Pile-up in Hard Single Diffraction and Forward Coverage. Mike Albrow. 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. Can Hard SD (with p detected) be done with Pile-up?. Answer:
Need for better forward coverage.
Pile-up in hard single diffraction …need for rapidity gaps.
Instrumenting TAS as “shower counter”
TAM, ZDC Q1 Q2 Q3
No, because you cannot attach the p to the dijet/W/Z
The probability that the p and dijet/W/Z are from
different events is high (>~ 10%) even when <n/x> ~ 0.1
You must kill pile-up by requiring >~ 1 unit rap-gap within
~ 3 (possibly 4) units of the p. Unfortunately CMS coverage
is 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.
If your p - trigger is for all
Trigger 1 on central di-jets (2 with ET > 5 (seed))
Trigger 2 on central di-jets + pbar in roman pot
count a lot!
E, pz cons.
Exercise for student
Most of blue curve (diffractive trigger) has xi’ > 0.1 and is
pile-up. This should be luminosity-dependent. One can only get very small xi
if there are not particles with large –ve eta (close to pbar), and pile-up kills that.
n (mean no./crossing) 0.36 0.54 0.83
Ratio ND/SD 3.4 5.4 14.5
Only ~ 1% of di-jets are diffractive, while ~ 10% of all interactions are
diffractive (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.
-3.6 < eta < -5.2 which makes a major contribution to the xi’ measurement
This 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 –ve
on the pbar side). Particles way over on the p-side are not
If you have no detectors within 2-3 units of the beam you cannot
get xi from the detectors to match with xi(p)
Classical probes of diffraction:
Diffractive structure functions
Structure of “pomeron”
(delivered) and the fraction useful (no-pileup) quite a bit smaller,
we still measured dijets out to masses ~ 150 GeV.
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)
“High cross section
Trigger rate with 2 fwd gaps in CDF
Optimum ~ 20E30 (cf 140E30 at LHC75)
Khoze Martin Ryskin Stirling luminosity
Exclusive events in low luminosity (single interaction) running
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?
Very forward region of CMS luminosity(Nikolai Mokhov, MARS)
BACK of TAS
They exist! Made at LBNL luminosity
There is a cavity each side – could insert shower detectors
One goes down in June ... too late. Other in ~ 10 months.
Not followed through.
Put detector, near hadronic shower maximum
What 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 shower
detection 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? luminosity
Details of space for counters. Thickness. luminosity
Technique (Radiation hardness, but only to ~ 1 fb-1)
Quartz fibers ?
Quartz plates ?
Diamond pads ?
Liquid? (slow ... unless very thin gaps.)
Can this technique be used in TAS?