P.S. As part of discovery story # 2 (rare top decays) below, I forgot to mention during the phone meeting earlier today
(but it is written below) that an observation of t _> c Z at the level of 10^(-5) might suggest a (rough) mass scale for the heavy
new physics which is at the origin of this process, e.g., "several" TeV KK scale in warped extra dimension.
So, we can then search **directly** for such new particles: e.g., for warped models, it would go back to discovery stiory # 1, i.e.,
t tbar etc. resonances.
And, in particular, it implies KK gluon and Z decaying into top + charm (in addition to t tbar) at a certain rate...so, we will try to study this channel, as per Michael (Peskin)'s suggestion (which was actually made in the context of discovery story #1).
Kaustubh
________________________________________
From: Kaustubh Sadanand Agashe
Sent: Thursday, June 13, 2013 12:00 PM
To: [log in to unmask]
Subject: RE: EF Conveners, Thursday, June 13
Hi Micheal and Chip (and others),
(a). Below are "discovery stories" that we came up with: some of them might not so well-developed/motivated, but we think could at least
be starting points for a discussion.
(b). We just wanted to add that the our Monday afternoon session (on NP in top) should be scheduled to be NOT in parallel with cross-frontier talks.
And, we point out again (in case it was a somewhat buried earlier) that this is **joint** with BSM group.
Regards,
Cecilia, Kaustubh, Kirill, Reinhard, Robin (top group conveners)
*********************** Discovery stories **************
(1). Resonances in t tbar
As first suggested in your earlier email, suppose an enhancement is observed at M(ttbar) = 3 TeV in the semileptonic channel
(probably using sophisticated boosted top techniques), but NO enhancement in dilepton invariant mass is found close to 3 TeV (the latter is obviously an easier search and would most likely be done earlier)...
-- Obviously, all hadronic t tbar channel needs to be checked for similar enhancement...
-- polarization and forward-backward asymmety of tops at this M(ttbar) could further solidify the case for BSM physics (since the new physics might prefer RH over LH tops for example, unlike QCD)...
-- composite Higgs/warped extra dimension might be candidate models for such a scenario (since they predict very small
decays of the heavy resonances into dileptons/diphotons)...
And, such scenarios would predict other resonances decaying into W/Z and Higgs at similar mass (or maybe the same one as t tbar
can decay also into these final states)...so that a search along these lines would be necesary (again it is somewhat difficult since it
might rely on boosted techniques for W/Z/Higgs as well)...
(2). Stealthy stops (following form discussions with Maxim Perelstein, Andrey Katz and Zhenyu Han):
These are stops with mass just a bit above top mass and decaying into top and (very) light/neutral LSP, thus their
pair production results in a final state looking quite a lot like SM t tbar (in particular, there is very small extra MET, i.e.,
from invisible LSP). Here's how it might (roughly) go:
-- 1st "hint" for stealth stops could be soin-correlations in t tbar deviating from SM (in a way as predicted for stealthy
stops) since it seems this observable might be the most robust discriminator...
-- as a follow-up/cross-check, rapidity gap; total cross-section; leptonic MT2 can be used...
-- if stop is so light, then gluino is also expected to be light, say, below 1 TeV: such a mass (but not too much below 1 TeV) might
be still allowed by 7-8 TeV LHC run since this gluino (decaying into top and stop) also gives very small extra MET...
...so a search for such gluino could shed light on the situation...
-- Finally, ILC, especially a scan "near" 350 GeV (i.e., stop threshold) might settle the issue (in case the situation still not clear
after LHC runs)...
(3). Rare top decay (as written by Nathaniel Craig):
An intriguing scenario is the observation of the rare flavor-violating decay t > Zc at the LHC with a branching ratio on the order of 10^-5, at the limit of the projected high-luminosity reach. Such a branching ratio would be some nine orders of magnitude larger than the Standard Model expectation and a clear indication of new physics. At the LHC the primary backgrounds to this channel are Standard Model diboson ZZ and WZ production with additional jets, with a lesser component from Z+jets and rarer SM top processes ttW and ttZ. The diboson backgrounds are fairly well understood and in excellent agreement with simulation, and even the rare contributions from ttW and ttZ will be well-characterized by the end of the high-luminosity LHC run, making the observation of t > Zc fairly reliable.
Such a signal would be consistent with new physics arising from, e.g., warped extra dimensions, a composite Higgs, or a flavor-violating two-Higgs-doublet model. Ancillary probes of FCNC processes become crucial for validating the signal and identifying its origin. Some of the most important probes are the rare decays t > g c, t > gamma c and t > h c, which have similar reach at the high-luminosity LHC. In the case of warped extra dimensions or a composite Higgs, the corresponding branching ratios for t > g c and t > gamma c are orders of magnitude below the sensitivity of the LHC, but the branching t > h c may be as large as 10^-4, within the reach of high-luminosity LHC. Thus a signal in t > Z c with a tentative signal in t > h c but no other channels would be indicative of warped extra dimensions or a pseudo-Goldstone composite Higgs. Rates of this magnitude would also suggest e.g. a relatively low KK scale, so that complementary direct searches for heavy resonances would play a crucial role in testing the consistency of this possibility. In contrast, in flavor-violating two-Higgs-doublet models, a visible t > Zc signal can be accompanied by comparable signals in t > g c and t > h c, allowing this scenario to be similarly differentiated.
Instrumental complementary information can be provided by the ILC. Projections of the 500 GeV ILC with 300/fb place its sensitivity to t > Z q coming from a gamma^mu spin structure at the level of 10^-4, but sensitivity to t > Z q in single top production from a sigma^mu nu structure at 10^-5. The observation of comparable t > Zc signals at the LHC and ILC could then favor a sigma^mu nu coupling and rule out candidate explanations such as warped extra dimensions.
***********************
________________________________________
From: Kaustubh Sadanand Agashe
Sent: Wednesday, June 12, 2013 11:02 AM
To: Raymond Brock; [log in to unmask]
Cc: [log in to unmask]; [log in to unmask]; [log in to unmask]; [log in to unmask]
Subject: RE: EF Conveners, Thursday, June 13
Hi Chip and Michael,
We will try to send you discovery stories later. Meanwhile, here's the (rough) schedule for top quark group sessions:
Sunday: Top quark mass (1 hour for presentation of studies/detailed conclusions, followed by 1 hour for discussion); Couplings, including rare decays (similarly, i.e., 1 + 1)
Monday: New particles decaying into top-like final states (1+1)...this is **jointly** with BSM group...
Tuesday: Kinematics (1+1); Detectors and algorithms (1+1)
** In particular, as per the indico page:
https://indico.fnal.gov/conferenceTimeTable.py?confId=6969#20130630
(and earlier schedule of blocks), we had budgeted for **4 hours** for our group on **Sunday** afternoon.
However, your email below seems to mention only 2 hours: so, can you please clarify?
Regards,
Cecilia, Kaustubh, Kirill, Reinhard, Robin (top group conveners)
________________________________________
From: [log in to unmask] [[log in to unmask]] on behalf of Raymond Brock [[log in to unmask]]
Sent: Wednesday, June 12, 2013 9:42 AM
To: snowmass-ef
Subject: [SNOWMASS-EF] EF Conveners, Thursday, June 13
Hi everyone,
We will meet at our regular time and "place":
Energy Frontier Conveners' meeting
June 13: 11:00 PDT / 2:00 EDT
Contact information:
You call: domestic... (877) 287-0283
international...(303) 433-0165
participant code: 290-043
Agenda and Homework for the EF convener's meeting, June 13
First, the homework:
1. Please send to Chip and Michael by email your proposed sessions for Seattle meeting. We will try to mix and stir these and come out with an overall schedule. The times that you have to fill are:
Sunday June 30 2 hours
Monday July 1 2 hours plus (if you wish) 2 hours in parallel with the
Cosmic Frontier and Intensity Frontier talks
Tuesdy July 2 4 hours
We encourage you to reserve some of this time for discussion, especially on the draft overall conclusions of your report, which you will present on Sunday morning.
2. Please send to Chip and Michael your lists of "Discovery Stories" as we discussed in Brookhaven. That is, what possible scenarios for discovery will you write up as illustrations of what can be learned in Energy Frontier? We need to go over what you have to say about the stories you will promote and also ways that other working groups can contribute to filling out these stories.
The agenda of the meeting will follow these items:
1. Discussion and clarification of the Seattle agenda.
2. Discussion of the "Discovery Stories"
3. Any further discussion of the case for 300 to 3000 fb-1 that I circulated after our meeting last week?
4. A. O. B.
---------------------------------------------------------------
Raymond Brock * University Distinguished Professor
Department of Physics and Astronomy
Michigan State University
Biomedical Physical Sciences
567 WIlson Road, Room 3210
East Lansing, MI 48824
sent from: [log in to unmask]<mailto:[log in to unmask]>
cell: (517)927-5447
MSU office: (517)353-1693/884-5579
open fax: (517)355-6661
secure fax: (517)351-0688
Fermilab office: (630)840-2286
CERN Office: 32 2-B03 * 76-71756
Twitter: @chipbrock
Home: http://www.pa.msu.edu/~brock/
ISP220: http://www.pa.msu.edu/courses/ISP220/
ISP213H: http://www.pa.msu.edu/courses/2007spring/ISP213H/
Facebook: http://msu.facebook.com/profile.php?id=2312233
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