search for exotics at jefferson lab
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Search for Exotics at Jefferson Lab. Raffaella De Vita INFN – Genova For the CLAS Collaboration. PINAN11 Partons in Nucleons and Nuclei Marrakesh, 27 September 2011. p. p. Why Hadron Spectroscopy. QCD is responsible for most of the visible mass of the universe - PowerPoint PPT PresentationTRANSCRIPT
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
Search for Exotics at Jefferson Lab
Raffaella De VitaINFN –Genova
For the CLAS Collaboration
PINAN11Partons in Nucleons and Nuclei Marrakesh, 27 September 2011
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
Why Hadron Spectroscopy• QCD is responsible for most of the visible mass of the
universe• Understanding the origin of this mass, i.e. the mass of
hadrons, is a necessary step to reach a deep understanding of QCD
- Revealing the nature of the mass of the hadrons- Identify the relevant degrees of freedom- Understand the origin of confinement- Validate LQCD predictions
• Meson spectroscopy is a key tool to investigate these issues
Mesons & Baryons
pp
> 1 fm
Effective Degrees of FreedomQuarks and Gluons
0.1 – 1 fm<< 0.1 fm
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
Meson SpectroscopyMesons are the simplest quark bound state, i.e. the best benchmark to understand how quarks interact to form hadrons and what the role of gluons is
Historically, the study of meson properties led to some of the most relevant discoveries in particles physics
• in 1947 the discovery of the pion by Powell, Occhialini and Lattes
• in the same year, the discovery of strange particles by Rochester and Butler
• the interpretation of the φdecay to KK by Zweig and others in 1963
• the discovery of the J/ψ in 1974• …
C.F.Powell, Nobel Lecture, 11th December 1950
K0
p-
p+
G.D. Rochester and C.C. Butler, Nature 160 (1947) 855.
The new frontier in meson spectroscopy is the search for unconventional states with quark-gluon configuration different from regular quark-antiquark states
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
Unconventional States and Exotics Known hadron configurations are baryons, made of three quarks, and
mesons, made by a quark and antiquark pair QCD does not prohibit the existence of other configuration and other color
singlet states, such as tetraquarks, glueballs and hybrids can also exist These unconventional configurations can have the same quantum numbers
as regular mesons or have “exotic” quantum number Finding a proof of their existence is a both a fundamental validation of the
theory and a precious source of information Many experiments in the world have searched and will search for these
states …• proton-antiproton annihilation: Crystal Barrel at
CERN, LHC, Panda at GSI, ...
• e+ e- annihilation: LEP, Babar at SLAC, DAΦNE at Frascati, CLEO at Cornell, BES at Beijing, …
• proton-proton scattering: WA experiments at CERN, GAMS at Protvino, …
• pion beams on fixed target: E852 at BNL, COMPASS at Cern, VES …
• photoproduction experiments: CLAS at Jefferson Lab, GlueX and CLAS12 at Jefferson Lab
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
Search for Hybrid MesonsUnderstanding the role of gluons and the origin of confinement is crucial to complete our picture of strong interaction
• At high energy experimental evidence is found in jet production
• At lower energies the hadron spectrum carries information about the gluons that bind quarks
• Can we find hints of the glue in the meson spectrum?
Search for non-standard states with explicit gluonic degrees of freedom
q q
q q
Regular meson
Hybrid meson
• Predicted by various models as the Flux Tube model, the Bag model, QCD Sum Rules, ..
• Now predicted by lattice QCD calculations
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
Hybrids and Exotics
Normal meson:flux tube in ground state
m=0, PC=(-1)S+1 qq
Hybrid meson:flux tube in excited state
m=1, PC=(-1)S qq
Excitation of the flux tube leads to a new spectrum of hadrons that can have exotic quantum numbers JPC = 0+- , 1-+ , 2+- ...
Masses are predicted to be around 2 GeV, a range that can be explored at Jefferson Lab
The best option to identify unambiguously a meson as an hybrid state is to look for exotic quantum numbers
Normal mesons (qq) are classified according to their JPC where P=(-1)L+1 C=(-1)L+S
JPC= 0-+ (π,K,η,η’)1-- (ρ,K*,ω,Φ)1+- (b1,K1,h1,h1’)...
S1
S2
L
Some combinations of JPC are not allowed for conventional qq systems but can exist for “unconventional” states as hybrids
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
Lattice QCDJ. Dudek et al., Phys. Rev. D82, 034508 (2010)
1S
2S
3S?
1D
1P
2P1F 1-+
Existence of exotics is supported by LQCD
Fully dynamical calculation by the JLab Hadron Spectrum Collaboration: two flavors of light
quarks and an heavier (strange) quark
two lattice volumes large set of operators stable dependence on
quark masses• Good agreement of regular meson spectrum with known states• Exotic multiplets with quantum numbers 1-+,0+- and 2-+ are predicted
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
Exotic Candidates: Experimental Evidence The lightest exotic hybrids are expected in the 1-+ wave:
• π1(1400): observed in ηπ final states by several experiments( GAMS, KEK, E852, Crystal Barrel) with a width of few hundreds MeV. Mass lower than expectation and interpretation still unclear
• π1(1600): observed in several decay modes (ρπ, η’π, f1π, b1π) by different experiments (E852,VES,COMPASS) but with different
production mechanism; not observed in reanalysis of E852 data and by CLAS . Evidence of the state still controversial
• π1(2000): seen by E852 in f1π and b1π final states produced in peripheral πp scattering. Further confirmation is desirable
M. G. Alekseev et al.(COMPASS),PRL 104, 241803 (2010)
M. G. Alekseev et al.(COMPASS),
PRL 104, 241803 (2010)π1(1600)
• Most of experimental evidence comes from pion (S=0) beam experiments (E852, VES, COMPASS)
→ collecting more data with different production mechanism (different probes) is crucial • Controversial evidence may arise from
PWA ambiguities → larger data sets, polarization
information, more sophisticated analysis tools, large
computing resources
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
Exotics in Photoproduction
Pion BeamQuark spins anti-alignedJPC = 1-- , 1++
Quark spinsalready alignedJPC = 0+- , 1-+ , 2+-
Photon Beam
regular mesons @ Eg = 5GeVX = a2
Exotic meson @ Eg = 8GeVX = p1(1600)
Photoproduction: exotic JPC are more likely produced by S=1 probe
Few data (so far) but expected similar production rate as regular mesons
Production rate for exotics is expected to be comparable to regular mesons
A. Szczepaniak and M. Swat, Phys. Lett. B516 (2001) 72
Knowledge of the photon polarization can be used as a filter in the PWA
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
Jefferson Laboratory
A B C
Continuous Electron Beam Accelerator Facility
® E: 0.75 –6 GeV® Imax: 200mA® RF: 1499 MHz® Duty Cycle: 100%® s(E)/E: 2.5x10-5
® Polarization: 80%® Simultaneous
distribution to 3 experimental Halls
Injector
LIN
AC LINAC
Experimental Halls
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
6 GeV CEBAF
CHL-2
Upgrade of the arc magnets
The 12 GeV Upgrade
Construction of the new Hall D
Beam Power: 1MWBeam Current: 90 µAMax Pass energy: 2.2 GeVMax Enery Hall A-C: 10.9 GeVMax Energy Hall D: 12 GeV
Upgrade of the instrumentation of the existing Halls
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
CLAS12 and GLUEXMeson spectroscopy is one of the main topics that will be studied with the Jlab 12 GeV upgrade. Key elements are:• High intensity tagged photon beams• Detectors with large acceptance and good particle identification
capabilities
GlueX in Hall D CLAS12 in Hall B
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
The GlueX Detector
TOFtime of flight
SCstart counter
• 2.2T superconducting solenoidal magnet• Fixed target (LH2)• 108 tagged g/s (8.4-9.0GeV)• hermetic
2.2 TeslaSolenoid
Calorimetry• Barrel Calorimeter (lead, fiber sandwich)• Forward Calorimeter (lead-glass blocks)
PID• Time of Flight wall (scintillators)• Start counter• Barrel Calorimeter
Charged particle tracking• Central drift chamber (straw tube)• Forward drift chamber (cathode strip)
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
The Hall D Photo Beam
1.5 T dipole
magnet
12m long vacuum
chamber
e-
20mm diamond radiator
coherent bremsstrahlung spectrum
Microscope:• Movable to cover different energy ranges• 100 x 5 scintillating fibers (2mm x 2mm)• 800MeV covered by whole microscope• 100MHz tagged g/sec on target• ~8MeV energy bite/column
Fixed array hodoscope:• 190 scintillators• 50% coverage below 9GeV g• 100% coverage above 9GeV g• Tags 3.0-11.7 GeV g• ~30MeV energy bite/counter• 3.5 – 17 MHz/counter
Photon Polarization:• 20 mm diamond radiator• Coherent peak is linearly polarized
• ~40% polarization with peak @ 9GeV
• Peak location tunable with diamond angle
•Crucial to simplify PWA!!
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
The Hall D Complex3
~100 meters
electron beam
Groundbreaking, April 2009 In the Hall, February 2011
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
GlueX: expected performance
Design Goal: high and uniform acceptanceComparison of acceptance plots between BNL E852 and GlueX in a sample channel:high and uniformacceptance in invariant mass and Gottfried-Jackson angles.
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
CLAS12 1Forward Detector:- TORUS magnet- Forward SVT tracker- HT Cherenkov Counter- Drift chamber system- LT Cherenkov Counter- Forward ToF System- Preshower calorimeter - E.M. calorimeter (EC)
Central Detector:- SOLENOID magnet - Barrel Silicon Tracker- Central Time-of-Flight
Proposed upgrades:- Micromegas (CD)- Neutron detector (CD)- RICH detector (FD)- Forward Tagger (FD)
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
The CLAS12 Forward Tagger 1
Forward TaggerE’ 0.5-4.5 GeVn 7-10.5 GeVq 2.5-4.5 degQ2 0.007 – 0.3 GeV2
W 3.6-4.5 GeVPhoton Flux 5 x 107 g/s @
Le=1035
Photon Polarization
10-70%
e-γ*
p
e-CLAS12Forward
Tagger
Electron detection via Calorimeter+Tracker+Veto• calorimeter to determine the
electron energy with few % accuracy → homogenous PbWO4 crystals
• tracker to determine precisely the electron scattering plane and the photon polarization → MicroMegas
• veto to distinguish photons from electrons → scintillator tiles with WLS fiber readoutPbWO4
Calorimeter424 Crystals
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
Experiment Layout
Moller Shield
Calorimeter
Tracker
Scintillation
Hodoscope
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
PWA in CLAS12
Test for 2 t bins:- line: generated
wave- |t|=0.2 GeV2
- |t|=0.5 GeV2
As a function of M3πThe CLAS12 detector system is intrinsically capable of meson spectroscopy measurements
In preparation for the experiment, PWA tools are being developed and tested on pseudo data (Monte Carlo) for different reactions as γp→nπ+π+π-
a2→ρπ D-wave a1→ρπ S-wave a1→ρπ S-wave
π2→ρπ P-wave π2→ρπ F-wave π2→f2π S-wave
π2→f2π D-wave π2→f2π P-wave 3π all wave
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
SummaryMeson spectroscopy is a key field for the understanding of fundamental questions in hadronic physics as what is the origin of the nucleon mass and what is the role of gluons
Jefferson Lab has launched a broad and comprehensive program to study meson spectroscopy via photoproduction:
• Study of meson spectroscopy in the light –quark sector for masses around 2 GeV• Two complementary experiments will run in Hall B and D• GlueX: bremsstrahlung tagged photon beam, hermetic detector with excellent
coverage for neutral an charged particles• CLAS12: quasi-real photon beam, high resolution and large acceptance detector
with excellent Pid capabilities• Analysis tools are being developed and usage of GPUs to reduce computing time
is being explored• A series of workshops on Partial Wave Analysis involving theorists and
experimentalists was started (INT Nov. 2009, ECT* Jan. 2011, Jlab June 2011,…)
Detector construction is in progress and first 12 GeV beam is expected in 2014
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
Summary
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
Quasi-Real PhotoproductionStudies at large W (~100 GeV) show a smooth transition between Q2=0 and Q20
Technique used in high energy experiments:
Q2 < W2
COMPASS: <1 GeV2 <Q2> ~ 10-1
GeV2
ZEUS: 10-7 – 0.02 GeV2 <Q2> ~5 10-5 GeV2
H1: <2 GeV2
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
Quasi-Real PhotoproductionAnalysis of existing CLAS data shows clear peaks associated to known mesons in
ep®(e’)pp0p0
ep®(e’)pp0h
a0(980)f2(1270)f0(980)
The Technique works!!
R. De Vita Search for Exotics at Jefferson LabMarrakesh, 27 September 2011
KinematicsElectron kinematics:
• E=0.5-4 GeV• q=2-5 deg.
• Q2=0.007-0.33 GeV2
• Eg=7-10.5 GeV• Photon Polarization:
10-65% (determined on an event-by-event basis)