Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://zebu.uoregon.edu/~uochep/talks/talks03/lcw.pdf Äàòà èçìåíåíèÿ: Wed Jul 23 00:50:21 2003 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 09:35:57 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: http www.astronomy.ru forum index.php topic 4644.0.html

Studies of Correlated Beamstrahlung

· Intro duction and Motivation ­ what do es this have to do with new physics?

· Cross section measurements

· Unfolding the luminosity sp ectrum

· GuineaPig Results

· Future plans

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Beamstrahlung and New Physics

· An imp ortant mission of our group is to identify detector and machine parameters which may limit the reach of indirect new physics interpretations, eg: ­ Contact Interactions ­ Extra-dimensions ­ Doubly charged Higgs...

· Indirect limits on these pro cesses require precise measurements of two-fermion pro cesses: e+e- f¯ f Usually the cross section measurement is the most difficult
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· At LEP 2 (see my Santa Cruz talk) these kind of limits, in the case of e+e- e+e- were limited by theory.

· At a linear collider we exp ect the theory to b e solved, but luminosity sp ectrum may b e the main challenge: understand the luminosity sp ectra at the 0.1%.

2 · Since most cross section go like 1/s = 1/Ecms : understand the cms energy to b etter than 0.05%. (250 MeV at s = 500 GeV)

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Measuring cross sections

· Cross sections are usually measured for in some range of s / s where is s is the ¯ invariant mass of the f f system. At LEP we used s > 0.85 s

f f f f

Measurement of s is effectively based on angles and dep ends on the ¯ p olar angle of f and the f : 2 sin(f + f ) s ¯ = 1- s sin(f + f ) - sin f - sin f ¯ ¯
Cornell American Linear Collider Meeting

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· Note that for f f /2 ¯ s 1 1-1- s 2 where is the acollinearity = f + f - ¯ · At small angles (e.g. Bhabha scattering ) s 1 1 - / 1 - s 2 where is the smaller of f and f ¯ 10â b etter resolution needed at 100mrad than at /2

Cornell American Linear Collider Meeting

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OPAL 206 GeV preliminary
Events Events

· Require s > 0.85 s for qq, µ+µ- and + - · Require

(a) hadrons
10 3

10 4 10 3

(b) e e

+-


10 2 50 500 450 400 350 300 250 200 150 100 50 0 100 150 200 s /GeV Events

10 2

10 50 300 250 200 150 100 150 200 s /GeV

Events

acol < 170 and |cos| < 0.9 for e+e- · Note fuzziness of s cut

(c) µ µ

+-

(d)

+-


50 100 150 200 s /GeV

100 50 0 50 100 150


200 s /GeV

Cornell American Linear Collider Meeting

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The Luminosity Sprectrum at an LC · We can measure this using Bhabha scattering for single photon case · At small angles higher precision is needed on the acollinearity to get the same precision on s , eg at 100mrad: s = 100µrad = 1.4 â 10-3 s Caution: could b e dominated by machine effects, b eam divergence is 30µrad
350 GeV Machine + ISR + Beamstrahlung 99% 90% 50%

1

10-

1

10-

2

10-

3

10-4 300

310

320 330 340 Collison Energy (GeV)

350

360

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· In a second approximation assume no correlation: dL = f ( x1 ) f ( x 2 ) dx1dx2 where x1 and x2 are the energy fractions of the electron and p ositron. (See studies by Klaus M¨ onig and Dave Miller)

· How go o d is the assumption that there are no correlations in the b eamstrahlung? In M¨ onig's studies effects were small, but this may dep end on b eam parameters

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GuineaPig Studies · D. Schulte's program GuineaPig simulates interaction of two b eams at an LC · Calculates energy loss and p osition of individual electrons and p ositrons · Turn off initial state radiation (assume additional correlations can b e computed exactly...) · Simulate NLC machine with s = 500 GeV · Simulate s cut with a cut on difference in energy b etween electron and p ositron | | | E1 - E2| < 50GeV E1 - E2| < 25GeV E1 - E2| < 5GeV

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240

Example cut in e1 e2 plane This sample includes simulation of NLC optics In this plot and following, ISR is turned off

220

200

180

160
|< 25 GeV

140

120

100 100

120

| e1-e2

140

160

180

200

220

240

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faction/2 GeV

no cut
-1

10

| e1-e2 | < 50 GeV | e1-e2 | < 25 GeV | e1-e2 | < 5 GeV

s inside cuts This sample includes full simulation of NLC optics No ISR off
-3 -2

10

10

-4

10

200

250

300

350

400

450

500 sqrt(sprime)

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faction/2 GeV

-1

Includes NLC optics Compare s with randomly chosen electron and p ositrons Largest effect is due to intentional correlation b etween energy spread and p osition Statistically limited

10
-2

| e1 - e2 | < 25 GeV

10
-3

10
-4

10

400

420

440

460

480

500 sqrt(sprime)

0.01 0.008 0.006 0.004 0.002 0 -0.002 -0.004 -0.006 -0.008 -0.01 400 Fractional Difference/2 GeV

acceptance =4.4+/-2.1/1000 energy = -16+/-63MeV

420

440

460

480

500 sqrt(sprime)

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faction/2 GeV

-1

Standard, |e1 - e2| < 25 GeV Compare s with randomly chosen electron and p ositrons Total change in acceptance is 2.2/1000. Just ab ove threshold Change in mean energy not significant

10
-2

| e1 - e2 | < 25 GeV

10
-3

10
-4

10

400

420

440

460

480

500 sqrt(sprime)

0.005 0.004 0.003 0.002 0.001 0 -0.001 -0.002 -0.003 -0.004 -0.005 400 Fractional Difference/2 GeV

acceptance =2.2+/-0.3/1000 energy = -51+/-10MeV

420

440

460

480

500 sqrt(sprime)

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Acceptance effect larger for tighter |e1 - e2|

acceptance change/1000

6

5

4

· Shows largest effect near p eak (soft photons)

3

2

Standard conditions

1

0

0

10

20

30

40 50 60 Energy difference cut (GeV)

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Acceptance and Energy Shift

|e1 - e2| < 25 GeV Conditions: 1. Standard 2. yoff + 1nm 3. yoff + 2nm 4. yoff + 3nm 5. rot = 100mrad

5 4 3 2 1 0 -1 -2 -3 -4 -5

Acceptance change /1000

Std

+1nm

+2nm

+3nm

100mrad

100 80 60 40 20 0 -20 -40 -60 -80 -100

Shift in sqrt(sprime) (MeV)

Std

+1nm

+2nm

+3nm

100mrad Condition

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Conclusion

· Correlated Beamstrahlung intro duces effects of order 2-3/1000 into the acceptance of fermion pair cross sections These acceptance shifts can not b e decuded from the acolinearity of fermion-pairs

· These shifts do not app ear to b e highly dep endent on b eam alignment, but only a small p ortion of parameter space has b een explored

· Need to understand the co cktail effect

· So far only initial-state effects have b een studied. Final-state Beamstrahlung and scattering could b e imp ortant.
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