Physics at a low energy collider Steve Asztalos LLNL

Physics at alow energy collider

Steve Asztalos

LLNL

Steve Asztalos - LLNL 2

The basic idea…


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


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


Assemble subsystems at a test facility

Would demonstrate essential elements of an NLC-like IR


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


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


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


…and is verifiable

Kinematics allows separation of reaction products.

Pandora


-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)


Status of heavy resonances

~ 100 MeV

?

x x

ccX


x x

bb

bb

bbX

Bottom mesons are more challenging

?

? ?

?

?


1S13S1

11S0

c

Spin-spin interactions:

Spin-orbit interactions:

1P2(13P2)

1(13P1)

0(13P0)

Meson physics

One-gluon exchange plus confinement:


- 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)


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


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


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


Pandora Luminosity Modification for

Built-in Pandora luminosity class adequately treats Compton-backscattering process…

ppγγ X

…but does not include multiple interactions nor beamstrahlung.


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.


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


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


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)


Clear meson signals

c(1S) c(2S)

c0 (1P)


Exploit angular information to suppress background

c(1S)

c(2S)c0 (1P)


How do we match up?

Weiszacker-Williams spectrum


Comparing BELLE and LINX luminosities


Mesons from virtual photons (BELLE results)


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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Physics at a low energy collider Steve Asztalos LLNL