
p
H
_
p
M
p
H
_
p
M
M
all JPC available
Even exotic quantum numbers
can be reached σ ~100 pb
Exotic states are produced with rates similar to qq
conventional systems
All ordinary quantum numbers
can be reached σ ~1 μb
Formation
_
only selected JPC
p
p
p
p
G
_
p
H
H
_
p
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Exotic hadrons
In the light meson region, about 10 states have been
classified as “Exotics”. Almost all of them have been seen in
pp...
Main non-qq candidates
f0(980)
4q state - molecule
f0(1500)
0++ glueball candidate
f0(1370)
0++ glueball candidate
f0(1710)
0++ glueball candidate
h(1410); h(1460)
0-+ glueball candidate
f1(1420)
hybrid, 4q state
p1(1400)
hybrid candidate 1-+
p1(1600)
hybrid candidate 1-+
p (1800)
hibrid candidate 0-+
p2(1900)
hybrid candidate 2-+
p1(2000)
hybrid candidate 1-+
a2’(2100)
hybrid candidate 1++
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Charmonium region
Charmonium spectrum, glueballs, spin-exotics cc-glue
hybrids with experimental results
From G. S. Bali, Int.J.Mod.Phys. A21 (2006) 5610-5617
arXiv:hep-lat/0608004
Only with high statistics and different final states, quantum number assignment
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become clear
Antiproton’s power
e +e -
→ Y’
→ gc1,2
_
p p→ c1,2
→ ggJ/y
→ gge+e-
→ gJ/y
→ ge+e-
 e+e- interactions:
- All states directly formed
(very good mass resolution)
cc1
3500
_
Br(pp → hc)= 1.2 10-3
1000
E 835 ev./pb
_
 pp reactions:
CBall
E835
100
CBall ev./2 MeV
- Only 1-- states are formed
- Other states only by secondary
decays (moderate mass resolution)
3510
3520 MeV
ECM
Br(e+e- →y) ·Br(y → ghc) = 2.5 10-5
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Antiproton’s power
p-beams can be cooled  Excellent resonance resolution
Resonance
cross
section
 Crystal Ball: typical
resolution ~ 10 MeV
Measured
rate
 Fermilab: 240 keV
Beam
CM Energy
 PANDA: ~30 keV
The production rate of a certain final state  is a convolution of the
BW cross section and the beam energy distribution function f(E,E):
  L0   dEf ( E , E ) BW ( E ) +  b 
The resonance mass MR, total width R and product of branching ratios into the
initial and final state BinBout can be extracted by measuring the formation rate for
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that resonance as a function of the cm energy E.
The hadron’s structure
The characteristics hadrons are given only in minor part by the constituent
quarks.
Quarks and gluons dynamics plays a fundamental role in the definitions of
hadron’s properties: mass, spin, etc…
Generalized Parton Distributions functions (GPDs)
contain both the usual form factors and parton
distributions, but in addition they include
correlations between states of different
longitudinal and transverse momenta. GPDs give a
three-dimensional picture of the nucleon.
Nucleon Form Factors have been mainly studied
using electromagnetic probes, but the physical
diagrams can be reverted… and a
complementary approach can be used
In a similar way Deeply Virtual Compton
Scattering (DVCS) can be crossed-studied
non-perturbative QCD
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perturbative QCD
Our Playground
p Momentum [GeV/c]
0
2
Meson spectroscopy
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ΛΛ
ΣΣ
ΞΞ
• light mesons
• charmonium
• exotic states
− glueballs
− hybrids
− molecules/multiquarks
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ΩΩ
qqqq
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10 12
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Λc Λc
ΣcΣc
Ξc Ξc
Ωc Ωc
DD
DsDs
ccqq
nng,ssg
ccg
nng,ssg
• open charm
ccg
ggg,gg
Baryon/antibaryon production
ggg
Charm in nuclei
Hypernuclei
Em. form factors of the proton
Generalized Parton Distributions
light qq
π,ρ,ω,f2,K,K*
1
cc
J/ψ, ηc, χcJ
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3
4
Mass [GeV/c2]
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6
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Production Rates (1-2 (fb)-1/y)
Final State
cross section
hc  K S0 K  p 
10 nb
107

50b
1010
 (  A)
y (3770)  DD
J /y ( e + e – , +  – )
c 2 ( J /y + g )
 c c
2b
107
630nb
109
3.7nb
20 nb
0.1nb

70 m b
(pp)
108 (105 )
3 nb
 c c
T
# rec. events/y
107
107
105
Key elements : Low multiplicity events
Possibility to trigger on defined final states
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Charmonium spectroscopy
Charmonium energy is the transition range
between perturbative and non-perturbative
regime. It is the energy range where models
are tuned
below DD threshold
• all the predicted states have been detected,
but
• there is lack of precise measurements of
masses, widths and branching ratios
(i.e. hc, hc(2S), hc)
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Charmonium above DD threshold
This is the more obscure region: old and
new measurements at electron machines
seem not in agreement.
On the other side several new states
showed up at the B-factories
for most states JPC is not well established…and
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Newly-born
new Charmonium-like states from Belle
Y(4361)
Y(4664)
Z(4430) →ψ(2S)π±
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Open charm states
•
•
•
•
•
Open charm sates are the QCD
analogon of hydrogen atom for QED
Narrow states Ds0(2317) and
Ds1 (2458) recently discovered at Bfactories do not fit theoretical
calculations.
Quantum numbers for the newest
states DsJ(2700) and DsJ (2880) are
open
At full luminosity at p momenta larger
than 6.4 GeV/c PANDA will produce
large numbers of DD pairs.
Despite small signal/background ratio
(510-6) background situation
favourable because of limited phase
space for additional hadrons in the
same process.
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An example…
• The width of Ds0*(2317) can be measured in
the reaction ppDsDs0*(2317)
threshold
Ds*Ds0*
By making an energy scan around threshold → counting signal events,
determine the excitation function and extract the width
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: the new antiproton facility
Facility for Antiproton
and Ion Research
Primary Beams
•1012/s; 1.5 GeV/u; 238U28+
•Factor 100-1000 present in intensity
•2(4)x1013/s 30 GeV protons
•1010/s 238U73+ up to 25 (- 35) GeV/u
Secondary Beams
•Broad range of radioactive beams up to
1.5 - 2 GeV/u; up to factor 10 000 in
intensity over present
•Antiprotons 3 (0) - 30 GeV
Storage and Cooler Rings
•Radioactive beams
•e – A collider
Key Technical Features
•Cooled beams
•Rapidly cycling superconducting magnets
•1011 stored and cooled 0.8 - 14.5
GeV antiprotons
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HESR - High Energy Storage Ring
• Production rate 2x107/sec
• Pbeam
= 1 - 15 GeV/c
• Nstored =
5x1010
_
p
• Internal Target
High resolution mode
• dp/p ~ 10-5 (electron cooling)
• Lumin. = 1031 cm-2 s-1
p
Pellet-Target
H2 (ρ=0.08 g/cm2)
70000 pellets/s
d = 1 mm
ΔTp  ρH2 d
High luminosity mode
1032
cm-2 s-1
from RESR
• Lumin. = 2 x
• dp/p ~ 10-4 (stochastic cooling)
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General Purpose Detector
Detector requirements:
• nearly 4p solid angle
(partial wave analysis)
• high rate capability
(2·107 annihilations/s)
• good PID
(g, e, , p, K, p)
• momentum resolution (~1%)
• vertex info for D, K0S,  (ct = 317 m for D±)
• efficient trigger
(e, , K, D, )
• modular design
(Hypernuclei experiments)
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Pellet or cluster-jet target
2T Superconducting solenoid
for high pt particles
2Tm Dipole for forward tracks
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Central Tracker
Silicon Microvertex detector
Forward Chambers
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Muon Detectors
Forward RICH
Barrel DIRC
Barrel TOF
Endcap DIRC
Forward TOF
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PWO EMC
Forward Shashlyk EMC
Hadron Calorimeter
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Collaboration
• At present a group of 420 physicists
from 55 institutions of 17 countries
Austria – Belaruz - China - Finland - France - Germany – India - Italy – The Nederlands Poland – Romania - Russia – Spain - Sweden – Switzerland - U.K. – U.S.A..
Basel, Beijing, Bochum, IIT Bombay, Bonn, Brescia, IFIN Bucharest,
Catania, Cracow, IFJ PAN Cracow, Cracow UT, Dresden, Edinburgh,
Erlangen, Ferrara, Frankfurt, Genova, Giessen, Glasgow, GSI, Inst. of
Physics Helsinki, FZ Jülich, JINR Dubna, Katowice, KVI Groningen,
Lanzhou, LNF, Lund, Mainz, Minsk, ITEP Moscow, MPEI Moscow,
TU München, Münster, Northwestern, BINP Novosibirsk, IPN Orsay,
Pavia, Piemonte Orientale, IHEP Protvino, PNPI St.Petersburg,
KTH Stockholm, Stockholm, INFN Torino, Torino, Torino Politecnico,
Trieste, TSL Uppsala, Tübingen, Uppsala, Valencia, SINS Warsaw, TU
Warsaw, SMI Wien
http://www.gsi.de/panda
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Summary
Thanks to the new HESR antiproton ring at FAIR
we will be able to...
perform high resolution spectroscopy with
p-beam in formation experiments:
E ≈ Ebeam
produce, with high yields, gluonic excitations: glueballs, hybrids,
multi-quark states
 ≈ 100 pb
study partial chiral symmetry restoration
by implanting mesons inside the nuclear medium
produce hyperon-antihyperon taggable beams
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Space: The final frontier…
In the Star Trek universe, spaceships use the enormous energy of matterantimatter annihilation to leap across the universe.
This is science fiction, but antiproton-proton annihilation is not
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A new challenging Enterprise is started!
If you are interested….Jump on!
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