10 - January - 2002

               Thursday

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Andrei Seryi :

LINX Proposal at SLAC
30 GeV electron beams, but could be higher.  costs money.

LINX IR and optics - similar to NLC FF
Plan to use the SLD, with some added quadrupoles and other magnets.

R&D on final focus quadrupoles
stabilization with digital fedback in real time:
inertial sensors, with springs and electrostatic
pushers.  dramatic improvement seen for a smalll test body.  next
step: an extended object.

nanometer stability of colliding beams.
there is very good resolution for centering: 1nm resolution,
which is sufficient for NLC.  Comes from beam-beam deflection
which comes when the beams are not aligned with each other.
This cna be used to study the stability of the collision point.
It is applicable to NLC -- it is model-independent.

Controlling beam background with nonlinear elements.
Inser octupoles to help reduce tails.  Beam will be mich smaller.
If this can be demonstrated, would lead to significnat savings
of luminosity and the material and size of the collimation system.

Technical Feasibility.
parasitic to PEP-II operation: 30Hz, 30 geV
some improvements to damping rings (horizontal)
Linac is no different thatn 1994-7 FFTB runs and recent (e150,E157)
FFTB plasma runs.
FF optics are "easy" aside form the extra octupoles.

LINX staging
Stage it in order to concentrate on one goal/problem at a time.
Step 1 and 2: demonstrate that the SLC can be revived!
3. produce ultra-short beams
3. bg suppression in new FF optics
4. prodice ultra-low emmittance beams
5. fast feadback for mechanical stability
6.
7.

timeline
rstore quipment by summer 2002
decision on LINX proposal mid-2002
funding startes in 2003
steps 3-5 up until early 2004
steps 7-8 until early 2005
important: this is decoupled from NLC CD-1 decision.

Recent progress
started vacuum survey of arcs and FF in Sept 2001
leaks localized or repaired
want to put beam throughg south arch by June 2002 (challenging but possible)
need several small repairs in BSY - work starting in Jan 2002.
 needs to be continuued, will have to wait for next ROD
 (repair opportunity day)

Goals:
demonstrate gamma-gamma collisions, then do some physics.

....
questions:
1. how to revive the SLD?  magnet is warm?  how low in angle can you go?
2. how low to go in energy?  10 geV cm?
3. can there be experimetns in the beam dump areas?
4. laser: use one laser, split it, to produce ga-gam collisions

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David Asner,  Prospects for finding a light A0 at a low energy
              gamma-gamma collider

This work done with Jeff Gronberg and Jack Gunion.  Some of the
motivation comes from papers by Maria Krawszyk.

luminosity calculation based on CAIN
note: laser does not have a tunable frequency!
For E=30, x=1.62 and for 45 GeV, x=2.44
polarized beams (80%), increase rep rate from 30 to 120 hz
possibilities to increase the power.

A light A0 is allowed in the 10-100 GeV tange in a *general* 2HDM
also in the nMSSM.  (The plot needs to be remade with more
recent information.)

Use nominal 30 GeV e+e- beam parameters.  emittances are
more pessimistic thatn Andrei projected.  Assumr running
at 120 Hz and increasing the bunch charge.

dominant backgrounds are bb and cc

one could run with one-beam polarized.  the gam-gam mean lambdalambda'
is still high.  energy spectrum is less peaked.  there *will* be
enough spin-2 suppression.

Large cross sections at 10,000 fb*GeV !

Table of yoelds in one snowmass year as function of
mass and tnabeta.   Large in some parts

Backgrounds estimated with untuned anlaysis.  Quite low
at higher masses.

In favoirable case, could see 3sigmna effect on PC asymmetry
(with lin pol beams) in one year.
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Mayda -- looking for light sbottom, etc.

Heather Logan has calculated the cross section and put it
into PANDORA.   Cross sections are very large when
masses are light and energies are high.

total cross section for bbbar is 20* cross section for sbottoms
for Ecm(ee) = 30 geV and above.

Another exotic possibility would be
   gamma + e-   -->   mu-
ie a test of FCNC.

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Stefan, Photon QCD structure at LINX

advanategs of LINX over LEP.
Problems at in e+e-
* in e+e- you don't know the beam energy, so you need to use
  complicated unfolding techniques to get the structure functions.
* at low W, the hadronic system is strongly boosted along the beam
* statistics are low at high W due to luminosity (WW) function
* virtualities are 10**-4 to 10**-2
Advantages at gaga
* beam energy is better known and better controlled
* boost is smaller
* the photon really is real (Q2 = 0)

total hadronic cross section
Does sigmatot(W) rise faster for photons induced processes
than for real hadrons?  Ties in to photon structure and
results from HERA.  LEP preliminay results seem to say yes.
All current measurements have terrible systematics
problems, from acceptance and from W resolution.

At LEP largest cross section is gamma-gamma -> pi+pi-pi+pi-
elastic scattering (ie pomeron exchange).    But very hard
to observe because pions go down the beampipe.

At LEP, single-tag events give one really virtual photon,
but measurements still difficult.  At LINX, might be
much better, utilizing e-gamma collisions.
Could to low X, high W, where photon should really be
hadronic.  Depends on ability to tag the scattered electron.

Could measure charm content of the photon (following
a preliminary analysis at OPAL).

Look at inclusive cc bb production, which depends on the
charm and bottom masses as well as alphaS.

Measurement of eta_b : the eta_b has never been observed.
Since it is a 0+- state, gaga would be ideal.

Might be able to use PHOJETS to estimate rates.

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Mayda - DISCUSSION

Aside from LINX -- looking forward to Korea.   (last week in August)

We need to look at gamma-gamma -> stop stop* and to charginos.
and also of importance: gaga -> H, A0   and H+H-
and probing trilinear coupling of higgs.

Proposal:
Make a big splash in Korea and do an adequate job for the physics
for LINX.  The physics case for stage-I approval is unimportant.
Also, they can start to attack the physics case which can be
harder to defend than machine R&D.  Also, the machine people
may not welcome the User community.
 

upcoming meetings:
  Europe   -- April   (gaga -> QCD)  Get feedback on SUSY physics
  USA      -- June
  Korea    -- August
  ?        -- Nov      LINX photons
 

Signal cross sections are well in hand, relying on PYTHIA for
the decays.  The four-fermion background is a bigger problem.
We might be able to use WIZARD, perhaps after some modifications.
 

Other interesting questions:
 - extraction of CP for heavy higgses
 - extraction of SUSY parameters, such as tanbeta
 - compare and contrast with e+e- at the same machine
 

What needs to be added to PYTHIA to make sure hard gluons
are included in bbg and ccg?
Stefan could do comparisons, using matrix element
calculation from Jikia.
  David/Steve/Stefan/Jikia will collaborate.

Phone conference on Feb 11-15.

bbbar mass resolution: needs to be taken into into account.
Not just the same as generic jets.