[Hps] LHCb arXiv:1509.06765

[Nelson, Timothy Knight]

Hi Valery,

Actually, in the paper they point out that the the 5-sigma discovery region is (obviously) smaller than the 2-sigma contours on their plots and *imply* that the 5-sigma contours don’t cover the gap:

"The predicted reach in Fig. 2 covers most of the avail- able A′ parameter space for mA′ 􏰁 100 MeV, and one expects that LHCb could fully cover this region with modest improvements. That said, this reach is based on simulation, so despite our conservative approach, the ac- tual reach may be less than predicted. Furthermore, the ultimate goal is to discover an A′ boson and measure its properties. Discovery requires 5σ sensitivity, which our search provides over most of the relevant A′ parameter space but not all of it.”

A bigger problem is that they have not looked very carefully into the backgrounds, many of which are impossible to study with Monte Carlo.

It’s also worth noting that we already have an idea how an HPS successor could close Mont’s gap.  However, it may not be reasonable to imagine that such an experiment would run before 2020.

Tim
 
> On Sep 24, 2015, at 1:28 PM, Valery Kubarovsky <vpk at jlab.org> wrote:
> 
> Hi Natalia,
> They described in the paper why the resonant and displaced search regions overlap for LHCb but not for HPS. It looks like LHCb has discovery potential in "Mont's gap". And you are right we still have the advantage to set the limit (or discover) earlier. 
> Regards,
> Valery
> 
> ----- Original Message -----
>> From: "Natalia Toro" <ntoro at perimeterinstitute.ca>
>> To: "Valery Kubarovsky" <vpk at jlab.org>
>> Cc: "HPS" <hps at jlab.org>
>> Sent: Thursday, September 24, 2015 11:07:05 AM
>> Subject: Re: [Hps] LHCb arXiv:1509.06765
> 
>> Hi Valery, all,
>> 
>> Yes, I think their prospects look very exciting and if they hold up will
>> completely change the landscape below 100 MeV.  One thing worth noting is
>> the timeline -- as they say, the search relies on Run 3 upgrades and the
>> full run-3 dataset (currently planned for 2020-2023).
>> 
>> I also don't know whether they have discovery potential in "Mont's gap" or
>> only exclusion...
>> 
>> Best,
>> Natalia
>> 
>> On Thu, Sep 24, 2015 at 10:48 AM, Valery Kubarovsky <vpk at jlab.org> wrote:
>> 
>>> LHCb will cover
>>> LHCb can explore nearly all of the dark photon parameter space between
>>> existing prompt-$A^{\prime}$ and beam-dump limits for heavy photon mass <
>>> 100MeV.
>>> 
>>> 
>>> [2]  arXiv:1509.06765 [pdf, other]
>>> Dark photons from charm mesons at LHCb
>>> Philip Ilten, Jesse Thaler, Mike Williams, Wei Xue
>>> Comments: 18 pages, 11 figures, 1 table
>>> Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy
>>> Physics - Experiment (hep-ex)
>>> We propose a search for dark photons $A^{\prime}$ at the LHCb experiment
>>> using the charm meson decay $D^*(2007)^0 \!\to D^0 A^{\prime}$. At nominal
>>> luminosity, $D^{*0} \!\to D^0 \gamma$ decays will be produced at about
>>> 700kHz within the LHCb acceptance, yielding over 5 trillion such decays
>>> during Run 3 of the LHC. Replacing the photon with a kinetically-mixed dark
>>> photon, LHCb is then sensitive to dark photons that decay as
>>> $A^{\prime}\!\to e^+e^-$. We pursue two search strategies in this paper.
>>> The displaced strategy takes advantage of the large Lorentz boost of the
>>> dark photon and the excellent vertex resolution of LHCb, yielding a nearly
>>> background-free search when the $A^{\prime}$ decay vertex is significantly
>>> displaced from the proton-proton primary vertex. The resonant strategy
>>> takes advantage of the large event rate for $D^{*0} \!\to D^0 A^{\prime}$
>>> and the excellent invariant mass resolution of LHCb, yielding a
>>> background-limited search that nevertheless covers a sig!
>>> nificant portion of the $A^{\prime}$ parameter space. Both search
>>> strategies rely on the planned upgrade to a triggerless-readout system at
>>> LHCb in Run 3, which will permit identification of low-momentum
>>> electron-positron pairs online during data taking. For dark photon masses
>>> below about 100MeV, LHCb can explore nearly all of the dark photon
>>> parameter space between existing prompt-$A^{\prime}$ and beam-dump limits.
>>> 
>>> _______________________________________________
>>> Hps mailing list
>>> Hps at jlab.org
>>> https://mailman.jlab.org/mailman/listinfo/hps
>>> 
>> 
>> 
>> 
>> --
>> Natalia Toro
>> Perimeter Institute
>> 31 Caroline St N, Waterloo, ON
>> (519) 569-7600 x8725
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