Need for better forward coverage. Pile-up in hard single diffraction …need for rapidity gaps

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Mike Albrow TAS Meeting May 4th 2006

Need for better forward coverage.

Pile-up in hard single diffraction …need for rapidity gaps.

Instrumenting TAS as “shower counter”

Beyond TAM, ZDC Q1 Q2 Q3

| | 7.5

Pile-up in Hard Single Diffraction and Forward CoverageMike Albrow


Can Hard SD (with p detected) be done with Pile-up?

Answer: No, because you cannot attach the p to the dijet/W/ZThe probability that the p and dijet/W/Z are fromdifferent events is high (>~ 10%) even when <n/x> ~ 0.1Remedy:You must kill pile-up by requiring >~ 1 unit rap-gap within~ 3 (possibly 4) units of the p. Unfortunately CMS coverageis v.poor there: need to add detectors |eta| > 6.5 (TAS +)on at least one side.

Also probably want a -cut at L1 in p-trigger.

I will give some CDF experience.

>~ 0.01


2 1

32 2 1/

2

26 2

Prob(pjj)Prob(p+jj)

( )where at 25 ns3 10 ( )

Example: 10 as at Tevatron (JJ,W,Z)

80 mb 8.10 ;

( 0.01) 1 mb (?) 1

pjjin

p jj

in

x s

pjj

jj

in

p

n

L L cm sn tn cm s

cm

27 20

Prob(pjj) 0.8 at 1 (55% background)Prob(p+jj)

cm

n

Simple estimate valid for modest luminosities:

If your p - trigger is for all , 10 15 mb, and BG:S = 8 - 18 p !!


Q: Can hard single diffraction be done with pile-up?CDF experience.Trigger 1 on central di-jets (2 with ET > 5 (seed))Trigger 2 on central di-jets + pbar in roman pot

' ( )( )

1Calculate from p p Tparticles

E es

Most of blue curve (diffractive trigger) has xi’ > 0.1 and ispile-up. This should be luminosity-dependent. One can only get very small xiif there are not particles with large –ve eta (close to pbar), and pile-up kills that.

p

These particleshardly count

These particlescount a lot!

Exact.E, pz cons.

Exercise for student


We look at this plot for different bins of instantaneous luminosity(linear scale)

n (mean no./crossing) 0.36 0.54 0.83Ratio ND/SD 3.4 5.4 14.5

Even when n < 1 most p+JJ (p+W etc) triggers are pile-up. Only ~ 1% of di-jets are diffractive, while ~ 10% of all interactions arediffractive (a pbar in pots). One must require at least part of a rapidity gap(say >= 1 unit) or measure xi’ which needs very forward gap detectors.

PILE-UP

pJJ SIGNAL

n

Approximate formula (CDF):NDR 7.n.eSD


CDF diffractive di-jet study uses the MiniPlug calorimeter-3.6 < eta < -5.2 which makes a major contribution to the xi’ measurementThis shows the xi’ distribution for J5 data (ND) when you include the MP energy(red) or when you set it to 0 (so it thinks there was a gap there).

It contributes a lot because of the e^-eta term (eta is –veon the pbar side). Particles way over on the p-side are notimportant.

If you have no detectors within 2-3 units of the beam you cannotget xi from the detectors to match with xi(p)



Single Forward Gaps, SDE, e.g. GJJ, G-BjBj, GZ, GW

1 6

4

In 100 pb ~ 3.10 / total(ND)

Probably ~ 1% are SD 3.10 / SDand ~ few % of those are DPE ~ 1000(These are only rules of thumb based on Tevatron)

W e

W e

Classical probes of diffraction:Diffractive structure functionsStructure of “pomeron” p IP

J

J


Even though the CDF Run II di-jet dataset was only 9 pb^-1(delivered) and the fraction useful (no-pileup) quite a bit smaller,we still measured dijets out to masses ~ 150 GeV.


Single Interaction scenario and Effective Luminosity

Rapidity gap physics can only be done when no other interaction.Optimum scenario is when <n> = 1, then P(no spoiler) = exp(-<n>) = e^-1 = 0.37.

LHC circ = 27 km, #bunches = 2808 (25ns)/936 (75ns)Say <dt> ~ 90ns (75ns case)

-27 2 180mb=8.10inel cm s

32 2 1

31 2 1

-1 6

11 when 1.4 10dt

Then 0.37 5.2 10

~ 100 pb in 2 10 sec...perhaps in a year

inel

neff

n L cm s

L e L L cm s

Trigger rate with 2 fwd gaps in CDFOptimum ~ 20E30 (cf 140E30 at LHC75)

“High cross section physics”


: QCD and calibrationpp p p p H p Khoze Martin Ryskin Stirling

1

60 events in ( ) 5 GeV/c, | | 2

in 100 pb (factor "3-5" uncertainty)Tp


Aim: As complete coverage as possible of veto counters Exclusive events in low luminosity (single interaction) running

Questions:How much effective luminosity with single interactions? Estimate ~ 400pb-1 with factor 2 uncertainty (200-800)How much signal remnant in all detectors from previous x-ing?Can we trigger on 2 EM~5 GeV + forward veto?Need absolute minimum solid angle not covered.

HCAL + CASTOR 6.5 full azimuth.Beyond CASTOR? (ZDC small coverage, mainly 0deg neutrals.)

TAS : Copper shielding, instrument somehow?Beyond: BSC around Q1-Q3?

~ 7.6


Very forward region of CMS (Nikolai Mokhov, MARS)

8.2 (0.55 mr)

7.5PIPE BACK of TAS

TAS



They exist! Made at LBNL

There is a cavity each side – could insert shower detectorsOne goes down in June ... too late. Other in ~ 10 months.


Cavity was foreseen for possible luminosity monitorNot followed through.

Put detector, near hadronic shower maximumWhat is efficiency for particles hitting front face?Radiation levels to be withstood?

Possible solution: quartz fiber “calorimeter” brick.Can fibers be at 90deg to shower axis?

Do not need resolution or “calibration”, just showerdetection with reasonable (> 95%?) efficiency.

Would like in L1 trigger in veto (not essential)

Radiation levels and shower acceptance studies(Nikolai Mokhov & Sergei Striganov)


Details? Space?

53.6 m

8.2 (0.55 mr)


Are these possible places to insert shower counters?


Details of space for counters. Thickness.Technique (Radiation hardness, but only to ~ 1 fb-1)

Quartz fibers ?Quartz plates ?Diamond pads ?Liquid? (slow ... unless very thin gaps.)


This is very far forward (140m) and covers small solid angle.Can this technique be used in TAS?


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Need for better forward coverage. Pile-up in hard single diffraction …need for rapidity gaps