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Physics at alow energy collider
Steve Asztalos
LLNL
Steve Asztalos - LLNL 2
The basic idea…
Steve Asztalos - LLNL 3
Compelling physics case for a photon collider at NLC
(but is it technically feasible)?
• Though proposed in 1981, only have recent (laser) developments made it possible to achieve high luminosities.
• Demonstration prototype at an existing e+e- machine.
• Technical requirements:
-Lasers: ~ 1 m, rep rate ~ 10 Hz, 0.1 J , 2 ps
-Optics: /50, diffraction limited, focus and alignment
-Mechanical: Beam line, tight tolerances
Steve Asztalos - LLNL 4
LLNL has demonstrated the individual technologies
Mechanical System
Optics Assembly
Interferometric Alignment Optics System
0.1J x 2 x 30Hz, 6W average power laser
OPCPA LASER System
Steve Asztalos - LLNL 5
Assemble subsystems at a test facility
Would demonstrate essential elements of an NLC-like IR
Steve Asztalos - LLNL 6
One such suitable facilityBeam Energy
DRx,y (m-rad)
FFx,y (m-rad)
x / y
z
x,y
N
30 GeV
1100 / 50
8 / 0.1 mm
0.1 – 1.0 mm
1500/55nm
6.0E9
Rough estimate ~$10M total project cost (incl. manpower)
See http://www-conf.slac.stanford.edu/lepcf/program.html
Steve Asztalos - LLNL 7
A snapshot of the CP~ 1m, E ~ 0.1 J, x ~ 1.4 m, y ~ 50.2 nm, z ~ 0.1mm
N/Ne ~ 109
Photons receive a maximum of 1/3 of e+e- energy
CAIN
Steve Asztalos - LLNL 8
This IP would deliver the world’s largest luminosity…Assuming e+/e- bunch charge of 4x1010 appropriate for a NLC-like beam a photon luminosity ~ 3x1032 cm-2sec-1
could be achieved.
L/E ~ 4x1031cm-2sec-1GeV-1
CAIN
Steve Asztalos - LLNL 9
…and is verifiable
Kinematics allows separation of reaction products.
Pandora
Steve Asztalos - LLNL 10
-Resonances:
-Photon structure function:
-Quark models: diquark or three quark
-Triangle anomaly and sum rules
Budnev, et al., Physics Reports, 15 (1975) 181
A low energy program
Xγγ
llcqc
Vnc
lq
Vbare γγ
c
Steve Asztalos - LLNL 11Steve Asztalos - LLNL 8
Photon collider does complementary physics
n photons are assigned a charge conjugation
number C of (–1)n
- Two photon initial state has C = +1
- Charge conjugation is conserved, so intermediate and final states must have C = +1
- Eliminates states having JPC with C = -1
- J =1 states are forbidden from decaying into C.N. Yang, Physical Review 77 (1959) 242)
Steve Asztalos - LLNL 12
Status of heavy resonances
~ 100 MeV
?
x x
ccX
Steve Asztalos - LLNL 13
x x
bb
bb
bbX
Bottom mesons are more challenging
?
? ?
?
?
Steve Asztalos - LLNL 14
1S13S1
11S0
c
Spin-spin interactions:
Spin-orbit interactions:
1P2(13P2)
1(13P1)
0(13P0)
Meson physics
One-gluon exchange plus confinement:
Steve Asztalos - LLNL 15
- c(2s) discovery (1980) reconfirmed only last year at BELLE. Large mass confounds theoreticians
(PRL 89, 102001 (2002), PRL 89 (16) 162002-1)
- resonances continue to elude detection.
Hydrogen spectroscopy gave us the Bohr atom
,...)2,1(),1( bc SSPh
(Stephen Godfrey, Quarkonium Spectroscopy 2nd International Workshop on Heavy Quarkonium 2003)
Steve Asztalos - LLNL 16
Meson production with virtual photons. Take advantage of 102 increase in luminosity.
Exploit control over laser polarizations to enhance particular states. For example, circular polarization enhances 0+ (signal) states over 2+ (background) states.
Why final states?
- Appreciable BR in resonance decays ~ 10-4
- Simple event reconstruction
- Well characterized background
We can do better with ppγγ X
ppγγ
pp
Steve Asztalos - LLNL 17
Preparing the tools: Physics and Detector
Pandora/Pythia: SM and MSSM Event generation
• Packaged or user-defined luminosity and cross section classes.
• Delivers parton listing and luminosity-integrated cross section.
• Partons passed to Pythia for hadronization (as needed) and StdHep formatting
http://www-sldnt.slac.stanford.edu/nld/new/Docs/Generators/PANDORA.htm
LCDROOT: Detector Simulation and Event reconstruction • Track smearing
• Reconstruction of invariant mass
• Fitting
http://www-sldnt.slac.stanford.edu/nld/New/Docs/LCD_Root/root.htm
Steve Asztalos - LLNL 18
Luminosity:• User-defined luminosity based on CAIN. • 4 x 10000 array of photon weights sorted by
energy and helicity.
Physics:• Define new resonance classes.
• Decay mesons to massive final states.• Pandora’s luminosity integrated cross section
not reliable for very narrow widths (< 10 MeV).• Override randomly generated final states.
Interface:• Identification of intermediate and final states in
event structure
Pandora modifications for ppγγ X
Steve Asztalos - LLNL 19
Pandora Luminosity Modification for
Built-in Pandora luminosity class adequately treats Compton-backscattering process…
ppγγ X
…but does not include multiple interactions nor beamstrahlung.
Steve Asztalos - LLNL 20
11|2/112|2/111|10|
10|2/121|2/110|11|
00|3/120|3/210|10|
11|2/121|2/111|10|
10|2/121|2/110|11|
22|11|11|
or 00|3/110|2/120|6/111|11|
or 00|3/110|2/120|6/111|11|
2|2|11|11|
011|11|
00|11|11|
00|11|11|
011|11|
|||| 21
)(
)( )()()(
)( )()()(
)(
1P
1S1P1P1P
1S1P1P1P
1P
2
0012
0012
2
c
cccc
cccc
c
JmJmm
Real photons only have transverse polarizations (helicity {1,-1}).
Associating luminosity with mesons
For L =1 Clebsch-Gordan coefficients give the (9) possible product states.
Steve Asztalos - LLNL 21
Pandora Physics Modifications for background
cross section of interest in resolution of controversy between three quark (Nucl. Phys. B 259,
(1985) 702) and diquark hadron models (Phys. Lett. B 316,
(1993) 546). Both models predict
ppγγ **
-15E~σFor our purpose, is background whose functional behavior scales as
ppγγ
θ)cos1(
θ)cos1(E~
d
dσ2
215-
Chen-Cheng Kuo, Photon 2003 - Frascati
-12E~σ
ppγγ
Steve Asztalos - LLNL 22
Breit-Wigner Signal with Power Law Background
No. of signal events:
No. of background events:
dE)dσ(E,t NE
L
6.
6.
0.4
75.22
totx22
x2
totxγγ
)m()mE((
π8dE)θ(dt)ppxBR( N
E
Lf
6.
6.
0.4
75.215
6
2
2
E
1015.1dE
)θcos1(
)θcos1(dt N
E
L
6.
6.
tot2totx
totxγγx )θ(d
)m(
π8)(mt)ppxBR( N fL
Steve Asztalos - LLNL 23
Event numerology
MassΓγγ/ Γtot Γtot Events
c(1S) 2.979 --- 4.6 x10-4 0.0161 0.0012 3263
c(2S) 3.665 --- 4.6 x10-4(1) 0.0161 0.0012*
0.411(2)
2643
c0 (1P) 3.415 --- 2.4 x10-4 0.0107 2.4x10-4 194
c2(1P) 3.556 2.4 x10-4 0.0021 6.8x10-5 6
b(1S) 9.3 --- 4.6 x10-4*
(QbMb/QcMc)2
0.014(3) 0.0012 (4) <1
--- --- --- --- 9119
Total 15227
ppγγ
)θ(f
)θcos1(
)θcos1(2
2
22
4
θ)3cos-(1
or θsin
)ppxBR(
(1) Assumed to be same as for c(1S)
)ppxBR( )ee)1(/)/BR(ee)2(/BR( -- SJSJfor c(1S) times(1)
Steve Asztalos - LLNL 24
Clear meson signals
c(1S) c(2S)
c0 (1P)
Steve Asztalos - LLNL 25
Exploit angular information to suppress background
c(1S)
c(2S)c0 (1P)
Steve Asztalos - LLNL 26
How do we match up?
Weiszacker-Williams spectrum
Steve Asztalos - LLNL 27
Comparing BELLE and LINX luminosities
Steve Asztalos - LLNL 28
Mesons from virtual photons (BELLE results)
Steve Asztalos - LLNL 29
Summary
• Compare events generated by Compton-backscattering with Weizsacker-Williams method
• Study different mesons decay modes
• Address effects of laser and electron polarizations
bb
Still to come…
• Charmed mesons should be copiously produced at a collider. This would allow for detailed studies of their properties.
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