Observation of Multiplicity Dependent Prompt χ_{c1}(3872) and ψ(2S) Production in pp Collisions

The production of χ_{c1}(3872) and ψ(2S) hadrons is studied as a function of charged particle multiplicity in pp collisions at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 2  fb^{-1}. For both states, the fraction that is produced promptly at the collision vertex is found to decrease as charged particle multiplicity increases. The ratio of χ_{c1}(3872) to ψ(2S) cross sections for promptly produced particles is also found to decrease with multiplicity, while no significant dependence on multiplicity is observed for the equivalent ratio of particles produced away from the collision vertex in b-hadron decays. This behavior is consistent with a calculation that models the χ_{c1}(3872) structure as a compact tetraquark. Comparisons with model calculations and implications for the binding energy of the χ_{c1}(3872) state are discussed.

Search for Coherent Elastic Scattering of Solar ^{8}B Neutrinos in the XENON1T Dark Matter Experiment

We report on a search for nuclear recoil signals from solar ^{8}B neutrinos elastically scattering off xenon nuclei in XENON1T data, lowering the energy threshold from 2.6 to 1.6  keV. We develop a variety of novel techniques to limit the resulting increase in backgrounds near the threshold. No significant ^{8}B neutrinolike excess is found in an exposure of 0.6  t×y. For the first time, we use the nondetection of solar neutrinos to constrain the light yield from 1-2 keV nuclear recoils in liquid xenon, as well as nonstandard neutrino-quark interactions. Finally, we improve upon world-leading constraints on dark matter-nucleus interactions for dark matter masses between 3 and 11  GeV c^{-2} by as much as an order of magnitude.

Measurement of CP Violation in the Decay B^{+}→K^{+}π^{0}

A measurement of CP violation in the decay B^{+}→K^{+}π^{0} is reported using data corresponding to an integrated luminosity of 5.4  fb^{-1} collected with the LHCb experiment at a center-of-mass energy of sqrt[s]=13  TeV. The CP asymmetry is measured to be 0.025±0.015±0.006±0.003, where the uncertainties are statistical, systematic, and due to an external input. This is the most precise measurement of this quantity. It confirms and significantly enhances the observed anomalous difference between the direct CP asymmetries of the B^{0}→K^{+}π^{-} and B^{+}→K^{+}π^{0} decays, known as the Kπ puzzle.

First Observation of the Decay B_{s}^{0}→K^{-}μ^{+}ν_{μ} and a Measurement of |V_{ub}|/|V_{cb}|

The first observation of the suppressed semileptonic B_{s}^{0}→K^{-}μ^{+}ν_{μ} decay is reported. Using a data sample recorded in pp collisions in 2012 with the LHCb detector, corresponding to an integrated luminosity of 2  fb^{-1}, the branching fraction B(B_{s}^{0}→K^{-}μ^{+}ν_{μ}) is measured to be [1.06±0.05(stat)±0.08(syst)]×10^{-4}, where the first uncertainty is statistical and the second one represents the combined systematic uncertainties. The decay B_{s}^{0}→D_{s}^{-}μ^{+}ν_{μ}, where D_{s}^{-} is reconstructed in the final state K^{+}K^{-}π^{-}, is used as a normalization channel to minimize the experimental systematic uncertainty. Theoretical calculations on the form factors of the B_{s}^{0}→K^{-} and B_{s}^{0}→D_{s}^{-} transitions are employed to determine the ratio of the Cabibbo-Kobayashi-Maskawa matrix elements |V_{ub}|/|V_{cb}| at low and high B_{s}^{0}→K^{-} momentum transfer.

Model-Independent Study of Structure in B^{+}→D^{+}D^{-}K^{+} Decays

The only anticipated resonant contributions to B^{+}→D^{+}D^{-}K^{+} decays are charmonium states in the D^{+}D^{-} channel. A model-independent analysis, using LHCb proton-proton collision data taken at center-of-mass energies of sqrt[s]=7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9  fb^{-1}, is carried out to test this hypothesis. The description of the data assuming that resonances only manifest in decays to the D^{+}D^{-} pair is shown to be incomplete. This constitutes evidence for a new contribution to the decay, potentially one or more new charm-strange resonances in the D^{-}K^{+} channel with masses around 2.9  GeV/c^{2}.

Constraints on the K_{S}^{0}→μ^{+}μ^{-} Branching Fraction

A search for the decay K_{S}^{0}→μ^{+}μ^{-} is performed using proton-proton collision data, corresponding to an integrated luminosity of 5.6  fb^{-1} and collected with the LHCb experiment during 2016, 2017, and 2018 at a center-of-mass energy of 13 TeV. The observed signal yield is consistent with zero, yielding an upper limit of B(K_{S}^{0}→μ^{+}μ^{-})<2.2×10^{-10} at 90% C.L.. The limit reduces to B(K_{S}^{0}→μ^{+}μ^{-})<2.1×10^{-10} at 90% C.L. once combined with the result from data taken in 2011 and 2012.

Expression, purification and characterization of three odorant binding proteins from the diamondback moth, Plutella xylostella

Odorant binding proteins (OBPs) are critical components in insect olfactory systems where they bind, solubilize and transport odorant molecules to receptors. Here, we cloned three OBPs (PxylGOBP1, PxylGOBP2 and PxylOBP24) from the diamondback moth, Plutella xylostella, one of the most destructive pests of cruciferous crops. These three OBPs were expressed in Escherichia coli as recombinant proteins, purified and characterized by fluorescence binding assays with 39 ligands including sex pheromone and plant-derived chemical compounds. PxylGOBP1 and PxylGOBP2 showed significantly different binding affinities to theses ligands, suggesting distinct binding preferences of these two general odorant binding proteins. PxylOBP24 showed no or extremely low binding activities to selected ligands, suggesting it may be involved in non-olfactory functions. Circular dichroism spectral results demonstrated that PxylGOBP1 and PxylGOBP2 shared similar secondary structures while PxylOBP24 was significantly different. This study improves our knowledge of insect OBPs, which will assist in a better understanding of insect olfactory system and developing more environmentally friendly pest control strategies for P. xylostella.

Observation of Enhanced Double Parton Scattering in Proton-Lead Collisions at sqrt[s_{NN}]=8.16 TeV

A study of prompt charm-hadron pair production in proton-lead collisions at sqrt[s_{NN}]=8.16  TeV is performed using data corresponding to an integrated luminosity of about 30  nb^{-1}, collected with the LHCb experiment. Production cross sections for different pairs of charm hadrons are measured and kinematic correlations between the two charm hadrons are investigated. This is the first measurement of associated production of two charm hadrons in proton-lead collisions. The results confirm the predicted enhancement of double parton scattering production in proton-lead collisions compared to the single parton scattering production.

Age-related histological changes in rat tibial

BACKGROUND

At present, studies on osteochondral morphogenesis only focus on a certain period of time or only provide a pattern diagram, but lack of dynamic tracking observation from the initiation of development to maturity. This study was to dynamically observe the changes of skeleton morphology and structure from embryo to adult, to provide research data for enriching the knowledge of bone and cartilage tissue structure.

MATERIALS AND METHODS

In the intrauterine experiment, 5 normal pregnant Wistar rats were sacrificed under anesthesia at gestational day (GD) 14, 17, 20, respectively. One of their offspring was randomly selected, and a total of 5 offspring were obtained at each time point. In the postnatal experiment, on the 7th and 10th day after birth and at postnatal weeks (PW) 2, 3, 6, 12, 28, 5 offspring rats from 5 different pregnant Wistar rats were randomly selected and sacrificed under anesthesia at each time point. After obtaining the above offspring, the soft tissue was removed, and the tibia of hind limbs was retained for paraffin-embedded section. After stained with Safranin-O-fast-green and hematoxylin, the morphological development of the tibia was observed under an optical microscope.

RESULTS

At GD14, there was no obvious joint space, the whole hind limb was cartilage and bone tissue was not visible. At GD17, visible joint space was seen and the chondrocytes in the center region appeared to hypertrophy. At GD20, the primary ossification center was obvious, and a typical epiphysis growth plate structure could be seen. On the 7th day after birth, the chondrocytes in the center of epiphysis cartilage were hypertrophic and differentiated, the cartilage canal grow from the cartilage surface toward the center of the epiphysis cartilage, at postnatal day 14, the secondary ossification center was formed. At this time, the tibia had typical morphological characteristics of the metaphysis, however, there was no obvious layered structure of articular cartilage; the stratified structure of articular cartilage could be seen at PW6, but its mature marker (tidemark) was still not visible; however, at PW12, typical four layers of articular cartilage appeared, and the tidemark was visible. The growth plates were clearly visible at PW2, 6 and 12. At PW28, growth plates could still be observed, but its morphology is abnormal.

CONCLUSIONS

Our results, for the first time, dynamically observed the morphological changes of osteochondral at critical period of development from embryo to adult, especially the process of cartilage canal participating in the formation of secondary ossification center.

[Investigation on the status of monotherapy for newly diagnosed tic disorders and its comorbidity in children]

Objective: To investigate the status of monotherapy for newly diagnosed tic disorders and its comorbidity in children, so as to provide a reference for clinical medication. Methods: A questionnaire survey was conducted to collect the application experience of monotherapy for newly diagnosed tic disorders and comorbidities in 110 pediatric neurologists and psychiatrists from Chinese Tic Disorders Study Consortium from February to August in 2019. Doctors were asked to rate treatment options based on a rank 5-point scale with "1" least appropriate and "5" most appropriate. The drug evaluation index was based on the comparison of the median score of a single drug with the overall scores of all drugs in this disease (M (Q₁, Q₃)), single drug M ≥ overall Q₃ was recommended as preferred drugs; overall Q₁≤ single drug M < overall Q₃ was considered as secondary drugs; single drug M < overall Q₁ was considered as unsuitable drugs. Results: Among 110 electronic questionnaires, 94 (86%) were availably responded, responding doctors included 37 (39%) males and 57 (61%) females, the age of responding doctors was (48±10) years, and their working year was (17±10) years. In the investigation of the first and second monotherapy for newly diagnosed tic disorders in children without comorbidities, there were no preferred drugs for mild transient tic disorders. The scores of clonidine, aripiprazole and tiapride were 4 (3, 4), 4 (3, 4), 4 (4, 5) scores respectively, and were greater than overall scores (3 (2, 4) scores), so they could be recommended as the preferred drugs for moderate chronic tic disorders, the recommendation for initial mild Tourette syndrome (TS) treatment was the same as preferred drugs for moderate chronic tic disorders. Similarly, clonidine, aripiprazole, tiapride and haloperidol could be recommended as the preferred drugs for other kinds of tic disorders. As for the second monotherapy, the preferred drugs for moderate transient tic disorders, mild chronic tic disorders and severe TS were all aripiprazole, tiapride, haloperidol, sulpiride, clonidine and topiramate. While clonidine, aripiprazole, tiapride could be considered as preferred drugs for severe transient tic disorders, moderate to severe chronic tic disorders and mild to moderate tic disorders. In the investigation of monotherapy for newly diagnosed tic disorders in children with comorbidities, for moderate chronic tic disorders and TS comorbid with obsessive-compulsive disorder, aripiprazole (4 (3, 5) scores) and sertraline (4 (3, 4) scores) were preferred drugs,the median scores of which were all greater than overall scores (3 (3, 4) scores), they were also the preferred treatment for severe transient tic disorders and mild chronic tic disorders. For mild and moderate transient tic disorders, severe chronic tic disorders and TS comorbid with obsessive-compulsive disorder, aripiprazole, fluvoxamine, fluoxetine, haloperidol and sertraline were preferred drugs. When comorbid with attention deficit hyperactivity disorder (ADHD), severe transient tic disorders, moderate chronic tic disorders and TS, tomoxetine and clonidine were recommended as preferred drugs (both 4 (4, 5) scores), and tomoxetine and clonidine were also the preferred treatment for severe TS. For severe chronic tic disorders comorbid with ADHD, clonidine (5(4, 5) scores) was preferred drug, greater than overall scores (4 (3, 5) scores), while for mild and moderate transient tic disorders clonidine, tomoxetine, guanidine and methylphenidate were recommended as preferred drugs. For mild chronic tic disorders and TS comorbid with ADHD tomoxetine was preferred drug. When comorbid with sleep disorders, there were no preferred drugs for mild transient tic disorders; estazolam (3 (2, 3) scores) was the preferred drug for mild chronic tic disorders and TS comorbid with sleep disorders. For othe kind of tic disorders comorbid with sleep disorders, estazolam, melatonin and clonazepam were preferred drugs. When comorbid with anxiety and depressive disorders, for all kinds of tic disorders sertraline was recommended as preferred drugs, the median scores of sertraline were all (4 (3, 5) scores) in severe transient tic disorders, moderate to severe chronic tic disorders and moderate TS, and greater than overall scores (3 (3, 4) scores). While severe chronic tic disorders comorbid with anxiety and depressive disorders, fluvoxamine could also be chosen as preferred drugs. Conclusions: Drug therapy is not recommended for mild transient tic disorders, while tiapride, aripiprazole, clonidine, and haloperidol are mainly preferred drugs for the other kinds of tic disorders. Corresponding drugs should be selected when tic disorders are combined with obsessive-compulsive disorder, ADHD, sleep disorders, anxiety, depression, etc.

[Clinicopathological features and prognosis of 59 patients with platelet-derived growth factor α-mutant gastrointestinal stromal tumor]

Objective: Platelet-derived growth factor α (PDGFRA)-mutant gastrointestinal stromal tumor (GIST) is a relatively rare disease, whose clinicopathological characteristics and prognosis have been poorly studied. In this paper, the clinicopathological features and prognostic factors of PDGFRA-mutant GIST are investigated to provide more data for its understanding and treatment. Methods: A retrospective case-control study was used to collect the medical records of patients with GIST who underwent surgical resection in Zhongshan Hospital of Fudan University from January 2015 to August 2019. Patients with PDGFRA-mutant GIST were enrolled, and those with synonymous PDGFRA mutations, non-tumor-related deaths, and lack of clinicopathological data were excluded. The clinicopathological data were collected and the risk factors associated with prognosis were analyzed. Results: Among the enrolled 59 patients, there were 41 males (69.5%) and 18 females (30.5%) with the median age of 60 (25-79) years. All tumors originated from the stomach. The tumor size was 5 (3-7) cm, and the mitotic count was 2 (1-4)/50 high-power fields (HPF). According to the modified NIH risk stratification, 8 cases were classified as very low risk (13.6%), 25 cases as low risk (42.4%), 14 cases as moderate risk (23.7%), and 12 cases as high risk (20.3%). There were 7 cases of exon 12 mutation and 52 cases of exon 18 mutation (including 36 cases of D842V mutation). A comparison of clinicopathological features between the D842V mutation group and the non-D842V mutation group showed no statistically significant difference (all P>0.05). During a median follow-up of 21 (0-59) months, the 1- and 3-year relapse-free survival (RFS) rates of all the patients were 96.6% and 91.5%, respectively. There were 8 cases of recurrence and 3 cases of death. Six GIST patients with D842V mutation had tumor recurrence after operation, of whom 4 cases achieved varying degrees of tumor remission after being treated with dasatinib or avapritinib. Log-rank analysis showed that the overall survival (OS) of male was better than that of female (100% vs. 83.3%, P=0.046), but there was no significant difference in OS among patients with different risk grades (P=0.057). The RFS and OS of patients with D842V mutation and non-D842V mutation, exon 12 and exon 18 mutation were similar (all P>0.05). Univariate Cox analysis showed that RFS was associated with gender (P=0.010), tumor size (P=0.042), mitotic count (P=0.003), and the modified NIH risk stratification (P=0.042), while multivariate analysis revealed that higher risk grade was an independent risk factor for recurrence of PDGFRA-mutant GIST (HR=12.796, 95%CI: 1.326-123.501, P=0.028). Gender was an independent factor for recurrence, and the risk of recurrence in males was lower than that in females (HR=0.154, 95%CI: 0.028-0.841, P=0.031). Conclusions: Gender and the modified NIH risk stratification are independent risk factors for recurrence of PDGFRA-mutant GIST, while patients with D842V and non-D842V mutation, and exon 12 and exon 18 mutation have a similar risk of recurrence and death.

Measurement of CP-Averaged Observables in the B^{0}→K^{*0}μ^{+}μ^{-} Decay

An angular analysis of the B^{0}→K^{*0}(→K^{+}π^{-})μ^{+}μ^{-} decay is presented using a dataset corresponding to an integrated luminosity of 4.7  fb^{-1} of pp collision data collected with the LHCb experiment. The full set of CP-averaged observables are determined in bins of the invariant mass squared of the dimuon system. Contamination from decays with the K^{+}π^{-} system in an S-wave configuration is taken into account. The tension seen between the previous LHCb results and the standard model predictions persists with the new data. The precise value of the significance of this tension depends on the choice of theory nuisance parameters.

Observation of New Ξ_{c}^{0} Baryons Decaying to Λ_{c}^{+}K^{-}

The Λ_{c}^{+}K^{-} mass spectrum is studied with a data sample of pp collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 5.6  fb^{-1} collected by the LHCb experiment. Three Ξ_{c}^{0} states are observed with a large significance and their masses and natural widths are measured to be m[Ξ_{c}(2923)^{0}]=2923.04±0.25±0.20±0.14  MeV, Γ[Ξ_{c}(2923)^{0}]=7.1±0.8±1.8  MeV, m[Ξ_{c}(2939)^{0}]=2938.55±0.21±0.17±0.14  MeV, Γ[Ξ_{c}(2939)^{0}]=10.2±0.8±1.1  MeV, m[Ξ_{c}(2965)^{0}]=2964.88±0.26±0.14±0.14  MeV, Γ[Ξ_{c}(2965)^{0}]=14.1±0.9±1.3  MeV, where the uncertainties are statistical, systematic, and due to the limited knowledge of the Λ_{c}^{+} mass. The Ξ_{c}(2923)^{0} and Ξ_{c}(2939)^{0} baryons are new states. The Ξ_{c}(2965)^{0} state is in the vicinity of the known Ξ_{c}(2970)^{0} baryon; however, their masses and natural widths differ significantly.

Search for the Rare Decays B_{s}^{0}→e^{+}e^{-} and B^{0}→e^{+}e^{-}

A search for the decays B_{s}^{0}→e^{+}e^{-} and B^{0}→e^{+}e^{-} is performed using data collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of 7, 8, and 13 TeV, corresponding to integrated luminosities of 1, 2, and 2  fb^{-1}, respectively. No signal is observed. Assuming no contribution from B^{0}→e^{+}e^{-} decays, an upper limit on the branching fraction B(B_{s}^{0}→e^{+}e^{-})<9.4(11.2)×10^{-9} is obtained at 90(95)% confidence level. If no B_{s}^{0}→e^{+}e^{-} contribution is assumed, a limit of B(B^{0}→e^{+}e^{-})<2.5(3.0)×10^{-9} is determined at 90(95)% confidence level. These upper limits are more than one order of magnitude lower than the previous values.

Measurement of f_{s}/f_{u} Variation with Proton-Proton Collision Energy and B-Meson Kinematics

The ratio of the B_{s}^{0} and B^{+} fragmentation fractions f_{s} and f_{u} is studied with B_{s}^{0}→J/ψϕ and B^{+}→J/ψK^{+} decays using data collected by the LHCb experiment in proton-proton collisions at 7, 8, and 13 TeV center-of-mass energies. The analysis is performed in bins of B-meson momentum, longitudinal momentum, transverse momentum, pseudorapidity, and rapidity. The fragmentation-fraction ratio f_{s}/f_{u} is observed to depend on the B-meson transverse momentum with a significance of 6.0σ. This dependency is driven by the 13 TeV sample (8.7σ), while the results for the other collision energies are not significant when considered separately. Furthermore, the results show a 4.8σ evidence for an increase of f_{s}/f_{u} as a function of collision energy.

[Vertical supraumbilical incision versus left lower oblique incision for specimen retrieval during laparoscopic rectal surgery]

Objective: To compared the short-term surgical outcomes of the vertical supraumbilical incision with the left lower oblique incision for specimen retrieval in laparoscopic resection for rectal cancer. Methods: A retrospective cohort study was performed. Inclusion criteria: (1) rectal cancer confirmed by colonoscopy and pathological examination; (2) undergoing the operation for the first time; (3) laparoscopic rectal surgery performed by the same surgeon team; (4) age of > 18 years and < 76 years old. According to above criteria, clinical data of 178 consecutive patients scheduled for laparoscopic surgery for rectal cancer at Department of Gastrointestinal Surgery of Renji Hospital between March 2015 and December 2017 were collected. Based on incision site of the mini-laparotomy, patients were classified to the vertical supraumbilical incision group (n=75) and the left lower oblique incision group (n=103). There were no significant differences in baseline data, such as age, gender, body mass index (BMI), tumor diameter, preoperative carcinoembryonic antigen (CEA) level, score of American Society of Anesthesiologists, TNM stage, between the two groups (all P>0.05). Perioperative variables and follow-up data were compared between two groups. Results: Between the vertical supraumbilical incision group and the left lower oblique incision group, the operation time [(131.7±3.7) minutes vs. (138.5±3.5) minutes], operative bleeding volume [(138.9±11.5) ml vs. (154.3±10.3) ml], length of auxiliary incision [(4.0±0.1) cm vs. (4.0±0.1) cm], and distance from anastomosis to dentate line [(3.8±0.1) cm vs. (4.2±0.1) cm] were not significantly different (all P>0.05). As compared to the left lower oblique incision group, patients in vertical supraumbilical incision group had earlier flatus [(62.7±2.3) hours vs. (69.2±1.7) hours, t=2.282, P=0.023], earlier ambulation [(41.9±1.8) hours vs. (46.78±1.42) hours, t=2.131, P=0.032], lower pain VAS scores at postoperative 24 hours (2.0±0.1 vs. 2.4±0.1, t=2.172, P=0.032) and 48 hours (2.7±0.1 vs. 3.0±0.1, P<0.05), and lower incidence of postoperative incisional hernia [6.7% (5/75) vs. 9.7% (10/103), χ(2)=3.942, P=0.042]. However, the postoperative fluids intake time, hospitalization days, pain VAS scores at postoperative 12 hours and postoperative complications (wound infection, anastomotic leakage, urinary retention, intestinal obstruction) were not significantly different between the two groups (all P>0.05). Conclusion: The vertical supraumbilical incision in laparoscopic resection for rectal cancer can reduce the degree of postoperative pain, facilitate early recovery of intestinal function and decrease the incidence of incisional hernia.

Isospin Amplitudes in Λ_{b}^{0}→J/ψΛ(Σ^{0}) and Ξ_{b}^{0}→J/ψΞ^{0}(Λ) Decays

Ratios of isospin amplitudes in hadron decays are a useful probe of the interplay between weak and strong interactions and allow searches for physics beyond the standard model. We present the first results on isospin amplitudes in b-baryon decays, using data corresponding to an integrated luminosity of 8.5  fb^{-1}, collected with the LHCb detector in pp collisions at center of mass energies of 7, 8, and 13 TeV. The isospin amplitude ratio |A_{1}(Λ_{b}^{0}→J/ψΣ^{0})/A_{0}(Λ_{b}^{0}→J/ψΛ)|, where the subscript on A indicates the final-state isospin, is measured to be less than 1/21.8 at 95% confidence level. The Cabibbo suppressed Ξ_{b}^{0}→J/ψΛ decay is observed for the first time, allowing for the measurement |A_{0}(Ξ_{b}^{0}→J/ψΛ)/A_{1/2}(Ξ_{b}^{0}→J/ψΞ^{0})|=0.37±0.06±0.02, where the uncertainties are statistical and systematic, respectively.

Clinical outcomes of different therapeutic modalities for rectal gastrointestinal stromal tumor: Summary of 14-year clinical experience in a single center

OBJECTIVE

The optimal treatment for gastrointestinal stromal tumor (GIST) of the rectum is controversial due to the extremely low incidence of the disease. The aim of the present study was to compare the clinical outcomes of different treatment modalities for rectal GIST by reviewing the 14-year experience in our center.

METHOD

Medical records of rectal GIST patients who received surgical treatment in our center between January 2004 to December 2017 were reviewed retrospectively. Overall survival (OS) and recurrence-free survival (RFS) were used as the observation endpoints.

RESULTS

Included in this study were 71 GIST patients, including 42 patients who underwent local excision (LE) and 29 patients who underwent segmental resection (SR). There were differences in tumor size (P = 0.001) and malignant risk grade (P = 0.007). The LE approach achieved a lower rate of R0 resection than SR (29/42 vs.27/29, P = 0.015) and shorter hospital stay (P = 0.004). Preoperative imatinib mesylate (IM) therapy improved the rate of sphincter-sparing surgery for patients with tumors in the very low segment of the rectum (P = 0.012) and offered better R0 resection margins (P = 0.027). Multivariate analysis showed that the resection margin status (P = 0.014), risk stratification (P = 0.001) and IM therapy (P = 0.042) were independent factors affecting RFS of rectal GIST patients but not the surgical modalities (LE vs. SR, P = 0.802). Multivariate analysis showed no significant impact of these variables on OS.

CONCLUSION

Selection of surgical modalities has no significant impact on the prognosis. Local excision is the preferred surgical modality for resectable rectal GIST by virtue of less injury and shorter hospital stay. IM therapy has proved to be associated with improved RFS for rectal GIST patients.

First Observation of Excited Ω_{b}^{-} States

We report four narrow peaks in the Ξ_{b}^{0}K^{-} mass spectrum obtained using pp collisions at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9  fb^{-1} recorded by the LHCb experiment. Referring to these states by their mass, the mass values are m[Ω_{b}(6316)^{-}]=6315.64±0.31±0.07±0.50  MeV, m[Ω_{b}(6330)^{-}]=6330.30±0.28±0.07±0.50  MeV, m[Ω_{b}(6340)^{-}]=6339.71±0.26±0.05±0.50  MeV, m[Ω_{b}(6350)^{-}]=6349.88±0.35±0.05±0.50  MeV, where the uncertainties are statistical, systematic, and the last is due to the knowledge of the Ξ_{b}^{0} mass. The natural widths of the three lower mass states are consistent with zero, and the 90% confidence-level upper limits are determined to be Γ[Ω_{b}(6316)^{-}]<2.8  MeV, Γ[Ω_{b}(6330)^{-}]<3.1  MeV and Γ[Ω_{b}(6340)^{-}]<1.5  MeV. The natural width of the Ω_{b}(6350)^{-} peak is 1.4_{-0.8}^{+1.0}±0.1  MeV, which is 2.5σ from zero and corresponds to an upper limit of 2.8 MeV. The peaks have local significances ranging from 3.6σ to 7.2σ. After accounting for the look-elsewhere effect, the significances of the Ω_{b}(6316)^{-} and Ω_{b}(6330)^{-} peaks are reduced to 2.1σ and 2.6σ, respectively, while the two higher mass peaks exceed 5σ. The observed peaks are consistent with expectations for excited Ω_{b}^{-} resonances.

Search for A^{'}→μ^{+}μ^{-} Decays

Searches are performed for both promptlike and long-lived dark photons, A^{'}, produced in proton-proton collisions at a center-of-mass energy of 13 TeV. These searches look for A^{'}→μ^{+}μ^{-} decays using a data sample corresponding to an integrated luminosity of 5.5  fb^{-1} collected with the LHCb detector. Neither search finds evidence for a signal, and 90% confidence-level exclusion limits are placed on the γ-A^{'} kinetic mixing strength. The promptlike A^{'} search explores the mass region from near the dimuon threshold up to 70 GeV and places the most stringent constraints to date on dark photons with 214<m(A^{'})≲740  MeV and 10.6<m(A^{'})≲30  GeV. The search for long-lived A^{'}→μ^{+}μ^{-} decays places world-leading constraints on low-mass dark photons with lifetimes O(1)  ps.