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:
Pile-up in Hard Single Diffraction and Forward Coverage
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
Can Hard SD (with p detected) be done with Pile-up?
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.
Simple estimate valid for modest luminosities:
If your p - trigger is for all
Q: Can hard single diffraction be done with pile-up?
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.
We look at this plot for different bins of instantaneous luminosity
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.
CDF diffractive di-jet study uses the MiniPlug calorimeter
-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”
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)
“High cross section
Trigger rate with 2 fwd gaps in CDF
Optimum ~ 20E30 (cf 140E30 at LHC75)
Khoze Martin Ryskin Stirling
Aim: As complete coverage as possible of veto counters
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(Nikolai Mokhov, MARS)
BACK of TAS
They exist! Made at LBNL
There is a cavity each side – could insert shower detectors
One goes down in June ... too late. Other in ~ 10 months.
Cavity was foreseen for possible luminosity monitor
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)
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?